Originally posted by nsxtasy:
Actually, no they're not. The front tire is 3.0 percent larger than stock, and the rear tire is 1.8 percent larger than stock…
Well, yes, actually I think they are. I try to use the manufacturers specs for the exact tire because the variance that are meaningless for most applications become significant with the NSX. In this case I was no longer able to get S02 specs so I used S03. The OEM tires in particular don't quite match the calculations, but that's typically ignored which can be a problem when you start cutting it close.
OEM Fronts: 896 rpm (revolutions per mile)
OEM Rears: 807 rpm
Rear to front ratio : 1.11
Note: specs are based on stock rim widths.
S03 215/40/17: 875 rpm
S03 265/35/18: 820 rpm
Rear to front ratio : 1.067
Note: specs are quoted at rim widths of 7.5 and 9.5.
The difference between 1.11 and 1.067 is already significant. If his front rims are narrower and/or his rears are wider, it moves him further from spec. As you say, if the rears wear faster then that too adds to the difference. (Apparently his are not. Since I run OEM tires I always think of the rears being more worn than the fronts.
)
As for tire growth, I guess as a percent the front and rears might grow at similar rates, but there may be additional factors. The rears probably run higher temps which could make a minor difference, and I would think that a wider tire would grow more than a narrow one. (I don't have facts to support that, but it seems logical.)
No doubt each of these factors alone are minute, but the acceptable variance is quite small. Add them all together along with manufacturing tolerances for the tires and the TCS system and you might well find his particular combination to be marginal.