The Ultimate guide to Suspension and Handling.

Ok I have gained permission from Mike Kojima to repost this. This article was written by Mike Kojima,



The Ultimate Guide to Suspension and Handling Part 1: Wheels and Tires

By Mike Kojima

Horsepower is sexy and chicks dig it, at least a lot of meatheads think that way. Making horsepower is relatively easy. A lot of competent people know how to make power, lots of it. Until drifting became the rage in this country, handling and cornering prowess was for geeks, the road racing elite and autocrossers. Handling was for dweebs that raced around cones in parking lots, or loners prowling canyon roads at night, not for cool people in the scene.

How to tune a car's suspension was an unknown art in the world of mainstream performance, simply because most people didn’t care about handling. Most people emulated the world of road racing by making their cars low. Low was cool, low was handling.
Now that drifting, Time Attack, racetrack hotlapping and autocross are becoming popular, suspension tuning and handling are becoming important items for discussion, experimentation and debate. Building handling into a car is not necessarily any more complicated than building power; it’s just that the subject is somewhat more esoteric and definitive information is not as widely available.
Finding straight-line horsepower gurus for hire to help you is relatively easy, but finding an expert to make your car corner well is a tough deal, fraught with mystery and intrigue. The solution? Make yourself the guru. If your automotive interests are greater than the one-dimensional urge to blast straight down the 1320, brag about dyno sheets on internet forums or install neon and strobe lights to your interior and undercarrage, let’s get to work. There are 4 basic steps to achieving a well handling car and in this first part of our extensive series we'll discuss the first--wheels and tires.



Get Some Sticky Tires

Tires by far are the biggest contributor to finding more cornering force. By bolting on a set of gumball tires, you can make the biggest possible single net gain in cornering power in minutes. Generally, putting the widest tires and wheels that will fit inside your wheel wells without rubbing is the way to go. Specing out an ultra-high performance tire is also important. Most of these tires can perform decently during track days and are good for autocross in SCCA's ST street classes.

If you are doing track events, autocrossing or are just plain nuts and simply have to have the most grip possible, you can try a set of DOT approved racing tires. Some of these tires are nearly useable as everyday driving tires while others grip almost like racing slicks and last about the same length of time. Below is a chart which categorizes these tires. Note that this is somewhat subjective and there is some overlap here.

Sticky Ultra High Performance Street Tire
Race Tire, Nearly Streetable, Long Wearing, Many Heat Cycles




Race Tire, Sticky Medium Wearing, Medium Heat Cycle




Race Tire, Really Sticky, Fast Wearing, Low Heat Cycles



Yokohama Advan Neova AD008 Hankook Z214 C31
Hankook Z214 C51, C71
Hankook Z214 C91

Nitto NT05
Toyo RA-1
Toyo 888R
Hoosier A6, R6

Falken RT-615
Nitto NT01
Kumho Ecsta 700
Kumho Ecsta 710

Kumho XS KU36
Yokohama A048R
Goodyear GS-CS

Michelin Pilot Sport PS2
Michelin Pilot Sport Cup
BFG G-Force R1

Bridgestone Pontenza RE11
Kumho Victoracer V700

Avon Tech RA

Pirelli Pzero Corsa

Race compound DOT tires produce more road sucking grip than any suspension mod you can do but the drawbacks are many. First, these tires can be expensive; second, they wear quickly; third, the number of heat cycles that their rubber formulations can withstand before becoming oxidized and hard is limited; and fourth, many of them don’t do well in the wet and none work in the snow or ice. It is possible to end up with an expensive, fast wearing and not so grippy tire if these race tires are used on the street and subjected to many heat cycles. Most people who use these race tires have a second set of wheels and use them only for weekend warrior activities.



Within reason, put a wider wheel and tire on your car to put more rubber on the road. Generally you can stuff a tire two sizes larger than stock into most cars stock wheel wells. For instance a car that came with a 185/70-14 tire on a 5" inch wide wheel can usually easily accommodate a 205/50-15 on a 7" wide wheel with no modifications at all. On most cars you can roll the fender flange flat to get more tire clearance if needed. Do not accept any rubbing between the tire and any part of the car, be it the fender or the suspension, it can be very dangerous. When deciding which wider wheels for your car, try to stick to close to the stock proportions of offset to wheel width to maintain a reasonable scrub radius. We will explain why in later editions of our handling guide. Choose the size of your tire and wheel including the offset with this in mind for the best performance rather than going for the hella flush aesthetic unless that’s what floats your boat.


For all of our poking fun of Hella Flush, and overstreching tires on too wide wheels, stretching tires can improve response by making it harder to get sidewall flex under cornering load. Here the Cyber EVO, one of the fastest time attack cars ever built shows its stretched tires. For road racing we feel that this is not advisable due to the sensitivity to impact damage and de-beading if things are not exactly right but the Cyber EVO shows that this technique can work well. It is a trick that some autocrossers swear by as they need fast response.

Putting the tires on a wheel of the recommended width for the tire is important as well. Putting a wide tire on a narrow stock rim will cause the tread to tend to lift on the edges under side load. If you can’t get the exact wheel width recommended by the tire manufacture for your size of tire, then always err to the wider side if you have the choice. A tire that is slightly stretched on a wide wheel will be more responsive and flex less under side load than one whose sidewalls are bubbled due to too narrow of a rim. Some autocrossers looking for the maximum responsiveness out of their tires will stretch a tire on a rim as much as two inches too wide. When doing this, the rim and tire are more prone to damage and debeading under impact so this is not advisable for street use or road racing where you sometimes put wheels off the track or hit FIA curbs.


It's obvious that this isn't the greatest thing for performance.

Plus sizing, which is going to a larger diameter wheel and a low profile tire can help with faster response to steering input and less need for static negative camber for best grip due to the plus tires having a shorter and stiffer sidewall. For instance going from a 205/55-15 to a 205/40-17 on your typical FWD compact car will usually give crisper handling. Going overboard like several inches larger in your rim diameter and running ultra low profile tires generally is not always the hot tip.


Overstretched tires are prone to de-beading and damage to the tire and wheel from impact, wrong inflation pressure and side load

It is possible to over do it. Low stiff sidewalls don’t conform to bumpy surfaces easily. This makes ultra low profile tires sensitive to shock, as the super short, stiff sidewalls have very little compliance. Harsh surface inputs can make these tires skip and hop across the surface instead of digging in and finding grip making ultra low profile tires more sensitive to shock tuning. Big wheels are heavy creating a flywheel effect which is harder to accelerate and brake. Huge dubs also screw up your gear ratio contributing to sluggish acceleration.
Lastly, big heavy wheels and tires also add unsprung weight which reduces the effectiveness of the suspension. Unsprung weight is the weight of the components that are not suspended on a car. This includes the suspension arms, brakes, half of the shock absorber and the wheel and tire. Typically unsprung weight is 12-15% of the total weight of a car. For the suspension to work well, the ratio of sprung to unsprung weight must be kept as low as possible. For instance, have you ever noticed that the suspension of monster trucks hardly works? Even though they may have wheel travel measured in feet instead of inches, it’s hardly ever used and the trucks bounce and bang around like crazed Tonka toys. This is because Monster Trucks have a very high ratio of sprung to unsprung weight. Those huge earthmover tires possibly weigh more than the whole truck. When surface irregularities are hit, high unsprung weight generates significant force with an upward component which means a rough ride and difficulty keeping the rubber on the road. High unsprung weight also means that the shocks have to work much harder to damp wheel movement as well. Reducing the unsprung weight and the suspension is worked less, the ride improves and the tire can be kept in contact with the ground better.
For these reasons, putting a 215/35-18 on the same compact FWD car that worked well with a 205/50-15 will probably reduce its performance. Doing something really dumb like putting a 245/25-22 on an EVO is very detrimental to performance.
Generally for small bore naturally aspirated 4-cylinder like the older Honda Civics and Nisan Sentras, a lightweight 15x7" wheel is the best bet for performance. For larger cars about 18" is the usual practical maximum wheel diameter. Larger than this, you won’t find as many choices in sizes for true high performance tires. Wheels larger than 18" in diameter are mostly for show except in a few cases like the R35 GT-R which needs its big 20" wheels to clear its huge 15" brakes. Dub sizes don’t have ultra high performance applications either; the huge, oversized in diameter tires offered are mostly designed for the NBA player or gangsta rapper aesthetic.


