Ron's Rear Suspension
While we were trying to determine the correct tire pressure and launch rpm for the track, wheelhop became worse as we delivered more torque to the tire. Wheelhop is a result of spring wrap in leaf-spring–equipped or worn bushings and components in four-link cars. Also during the launch, it was clear the car was spinning the tires from a huge hit of torque when launching off the transbrake, hooking, then unloading again when the right rear tire rotated up into the body as the axle was loaded with engine torque. This occurred several times, making the car bounce or porpoise before finally gaining traction. The solution to both of these problems is a set of adjustable rear control arms. The new bushings solve the wheelhop problem, and the adjustability allows control of the initial location of the IC.
We also ordered a sway-bar kit. On the occasions the car did hook, it darted to the right and again unloaded the tires, causing a bit of scary fishtailing. The sway bar acts as a spring that keeps the axle housing from rotating up into the body and unloading the right rear that steers you into the guardrail. All these factors are either working with you or against you when launching a lightweight and powerful car like the Mustang at the dragstrip.
To get maximum droop, the MMS kit uses spacers to lower the strut in the car. We started w
On the left is the factory and on the right is the MMS camber plate. Aside from the obviou
This is the new, heavy-duty lower-rear-control-arm kit with ride height adjusters (arrows)
Ron's Front Suspension
Another place to look for problems is the front suspension. Under acceleration, weight transfer occurs, creating front suspension rise. The dampers control the speed in which the front end rises and droop allows the suspension to move without topping out and unloading the rear tires. The size of the front wheel and tire also have a direct effect on the 60-foot times, but we will get into that in a later story. Droop is simply the distance at which the tire and wheel move away from the body when the car is on jackstands, allowing the car to pitch-rotate and load the rear tires. The dampers we're using from Maximum Motorsports will allow us to control the amount of droop with spacers that fit under or over the upper strut bearing plate.
The springs (or a small front sway bar) help control roll stiffness, or the resistance to roll rotation, as engine torque twists the car clockwise (as viewed from the rear) toward the passenger side. Increasing front roll stiffness creates an equal and opposite reaction on the rear axlehousing, as torque lifts the driver front suspension and compresses the passenger front suspension. When torque is applied, the rear axlehousing tries to twist around the pinion gear, rotating the axlehousing in a counter-clockwise direction. Tuning and the 60-foot
The theory is that for every 0.10 second you can shave off the 60-foot time, you get 0.20 second off the e.t. in the quarter-mile. Fast race cars have a quick 60-foot time, so that is where you should start.
We spoke about deflection in the bushings causing wheelhop. Here you can see the differenc
On a solid-axle vehicle, the ratio of the front roll stiffness to the rear roll stiffness
This is the key to moving the IC. As the car is lowered, the front mount for the lower con
With the new suspension in place, we needed a baseline. The recommendation was to set the front damper at full soft to allow the front end to rise and add the thick bearing spacer to achieve as much droop as possible. In the rear, we set the shocks in the middle of the adjustment range.
Using the recommendation from Mickey Thompsons, we set the tire pressure to 12 psi and set the ride height to 273⁄4 inches using the adjustable rear suspension. With the stock suspension, Ron had a 60-foot time of 1.80, and with the new suspension and settings, the car immediately ran a 1.73. As the track got hotter, we moved the launch rpm from 3,000 to 4,000, and the car began to rotate and use the suspension. After multiple runs, and incrementally lowering the rear ride height, Ron ran a best 60-foot of 1.59 with a 7.53 e.t. at 92 mph, or 11.72 at 116.29. That is right on the power to weight ratio calculation for the e.t. and mph.