Wayne Cook
June 25, 2010

Track Day Testing
The object of any suspension upgrade is to improve handling performance. For this review we wanted to see exactly what gains could be realized on the ground after a substantial suspension upgrade. It's one thing to say that the car feels better in turns and has less body roll but we wanted to be able to quantify improved suspension performance in a measureable way, so this comparison was envisioned. We put our subject vehicle, a '68 Mustang coupe, through its paces at Mid-America Motorplex in Pacific Junction, Iowa. Before we installed the new suspension components, which included both front and rear direct-fit bolt-on upgrades, we tested our car out on the 2.23-mile road course. While the car handled OK on the stock replacement suspension, we still had our hands full trying to keep up with traffic on the course, such as the late-model Corvette seen here. On our best run we were able to complete one lap of the road course in exactly 1.55.00 minutes.

It should also be noted that at the time of the rebuild the worn stock front springs were replaced with shorter 620-lb/in springs and the front antisway bar was also upgraded to a 11/8-inch. The only other suspension modification was the addition of a rear antisway bar. The old suspension had less than 1,000 miles on it, so our test car wasn't a basket case. Even with the newer control arms and larger-than-stock sway bars, out on the track there was a lot of room for improvement. The front of the car pushed on nearly every corner (understeer) while the rear was somewhat unpredictable. Any bump or extra throttle would cause the rearend to lose traction and begin to oversteer and it would have been easy to spin the car. A big issue with the rear suspension was the amount of lateral movement and the 285mm section width tires rubbed on nearly every corner.

Other than driver impressions, track times and tire temperatures were also recorded. Track times are a simple way to keep tabs on how fast and consistent the car handles going around the course and tire temperatures give us a good idea of how effective the suspension is in keeping the tire's contact patch on the road. In the initial test, the track times were consistently in the 1:55.5 ranges with a best time of 1:55.00. Front tire temperatures were consistent throughout the day. We measured the tire in three sections including inner, middle, and outer. The results indicated that the suspension was not allowing the entire width of the tire to work. The outer tire temperatures throughout the day were nearly 20 degrees warmer than the inside of the tire.

For our track testing we installed new reinforced/boxed upper and lower control arms, new spring perches, and new urethane bushings up front; and new leaf springs and a Panhard bar in the rear. The new suspension components used are based on the stock configuration but were designed to improve both suspension geometry as well as component strength. All of the new equipment included more rigid bushings with most of the parts being direct bolt in.

Once the install was complete, the car went out to Mid-America Motorplex once again and the results were impressive. In our "before" test, the car felt like it was at the edge of its performance envelope at many points on the track. However, after the rather simple bolt-on suspension upgrade, the car felt more solid and confident in every aspect. It was more predictable on turn-in, the car understeered less through each corner, and the rear end remained planted regardless of what was done with the throttle. In the initial test, there was no need for more power. The suspension was clearly the weak link. But, with the new equipment more power could have been utilized. From a numbers point of view, the results were impressive. Average lap time with the new suspension was in the mid 1:52s with a best lap time of 1:51.00. This is a significant gain of more than 4 seconds as a result of changing the suspension. These gains were seen without the use of a rear sway bar, and with the same alignment specs from the initial test.

Average Tire Temperatures Recorded
BeforeInsideMiddleOutside
Left Front160188190
Right Front162186188
After
Left Front164174175
Right Front162170172

Because we were using the same alignment specifications, the temperature scales indicate that we were better able to use the whole tire contact patch with the new suspension. While there is still some room for improvement, it was significantly better than the initial setup. We'd like to offer our thanks to the guys at KR Performance & Restorations [www.krpandr.com; (402) 799-2056] for installation, track testing, and keeping great notes of the day's results.

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