275\40\18's
 

Will there be any clearence problems running this size tire on the back of a 03 touring 350z?

i have 03 touring.
currently running 245-40-18F, 275-40-18R on my nismo wheels.
That's recommended size by Nismo.
As long as you use aftermarket wheels, shouldn't be any issue.

Having JUST gone through this same process I will tell you, if you are trying to put those on a 18 x 8.0 or even a 18 x 8.5 wheel they are too wide and will not fit. If you manage to get them on the rims they will have quite a bit of bulge & not look good at all.

The widest tire for 18 x 8.5 will be 265/40's.

If you're running wider rims then you shouldn't have clearance problems.

I have 275/40/18 on 9.5 rims in the rear. There is plenty of clearance.