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      01-12-2010, 12:51 AM   #40
Drives: 2014 Shelby GT500
Join Date: Apr 2008
Location: Vancouver, BC

Posts: 923
iTrader: (4)


First, let me say I didn't have a charitable bone in my body when I did the work - I did it for me! I wanted to upgrade my suspension. It was only after I'd put the data together that I realized it might be useful for others.

Second, my measurements are as best as I could do them with the suspension still on the car. Some, like the droop of 4", I'm pretty sure of. Others, like the depth of the front and rear bump stops, I'm good within 1/4 inch, but probably no better. Other members, like RLDZHAO, will do better because they can measure the components when they're off the car.

Third, my assessment of the four "types" of suspension are generic and not intended to either criticize or endorse any particular product. Suspensions, at least at the level of "track day" and below, are not particularly finicky. I once ran 400# per inch rear racing springs (an increase of more than double the stock rate) on my E39 M5 with street-spec non-adjustable dampers (Koni FSD). The car rode like a limousine on the road and was superb on the track in the rain; only when the track dried was it obvious that the rear damping was softer than optimal.

The damper settings for compression and rebound, even when they're perfect, are a compromise. The needed "resistive" settings vary as the square root of the spring rate, so a 20% increase in the spring rate only changes the damper settings by 10%, which frankly is probably less than the margin of error in the manufacturing tolerances.

What's more, the car's damping needs change depending on whether you're cornering or going straight. The front sway bar couples both front sides together. Your carefully chosen spring rate and damper setting go out the window when the (undamped) sway bar drags the springs and dampers on the other side of the car into the calculations as you go around a corner. What's more, the rear suspension gets involved too. If it rolls more easily and farther than the front, it transfers weight forward in a turn. The damper setting has to be good enough, but perfect is just not feasible, even with four-way adjustable racing kit.

My point is that it's way too easy to over-think suspension design and settings for street-track vehicles. Your choice of seats will have as big an effect on lap-times as your suspension. Pick a reputable supplier, follow the instructions, and once you know how the kit works, make incremental changes one at a time with care.

YMMV, naturally.

Last edited by JAJ; 01-12-2010 at 01:12 AM.
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