Muscle Mustangs & Fast Fords
1995 Mustang GT Project CMC Part 4 - Road Race Tuning A Mustang GT Suspension
Our CMC Mustang Hits The Track After A Race-Prepped Alignment And Suspension Tuning.
Most gearheads are familiar with the basic terms of suspension alignment, including caster, camber, and toe, so we won't go into to the definitions. Suffice it to say that for a road-racing Mustang with limited suspension modifications, like our CMC racer, you will end up running as much positive caster as you can get, a lot of negative camber, and some amount of toe-out. Caster is pretty much a set-it-and-forget-it deal, especially since the Mustang's strut design is particularly challenged in this regard. Ideally, with a strut-type front suspension, positive caster should be 8 to 10 degrees or higher to negate the inherently poor camber loss characteristics of the design. Unfortunately, even the SN-95's improved geometry struggles to get much more than halfway there. To offset the loss of negative camber as the car rolls through a corner and weight is transferred to the outside tires, increased amounts of static negative camber are needed to keep the tire's tread in contact with the road surface. But there are trade-offs with adding too much negative camber. As it increases, so does inner tire edge wear, and there is also a corresponding loss of braking ability as the tire's contact patch is reduced in straight-line braking. For a street car, a range of 1.5 to 2.5 degrees of negative camber will provide a nice improvement in handling, while a dedicated road racer might need as much as 4 degrees or more. As with most tuning variables, the ideal balance of alignment setting must be sought and compromises are necessary. For example, increasing toe-out can help initiate sharper turn-in at the entry to a corner, but high amounts of toe-out increase rolling resistance and can cause darting and instability under braking.
Bumpsteer is a condition that occurs when the arc of travel of the lower control arm is not parallel to the arc of the steering tie rods. It commonly occurs when a Mustang is lowered too much, and the result is unintended changes in toe in or out as the suspension cycles through compression and rebound. Excessive bumpsteer may cause the car to dart side to side and feel skittish over rough road surfaces. Remedying this condition is relatively simple with a bumpsteer gauge and adjustable outer tie-rod ends, commonly called a bumpsteer kit. Bumpsteer is also affected by changes to caster, so bumpsteer corrections should only be made after the car has been aligned.
Tires and TuningThere are dozens of ways to affect the dynamic handling or balance of a car. Adjustments to spring rates, ride height, track width, sway bars, tire pressure, and more can change the way the car reacts in a turn. It takes a lot of time, money, and other resources to comprehensively test and sort out all the possible setup combinations on a race car, a process that's beyond the reach of most budget racers, so we'll focus on just a couple that are easy to adjust: sway bars and tires.
The goal of tuning is to achieve neutral handling where the front and rear of the car have equal levels of grip. Understeer occurs when the front looses grip before the rear and additional steering input is needed to keep the car steering along the intended path. Oversteer occurs when the rear end breaks traction before the front. The natural tendency of a front-heavy Mustang is towards understeer, but the design of the stock four-link rear suspension also lends itself to sudden and unexpected oversteer at the limits of traction. Finding an ideal balance can be tricky, and what works in one corner or section of the track may not be the ideal balance for other sections, so again, the trick is finding the best overall compromise that results in the fastest lap times for the track conditions. This is all part of the fun and challenge of racing.