Get Lightweight Wheels

The obvious way to make up for the disadvantages of increased wheel diameter and width is to use a light wheel. Light wheels are easier to accelerate and brake. They also reduce unsprung weight. Ever wonder why so many MotoIQ project cars run Volk wheels? Most Volks are forged. The forging process improves the grain structure and work hardens the metal (engineering terms for making it stronger!) It provides a superior strength-to-weight ratio. We like Enkei’s competition series wheels as well which have MAT formed rim sections. MAT helps improve the metal's mechanical properties much like forging for a fraction of the cost. Lower cost wheels are usually cast. The casting is a cheapest way to make wheels and nearly all low-priced wheels are cast aluminum.
The wheels listed below run the gamut of price point and quality but are all decent wheels with good weight.

Light wheels / low price

Enkei Racing Series wheels

5Ziggen FN01R-C, Pro Racer

Rays Gram Light C series

Team Dynamics Procomp

Team Dynamics Prorace

Kosei K1

Work Emotion, XSA

Axis Reverb

OZ Racing Series

Very light wheels / price not considered



Volk one-piece forged

SSR forged

Rays Gram Light F series

Work Meister

BBS RC

Wow

The Ultimate guide to Suspension and Handling Part 2, Controlling Body Motion
By Mike Kojima
Previously, we covered the most important aspect of handling, the tires. The next important suspension trick to increase grip is to reduce body motion such as roll under hard cornering, dive under braking and squat under acceleration. In later editions of this series we will get into the technical aspects of chassis dynamics but for now we are covering the basics and will gradually get into the harder to understand parts of the subject.


This 60's car shows all of the potential bad handling attributes that can be caused by excessive body roll. First the suspension is bottomed on the outside wheels causing a serious loss of traction, then you can easily see the huge amounts of bump and toe steer caused by the large amount of suspension stroking going on. Look at how the tires are pointed in different directions by inches! Next you can see how the camber is so far off, the tires are grinding on their edges. This car is so out of kilter it is in serious danger of rolling. Thank God they don't build them like they used to.

Contrary to popular belief, body motion does not harm grip during cornering due to weight transfer to the outside wheels in a hard turn. Other things are the major contributors to weight transfer and we will get into that later. You want to reduce body motion because it slows how responsive the car is to inputs from the steering, brakes and accelerator, things that you, the driver use to control the car. Body motion also gives the impression that the car is not handling well, roll, dive, squat and wallowing do not give a feeling that inspires confidence that a high performance car should have; instead these attributes are more appropriate for a boat or an ageing baby boomer’s ride to a long dirt nap. Watch an F-1 car in a turn; it nimbly darts around the corner with hardly any body motion. Now watch an SCCA showroom stock racer, it leans squirms and squeals its way around the track at a much slower pace.


This Lamborghini Countach cornering at the limit shows that older exotics were not perfect. Note the extreme turning angle indicating that the front tires are sliding in understeer. This is because the outside front suspension has bottomed out causing the front tire to lose grip. However notice that the tread of the outside front tire's tread is flat on the ground due to the Lambo's more sophisticated suspension geometry than the old 60's car above.


Sorry to use this photo again but here is the Dog II under heavy cornering load. The Dog II is based off of a Nissan Sentra, an Economy sedan with relatively crude suspension, however the suspension geometry has been reworked to optimize it. It also uses pretty sophisticated dampers, sway bars and high rate springs. Look how the body roll is under control and the camber is keeping the tires tread flat, even though they are distorted under side load. By looking at the tire steering angle and attitude, you can tell that the car is well balanced without excessive understeer. The distortion shows how hard the tire is being used. This little Sentra is pulling much more G's than the Lamborghini above. Surprisingly if someone would be willing to spend the money, the Dog II's suspension is
pretty streetable.


More insidious are some of the other bad side effects that excessive body motion can produce. Many softly sprung vehicles will roll over and bottom out the suspension on one end or even both ends of the car when cornering hard. This shocks the tires and will cause an instant loss of traction on the end of the car that first bottoms out resulting in unpredictable handling. If the suspension bottoms under a large amount of roll, a lot of weight will get transferred to the outside wheel where the suspension has bottomed causing a loss of grip.


Stroking the suspension through a wide range of travel dynamically in a turn can also result in the suspension geometry doing bad things. Most factory vehicles have compromised suspension geometry due to packaging reasons and usually two things can happen when the car really heels over in a turn, neither of them good. First the suspension can gain positive camber under roll on the outside wheels. This is worse in cars with the very common McPherson strut suspension. This when the car rolls, the tires don’t, making the outside of the tires tread tire heel over onto its shoulder, not using its full tread width effectively and tearing up the outside edge of the tread.


The other evil effect of roll is bump steer and Toe Steer. Bump steer is caused when the steering linkage and the rest of the links of the suspension travel in different arcs as the suspension moves. This is due to the steering linkage not being placed in the same geometric plane as the rest of the suspension’s control arms. Racecars are designed not to have much bump steer but production cars often have the location of the suspension’s control arms and steering links compromised by design. The result of this is that the tires can get steering input even if the steering wheel is not moved when the car heels over. The driver feels this as a car that is twitchy and unstable at the limit. Dive and squat when combined with roll can make all of these issues worse.



This illustrates tie rod and control arm pick up points for both McPherson strut and unequal length A arm suspension for minimal bump steer. Now go look at your car, chances are it's not going to be that close to this. When the control arms and the tie rods have different lengths and pick up locations, the steering is going to move independently of steering wheel movement and you get bump steer. This makes the car feel twitchy and unpredictable. Too much body motion means more bumpsteer. We will cover this phenomenon in more detail in future installments.

Toe steer is like bump steer but regarding the rear tires. Excess roll causes the rear tires to be steered in a direction other than straight ahead.




Toe steer is geometric movement of the rear wheels steering them way from the direction of travel when the suspension moves. Here are some examples of toe steer caused by trailing arms on a beam axle and semi trailing arms.


Moton Motorsport 3-way adjustable shocks as found on our EVO IX are an extreme and expensive example of stiffening the suspension to reduce body motion. The sophisticated valving of the Motons allow spring rates 3x stiffer than stock while maintaining a near stock ride. To better the already excellent EVO we went this way. The Moton's also have a lot of low speed damping which also controls body motion well.

OK so now you know body motion is bad, what can you do to control it? The first thing to do is to run stiffer springs, stiffer springs will resist roll and bottoming out under roll and combinations of roll, dive and squat. Of course stiffer springs have more rebound energy to them and to prevent you from bouncing like a pogo stick or floating in more mild cases, you need shocks with more damping, especially rebound damping. Shocks generally do not affect how much a car rolls but they do affect how the suspension responds to bumps and steering input. More rebound damping keeps the car from bouncing and floating over bumps and undulations. More damping also makes the car much more responsive to steering input. Too much damping is not good; it can prevent the suspension from returning once compressed, causing it to pack down, lose travel and gradually bottom out. We will get into the subtleties of shock tuning later.


Ground Control Advanced Design 2-way adjustable shocks as found on our 300ZX. We mostly use coil overs on our projects as we feel that most stock replacement performance springs are designed for cosmetic street lowering and are too soft and low for the kind of track use that we subject our cars to.

Another way to cut body roll is to add anti sway bars (also known as anti roll bars) or to install bars of a bigger diameter. Anti sway bars are torsion bars that interconnect the wheels. They do not come into play until the car starts to roll over in a turn. When this happens they resist the roll, as the bar must be twisted for the car to lean over. Anti Sway bars do not affect the ride as much as stiffer springs and have no affect on dive or squat. Generally the shock absorbers damping doesn’t need to be altered when the anti sway bars diameters are changed.

Stiffening the suspension will degrade the ride to some point and if stiff is good, more is not always better. It is possible to go too stiff to the point where the car will not be able to deal with bumps and will hop and slither its way around turns instead of compliantly absorbing the bumps and finding traction. Even racecars can be made too stiff. Some cars that are good from the factory with stiff suspension such as the EVO VIII, IX and the R35 GTR are notoriously hard to improve upon without seriously compromising overall drivability.

In future editions of this series, we will cover chassis balance and how to tune it.

The Ultimate Guide to Suspension and Handling Part 3: Balance the chassis

By Mike Kojima

Now that you have reduced body motion and improved steering response, we can work on the next major area of improvement, improving chassis balance. The goal for most of us is to have a car with neutral balance. Neutral balance, where all four tires slide the same amount, is the fastest way around a corner most of the time. This way the total maximum grip of each tire is being used. It might seem odd but experienced drifters prefer a neutrally balanced car because it allows them to have many control options for setting the car sideways. For example I set up Dai Yoshihara's Team Falken S13 in about the same way I would if it was a Time Attack car.

