The RSW Service Team presents our second installment of "Understanding Your Vehicle", Chassis Tuning; an introductory guide to understanding the effects of common aftermarket upgrades!
Our first segment covered the three most basic and readily adjustable of variables, they were Toe, Camber, and Caster. Today we are going to touch on three other important variables when it comes to chassis and suspension tuning, those are sway bar changes, spring rate changes, and corner balancing.
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Setting the alignment is a huge step in the right direction when it comes to performance street driving or track driving, but now that we have the wheel in the right position when the car is sitting still, we still have to concern ourselves about what happens when the car is cornering.
When you go around a corner the car "rolls". This is often referred to as "body roll". When the car goes around a corner it will start to lean towards the outside edge of the corner. If you are turning right, the body leans left, and vice versa. Like all chassis and suspension tuning there is a balance between too stiff and too soft when it comes to body roll. The easiest way to control body-roll is to install aftermarket anti-sway bars.
Sway Bar Balancing Notes:
- Stiffening the front sway bar typically adds more under steer, softening it traditionally decreases understeer.
- Stiffening the rear sway bar typically adds more oversteer, while softening it traditionally decreases oversteer.
- Depending on your specific car, application and balance you may not need more sway bar (or more stiffness) than you currently have. For instance, if you have a high horsepower rear wheel drive car and are having trouble putting the power down coming out of turns, stiffer or bigger sway bar will probably make that worse, just like putting more sway bar on a 500whp GTI will probably make it tough to get any power down to the inside wheel in corners. With lots of things in the automotive world more is usually with better, with chassis tuning this is situation dependent.
- Most front wheel drive cars will benefit most dramatically from rear sway bar replacement, as it will help the car rotate, especially mid-corner and on the brakes. Powerful rear wheel drive cars will often benefit from softening of the front bar to give the wheels more grip.
The variable we can control and change relatively simply and cheaply is spring rate. We are spoiled now-a days where we can get springs of varying length and rate for almost any vehicle out there. Whether it’s a German SUV or a Japanese Sports Car we probably have a handful of manufacturers to approach when it comes to increasing or decreasing spring rate. We tune the spring rate to try to keep the tire in contact with the pavement as much as possible. Spring rate tuning is really an art, there is no one ideal spring rate for one car, it will vary with tires, usage, roads, etc.
Spring Rate Tuning Notes:
- Stiffening the front spring rate will traditionally add more understeer. Softening the front will decrease understeer.
- Stiffening the Rear spring will traditionally add more oversteer. Softening the rear spring will decrease oversteer.
- When tuning spring rate it is important to take into consideration the shocks and or struts you are using in conjunction with the springs. If you are drastically changing the spring rates (>#200lb increments) and or drastically changing the ride height (shorter or longer springs) you are probably moving the strut and or shock out of its optimal range of operation. A shock and strut are tuned to perform at a certain sweet spot when it comes to wheel travel and frequency. Before slapping a set of aggressive dropped springs on your stock struts and blowing them out, consult us first!!! Adding spring slows down the transfer of weight from side to side, less spring speeds it up.
The last variable we can adjust when going with aftermarket perches or coil overs is ride height, and corner balancing. Many people choose to lower their car for aesthetic purposes, some choose to lower their car for better cornering, and some choose to raise their car for increased ground clearance. Again, like every variable we have ever discusses there is a balance between too low and too high. In addition to ride height there is corner balancing. Although on most street cars we do not have the flexibility to move components around to adjust the static balance of the car we can affect the cross-weighting. Cross weighting is the percentage of weights between diagonal corners on the car. If you do happen to be able to adjust the weight of heavy components (remove seats, relocate battery, install fuel cell, etc.) then we can actively try to achieve a more central balance. Also keep in mind we are not addressing squat or dive in this segment, which is referred to how much the level of the car moves up or down while accelerating and braking.
Ride Height/Corner Balancing Notes:
- Lower is usually better for cornering, As long as you still have sufficient suspension travel to avoid riding around on the bump stops of physically hitting things with your car. Sometimes suspension geometry can be compromised when lowering the car too much (such as roll center geometry) but in terms of body roll and weight transfer lower is better for performance
- With corner balancing, the goal is not to have every corner of the car reading the same exact weight, but rather to have a cross balance (the sum of (RF-LR) and (LF-RR)) balance as close to 50 percent of the total weight of the car. This ensures that the car will handle relatively equally turning right and left. Although counter intuitive raising the car in the corner that needs more weight will actually increase the amount of weight measured at the scale in that corner.
- Raising the ride height in once corner will also raise the weight in the diagonal opposite corner, and vice versa (if you raise right rear, the left front will go up, if you lower the right front the left rear will go down too). Vice Versa with lowering the car, will raise the weight on that corner and the one diagonal to it.
- Be realistic with what ride height you can live with. Don’t slam your car all the way down to the pavement unless it’s a race car or you are willing to deal with hitting bump stops and scraping your front lip.
There is SO much more to setting up a street or track car than what has been discussed above, but we are merely trying to cover the basics at a very cursory level.
If you have application specific questions, or are looking for a more in-depth understanding please Contact Us!