Ello,
Looking at fitting 18's to my gc8 wrx. What is the widest I can safely go tyre and rim wise ?? Would 235/40r18 be a bit much ?
Cheers
Stuart

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I am Banana Man ...

That tyre size would give a significantly larger overall diameter than stock affecting your speedo, guard clearance if lowered, ride height (it will look funny unless the car is dumped) and even acceleration. I have 225/35/18 tyres on my 18x7.5 rims. I would think 8-8.5 would be the widest you could go and with those widths your rim offset would need to be perfect to avoid too much guard scrubbing.

i dug out some info from a japanese mag and the safe recomended fitment for 18' is as below.

GC8: 7.5Jx18+48 215/40/18

hope this helps...

This is an awesome little page for working out rolling diamater and such....

http://www.miata.net/garage/tirecalc.html

Cheers for the input peoples.

Stuart

__________________
I am Banana Man ...

No chance for 235/40 without major guard mods
Can do 225/35 with the correct rim offset... usually a rim of 7.5" @ +50 to +53 offset

My favourite site for calculators is http://www.1010tires.com/tech.asp
Have a good tyre size and offset calculator.