Just got back from my second HPDE at VIR with the Carolina's Porsche Club running my 2000 M Roadster. Power Steering feels too light and over assisted for my likes. Does anyone know if there is an easy way to make the steering feel heavier, and consequently, more stable, especially at speed?
Uh, yeah, don't, particularly since it has a serpentine belt instead of a dedicated power-steering belt! Are your alignment and camber correct?
Car has been lowered. No, the camber and caster are probably not correct. I have maximum caster and neutral to slightly negative camber at the front, to help it turn quicker at the track. Front wheels seem to last fairly well, as I got nearly 15K miles on them before replacing, and that was driving hard and doing one track weekend on them. The rear has got negative camber. Rear tires only made it about 10K miles, before the insides wore out. I have rotated the rears at 5K this time from side to side, via dismantling and switching on the wheels. Still, the steering wheel feels light, and the car is quite twitchy at speeds. Ran 38 lbs in the tires cold at the track, getting up to 42 when hot. Wear indicators on the tires looked perfect. I am also running one size larger in width both front and rear. I expected the car to oversteer, but it pushes quite a bit on medium speed corners. I was told by several other BMW guys at the track that I needed a larger sway bar on the front? Still think I will have to replace all the front end bushings soon, and will try some polyurethane ones to see if that stiffens things up a bit. Thanks!
My best recommendation is to find an alignment specialist in your area who's experienced with setting up cars for racing and hpde's. I'm not an alignment guru, and would be a bit hesitant to start throwing out suggestions to try this or that, which could end up costing you money without solving or improving what you're experiencing. I'd say start by making sure everything is as it should be with suspension and steering components (for instance, no bad or overly worn bushings, loose tie rods or ball joints, & so on). You don't want to go chasing a problem without a solid baseline to start from. Then, get as much understanding as you can about suspension geometry, how it's all related, and what affects what (it's complicated). Make sure it's reliable sources - there is lots of great information on the 'net, but you have to consider the source; sometimes, you get what you pay for. Ask lots of questions. Then you'll have a better understanding of what you're experiencing and a better idea of how best to address it. I know that sounds kinda general, but there's so many variables involved that could be related to what you want to change that for any effective resolution, you'll want to be able to take a targeted approach. If you have neg. camber at all 4 corners, the only way to even the wear is flipping tires on the rims at an appropriate interval. As far as changing anything you mention, I think it could be said that, yeah, maybe, any of those (combined or individually) might address your issues - camber, caster, swaybars, tire pressure, etc. - but only if you have a known baseline to start with. If this first link is correct (I believe it is), then a bigger front bar is only going to make your car understeer more, all else remaining as it is. http://www.houseofthud.com/cartech/swaybars.htm Not BMW specific, but informative: http://www.se-r.net/car_info/suspension_tuning.html http://www.240edge.com/performance/tuning-caster.html I think TC Kline has a _lot_ of experience with Z's - might not be a bad idea to start with a discussion with them: http://www.tcklineracing.com/contact.htm
How much has the car been lowered? Are you running the stock staggered wheel/tire combo? Lowering the car will impact the geometry of the suspension and the relationship of the tire to the pavement. As mentioned above, find a good alignment shop that has experience with BMWs and track setup. Keep us posted.
Thanks Brian! I don't think the car was lowered much, as it still clears the tires front and back, and does not scrub. It does occasionally touch the ground in the front going over steep pitched curbs and entrances to parking lots and such. Has a set of RED springs with yellow Bilstein shocks all the way around, from previous owner. Looks similar in stance to your PIC of the Green M Coupe. I did find out the hard way that the front valance WILL clear a dead dear in the road, but nothing else under the car would, including my rear differential cooling fins and the right rear muffler. "Anyone for Venison Jerky"? I have had two shops look at the front alignment, but they only told me what I already knew. I feel as the alignment is good for what I wanted in handling, but just really wanted to take out some of the power assist of the steering, as it seems to light. If I ever have to replace the pump/rack, I may try undersizing the pulley, or seeing if there is a race rack that might work better. Thanks, Tommy
