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Suspension travel

Posted: October 2nd, 2015, 5:37 pm
by jphoenix
I watched Michael Varacins win the runoffs - what a great race that was!

I was looking at the amount of ground clearance on his car - significantly less than any other car it appears. Maybe Steve Davis' car is almost as low to the ground, (I watched the video again - it's car number 81 that appears next lowest) but most have 2 to 3 inches or more ground clearance. My FV has almost 4 inches of ground clearance and I've never bottomed the suspension of course, but I bet I have at least 2" of suspension travel in the front beam.

Is Michael's (and other's) car set up so stiff that the front suspension travels only an inch or just a bit over?

Is there an advantage to having the body close to the ground - perhaps a similar effect to the splitters and flat bottoms on sports racers (those that aren't feeding diffusers)?


Re: Suspension travel

Posted: October 4th, 2015, 12:50 pm
by hardingfv32
Generally you want the car as low as possible... but then there are always some compromises to be made.

1) The rear height is really dictated by the rear camber. The height of the engine and transmission have a little range of movement if you tilt them downward. The best you can do with the standard FV design is lower the frame rails during the initial chassis design.

2) The front height is a little more variable but is compromised by the angle of the control arms as you lower the beam. Highly angled arms cause suspension compliance issues under some operating conditions. Again the beam location relative to the frame is chosen during design.

3) Ground clearance is a classic design compromise. High ground clearance (say as high as 6") reduces drag. Low clearance reduces lift but increases drag. For FV 2.0" would seem the best compromise for a low CG and reduced drag. Higher ground clearance might have been useful at Daytona but would require a dedicated chassis design or a highly modified car.

The use of a splitter as seen on Davis's car would normally increase drag. The standard FV design compromise up to this point has always favored drag reduction over lift reduction.

4) You can safely run about 1.5" of ground clearance at most tracks using the standard FV front and rear spring package. You can use bump rubbers to control the one or two spots you find yourself bottoming at... usually braking points.