geo.aigel

I am rebuilding the suspension on my 81 SC and while I am at it, getting it ready for some weekend fun. Torsion bars, poly bushings, turbo tierods, shocks, strut inserts, stainless brake lines etc.

I have installed 22 mm torsion bars in the front and 27 in the back. I am running 15x7 in the front and 15x8 in the back for autocross. For the street I have the stock 16x6 and 16x7.

Can you give me input for a good all around ride height front and back? Something that I can still drive on the road? I am fine with ballpark number fender to floor (give me your tire size) but would be happier with the factory type measurement of ride height. (torsion bar center to wheel center)

Thanks!

George

Bill Gregory

First, on an SC, I'd use 28 or 29's in back. Bruce Anderson has some guidelines in his book...I want to say 25.5" in front road to fender lip and 25" in back, essentially Euro height, but you should confirm that. Make sure you use steering spacers or the ERP tie rod bump steer kit since you're lowering the ride height, and of course remove the big spacers at the top of the front struts. If you haven't read it already, the 911SC FAQ (on tech.rennlist.com) has some performance-related information.

geo.aigel

Bill:

Thanks for the input! I don't quite understand why you would go with stiffer torsion bars and not take advantage of the limited suspension travel and lower the car significantly below euro height? I have so far travelled well with the car 1" below euro spec in the front on the 22 mm bars. You just need to take the steepest driveways sideways.

I am working on it right now. I am at 24 inches on one back side using the 16 inch wheels with 50 profile tires. Looks like I am in the ballpark of where I want it. The rest should be adjustable without pulling the radius arm. Off to the other side...

I will post again with the results. I am scheduled for an alignment on Friday and have an autoX Saturday, so I better get back into the garage.

Cheers, George

Tom Tweed

George-
Make sure they check your corner balance when they do the alignment. Ride height changes will have altered your weight distribution.
TT

Alan Herod

The reason folks are cautious about going below Euro ride height is because the geometry changes. Intuitively you would think that lower is always better, but such is not always the case. I think the place where you can most readily see the effect of lowering is in the angle of the lower control arm or 'A' arm -- this angle has a profound affect on determining the height of your roll center. There are all manner of devices to correct this undesirable result - strut spacers, offset spindels, and rack spacers -- some help more then others. Some amount of lowering cannot be overcome by simple rack spacers. I am not sure if it is possible with the Porsche, to lower it so much that the roll center is below the ground, but it was on my old SCCA Z car -- absolutely diabolical handling. Strut spacers solved the problem and the handling was transformed.

Someone like Steve will probably be able to straighten this out if I have added further confusion.