From: Dave Darling [darling@simlab.arc.nasa.gov] Sent: Thursday, May 20, 1999 9:29 AM To: wayne@pelicanparts.com Subject: Re: [914] Autocross set-up Advice. >Date: Thu, 20 May 1999 09:28:46 -0700 >To: Ed Villela >From: Dave Darling >Subject: Re: [914] Autocross set-up Advice. >Cc: "914" <914@rennlist.org> >Bcc: >X-Attachments: > >At 8:20 AM -0700 5/20/99, EVill79996@aol.com wrote: >>Hi all, I need some suspension set-up advice for my 914. Set-up is for >>Autocross. My 914 is a 73 with a 4 cylinder. The suspension is as follows, >>front- 911 struts with Bilsteins, stock 914 t/b, urethane bushings, turbo >>tie >>rods and a 21mm Weltmeister bar. The sway bar was set with no preload to >>Weltmeister's specs. Front camber is -1 degree, toe is 0 and caster is 4.5 >>degrees. The rear has 140-LB springs, new Bilsteins, factory rubber >>bushings; >>the trailing arms and chassis are heavily braced. The wheels are 7x15 Fuchs >>front and 8x 15 rears. Rear caster is -1.75 degrees and 1/16-in toe in. I >>have new Yokohama AVS, 225/50's at all 4 corners. > > One presumes you have -1.75 camber at the rear, not caster? ;^) > >>I have autocrossed the car twice this year. Both times, the car displayed >>understeer and drifting. The only thing I adjusted was tire pressure. Lower >>pressures, 27 psi, gave me my fastest times. The car handles well and does >>not roll much. It drifts hard in tight turns, all 4 wheels, although more in >>the front. > > It sounds like you have a pretty reasonable setup. You have wider >tires and wheels than most of the local autoXers (rules specify no wider >than 205s and 6" rims), so that may be affecting things. > My car has a simlar setup in terms of alignment. I'm running 195/50 >tires on 5.5J15 Fuchs, and my front swaybar is only 19mm (and is too small!). >The wider rear rims (than front) on your car would tend to make it oversteer >a bit less, so possibly tweaking the front bar would be good. > I am usually a big fan of "just drive the car". You can affect how >the car handles a LOT by how you drive the car. Often, the answer to a ter- >minal case of understeer is, "get on the *correct* line". If your car still >understeers when you are OFF the throttle, you have something to worry about. >Otherwise, I would be tempted to just keep driving it as is, and modify the >behavior with the driving style. > If your car is really doing a four-wheel drift, then it is pretty >well balanced. You may have more slip angle than the tires want, in which >case you need to go a little slower in that particular part of the turn. Or, >the slip angle may be just about right, in which case that is where you want >to be. Remember, most of the suspension tuning stuff is about changing the >front-to-rear balance. > > When I used 195/50-15 AVSes, I thought that I got the best response >from them by pumping them up to about 36 PSI. I would have gone higher, but >I didn't want to go over the max rating. It was explained to me once that >most street tires gain more from having stiffer sidewalls with high pressure >than they lose by having a smaller contact patch. I never really did any >back-to-back testing on my own, though. I still feel that changes in the >line I am driving will have more effect than a few PSI in tire pressures. I >was able to affect the balance of the car by dropping the pressures in the >end I wanted to slide more. > > All in all, I'd keep the alignment where it is. Maybe tweak the >front bar (that's why it's adjustable, right?), try changing the pressures >in all the tires, but apart from that--just drive the car. > >--DD > Dave Darling 74 914 2.0 (decapitated) darling@simlab.arc.nasa.gov "OFF WITH ITS HEADS!"