Tire fit question
 

I have a 98 Boxster and was wondering if anyone knows if you can fit a 275/40 18X10 set up in the back. If you can what do you need to do to make it fit?

With the right offset, 275/35/18 tires (not 275/40) on 18" x 10" wheels should fit in the rear.

I think correct offset would be about ET45, more or less. May require some rolling of the fender lip.

275/40 no

275/35 maybe.

285/30 yes.

i have not personally, but i've seen several that have. and the 285/30 is much shorter, so it will be less likely to rub given the same offsets as the 275/35

after seeing what my 265/35 looks like, i have no doubt the right offset wheel would work with a 285/30 with no fender work.

A little more info
 

Thanks for the info. What spacers would the 285/30's need? Or is the best bet the 265/35's?

Some items to think about

1) Wheel Offset
2) Is the car lowered or not?
3) Camber setting
4) Rolled fender lips.

Yes, a 10" rim can fit, but you need to consider the above.

Porsche DID offer a 9x18 wheel for the rear of the boxster. Factory tire size was 265 width... I ran 275/35-18 rears. You might use this factory size and place a small spacer (5mm or less) to help fill out the rear fenderwell, if that was a goal.

see above. are you lowered? camber? what suspension are you running? does it have a big spring? or a 2.25 wide one? then look at what you have now, and use some online offset calculators, and figure out what you can fit back there.

ideally borrow the exact wheel/tire size that you want to try and see if it fits. if not, then, get 2-3 different sized wheels, with different sized tires that you have access to, then try them all and measure your clearances, and then you can figure out what size wheels/spacers and tires to get.

thats how i squeezed a 255 on a 9.5 up front. and to tell you the truth, i bet i could have gone 10 wide and gotten a wider tire up front, but this is good enough for me.