ThuG LyFe wrote:^actually it's not. at least not according to the miata conversion machine that i tried a while ago. it turned out to be like 1-2mm bigger than stock. (i had 15's too) also 235 on a 9" wheel isn't stretched that much...at least it seems like that to me.
The tire calculator assumes the tire is on a wheel sized such that the sidewall is parallel to the face of the wheel. (giving the biggest diameter that sized tire could possibly give) When you put a tire on a wheel that is wider than the tread width of the tire, the overall diameter is smaller than the diameter given by the calculator.
The 235 bridgestone re050s on my 17x9s are angled in (stretched) slightly, which would about make up for the increased diameter the 45 series tires would give had they been straight up.
ddgsxr504 wrote:
I am looking to retain "somewhat" of stock diameter for the speedo which is why I am running the set up I have now. Also I want to have the front and rear tires running similar diameter and sidewall height as well.
When I got the wheels from my friend it had 235/40 and 255/40/ However the sidewall on the front was super thin and the rear was fat. I run 235/45 now and they are almost identical sidewall height.
By switching to the size I offered the sidewalls and diameters will be very similar but will give me the needed stretch to tuck tire a little more so I can lower her down a bit more.
The tire sizes you posted (225/45 and 245/40) will definitely have similar sidewalls and diameters to eachother. Their diameter should also be close to stock. I would go with those.