safetyfastgt

I have a 2011 GT convertible with Koni STR.T and Steeda Sport Springs. I have some negative camber dialed in too. -1.4 as I recall. I'm currently running 18" 2010 GT500 wheels with 255/45-18 tires. I had a flat last week, which got me thinking about my next set of tires. I would like more tire, and would like a square set up. I was thinking of going 275, but I have two concerns. First, with the 255, I can barely fit a finger between the tire sidewall and shocks on the front. Will a 275 really not rub? Secondly, in the event of a flat, will a 275 fit in the trunk of a covertible?

Norm Peterson

A 275/40 runs only about 10mm wider than a 255/45 when both are mounted on 9.5" wide wheels. Figure 5mm or about 0.2" per side wider at the max section width, or that much less clearance.

The reason that 10mm kind of "disappears" is that the 275 tire is measured on a wider wheel than the 255 tire. When you stretch the 255 tire out to its max-recommended wheel width from its measuring wheel width of 8.5", it gains about 10mm section width. The 275-wide tire is on its measuring width wheel at 9.5" and gains nothing.


The bigger gains are in the wider tread - half an inch or more - and in the slightly shorter (and probably stiffer) sidewalls






Norm

safetyfastgt

Wow, thanks Norm! That makes sense. The wheels are 9.5" width, so that should be spot on.

Norm Peterson

You'll be fine. In fact, 275/40's on 18x9.5 GT500 wheels is exactly what Nuke (one of the most active members here) has been running for several years at this point. I don't think he's gone through the wheels & tires thing again quite yet.


It was pretty easy for me to put together and post that stuff because over the last few days I've been going through the same kind of numbers for a somewhat tougher fit . . . the 285/35-18's are supposed to show up on my doorstep today and either 10.5" or 11" wide wheels to mount them on will be coming soon.


Norm