- Joelís Bench: On-Road Suspension Essentials -

Tune to win!
Words: Joel Johnson

Todayís competition touring cars have the most adjustable suspensions ever and can be finely honed to any track and surfaceóif you know what youíre doing. Many drivers just donít know where to begin when itís time to fix a handling problem or get a little more out of a setup that works OK but isnít fast enough. In most cases, all you really need to know are the basics: camber, caster, toe and ride height. When you understand these essential elements of suspension tuning, youíll be on the fast track.

Camber is the angle of the tires in relation to the track and is the most basic adjustment that any racer can make. It is measured in degrees. When you look at the car from the front or rear, the tires are not perpendicular to the ground; they are typically angled in slightly toward the chassis. When the tires lean toward the chassis, thatís negative camber. When the tires lean outward, thatís positive camber. Adding a few degrees of negative camber increases a tireís contact patch when cornering; the tire stays flatter as the suspension rolls due to the cornering forces.

HOW IT IS ADJUSTED. Camber is usually adjusted by changing the length of the upper arm on the suspension or the camber link. One to 2 degrees of negative camber is generally all that just about any race car needs. Exceptions to this rule come into play only in extreme conditions.

NEGATIVE CAMBER. Negative camber means the tires are tilted in at the top (toward the chassis). This is most common setup for any race car. The camber setting should be dictated by how the tires wear. Hereís what to look for to adjust camber properly: if the tires wear more on their outside edges, and negative camber should be added. Adding negative camber on the front of a car can increase steering, but 1 or 2 degrees of extra negative camber (beyond the setting that causes the tires to wear flat) is all you should add.

POSTIVE CAMBER. Positive camber is when the tires are tilted out at the top (away from the chassis). This setting is very rarely used, but you should know the term. If the tires wear too much on their inside edges, the car has too much negative camber; positive camber should be dialed in. When I used a solid axle in the rear of my Trinity Reflex NT, I had to run about 4 degrees of negative camber to keep the tires wearing flat. This was necessary because of the camber rise in suspension and the tire wear that a solid axle causes.

BEST BET. I always adjust my camber so the tires will wear flat and leave it set up like that because there are many other ways to get more steering. If you look at the tire wear and then adjust the camber so that the tires wear flat, you have set the proper camber for your car.

Above: Most electric cars use a turnbuckle as the upper suspension link. This is where you adjust the camber by turning the turnbuckle to shorten or lengthen the upper link.

Left: this is an example of negative camber. Notice how the tire leans in towards the chassis.

Right: this is an example of positive camber. Notice how the tire leans away from vertical.

Above: this is an example of negative caster. The axis on which the spindle pivots is angled towards the rear of the car.
Above: to change the caster on a pivot-ball suspension, just change the position of the clips from the front of the upper A-arm to the rear of the upper A-arm or vice versa.

Caster refers to the angle of the front kingpin or the angle formed by the suspensionís steering-knuckle pivots; its adjustment depends on the carís design. Measured in degrees, caster is much more of a handling adjustment than camber is, and smart racers make this adjustment more often. The most common position of the kingpin in all setups is negative caster; that means that the top of the kingpin leans toward the rear of the car.

HOW IT IS ADJUSTED. Electric cars generally require a front caster-block change to alter the angle of the A-armís hingepin mounts. On most nitro touring cars, caster is added or subtracted by sliding the top A-arm back and forth on the hingepin.

NEGATIVE CASTER. Caster directly affects how a car turns by changing the size of the contact patch as a tireís steering angle changes. Adding negative caster will yield more high-speed steering and on-power steering while reducing the low-speed and off-power steering. Negative caster will also cause the car track much straighter than when no steering inputs are applied. In general, larger tracks require more caster and short, tight tracks require less.

POSITIVE CASTER. Positive caster is when the top of the kingpin is angled toward the front of the car; this setting is rarely used.

BEST BET. I recommend that you start with the caster thatís suggested in the kit setup and work from there. If you stray from the kitís setup, to dial in the true amount of caster, you must consider the angle of the front A-arm and then add that degree measurement to that of the caster block. For example, if the suspension arms have 10 degrees of kick-up and you install 10-degree caster blocks, youíll have 20 degrees of total caster. Depending on the design of your touring carís suspension, measuring the exact caster might require a setup board. When you get serious about racing, a setup board will be necessary.

Above: When checking ride height, be sure to always measure from the same location on the chassis. Also make sure the chassis isnít worn in the area you choose to measure as this will throw off your measurement.

