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so will the 18" wheels fit in our fenderwells
i had mine rolled to the 7.5 wide stock csl wheels
but this seems rather big.
anyone have this experience.
 
18" wheel would leave almost no tire. 16 is +2 over stock and about as large a wheel as the cars are comfortable with.
 
Alan,

there are a handful of coupes that run 17" wheels. think of it this way - stock size 195/70-14 = 24.8" to 24.9" diameter - overall section width is just under 8" wide with a 6.5" tread width.

the problem generally occurs in the front - a reasonable amount of spare room in the rear wells.

205/55-16 = 24.9" diameter x 8.4" width - 7.3" tread width
225/50-16 = 24.9" diameter x 9.2" width - 8" tread width

205/50-17 = 25.1" diameter x 8.5" width - 7.5" tread width
215/45-17 = 24.8" diameter x 8.3" width - 7.9" tread width
225/45-17 = 25" diameter x 8.9" width - 8.3" tread width

215/40-18 = 24.8" diameter x 8.6" width - 7.8" tread width
225/40-16 = 25" diameter x 9.3" width - 8.1" tread width

as you can see, tires get wider with the lower profile ... the other issue is that the tread width tends to get wider with lower profile tires. my experience is that 7.3" tread width tends to rub with 16" width. my guess is that you would need fully adjustable camber plates - coilover shocks with narrow springs to hope to get 18" wheels under the car. i'm not saying its impossible ... but in my mind, its probably not worth the effort. think about it, the 215/40-18 is 1/2" wider tread width ... to back that away from the fender, you are going to need a different offset wheel than an et-11 ... at least an et-35 ... and that's going to rub everything.
 
I have 225/45/17x8 ET 20 on the front and the closest point of approach is at the strut tude where I measure the gap with a feeler gauge. The fender is heavily rolled (almost flat) an is not a problem - enough room to put 3mm spacers in to move the wheel away from the strut if I so chose. If the offset was ET 18 it would be perfect.

I believe 245/40/17x9 ET26 is the largest rear combo I know of that has no issues and requires no modifications.

I'm putting in 5mm spacers on my 245/40/17x8 but would have trim the returns of the fender lips to safely go much larger - the limit to that is the spot welds that connect the inner and outer fenders. Also, anything more than 8mm and would have to replace the wheel studs. I went 10mm larger or risk the wheel passing me on the highway.
 
Given the limited availability of high performance 14" diameter tires the jump to larger rims becomes almost a necessity regardless of aesthetic desires.

Covered many times on the forum, but here it is again..the car wasn't designed with these tires in mind and their inherent wider / flatter contact patch has implications on how they will perform on our vehicles. Likely those of us who have gone to larger diameter rims will also have undertaken some suspension modifications...lowering, adding in negative camber, damping, stiffer bars, etc. addressing some of the above.

Just thinking there will be a tipping point where too tall a rim will have a drop in performance even after undertaking the usual upgrades. What that point is? can't say but would wager around 16 - 17". Beyond this point it is simply aesthetics...which is cool, but just that.

Be interested to hear if anyone has made a more technical assessment?

John
 
alan here

so it seems the 16" wheel is the most optimal
for traction and performance
i run goodrich comp ta's
 
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