Unfortunately for the enthusiast, most cars are tuned to understeer from the factory. Understeer occurs when the front tires slide before the rears at the limit of grip. Manufacturers do this because it is the easiest handling mode for the average driver to control. Understeer is not efficient for extracting maximum lateral acceleration because the car will use the front tires excessively while the traction contribution of the rear tires is wasted. It’s also the slowest and most boring way around a corner. Bottom line? Understeer sucks.



If we go too far in the quest to eliminate understeer through chassis tuning we will inevitably create oversteer. Oversteer occurs when, at the limit, the rear tires slide before the fronts. Drifters work at controlling and driving in a state of continuous oversteer, raising it into an artform. A fast autocross car is often set to oversteer as are most rally cars. Any sort of race car that is driven mostly in very tight corners will probably be faster if it tends to have a bit of oversteer. Due to consumer advocate Ralph Nader's highly publicized campaign against General Motors and the rear engined Corvair in the 60's which resulted in huge lawsuits against automakers, the entire automotive industry is adverse to producing a car with anything close to oversteer. When an oversteering car exceeds its limits, it "spins out" which lawyers like to make sound especially heinous. However this simply means that an understeeing car will plow off the road nose first and an oversteering car will go tail first. You are gonna crash either way!



http://motoiq.smugmug.com/MotoIQ/Tech/The-Ultimate-Guide-To/slip-angle/757401089_oP9rL-L-1.jpg

How do we tune a cars handling balance? By manipulating the tire’s slip angle. Slip angle is defined by the difference between the direction the wheel is pointing and the direction the contact patch of the tire is pointing. At extreme slip angles the contact patch actually slides across the pavement. A chassis' primary dynamic contribution to slip angle is the load placed on each individual wheel while cornering. A greater load on a given wheel/tire results in a greater slip angle of that wheel/tire when subjected to a sideways cornering force. A nose heavy front-wheel drive car has more weight and thus cornering load on the front tires, which causes them to run a larger slip angle, than the rear tires. The front tires start to slide first and the car understeers. A rear engine car has a larger proportion of its weight on the rear tires. The rear tires run a larger slip angle so the car’s natural tendency is to oversteer. A mid engine car usually has the most even weight distribution with near equal slip angles from the front and rear tires. This is naturally more neutral handling than the other chassis layouts.


This is a classic example of grinding understeer in a nose heavy front wheel drive car. I forget who this is but I know they are a member here who I have corresponded with.

Proper manipulation of tire loading and slip angle by controlling weight transfer is key to balancing the chassis. By altering weight transfer and tire loading during cornering, much can be done to change a car’s natural handling tendencies. Can you make a nose heavy front-wheel car oversteer? Sure, look at most successful racing front-wheel cars, they oversteer like crazy. To protect its customers, Porsche delivers most of its tail-heavy 911 models with a state of suspension tune that counters its natural tendency to overseer.



Another example of classic oversteer in a tail heavy rear engine Porsche 911.

How does a tuner manipulate tire loading and slip angle? By tweaking the spring rates, anti-roll bar rates, tire sizing, tire pressure and to a lesser degree the shock damping. The first and cheapest option a tuner has is to increase the tire pressure. The harder a tire is inflated, within reason, the smaller slip angle it develops. For example, in the case of a nose-heavy front-wheel drive car, if you add several psi to the front tires and take some pressure out of the rear, the front tires will run a smaller slip angle while the rear tires’ slip angle will increase. This alone will do quite a bit to reduce understeer.


In a corner, the car will roll toward the outside of the turn, transferring weight to the outboard wheels. Suspension tuning has all to do with manipulating this weight transfer with springs, shocks and antisway bars.

Changing the spring rate and anti-roll bar torsional rate has a large impact on slip angle. Running a stiffer spring or anti-roll bar on one end of a car will cause more weight to be transferred onto the outside tire as the car tries to roll in a corner. The softer end of the car will compress and the more stiffly sprung end will resist compressing putting more load into that tire causing it to run at a bigger slip angle. So for your theoretical understeering, front-wheel-drive car you can run a bigger rear anti-roll bar, stiffer springs or both to tune out understeer. Conversely, stiffening the front suspension and increasing the rear tire pressures can help tame an oversteering car.


Getting larger antisway bars or adding an antisway bar where none was before not only reduces roll on a corner but changing the ratio of stiffness allows tuning of the weight transfer affecting under and oversteer. Adjustable sway bars are perhaps the most effective tuning tool for the average guy. These Progress Group swaybars are three way adjustable.

Shocks can improve response and help with balancing the car. Adjustable shocks can be a powerful chassis tuning device as well. As an example soft shocks get the car to a steady point of weight transfer faster right after the initiation of a turn. When set stiff they will delay weight transfer. Thus shocks affect how the car feels at turn in and also how it feels past mid turn. A car with the shocks set fairly hard will turn in sharply. If the shocks are set too hard, the car’s balance might change later in the turn in an unpredictable way as the heavy damping slows the body roll and weight transfer down. An analogy is that shocks are weight transfer capacitors.


Putting the endlink in the closer holes increases the bar rate and putting it in the further holes reduces it. Unlike springs, adjustable bars can be quickly tuned at the track by someone of average mechanical skill.

Tires sizing can also affect chassis balance. Installing a wider tire on the end of the car that needs traction most is obvious. Rear engine Porsches have wider rear tires to help prevent oversteer. Powerful rear-wheel-drive cars also tend to have wider tires in the rear than in the front. Many front-wheel-drive autocrossers and road racers install a wider front tire to get more front grip.


A major advantage of coilovers is that you can choose from a large selection of race springs to give you endless tuning options. Hyperco, Eibach and Swift all make top quality racing style springs.

What’s considered to be ideal by most performance drivers and suspension tuners is a car that is basically neutral when cornering without brake or throttle input. At the limit of adhesion, the car slides with all four wheels. Being able to provoke slight oversteer by lifting the throttle and more aggressive oversteer with slight braking while cornering at the limit is useful as well. Being able to slow rotation and reduce understeer with slight throttle application is good. This applies to both front- and rear-drive cars. Rear-wheel-drive cars should also be able to invoke oversteer with large applications of throttle. Balance like this gives the skilled driver the most options to control the car at the limit of traction when driving.

Stiffer Softer
Front Antisway Bar More Understeer Less Understeer

Rear Antisway Bar More Oversteer Less Oversteer

Front Spring More Understeer Less Understeer

Rear Spring More Oversteer Less Oversteer

Front Tire Pressure* Less Understeer More Understeer

Rear Tire Pressure* Less Oversteer More Oversteer

Front Shock More Understeer, later in turn Less Understeer, later in turn

Rear Shock More Oversteer, later in turn Less Oversteer, later in turn

* This is a rule of thumb, extremes of under or over inflation will not act like this. Very high tire pressures will reduce grip due to crowning and low pressures may increase grip due to flattening out the footprint.

Finding this interesting and useful? Stay tuned as we will continue to unravel the mysteries of suspension tuning in the months ahead!

The Ultimate Guide to Suspension and Handling Part 4: Reduce weight transfer

By Mike Kojima

Now that you have reduced body motion and improved steering response, and tuned out under or oversteer to improve the chassis balance, our next step is to reduce weight transfer. Weight transfer is the movement of weight from the inside to the outside wheels of a car under cornering.






Grip goes up with load but the relationship rolls off at a certain point.

Excessive lateral weight transfer hurts handling. It is caused by centrifugal force working on the chassis’ center of gravity which loads the outside wheels and unloads the inside wheels reducing mechanical grip. Increased load on the outside wheels increases grip but not as much as decreasing the load on the inside wheels reduces their grip.

Weight transfer = ( Lateral acceleration x Weight x Height of CG ) / Track width

In case you didn't know, a car's center of gravity is the point where the car's mass is centered about, If you were balancing a car on your finger tip, the point it balances at is the lateral center of gravity. If you were balancing it on its side, that point would be the car's vertical CG location.




Contrary to popular belief, body roll does not contribute very much to weight transfer. The car's CG will only move laterally a fraction of an inch, not conducive to shifting weight. Typically this is only 1-1.5 percent.

Contrary to popular belief, very little weight transfer can be attributed to lean in a corner. Even at large roll angles weight transfer due to roll is quite small. So, lowering a car’s center of gravity and widening its track width will reduce weight transfer much more effectively than reducing roll angle by an order of magnitude. You can calculate the amount of weight transfer due to body roll thusly.