Ride height is the gap thatís between the bottom of the chassis and the ground.

HOW IT IS ADJUSTED. Ride height can be changed by adjusting shock preload by installing spacers inside the shocks, or by using downstops (aka ďdroop screwsĒ) in the suspension arms.

LOWER RIDE HEIGHT. In most situations, you want to run your car as low as the rules will allow. Lowering it lowers its center of gravity (CG), and that generally make it handle better. This is especially true on high-traction tracks because a lower ride height helps to control the chassis roll from side to side.

HIGHER RIDE HEIGHT. The only time you would want to increase the ride height is when you run the car on low-traction surfaces. The higher CG of an increased ride height causes the car to roll more from side to side. This transfers more weight to the wheels on that side of the car, and additional weight on a tire equals more traction.

BEST BET. To change the handling, some racers adjust the ride height so that itís different in the front and rear. By raising the front of the car, more weight will be transferred to the rear of the car when itís under acceleration. This additional forward traction causes the car to steer less when it exits turns. Running the front ride height lower than the rear will have the opposite effect: more on-power steering when the car exits the turns. This is simply the effect of weight being transferred from the front to the rear instead of from side to side.

Toe-in and toe-out are used on the front and rear of any touring car. Toe adjustments dramatically affect handling. In the front, toe-in or toe-out changes the steering.

The easiest way to spot this adjustment is to look at a car from the top. If the fronts of the tires point toward one another, the car has toe-in. Conversely, if the front of the tires point away from one another, there is toe-out. On a 4WD car, the typical setup is toe-out in the front and toe-in in the rear. Toe-in and toe-out are measured in degrees; they are referred to numerically, but not as positive and negative.

HOW IT IS ADJUSTED. Front toe is typically adjusted either by shortening or lengthening the front turnbuckles by the same amount.

TOE-IN. Running toe-in at the front of a car allows it to react more quickly when itís off-center, and it can cause it to wander while running straight.

TOE-OUT. When its front wheels toe out, a car will generally track straighter and initial turn-in will be decreased. Toe-out gives the car a more forgiving feel and is the preferred touring car setup.

BEST BET. In general, 4WD cars run about 1 degree of toe-out or toe-in. When checking the "toe" on the front of a 4WD car, make sure that you pull on the front edge of the wheels to take out any slop in the steering linkage. When a 4WD car accelerates, the front tires are pulled toward the rear of the car by the force of acceleration.

Rear toe-in is usually set by the arm mounts, and can only be adjusted by installing different mounts. Pivot-ball cars are the exception. To accurately set rear toe on a pivot-ball car, a setup board (like the one shown below) is a big help.

A high-quality setup board with measuring tools is an essential part of any serious racerís set. You should use these before every event.

In the rear, toe adjustment usually ranges from zero to 5 degrees of toe-in. Modest toe-in at the rear gives you the best of both worlds, but with rear toe-in, you must consider ďdrag.Ē The more wheels are angled, the more drag you will have; drag contributes to lower straightaway speeds and reduces efficiency. The most efficient setup is the one without any rear toe-in (to reduce drag), but this is very rare. In most setups, there is at least 1 degree of toe-in, if not more.

HOW IS IT ADJUSTED. The way toe-in is adjusted differs from car to car. Some sedans require a change of the rear hubs; in others, the inclination of the rear A-arm hingepins can be adjusted so the whole arm is swept forward. On most nitro touring cars, the length of the rear pivot ball on the bottom A-arm is adjusted. I suggest that you stay away from changing the rear hingepin inclination because that changes more than just the toe-in.

REAR TOE-IN. Adding toe-in will increase the on-power forward traction, but it wonít affect off-power lateral traction, or ďsidebiteĒ (as some call it). This means that when you enter a turn off-power, the car will generally rotate as well as or better than a setup with less rear toe-in, but when you apply power, the car will track straight. With that setting, it wonít finish the turn as well as a setup that has less rear toe-in.

rear toe-out. I have yet to see a car that runs any rear toe-out. Adding it will result in a highly unstable car.

BEST BET. When adjusting rear toe-in, stick with changing the rear hubs or adjusting the angle of the rear hubs or the pivot ball. If you need more forward traction, add 1 degree of rear toe-in at a time, and then run the car to see the difference. In general, this adjustment usually stays between 1 and 4 degrees.

There are many other factors involved in tuning a sedanís suspension, but if you learn and apply what each of these adjustments does to the carís handling in relation to your driving style, then youíll be well on your way to tuning your car like a pro.