Mazda Talk Forums

Brian wrote:Go 48 to 50mm 17x9 and that will plug and play on NC with 235/50/17. See our Enkei PF01 17x9.

Most popular choice for mix of autocross and track is our 17x9 Enkei RP-F1, 45mm offset. That needs a bit of fender roll for 235/40 tire size.

I'm a bit confused so let's see if I understood correctly:

17x9 with 235/50/17 on PF01 with 48 to 50mm and no fender roll
OR
17x9 with 235/40/17 on RP-F1 with 45mm and fender roll

I'm confused because this morning you wrote "Given that choice of 17x9, if we don't want to mess with fenders then the tire size is 235/40/17."

Notice the difference is offset.

Use 17x9 with 48-50mm offset and no fender roll for 235/40.

Push out to wider stance with 17x9 RPF1 45mm and you need some fender roll for that same 235/40

I was calculating offset the wrong way. Thanks for the clarification!

NaregM677 wrote:Is there a simple equation for tire width to wheel width? Something like:
7 inch to 205-225
7.5 to 215-235
8 to 225-245
8.5 to 235-255 and so on.

Does such an equation exist?

A Dunlop tire tech once told me that max steering response came from a wheel that was exactly the width of the tread. Narrower rims softened the ride and steering response. So, for the OEM RE050s, the tread is 7.4", so the better rim would be 7.5". I wonder is there is a detectable difference on a 7" rim.

Indeed for racing, autocross or track, we like to run wheels same width as the tire for max steering response and contact patch stability. But in the real world this has downsides including ride and curb rash potential.