Distance of CG lateral displacement= Height of CG x sin x degrees of body roll°

Total weight tranfer= Weight of car- (Weight of car x ( one half of track width / Distance of CG lateral displacement) / track width)

A typical performance street car might roll 3-4 degrees at maximum cornering speed. A modified high performance car will roll about 2-3 degrees. A race car might roll .7-1.5 degrees. So if you crunch some numbers on your car you will see that lowering the CG or making the track width wider affect weight transfer a lot more than limiting roll.


This grossly exaggerated example shows how load transfer is affected by body roll.


You could lower your car cheaply with lowering springs but typically these end up hurting your handling as almost every set we have ever tested is too low and too soft and the car bottoms under roll causing irregular handling. The proper way is with a shorter bodied shock which usually means a set of coilovers. This way the car can get lower with out loosing bump travel. These coilovers are made by the Progress Group.

Lowering the center of gravity or CG for short is best accomplished by lowering the car's ride height. It's best because you are lowering the entire mass of the car. Lowering the ride height also has the side effect of improving the car's aerodynamics as well. Lowering is usually accomplished with shorter springs. The smartest approach is to use shorter springs and shorter bodied shock absorbers or struts which maintain stock compression travel at a lower ride height.


You can go too low. Last year Formula D pro drifter Matt Powers was the hero of the hella flush fanboys. In last years trim, Matt's car was leaving a lot of performance on the table. Photo by Larry Chen

There is a point of diminishing returns though. Excessive lowering can change suspension geometry for the worse, including such bad side effects as causing positive camber under roll, causing excessive gain of negative camber under roll and contributing to increased bumpsteer. Over lowering can also cause more body roll by screwing up roll center location. We will get more into the details of what can happen in future editions of this series but lets say that most cars should only be lowered 1-2" because of these mitigating conditions hella flush or not.


This year Matt had to up his game as Formula D is getting a lot tougher. Matt raised his car up and it's working better. We are helping him with his set up too. Photo from our buddies at Speedhunters.

The easiest way to increase track width is to use wider wheels and tires that fill out the wheel wells. This also increases the amount of rubber on the road improving mechanical grip. Using wheel spacers and wheels with a more positive offset can also increase track width. Too much of a positive change in track width can increase the scrub radius. This is the distance from the centerline of the tire's contact patch to a point on the ground where an imaginary line drawn through the ball joints of the suspension meets the ground in the case of a multilink suspension.

On a car with McPherson struts the point is determined by drawing the line through the top strut mount bisecting the middle of the lower ball joint to the ground. The distance between this point on the ground, known to Coleman fans as the Dave Point and the center of the wheel forms a lever arm. The lever arm increases the forces that the tire generates causing torque steer in front-wheel-drive and all-wheel-drive cars. It will also cause twitchiness and steering pull while braking especially on split coefficient of friction surfaces or road surfaces with uneven surfaces.


To minimize the change in scrub radius it’s important to try to increase wheel width to the inside of the car as well as the outside by closely paying attention to the wheel offset. This puts more rubber on the road and increases the track while maintaining the same scrub radius.


It's not all about stance if it's retarded. Maxing out your track width and offset can reduce weight transfer and improve mechanical grip but taking it to an extreme is just plain dumb. This probably doesn't handle too well for obvious reasons. I don't think the owner cares though.

Increasing track width also changes the motion ratio of the suspension, which effectively reduces the suspension spring and anti-roll bar rates. Lastly, a very positive offset wheel puts a large strain on your wheel bearings, ball joints and steering linkage making them wear much faster. All of these are good reasons not to go crazy with this method of increasing track, hella flush, all about stance and whatever stupid trends be damned. A good rule of thumb is that it’s safe to use the largest wheels and tires you can stuff in your stock wheel wells doing no more than rolling the inner fender flange.


The Hella flush look can be performance enhancing if done correctly though!

A good guideline is to increase the track width and lower the car more on the end that that slides first in a corner. An understeering, nose-heavy front-wheel drive car can use more track width and a lower ride height in the front. A powerful, rear-engine car can be lower and have more track width in the rear. This play on physics will help in reducing weight transfer in both cases.


The Cyber EVO, the world's fastest time attack car uses maximum offset and fills its wide body out to the limit.

In the next installments, we will discuss more basic mods that you can do to greatly improve handling, some of the common deadly sins of modifying your suspension and basic tips on suspension geometry.

Ok here comes IMO the MOST IMPORTANT CHAPTER!!!! (hellaflush fan bois be warned)

The Ultimate Handling Guide Part V: The One Unforgivable Sin, Overlowering Your Car

By Mike Kojima



This is a primo example of Hella Flush. Super low, big offset so wheels are flush with and tucking into fenders. Although this is unfunctional and the car won't handle well, you gotta admit when done right, it sure looks good... Photo by Speedhunters.com

This sin is over lowering. Enthusiasts can hardly help avoiding committing it. It. is compounded by the efforts of the performance aftermarket. Nearly every company that makes suspension components, even very reputable ones, spew out thousands of sets of lowering springs that are both too low and too soft for optimal handling. Why do they do this? Are the engineers at these companies incompetent? Is it a conspiracy by domestic carmakers to make our cars suck?


Our buddy Formula D Pro Drifter Matt Powers before we started to help him was the hero of the hella flush fan bois. By poking fun at this trend we will be lambasted by them as this spreads around the net.

No the enthusiast is to blame for this issue. The majority of enthusiasts want a low ride height to fill the ugly gap in a car's stock wheel wells. They also won’t accept a ride that for the most part is a lot harsher than stock. Macho or not, most typical enthusiasts don’t drive hard enough or well enough to realize that their cars actually handle worse than stock, mistaking reduced roll as better handling.


Matt killing it. Look how low his car is!


The 2010 Formula D season has gotten a lot tougher with the cars getting much faster over the 2009 season. We started helping Matt and suggested raising the car to get more usable wheel travel among other things. Matt is killing it even more this year even with much tougher competition. Sorry superlow Matt fans, please continue to support Matt! There is a reason why the cars that normally populate the Top 16 are not super low any more, it doesn't work.

"Car style is not what I want to be known for. I would like my car to look as cool as possible granted, but this is a competition, not a car show. When that is a critique someone levels against me I want to say I don't take them very seriously in their opinion of or understanding of professional drifting." -Matt Powers Photo from Speedhunters.com


Lately the rise of the Hella Flush aesthetic is also to blame. The look of big lipped Wheels with stretched tires tucking into the wheel wells just missing the fenders brings another layer of stupid to the table. The fact is, cars are designed to run at close to the stock ride height and making them super low messes stuff up on many levels. Do you wanna be Hella Flush or Hella Functional? If it’s the latter read on.


This is a comical example of two retarded trends, Hella Flush and Demon camber. You should be able to figure out why this doesn't work!

FWD cars can be Hella Flush too where the offset works to increase torque steer and steering wheel fight. Another thing we don't get about the trend is the bike racks without bikes. Maybe your fixie goes here?

A Sentra SE-R is a typical example of a car that should not be lowered more than an inch. It can be lowered more than that but its suspension design isn't happy about it. This situation is common on many cars and not just indicative of the SE-R’s design, we have just thoroughly studied this car's geometry because we race one.


Hyperco lowering springs for the Sentra SE-R were an exception, they were made only 1" lower than stock and 100% stiffer. These actually helped handling when combined with a good set of shocks.

The first problem with lowering the SE-R (and most McPherson strut equipped cars) is that it only has about 2” of jounce travel at stock ride height in the front suspension. Let's say you lower the car the typical 1.5”, you are left with only about .5” before you hit the bump stops. Your typical aftermarket lowering springs only up the spring rate a paltry 20% or so, not enough to keep the car off the bumpstops with only 0.50” of travel. Not only does this ride poorly, bottoming out frequently and all the time if carrying passengers, but in a corner, when the car leans over, the suspension will quickly settle on the bump stop causing the spring rate to rapidly ramp up approaching infinity quickly as the bump stop smushes down. This causes huge amounts of weight transfer and a build up of slip angle in the outside front tire suddenly resulting in relentless understeer. When the car initially hits the bumpstop, the perceived increase in stiffness makes the car feel responsive, sort of like a go kart but this snappyness in steering response turns into inescapable understeer in a few milliseconds after turn in is initiated.


Mad Mike Whiddett is the most famous person representing the Hella Flush aesthetic in actual pro competition with the Bad Bull RX-8. He is going to go more conventional for next years Formula D season to get his car to handle better. Sorry Hella Flush fans, Hella Functional rules!

