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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.
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Okay, so now that 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.
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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.
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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.
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Robispec EVO antisway bars are not only stiffer than stock but adjustable as well.
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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.
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Whiteline's rear STI swaybar on bottom is a lot thicker and stiffer than the black stock part above. It is also adjustable.
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In future editions of this series, we will cover chassis balance and how to tune it.
