Hey guys quick question I drive a 328i E90 xdrive. I have 235/45r17 with 20mm wheel spacer in the front, they're great, but here is where I run into some issues. I somewhat went a little overboard on the back set and did 245/45r17 with 40mm wheel spacers. Almost every bump I hit in the road the tires would rub (shocker!). I ordered two heavy duty adjustable Koni shocks that I thought would fix the problem but I only minimized the rubbing over each pot hole etc. ...... Is there a way I can keep my setup but order stiffer springs for the rear that is stock height? If so where can I get them Turner? Thanks guys!
Hmmm..... anything's possible, I would guess it's unlikely anybody makes stiffer-rate stock-height springs. The reason you lower a car is to lower it's center of gravity, which translates to improved handling performance. More complicated than that though, there's roll center, roll rate, etc. etc. Lowering springs need to be stiffer to adequately control the car's mass and keep unwanted effects like bottoming, etc. from happening. I guess I'd say look at adjustable coilovers, but I wouldn't be surprised if most of what you find, since they're meant for lowering, to not have a maximum height level that allows the car to sit at stock height. You might want to explore if the rally world offers something, as rally cars need handling performance and ride height for road clearance. 2dr. & different car, but I run 255/40-17 square setup on my E92 on Apex 40mm offset 17x8.5 Arc-8's with no rubbing. I don't know how do-able 255's are on the 4drs, since you're not quite that wide, perhaps take a look where you're rubbing - might be a simple matter of different spacers, one way or another. Figure out your offset with the spacers and look up a BMW wheel fitment chart with offset range and you'll have a better idea what should work, although my guess would be narrower rear spacers than currently. "Shocks" are a bit of a misnomer, they are actually dampers, they "damp", ie control, the motion of the car's springs. They won't affect how much the springs compress, just the compression and rebound rates. If you're getting less rubbing with the Koni's, it's because they've slowed down the frequency the spring compresses. Koni's are usually 1-way adjustable, I think they typically adjust the rebound.
Thanks! I'll probably do 20mm wheel spacer all around like I originally had and look more into the springs and wheel fitment charts. I've also thought about a thinner side wall but performance tires in the snow are not such a good idea. Smaller wheel spacers right now are the cheapest solution.
Didn't think to mention it, but be aware of the handling effects from different shocks front & rear. Performance-wise, the same at all 4 corners is typically considered a better setup for balanced handling. Stiffening up the rear a good bit will bias the handling towards oversteer vs. neutral or the stock good-bit-of-understeer-transitioning-to-oversteer. Depending on the situation, you might have an oversteer skid happening suddenly/quickly &/or at a lower speed than you might otherwise expect, catching you by surprise & unable to catch the skid. At lower speeds (arguably normal street driving) there's more time to react, at higher speeds, having the back end lose grip and recovering is a sketchier proposition. When you can, I'd recommend putting the same type Konis on the front (if u like them), or go back to stock if you still have the rears and they're not too old/shot. Obviously if the rears were due & you've done that, it makes more sense to do fronts as time & budget allows. Tire compounding & construction choices are always a series of compromises to achieve particular performance goals - for snow, increased sidewall height might help to some degree, I think the most important factors for snow performance are the tread compound & tread design. Snow tires have more grooves & sipes for traction, as well as a tread compound optimized for grip and performance in cold & freezing temperatures. For snow, narrower width is also a benefit, as it changes the relative shape of the contact patch; less width = less snow to push out of the way. These days, there are performance summer tires that the makers recommend not to run in cold temperatures lest there be risk of damage to the tire - some may work in cold temps, if just adequately.