It gets worse, some cars like a Nissan B14 Sentra have very little rear wheel travel. If the car is lowered too much, it can bottom out in the rear first, resulting in a lot of sudden oversteer.

Many might argue that the lower CG of the lower ride height makes the car handle better due to reduced weight transfer but for sure, infinite spring rate on the outside wheel causes way more weight transfer in the wrong direction low CG or not, this sucks.


On cars with McPherson Strut suspension, the suspension loses negative camber under roll when the car is lowered to the point where the angle of the lower control arm to the strut is more than 90 degrees. This causes a loss of grip. A general rule of thumb is that if the arms are pointing upward, it's probably not good.

Wait, it gets even better. On the SE-R the lower control arms are positioned so that they start pointing upwards towards the wheels as soon as the car gets lowered more than just a little bit. Guess what? Now with your lowered SE-R, the camber starts getting positive as the car rolls, causing the tire to get up on its outside edge. This is not an effective use of your tire.


Notice what else happens when you lower a car too much without correcting the geometry. The roll couple gets longer. The roll couple is the distance between the roll center and the center of gravity. This is the lever arm that centrifugal force works about to create a tipping force to roll the car over in a turn. When the car gets lower, the lever gets longer and there is more force wanting to lean the car on its side. More tendency to roll and less wheel travel could mean trouble.

More bad things happen as well. As soon as the lower control arms start to point upward, the instant center (the imaginary point in space that the car rolls about) starts to drop rapidly and the roll couple (distance between the roll center and the center of gravity, this is the lever that centrifugal force works upon to roll the car over) greatly increases, it increases faster that the center of gravity drops due to the lowering. The bigger roll couple causes more body roll making everything worse.


The phenomina of incresed roll couple happens with unequal lenth A arm suspension as well, as illustrated here.

Finally as the control arms point upward, the steering tie rods start to point upwards much more rapidly because they are shorter, making them run in a much tighter arc out of plane with the lower control arms. This cause toe-out when the wheels deflect making the car twitch, especially when a single wheel bump is hit.


This picture illustrates ideal link placement for zero bumpsteer on a MacPherson strut suspension. Unfortunately most production cars are not exactly like this so they have bumpsteer under roll and compression. Usually bumpsteer is designed to at least be minimal close to stock ride height. When the car is lowered alot, the relationship of everything gets out of place and bumpsteer because really bad which makes the car feel squirrelly and unstable. On a Nissan Sentra for instance the bump steer is nearly as great as the wheel travel when the car is lowered more than an inch.


This picture illustrates ideal link placement for zero bumpsteer on an unequal length A arm suspension. Over lowering this type of suspension can cause lots of bumpsteer for the same reasons as the Mac strut but sometimes even worse.

These issues make a lowered SE-R a slow machine on the track if the lowering is done with parts designed for the demands of the market instead of what works. Unfortunately, this situation is not unique to the Sentra. The Neon is even worse for many of the same reasons. Many, many cars out there handle poorly with lowering springs. Most performance enthusiasts drive around blissfully unaware that their wonder-lowering job has actually reduced road holding and slowed their cars around a road course, skid pad or autocross. Fortunately for the market, many enthusiasts will never test their cars savvy in a competitive event.




The best way to lower your car is to get coil over suspension that is designed to be lowered. The DG Spec Scion TC sold by Dezod is an affordable example and these Moton EVO coil overs are a more exotic and expensive example.

What can you do as a suspension tuner to avoid overlowering?

• Make sure the car doesn’t get on the bumpstops under maximum cornering load. The easy way to tell this is with a zip tie tell tale on the shock shaft
• If you must run super low, do it race car style. Get short-bodied high-end coil over shocks and struts with higher rate springs that are designed for a lower ride height. This suspension is designed for a low ride height. Many popular cars have kits to adjust and correct roll centers, camber curves and bumpsteer when lowered with shorter coilovers, use them. If not, these parts can be fabricated with universal race car parts.
• If you can’t get a decent rate drop in spring for your car, Ground Control makes kits for many cars allowing the use of Eibach 2.5” ERS racing springs which come in nearly an infinite selection of rates and lengths. With Ground Control’s threaded spring perches, you can also adjust the ride height.
• If you can’t do any of this, run short soft progressive microcellular urethane bump stops so the wheel rate will ramp up gradually if the car gets up on the bump stops. Koni makes excellent bump stops.
• If you have McPherson strut suspension, be especially aware of short travel and suspension geometry problems. McPherson strut cars usually have a small window of where they can be lowered without messing things up. It is really typically best to run these cars at close to the stock ride height unless you significantly modify many other components.



A lowered Sentra handles horribly. We had to do a lot of things to correct the geometry when we lowered the suspension 3 inches. We had to relocate the lower ball joint lower to correct the roll center and camber curve. To reduce bumpsteer we had to flip the tie rod to the bottom of the spindle to lower it around 2 inches.

The biggest difficulty you as a tuner will encounter is convincing the dumped to the ground hella flush ricer with his super slammer springs that he has actually messed up his car. Actually don’t bother convincing them, if they are a fellow competitor, the convincing will be your smoking them on the track; after all it isn't all about stance.

The Ultimate Guide to Suspension and Handling: Part Six, Adding Negative Camber

By Mike Kojima


In the first 5 parts of this series you learned some basic steps to improving your car’s handling. The first four steps involved the use of basic performance suspension parts available for most cars, the parts that most people with an interest in handling obtain. Been there, done that? Then it's time to head for more advanced suspension tuning, involving the alignment, chassis stiffness and suspension geometry.

Step Six: Add Negative Camber

Adding negative camber the MotoIQ way should be done methodically to enhance cornering power and road holding. Getting a lot of camber so you can be Hella Flush and have stance is sorta dumb to us. Sometimes when seeing those pictures from the "all about stance" crowd with credit cards in the fender gap, I want to roll my eyes. At least that's my opinion, for all of the Stance Nation out there, do what you like and all the more power to you, just don't think your car is going to grip or drift better because of it!


Negative camber is shown on the left when the tops of the tire tilt inward. Positive camber is on the right where the tops of the tires point outward. Dynamically, negative camber improves grip in a corner unless it is over done.

For a tire to grip well it must use its entire contact patch. Thanks to problems like tire distortion and production car compromised suspension geometry this rarely happens. When a tire is subjected to side load its sidewalls flex, digging the outside tread into the ground and lifting the inside. If you drive hard, you have probably noticed that the outside edge of your tires gets chewed up much faster than the rest of the tread.


This picture really shows why negative camber helps grip. Look at the heavily loaded outside front wheel of this Sentra. The tire is so distorted, it is practically rolling over and the rim is almost hitting the ground. The tire's outside shoulder is loaded heavily and the inside of the tread is lifting off the ground. Effectively only about half of the tire's contact patch is being used. The result, a big loss of grip and grinding understeer.


This picture illustrates what happens to a tire and suspension under roll and heavy cornering load. As the car rolls, the bushings can deflect and the amount of negative camber gain in the suspension's geometry cannot keep up with the loss of camber under roll. The tire ends up tilting toward positive camber. In addition the tread lifts and distorts under roll, loading the outside and lifting the inside. You can see how adding a few degrees of static negative camber is going to really help a lot here. You might wonder why the engineers of the suspension system didn't design the suspension geometry to gain more negative camber under roll. The answer is that a high degree of negative camber gain gain will cause the car to feel unstable and hunt, especially over bumps when the car is going straight. The solution is to increase roll stiffness to limit roll, run harder bushings and increase negative camber.As a car rolls in a corner, the chassis roll tilts the tire onto its outside edge making the problem worse. Keeping the tires flat on the road is the primary reason to reduce roll. In Part One we listed several ways to do this, the easiest ways are to increase spring rate or use larger anti-roll bars. However, the primary tool used for combating tread lift is to run more negative camber. Camber is the inward or outward tilt of the tires when looking at them from the front. Positive camber is when the top of the tire tips outward while negative camber is when the top of the tire tilts inward.




High performance radial tires typicaly generate more camber thrust than this but the curve rolls off faster as the camber gets past 5 or more degrees. Camber thrust helps mechanical grip.

