Project 5.0 Mustang II – Improving the Suspension with Whiteline and KW Part One
by Mike Kojima
In the first segment of our Project Mustang we took the car to the Streets of Willow Springs and although we liked the car a lot, it was easy to see that its biggest shortcoming was its suspension. The stock suspension was very soft allowing for a lot of body roll. There was also a bunch of nose dive and squat. Even with the car’s excellent engine, stiff body structure and good brakes, the car would have an annoying tendency to understeer with the excess dive and squat making the car harder to balance under braking and acceleration.
The suspension was hampering what would otherwise be a very fun car to drive on the track. Fortunately there are many tuning options for the Mustang chassis and we chose two of the best for our project. You might realize that we currently have two 5.0 liter Mustang Projects, a Grey automatic that Vince Illi uses mostly for Autocross and this car, the white six speed that is an all around track day machine.
Our white Project 5.0 Mustang is a 2013 six speed with the Brembo brake package, perfect for us to build on. In this installment we will be focusing on the Achilles’ heel of the car, its suspension.
We sourced new tubular trailing arms from Whiteline
(part number KTA195) to help locate the live rear axle. The Whiteline arms are adjustable in length which helps adjust the amount of rear antisquat a little bit. It is also handy for centering the rear tires in the wheelwells on a lowered car. The stock squishy large diameter rubber bushings are replaced by Whiteline’s firm yet compliant urethane parts. Getting rid of a lot of rubber compliance in a live axle car helps reduce wheel hop.
These trailing arm brackets are unique to Whiteline
(part number KBR37). Whiteline is one of the companies that pioneered correction of suspension geometry issues throughout their product line. In the case of the Mustang, the rear axle has a slight amount of pro-squat geometry which is sort of unusual. Most production cars have anti-squat in the rear suspension. We think this is done to make the car less likely to transition to sudden oversteer when the throttle is applied hard in a corner. However the car is pretty softly sprung and damped so when the throttle is applied hard, the rear suspension compresses through dynamic weight transfer and the pro-squat. This causes the suspension to sort of over center deeper into the pro-squat range to where the engine’s torque load through the suspension links is actually squatting the rear of the car even more causing a drastic amount of squat as well as preloading the rear suspension springs. The Whiteline brackets relocate the axle side of the trailing arms down lower to where the suspension now has a slight bit of anti-squat in the geometry. This is better and the car’s geometry is actually pretty neutral when the squat of weight transfer occurs. This frees up the back of the car, making it less bound by torque reaction and helps the rear axle find more grip. This helps both off the line traction and traction coming off the corners.
Whiteline also replaces the upper third link of the rear suspension
(part number KTA141A). It is much beefier that the stock upper link which is known to break under hard use. It also has less compliant urethane bushings. Perhaps the link’s most profound feature is that the chassis side bushing is eccentric which allows some adjustment of the pinion angle and the amount of antisquat in the rear suspension. The link comes with the bushing in the highest location which is the minimal amount of anti squat. We feel that this is probably the best for all around use. Raising the pivot reduces the quickness of the chassis response to torque reaction which is also important. The third link is very short due to the production car having to have room for a rear seat. The result of that shortness is that small changes in the angle of the third link make a disproportionately large difference in how the rear suspension reacts to torque load.
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