In Reply to: 26.3 is way to big(more)... posted by m.gilbert on August 23, 2000 at 09:05:20:
See below Diameter list for tire selection:
205/55-15 (23.9" = factory diameter for an E30)
225/50-15 (23.9" same diameter as stock)
205/45-16 (23.3" dia)
215/45-16 (23.9" dia)
225/45-16 (23.9" dia = 16" OEM OPTION)
205/50-16 (24.1" dia)
205/40-17 (23.5" dia)
215/40-17 (23.8" dia)
245/35-17 (23.8" dia)
225/40-17 (24.1" dia)
205/45-17 (24.3" dia)
235/40-17 (24.4" dia)
215/45-17 (24.6" dia)
225/45-17 (25.0" dia)
Running 26.3" will increase (numerically lower) your final drive which hurts acceleration. If you swap in a 4.40 rear-end then you will take advantage of the lighter, bigger wheels. Note, you would be wise to roll fenders and remove well-skirts to avoid rubbing, damage... etc.
Otherwise, try to keep as close to stock diameter as possible.
Cons:cost--sure 18" wheels and tires cost more than 15"-17" but if that is what you want(and can afford) don't settle for less. Harsh ride--true, however, the upside is increased cornering ability, traction...increased weight--not always. I have an E36 M3 and the stock wheels are 23#'s and the BBS RC's that will replace them are 18#'s (according to tirerack)so right there I dropped 20#'s of rotating mass from the car. I belive that this translates into INCREASED acceleration and a suspension that will work a little easier. Reduced tire selection??? Check out tirerack.com and find someone who DOESN'T offer an 18" tire. Reduced performance--covered that one already. Rubbing or fender damage--no comment. Wheel damage--no more so than with any other size.
On wheel damage, you do agree you will need to run rubber bands around those wheels no? Probably 35 series tires. Not much protection against bending a rim on a pothole with a 35 series tire.
Reduced performance, those big wheels will change your final drive ratio, hurt not help. On lightweight, you are correct but I bet I can find a lighter 15" wheel than those RC's, and cheaper too. Then there's the little issues like finding someone to mount 18" rims w/o boogering up your nice forged 18" babies. Maybe not an issue if you're in El Lay but where I live I can barely get anyone to mount 45 series tires on a 16" rim.
CFL, the way I understand it is that those "big wheels" fit into the same(or nearly) size OD tire. For example, a 235/60/15 has a 26.1" OD while a 235/45/18 has a 26.3" OD. I don't think that .2" is going to cause a dramatic loss in performace. Btw, I am along way from El Lay(as you put it) but I do have access to a Coats rim clamp tire mounter so finding some one to mount them is not an issue for me.