NOTE: Because shocks have the same effect on the chassis of a car as springs, apply what you learn here also to the shock adjustments. However, do not tinker with the shocks at this stage of a setup. Save that for last. For now, set all shock compression and rebound stiffness to an equal value which is one-half the allowable range for your car. Use the shocks to fine tune a car’s handling only after you’ve firmly established ride heights, spring stiffness, and the tires.
The spring rate determines how stiff (or soft) the springs are at each corner of the car. Changing the spring rate also changes the ride height, but if you’re doing these steps in order, you’ll know what ride height to “keep” if you decide to change the spring rate at one or more of the corners.
IMPORTANT: Be sure to detach the front anti-roll bar (“ARB”) and reset the rear truck arm preload to as close to zero as possible when making spring or spring perch changes. Ensure that you re-attach the front ARB and reset the preload when you’re done with your changes before saving and test-driving your setup.
In general, the tests done to help establish the optimal ride height will also reveal whether your car is “tight” (reluctant to turn) or “loose” (tendency to over-rotate or spin). With that information in hand, you can now move towards the spring rates to correct that problem and “dial in” your car’s handling at this next early stage of the setup.
The spring rates are measured in “pounds per inch.” An 850 lb./in. spring will compress 1-inch per 850-pounds of weight put upon it. The higher the number, the stiffer the spring. The stiffer the spring, the shorter it is. Springs measuring in the thousands of pounds per inch are very stubby; while springs measuring just a few hundred pounds per inch are very tall. This affects ride heights and how the chassis behaves in certain situations.
In general, you want your car as neutral as possible when cornering. First, you must establish basic spring rates as a starting point. Spring adjustments have significant impact on your ride heights, so you must be prepared to do a lot of test drives in order to prove out your spring rates and ride heights before moving on to the completion setup steps.
Overall Spring Stiffness
You can summarize the effects of the average spring stiffness at the front and rear of the car using the following table:
Individual Spring Stiffness
Normally, springs are adjusted in pairs; e.g., the front two springs, the rear two springs, the left two springs, the right two springs, the wedge springs (left-rear and right-front), and so forth. Individually adjusting a single spring will affect the car’s chassis as follows:
You will note that the spring adjustments that increase wedge (e.g., stiffen the left-rear and/or right-front) will tighten the car; while adjustments that decrease wedge (e.g., stiffen the left-front and/or right-rear) will loosen it.
Left-to-Right Spring Stagger
“Spring stagger” is the difference between the left and right spring rates on either the front or rear of the car:
stagger = right-spring-rate - left-spring-rate; e.g. a left spring rate of 650 and a right spring rate of 950 equals a front stagger of +300.
Stagger affects the behavior of the car under braking and acceleration (corner entry and corner exit, essentially). The higher the stagger, the greater the chassis response. You can adjust your springs to control the tendency to spin or plow into or out of turns as follows.
Front Spring Stagger
The front spring stagger strongly affects turn entry. However, it will also influence the middle and turn exit as well.
|Left Front||Right Front||Entry||Middle and Exit|
Rear Spring Stagger
The rear spring stagger strongly affects the middle of the turn and the on-throttle exit. However, it will also influence the turn entry as well.
|Left Rear||Right Rear||Entry||Middle and Exit|
Roll Couple Distribution
In the left-hand turns of oval racing, the roll couple distribution of the chassis is controlled by the springs on the right side of the car. When the body rolls to the right in a left turn, the stiffer right-side spring (front or rear) will have less grip. This has a profound effect on the car’s ability to roll the bottom of the turn and fire off on exit.
Roll Couple Distribution: Right-side springs effect on the middle and exit of a turn:
On the left side of the car, the car’s wedge is controlled by the spring rates on the left side of the car. Wedge is used to determine whether a car is generally loose, neutral, or tight throughout the run.
Wedge: Left-side springs effect on the handling of the chassis in general:
Wedge and “Cross-weight” (see below) are your principle means of neutralizing the setup for the long run.
The cross weight is the ratio between the corner weights of the left rear and right front corners of the car against that of the left front and right rear:
cross-weight = (LRw + RFw) / (LFw + RRw).
- Higher cross-weight means the car will be generally “tight” and resist rotation and turning.
- Lower cross-weight means the car will be generally “loose” and prone to spinning out.
- A tight, high cross-weight chassis will be notably faster early run, but will burn up the right front tire, and fall off quickly (usually about 15-miles of racing) and become uncontrollable.
- A loose, low cross-weight chassis will be generally unmanageable, burn up the right rear tire, and be unable to put the power down on turn exit at any kind of speed.
In a left turn, the left rear wheel is powering the car forward harder than the right; and the front right wheel is working the hardest out of all four in order to turn the car.
For now, just be aware of the cross-weight and try to keep it as close to 50% as possible as you get your initial ride heights set.
How to Change Cross-Weight
Change the cross-weight of the car by changing the ride heights at opposite corners of the car. Make sure to note the front anti-rollbar (ARB) preload. You will need to reset this value after making cross-weight adjustments. You will also need to zero-out the truck arm preload (on some cars, this is called the rear ARB preload).
To increase cross-weight, do either or both of these:
- slightly lower the left front and slightly lower the right rear.
- slightly raise the left rear and slightly raise the right front.
To decrease cross-weight, do either or both of these:
- slightly raise the front left and slightly raise the right rear.
- slightly lower the left rear and slightly lower the right front.
To raise a corner, use the left-facing arrow on its spring perch (sometimes called a “shock collar”) offset adjustment.
To lower a corner, use the right-facing arrow.