Another often overlooked positive factor regarding adding negative camber is camber thrust. Tires, when tilted towards negative camber, particularly radial tires, generate an inward facing force. This force is generated by the tire wanting to return to its normal undistorted condition. It is both an elastic and a pneumatic force. In a corner, the heavily loaded outside tires when run with a lot of negative camber can provide an inward force vector of up to several hundred pounds. This helps generate more mechanical grip. Typically a modern radial competition tire generates peak camber thrust at around 4 degrees negative camber. Unfortunately most tire companies will not release this data so it must be estimated through tuning and trial and error.


This illustration shows the tire profile distortion typical of what happens under side load. This is not exaggerated. On the track it can be much worse to where the tire actually runs up on the sidewall and half the inside tread lifts off the ground. Negative camber counteracts this.

Dialing in negative camber helps combat tread lift and roll related wheel tilt. Camber thrust is also generated. The trick is to add just enough negative camber so the tread stays flat and 100 percent engaged with the ground under side load and roll while maximizing the camber thrust effect. Adding too much negative camber will hurt more than it helps. Too much negative camber will:

• Reduce braking traction.
• Reduce acceleration traction if it’s applied on the drive wheels.
• Increase the tendency to tramline (following cracks and grooves in the pavement)
• Increase crown sensitivity (wandering caused by road contour).
• Affect tire wear; the insides of the tire tread will wear faster with more negative camber if you don’t corner hard. Conversely, if you constantly corner hard, your tires will wear more evenly and last longer


Adding negative camber will increase the height of the slip angle curve and extend the point where cornering force rolls off to the right.

Your car and your driving demands together determine how much negative camber you need. Aggressive drivers should use more. Those concerned about tire life while commuting should use less. Even though their sport involves sliding the car, many top drifters also prefer road racing type camber settings to get the best balance and most even wear from their tires. Suspension design also matters. McPherson strut cars need more negative camber to work well under cornering load; unequal length A arm and multi-link suspensions generally need less negative camber. Softer suspended cars that lean over in turns generally need more negative camber to grip well.


A 3D example of the tire distortion present under lateral loading. The forces generated are quite large. Negative camber can overcome much of the bad effects caused by this distortion.


The following table provides a rough guideline of how much negative camber to run based on your driving style, keeping in mind that tire wear matters. Surprisingly, the baseline settings are roughly the same for all typical chassis layouts, front engine front-wheel drive, front engine rear-wheel drive, front engine all-wheel drive, and mid engine rear wheel drive.

Driving Use Front Rear

Multi MacPherson Multi Link/Unequal A-Arm MacPherson
Link/Unequal A-Arm Strut Strut

Aggressive Street
Driver -1.5-2 -1.75-2 -0-1 -0.5-1
Weekend Hot Lapper -1.5-2.5 -1.75-3 -0-1.5 -1-1.5
Racer Only/ Serious Drifter -2.5-4 -3-5 -0-2 -1-2.5


A camber plate allows for fast adjustment of camber on MacPherson strut suspension. However adjusting the camber at the top of the strut affects the steering axis angle which can have other effects.

Unfortunately, camber is not adjustable on most modern cars. Even if camber is adjustable, it’s rarely adjustable enough to align a lowered car correctly. The best way to adjust camber on the typical MacPerson Strut is to use a camber plate. MacPherson Strut camber plates use an adjustable top mount which locates the upper shock mount spherical bearing in a retainer plate that slides laterally on a slotted track.


Elongated bolt holes with a lower eccentric are a pain but a better way to make large adjustments of negative camber in strut cars. You can duplicate this cheaply by slightly grinding out , drilling or slotting one of your strut mounting bolt holes so you can move the wheel toward negative camber. This is typically better than using small diameter cammed camber bolts which usually end up slipping.

A less expensive but less handy way to make your camber adjustable is to weld a U-channel bracket to the lower control arm mounts and install a lower control arm bolt with fixed eccentric cams riding in the U-channel. Turn the bolt and the eccentrics move the lower control arm in and out adjusting the camber.


For multi link suspension, adjustable links are the best way to adjust camber like these parts from SPL.

Simply enlarging the two lower mounting bolt holes in the strut housing about 1/16” with a drill, holding the wheel in the direction of negative camber and retightening the bolts can give you quite a bit of no-cost camber adjustment.


Eccentric bushings like these Whiteline parts can also be used to adjust camber on some cars.

Avoid using the undersized shaft, eccentric cammed bolts sold under the name of crash bolts. Crash bolts are sold as a cheap way to adjust camber on crash damaged cars. Because of the small shaft diameter, they usually stretch and allow the camber adjustment to slip under the load of hard driving with sticky tires.


MacPherson struts will slightly gain negative camber under roll at first which is good, but as the roll angle increases they will actually lose negative camber, not good! It is really important to limit roll on strut equipped cars for this reason. The lower rate of negative camber gain is why you must usually run more negative camber on a strut car when compared to multi link or unequal length A arm suspension cars.

Cars with multilink or unequal length A-Arm suspension can sometimes use adjusting shims in the upper control arm mount to adjust camber. For popular sports models like the 240SX, 300ZX, 350Z, STI and EVO there are plenty of adjustable links on the market to adjust camber. Many multilink or unequal length A arm cars have adjustable camber from the factory.


Cars with unequal length A arm or multi link suspension gain camber through the entire suspension travel. They are engineered to have a faster rate of negative camber gain under roll than what is possible with the crude and simple MacPherson strut. This is a reason why cars with this sort of suspension typically handle better and why more expensive cars have this type of suspension.

Adjusting camber is well worth the effort, optimizing the camber for your type of car and driving style can often make a bigger difference in the amount of stick the car can generate than any other mod besides tires.

The Ultimate Guide to Suspension and Handling: Part Seven - Tuning your Toe

By Mike Kojima


Previously in our series we were talking about general tips for you to follow when tuning your suspension. In our last installment we talked about adjusting your camber to gain more grip. Today we will talk about an easier and more basic adjustment that has a great influence in handling, adjusting your toe settings.

Tune Your Toe

Toe refers to the direction a car’s tires are pointed relative to each other when viewed from above. Toe in means the front of the tires are closer to each other than the rears. The opposite is toe out.




From the left to right, toe in, toe out and zero toe as shown from above looking downward. Of course this is the front wheels but you can also tune toe on the rear wheels with good effect as well.

Fine tuning toe settings will allow a measure of control that is often overlooked. It also has a significant effect on how a car behaves in a corner. Front toe settings make a big difference in how a car handles in the first third of the turn, the critical turn in phase where cornering force is initiated. Rear toe settings can be critical for helping a RWD car get on the gas on the exit of a corner harder and sooner.

Toe adjustments are not well understood but can make a big difference and can be used to help you go faster in all motorsports from autocross, to road racing, to rally and drifting.

The cool thing is that toe settings are probably one of the easiest alignment settings to do and all cars are toe adjustable with the exception of rear toe in cars with beam and solid rear axles. This makes it so you can experiment with different toe settings and get a feel for how they affect chassis balance.

FWD cars like Dez Ballard's Mini can almost always benefit from some amount of toe out. The only potential drawback is accelerated tire wear. On a really high powered FWD car too much toe out can cause a lot of torque steer.

Front Toe Out

Front toe out is a useful tool that can really help a car when used in moderation. Many cars and situations can be helped with a little toe out. Generaly front toe out speeds steering response and reduces understeer in the first quarter to third of a turn.

Front Toe Out



Just Right Too Much
Helps reduce understeer on turn-in Makes car twitchy under braking
Makes car more responsive to steering input Unstable in a straight line, especially over single-wheel bumps or split traction surfaces
Helps FWD and AWD cars counter their natural tendency to toe-in under throttle load. An extreme amount of front toe-out will cause the car to refuse to turn and go into unrecoverable understeer
Car will be very crown sensitive and tend to follow the contour of the road strongly.

AWD cars like the EVO and STI almost always benefit from front toe out as well. Nose heavy AWD cars with transverse engines derived from FWD cars can particularly benefit.

Mid engine cars can sometimes benefit from a slight amount of toe in to prevent wandering and to keep them from feeling too twitchy.

Front Toe In

Front toe in can be used to help straight line stabilty, especialy with RWD rear and mid engine cars. Front toe in usualy slows steering response and can cause understeer in the first third of a turn,

Front Toe In



Just Right Too Much
Generally helps make the car feel more stable. Usually done in small amounts on RWD and rear engine cars. Wandering under braking
You would probably do this on your mom’s car or a car that you mostly care about driving on the street for normal use. The car will refuse to turn in or turn in very quickly and immediately go to understeer, feels sluggish to steering input.

Rear engine cars can benefit from a little toe in like mid engine cars. A lot depends on driver preference.

