- Spring/Shock/Anti-Roll
Bar
Suspension Project - Results
- Suspension FAQ
- Front Suspension Photos
- Rear Suspension Photos
- Video
- Motion Ratio
- Measuring the Motion Ratio
- Cobra Suspension Spreadsheet
- Suspension FAQ
- Other Suspension Mods
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This one seemingly innocuous decision led to a much larger project, one that has occupied this entire summer.
In April, running with our new Kumho DOT-legal race tires for the first time at Loudon, we found the suspension was bottoming in turns 3 and 4 and also in turn 10.
It was clear we needed to do something to address this, lest we eventually destroy the suspension. Already there was a small dent in a frame tube where the rear upper control arm had hammered into it.
After talking with a number of people who race FFR Cobras like ours - and getting as many opinions as I made phone calls - I finally called Doug Arnao, of Vehicle Craft in New Jersey.
Doug is a former SCCA national champion who specializes in setting up Porsches for the track. One conversation with him convinced me he was our man.
Doug has developed a computer program which allows him to determine spring rates, anti-roll bar rates, and shock rates for any car, given the car's weight, weight distribution, wheelbase, track, and some more esoteric numbers like center of gravity and roll center heights and suspension motion ratios.
We gave Doug our numbers, and he told us what we needed for our car. He was able to supply springs and shocks, but we had to engineer and build our own anti-roll bars. This was a fairly major project!
We spent the summer gradually applying the bits and pieces needed to bring the car up to Doug's specs. As funding and time allowed, we upgraded the front springs, then the front shocks, then added the front anti-roll bars, then the rear springs and shocks, and finally the rear anti-roll bar.
Along the way we also switched to FFR tubular front lower control arms and competition upper front control arms, and found ways to make our stock Mustang and Thunderbird brakes survive on the road courses.
The results speak for themselves.
In 2000, our best time on the chicane-chicane configuration was a 1:27.7. Last Friday, on the same configuration, I did a series of laps in the 1:19's, with a best of 1:19.2.
Had I done that time in COMSCC's August or October time trials, I'd have been first or second in Street Prepared A, the club's largest class. Unfortunately, we wore out our tires before the time trial runs on Sunday!
See also my Suspension Project Results page which discusses the project in a bit more detail, and describes the changes in the way the car handles and rides with the suspension revisions.
If you think 800 lb front springs are going to make your car ride too hard, read about Motion Ratio and its affect on wheel rate, ride, and handling.
Also, you might want to look at a video of our car at Loudon in October and view photos of the revised front and rear suspension.
Also check out photos at NORCAL FFROG of the anti-roll bars built by Wayne Presley and David Borden (sway bars in FFR1046 and three piece front bar). Wayne and David inspired our efforts and gave us invaluable assistance.
And finally, you might want to check out the thread on the Cobra Forum in which I introduced these pages. Some of my comments have generated a fair amount of controversy!
For more information about the Bilstein spring and shock package, contact Doug Arnao at Vehicle Craft, 973-366-6577.
If you are interested in adding anti-roll bars to your car, contact Mark Reynolds at Breeze Automotive, 508.612.0393.