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Stiffening the suspension will degrade the ride, and it's easy to make your car too stiff. If this happens, the suspension will not be able to deal with bumps and will hop its way around turns instead of compliantly absorbing the bumps and finding traction.
Step three: Balance the chassis
Now that you've reduced body motion and improved steering response, we can work on the next major area of improvement. The goal for most of us is to have neutral handling. Neutral balance, where all four tires slide the same amount, is the fastest way around a corner most of the time. This way you use each tire's maximum grip. It might seem odd, but many experienced drifters prefer a neutral car because it allows them to have many control options for getting sideways.
Unfortunately for the enthusiast, most cars are factory tuned to understeer. Understeer occurs when the front tires slide first when at the limit. Manufacturers do this because it's the easiest handling mode for the average driver to control. Understeer isn't 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, we'll 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 to an art form. Oversteer can make you a hero or a douche bag. Do it well and everyone will love you. Do it poorly and they'll laugh when you're riding home in the flatbed.
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How do we tune a car's handling balance? By manipulating the tire's slip angle. Slip angle is defined as the difference between the direction the tire is moving and the direction the contact patch of the tire is pointing. At extreme slip angles, the contact patch actually slides across the pavement.
The 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, causing understeer. 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 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 creates more neutral handling.
Properly manipulating tire load 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-drive car oversteer? Sure. Look at most successful front-drive racecars; they oversteer like crazy.
How does a tuner manipulate tire loading and slip angle? By tweaking the spring rates, anti-roll bar rates, tire sizing and pressure, and to a lesser degree, the shock damping. The first option a tuner has is to increase the tire pressure. The harder a tire is inflated, within reason, the smaller slip angle it develops. 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 can do quite a bit to reduce understeer.
Changing the spring and anti-roll bar rates has a large impact on slip angle. Running a stiffer spring or anti-roll bar on one end will cause more weight to be transferred onto the outside tire as the car tries to roll in a corner. The softer end will compress and the more stiffly sprung end will resist compression, putting more weight into the tire and causing it to run at a bigger slip angle.
The best thing to do for your understeering, front-wheel-drive car is run a bigger rear anti-roll bar to tune out understeer. Conversely, stiffening the front suspension and increasing the rear tire pressures can tame oversteer.
By Ti Tong
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