RWD front engine cars like this S2000, especially ones with a close to 50/50 weight distribution can also sometimes do well with a little front toe in.

Rear toe out has limited use. One of the times it sometimes works is on a FWD car being used for stock class in autocross. It can help the car rotate in tight low speed turns where it would normally get grinding understeer and you are not allowed to do anything else in the way of mods to fix the issue. Sometimes it can work surprisingly well. It can make the car tricky to drive at high speeds so caution must be used.

Rear Toe Out

Rear toe out is not a very useful setting. It hurts in almost all cases except for helping rotation on a FWD car when you are completely out of tuning options. We have only used this successfully for Stock Class Autocross and Rally in FWD cars.

Rear toe out works surprisingly well for FWD dirt autocross too. This Mini looks like it could use some!
Rear Toe Out




Just Right Too Much
Helps the car rotate in mid turn and get away from overloading the front tires with understeer. Generally this is a FWD only trick usually for stock autocross classes or rally. Causes sudden onset of oversteer on throttle in RWD applications. Causes violent oversteer all the time on anything other than a FWD car. Car feels unstable.
Generally you would not ever want to do this unless you had no other tuning option. Makes a car rotate violently when the throttle is lifted or when the car is trail braked into a turn. Generally not good.

Rear toe out can help FWD rally and rallycross cars rotate. For high speed tarmac special stages, this might have to be dialed back.

Rear Toe In

Rear toe in is a useful setting that can make the car more stable under power application while turning. It can also be used to reduce trailing throttle oversteer or snap oversteer. Don't overdo it, too much rear toe can cause initial understeer and snap oversteer.

High powered drift cars often run a lot of rear toe in which stabilizes the back of the car allowing the driver to really step on the gas and get more wheel spin. This is a crutch for proper suspension tuning but it is a quick and dirty suspension tuning trick that can be called upon in the fast paced environment of drifting.
Rear Toe In




Just Right Too Much
Helps a RWD car get on the throttle sooner and harder, making power oversteer feel more natural and manageable. Makes a car sluggish in response and creates a tendency to understeer in mid turn and sometimes on exit.
Helps a driver of a drift car stand on the gas and sometimes get more forward bite under drift. Gives a car a weird rocking wandering feeling on turn in. It feels very strange, unstable and awkward.
Less or zero toe can help an underpowered drift car maintain angle at high speed when the engine doesn’t have enough power to maintain wheel speed. Makes a drift car twitchy under drift and want to grab traction and straighten out suddenly. Extreme toe in can cause initial understeer with a sudden transition to oversteer.
Can reduce or eliminate over rotation under trailing throttle or trail braking.

An AE86 has a solid rear axle. If you want to adjust the toe setting you have to bend the axle housing. A good chassis shop can do this.

B14 and B15 Nissan Sentras have beam rear axles. The axle has a lot of rear toe in from the factory which makes the handling twitchy at the limit. The rear beam axle must be bent to remove the toe in.

Toe plates are handy for quick toe checks on the fly. They are simple and easy to use.

Too much toe-in or out:
• Causes tire wear on the outside and inside edges of the tire respectively. Toe can ruin a tire very quickly.
• Any toe setting past 1/8" of an inch either way has a very negative effect on tire life in street driving.
• Too much toe has probably ruined more tires on lowered cars than any other single attribute.
• Anytime you use more than ¼" of toe, you are risking getting into the too much zone, proceed with caution.

Smart strings are super accurate and are used to set the toe on all 4 wheels at once off of a common datum plane.

Every car is adjustable for front toe through the steering tie rod ends. All multilink cars are adjustable for toe front and rear. Cars that are live or beam rear axle usually must have the axle or axle-housing bent to adjust toe by an experienced chassis shop although some can be adjusted with wedge type shims under the hub carriers.

Below are some typical toe adjustments for different cars, tire wear expectations and styles of driving.*

Driving Use FWD/ AWD
RWD
FWD/AWD
RWD

Aggressive Street Driver
Front 0
Front 0 to 1/16” in
Rear 0
Rear 1/8” in

Weekend Hot Lapper Front 0-1/8” out Front 0 to 1/8” out Rear 0-1/8” out Rear 1/8” in
Racer Only/ Serious Autocross/ Serious Drifter Front 1/8-1/4” out Front 0 to ¼” out Rear 0-1/4” out Rear 0-1/4” in

*The Nissan GTR and GT-R uses alignment settings more like a RWD car instead of an AWD car as it behaves more like a RWD.

Since toe is easy to adjust, we suggest you use the above as a rough guideline and experiment to tune your chassis to your preference.

The Ultimate Handling Guide Part 8: Understanding Your Caster, King Pin Inclination and Scrub

By Mike Kojima

Understanding what caster does and how to use it is a powerful tool in the box of a suspension tuner. Since caster is not adjustable on nearly all FWD cars and usually not adjustable for many late model cars as well, we saved its discussion until now. Discussions of caster pertain to the front suspension only as caster comes into play as steering angle is induced.


Caster in a car is like fork rake on a bike. They have about the same effect on both.

Caster is the angle from vertical of an imaginary line drawn when looking at a car from a side view through the ball joints of a multilink suspension car to the ground. On a MacPherson strut car the caster angle is the angle of the line from vertical drawn from the top strut mounting point through the lower ball joint to the ground. Think of caster as the fork rake angle of a bicycle or a motorcycle.


This is positive caster in a car. It is the angle about which the steering pivots in relation to the front and rear of the car.

Positive Caster is when the angle is sloping backward toward the rear of a car like fork rake on a bicycle or motorcycle. Negative caster is when the angle slopes forward. Negative caster in the steering geometry just doesn’t work so we won’t discuss it any further. Vehicles do not use negative caster.


This illustration shows positive caster, negative caster which no car ever has to our knowledge and the shopping cart caster analogy which we will discuss on the next page. You should be getting the idea by now!

Caster works with another aspect of steering geometry known as kingpin inclination angle or KPA for short. Another name that can be interchanged with this is steering axis. This is the angle of the line from vertical drawn through the same joints as caster but viewed from the front of the car instead. The KPA is always sloping towards the center of the car and expressed as degrees. KPA is not adjustable on production cars but commonly is on race cars.


Kingpin Inclination Angle or KPA is demonstrated by the red dotted line. This is the view when looking from the front of the vehicle. For a MacPherson strut car the KPA is measured by drawing a line from the top strut mount through the lower ball joint to the ground. The point where the line hits the ground is called the Dave Point because Dave Coleman could not find an official name for this point so he named it after himself.

Caster and KPA greatly affect straight-line stability. Increasing positive caster projects the Dave point (the point where the steering axis projected line meets the ground) further away from the tire's contact patch. This creates what is known as caster trail. When the tire contact patch is behind the steering axis, the steering wants to stay centered behind the axis much like how a shopping cart's casters naturally line up in the direction of travel. I wonder if this is why they call it caster?

For grip driving positive caster is used to increase negative camber gain as the wheel is turned. The feel is typically improved turn in and straight line stability. Sometimes you can increase positive caster which will allow you to reduce static negative camber for better braking. Too much positive caster is felt as mid turn and later understeer and or bumpsteer. You must use caution using more than 8 degrees or so positive caster, especially with wider tires.

The distance between the Dave point and the tire contact patch forms a moment arm (engineer speak for a lever arm) creating a self aligning torque, lets call this SAT. The greater the positive caster angle, the bigger this moment is and the greater the SAT. It takes more of a deflecting force to overcome the SAT, which the driver perceives as greater straight line stability and on center steering feel, both of which are good things.


Perhaps the motorsport where caster and KPA are the most critical is drifting. Drift cars need a strong self steering effect as drivers use it to feed in large amounts of opposite lock quickly. Look at the large amount of wheel tilt seen in Dai Yoshihara's S13. Dai prefers strong self steering so this is all dialed into the suspension. Drifting is unique in the fact that front grip is mostly important at shallow drift angles as the throttle is used to steer the car to a degree at larger angles. This amount of KPA and caster would probably be detrimental for front traction in grip driving.

Increasing the SAT also increases the self steer effect. This is when the steering is turned, if the steering wheel is released, it will tend to self center in the direction of travel. This is handy in drift, dirt track and rally cars as it can be used to help a driver countersteer faster than he could by hand simply by releasing the steering wheel. SAT also helps a driver as it increases steering feel. If a car is starting to understeer, the steering will get lighter in the driver's hand. If the front has good bite, the steering will feel heavier.

