Most racecar suspensions have much less anti-dive and anti-lift than street car suspensions. On racecars, the stiff suspension is used to control body motion instead of redirecting braking or acceleration forces. Most kits available for serious wrenchers to alter anti-dive and anti-lift work to reduce these factors.
On front- and all-wheel-drive cars, this same geometry also resists front-end lift under acceleration. Subaru's WRX is notorious for large amounts of anti-dive and anti-lift, causing nonlinear steering response. Bushings reducing anti-dive and anti-lift are designed to give more natural steering response and improve corner-exit traction on WRXs by eliminating these compromises.
Anti-lift geometry greatly affects launch traction for front-wheel-drive drag cars, yet only recently have tube-frame pro class front-wheel- drive drag racers begun to consider using front-end anti-lift geometry.
Whiteline has suspension mounts and bushings to tune the anti-lift and anti-dive out of many popular all-wheel- and front-wheel-drive cars. Kits are available for all WRXs, the Sentra SE-R, many Celicas, the Mazda 323 and the Galant/ Eclipse. A few Japanese tuners offer subframe mounts for the Nissan S13, S14, Z32 300ZX, R32, 33 and 34 Skyline to change the height of the front instant center.
Anti-squatAnti-squat is the exact same geometry applied at the back axle of a rear-wheel-drive car. Unlike the front of the car, small amounts of anti-squat are generally a good thing for a rear-drive car since it allows for softer rear suspensions without the excess squat.
Cars like the Nissan R32 Skyline GT-R, Z32 300ZX and S13 240SX have a great deal of anti-squat in their rear suspension geometry. This makes them transition to on-throttle oversteer very rapidly because anti-squat, like anti-dive, significantly increases the wheel rate. This is why the S13 works so well for drifting.
Extreme anti-squat can cause wheelspin and rear wheel hop under power, which is why the Z32 is notorious for launching poorly at the dragstrip.
Rear-wheel-drive drag racers have made a science of anti-squat tuning to maximize rear-wheel traction. Drag cars often have so much anti-squat geometry that the back of the car actually lifts when launching, driving the tires into the ground. Drag cars have adjustable four-link rear suspensions,so this percentage is tunable for the amount of bite desired in different conditions (see sidebar on page 102 to learn how to calculate anti-lift, anti-dive and anti-squat).
Ackerman angleWhen cornering, the inside and outside wheels have to travel different distances and different arcs. If both wheels are at the same steering angle, then one or both tires would be scrubbing.
Think of Ackerman as dynamic toe-out, which increases toe-out as the steering wheel is turned. This gives the quick turn-in advantage of having toed-out alignment while turning without the handling and tire-wear drawbacks of static toe-out in a straight line.
Just about all cars have Ackerman built into their steering geometry. It is, for all practical purposes, non-adjustable. The Ackerman angle can only be changed by moving the steering rack. A simpler solution is to just dial in some static toe-out, which will multiply the Ackerman effect that's already engineered in the car's steering geometry.
Camber curveOne drawback of independent suspension design is its inability to maintain a consistent contact patch as the car's body rolls in a turn. Suspension engineers counter with designs that gain negative camber under roll, which increases cornering grip.
Christian Rado's tube-frame front-drive Scion tC drag car uses an adjustable front suspens
Multilink and A-arm suspensions are designed with shorter upper links or different rotation points so the upper components sweep in a tighter arc than the lower links. The different arcs make the wheel gain negative camber as the suspension compresses.
However, there can be drawbacks. Too much camber gain can cause side scrub. Side scrub occurs as a control arm sweeps through its range of motion and pulls the tire laterally, which adds further traction load on the tire. This can cause instability over bumps, especially if the bumps only affect one side of the car.
Placing the suspension links for negative camber gain also affects the roll center location. Fortunately, it's easy to find a good compromise between roll center location, negative camber gain and minimal side scrub. Companies like SPL offer adjustable suspension links, which allow for camber curve and roll center location adjustments.
On MacPherson strut-equipped cars, the wheel will gain negative camber under roll as long as the lower control arm is positioned less than 90 degrees relative to the strut axis. Unfortunately, many enthusiasts with MacPherson strut-equipped cars lower their cars too much and make this angle greater than 90 degrees. Beyond 90 degrees, the suspension will gain positive camber instead of negative as it compresses, significantly compromising grip (see illustration below).
By Ti Tong
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