Lots of positive caster causes the wheels to flop to the side when turning, gaining negative camber in a turn, right when you need it the most, a good thing. Think of a parked chopper with the wheel flopped to the side. That’s an extreme example of negative camber gain with positive caster.


Kingpin Inclination Angle makes the spindle's stub axle move in an upside down smile as the wheels are steered from one side to another. It causes the car to lift as the wheels are turned. The car naturally wants to stay at the top of the arc where the weight of the car isn't being lifted. This is what causes good straight line stability and self steering.

KPA increases stability by making the axle path travel in an upside down U shaped arc when viewed from the side during tuning. The apex of the arc is when the steering wheel is centered. When the wheel is turned, the steering actually lifts the entire front of the car, the lowest point being at the centered point. This makes the steering naturally want to stay centered in the direction of travel with the steering effort increasing the more you turn the wheel away from this center. This contributes greatly to steering feel and straight-line stability. It is possible to run too much KPA making steering impossibly stiff. KPA also causes the wheel to tilt outwards when the steering is turned increasing positive camber, which is not good for cornering traction.


A rally or rallycross car has a lot of the same requirements for the front end geometry as a drift car. They can use a lot of caster and KPA, usualy both having an equal angle.

To counter this effect of KPA, the suspension designer balances KPA with positive caster, the positive caster canceling out KPA’s tendency to make the camber turn positive. In modern cars, there is usually quite a bit more positive caster than KPA so the steering geometry will generate more negative camber while turning. If you notice that certain cars renowned for straight line stability and good on center steering feel like Mercedes and BMW tilt there wheels inward when the steering is turned, it's because those cars have a lot of positive Caster and KPA built into their steering geometry. The Nissan 240SX and 300ZX also exhibit those traits and have a lot of both in their geometry as well.


A road racing or time attack car will have the bias more toward positive caster and less toward KPA as camber gain under turn in is more important than self steering action.

The balance between positive caster, KPI and scrub radius is particularly critical in high powered FWD and AWD cars as all of these factors can really affect torque steer.

If some of this is good, more positive caster and KPA are not necessarily better. The same moment that creates the self-aligning torque can contribute towards torque steer in a FWD or AWD car. This is why FWD and AWD cars often have less positive caster and KPA in their geometry. Excessive caster and/or KPA can result in understeer because tipping the tire on edge and lifting it extremely can cause the corner weight on the outside tire to drastically increase, artificially increasing weight transfer. Extremely wide tires exaggerate this effect. Sometimes when running much wider wheels and tires on certain cars like a 300ZX, you want to actually reduce the positive caster.


The Dog II runs 6 degrees of positive caster, a large amount for a FWD car. It doesn't have much torque or front scrub and the tilt of the caster actually moves the tie rods to a position with less bump steer on this particular car.

In severe cases it can result in too much negative camber is the case of excessive positive caster or too much positive camber in the case of excessive KPI. You can see this in some drift, dirt or rally cars as contact patch is sacrificed to get stronger and faster self steer action. Too much positive caster and or KPI can also result in more bump steer as it changes the relationship of the tie rod ends to the ball joint and inner lower control arm pivot.


The RWD Berk BMW has a lot of positive caster in its suspension geometry like all BMW's. Road racing cars tend to have a few more degrees positive caster than KPI while drift cars tend to have about an equal amount. This is because road racers need the negative camber gain while drifters need strong self steer.

Scrub radius comes into play in the game of balancing positive caster and KPI. To review; the scrub radius is the distance between the centerline of the tires contact patch and the point where the steering axis line (or KPA line extended or Dave Point) hits the ground. The scrub radius is a moment arm where the tire's contact patch can give feedback to the steering.


Here is your review of scrub radius. Hellaflush advocates take notice. This stuff matters if you care about performance. With careful tuning you can have a functional Hellaflush car. If you increase your KPA you can reduce your scrub even with a wheel with more offset. Increasing KPA moves the Dave point toward the center of the tire. It should be balanced with more positive caster though.

It is good to have a little scrub radius as it helps develop steering feel, the feeling of the steering wheel getting light as the front tires lose grip and firmer with more grip. It also helps improve the self steering effect. For a RWD car you generally want to run between ¾ of an inch to as much as 3”. In AWD and FWD cars, you want to try to limit the scrub radius to less than 2” because it increases the effects of torque steer.


Powerful AWD cars like the GST Impreza L must also be aware of the implications of running too much front caster just like a powerful FWD car.

Increasing the scrub radius too much can cause wheel fight and twichyness under braking, especially on split friction surfaces and more sensitivity to bump steer. An extreme amount of scrub will result in an overall loss of traction as turning the wheel will add a sideways sliding component to steering which will reduce traction.


Mike Essa's 2010 car shown here at Ken Block's Gymkhana had a huge amount of scrub in its front suspension geometry by design. It severely hampered its handling in both drift and grip events like this. His new car was designed to have correct geometry in the front from a clean sheet of paper and it handles much better.

It’s best to try and not deviate too much from the amount of scrub engineered into the car from the factory. To minimize the change in scrub radius it’s important to try to increase wheel width to the inside of the car as well as the outside by closely paying attention to the wheel offset, thus going wider while keeping the scrub radius the same. HellaFlush fanatics need to consider this.


You can have a Hellaflush car and still be functional. Dai Yoshihara's Team Falken S13 is pretty low and pretty flush. This is all OK because the highly adjustable suspension can be made to work like this and the nature of the setup allows it. We run a lot of KPA and positive caster so we have a good scrub radius even with a lot of offset. We also correct the roll center and bumpsteer to be correct with the car low. We also still have a lot of wheel travel. This is more like Hellafunctional. I guess I use Dai's car a lot as an example because I work on it quite a bit and know its setup inside out.

KPA affects scrub radius, more KPA reduces the amount of scrub radius so sometimes this is a good way to decrease scrub due to offset changes. Generally if you have a race car with adjustable KPA you usually set the car up with a couple of degrees less KPA than positive caster so you end up with a good but not excessive amount of negative camber gain with turn in. This way you might be able to get away with less static negative camber. In some cases you may want the KPA to equal the caster. KPA affects the scrub radius so sometimes you end up balancing caster, KPA and scrub to get the car to handle in a desirable way.


Stance is Everything yo! Dai's car is as Hard As F__k and so is the stunna flossing the carbon fiber credit card. Tiite! Who says I hate Hellaflush? If it doesn't affect performance it looks badass!

A lot of race cars use the camber plates to adjust KPA and really adjust the camber at the spindle or somewhere else. You should keep in mind that when adjusting the camber at a camber plate or upper control arm you can be affecting KPA and the scrub radius a lot!


These Sentra lower control arms were modified for more caster and KPA by offsetting the lower balljoint forward and making them longer. This also widens the front track and gives more negative camber, all helpful stuff.


Ground Control weld in plates adjust camber and caster at the top. We try to do most of our adjustment at the bottom and only do fine adjustment at the top due to the effect of altering KPA and scrub.

Adding positive caster:
• Generally improves straight-line stability,
• Sharpens turn in.
• Improves traction everywhere in the turn.
• Improves steering feel
• Improves self centering and self steer effect.

Too much positive caster:
• Makes the steering effort too high.
• Gives sharp turn in but increases understeer from mid turn onward.

The little table below gives you some adjustment guidelines for caster

FWD/AWD Degrees Positive Caster 3-4

RWD Degrees Positive Caster 4-10

Adding more KPA:
• Improves steering feel.
• Improves straight line stability.
• Gives a stronger self centering steering effect.

Too Much KPA:
• Makes the steering effort too high
• Makes the front wheels loose grip due to the addtion of positve camber unless balanced with positive caster.

Wheeww! Ok until Mike posts up another chapter the Ultimate Handling is up-to-date! I once again thank Mike Kojima and I hope all of you well read this carefully and hope it helps you and your project!

Good Shit! Gonna take a little while to read all of it, but definitely something worth reading.

No problem I hope it gets made into a sticky so everyone can learn a little and hopefully will help put more thought into suspension mods besides just "needs moar low". Big thanks to the legend himself, Mike Kojima for writing this article.

bumppp good shit man hope eveeryone reads this

Thats alot of info to take in! Great post, i'll have to sit down and read through it to get a better idea.

Thanks for the info dude!

Thanks man like I said I hope it is made into a sticky that all newbie's should read. I actually posted it at first out of frustration over the trends in today's scene ( read my rant thread in the general discussion section) but I hope it helps everyone and like I said before this would not have been possible without Mike Kojima writing this awesome article.

Yea, should deff be made into a sticky!