Mazda Talk Forums

Alright Brian, I'm ready to buy. I see a lot of nice 17x9 options out there. Before, I would have asked "What is the widest tire I can put on a 17x9 without a fender roll for autocross or track days", but after our recent discussion, I need to ask "What is a good size tires I can put on a 17x9 without a fender roll for autocross or track days that is good for the characteristics we spoke about:
"I like steering feel, so I go the other direction.....tending to use 10 inch rims for the same amount of tire other guys use a 9 inch rim. So, for example, on track days I have a 255/40 tire on 17x10 despite fact most MX5 guys would put that tire on 9 inch wide wheels,...and I would use 11 inch wide if I could find it! The result of 10 inch with that 255m is that my tire lasts longer and turn-in response is amazing. Look around at the NA/NB track guys and notice more and more put a 205mm tire on 8 inch wheels, and 225mm tires on 9 inch wide wheels....the reason is because it is faster, and MUCH more confidence inspiring to drive at the limit when the tire sidewall is stabilized. Since that tire is NOT sloshing all over the rim you can actually feel what it is doing!" -Brian

I'm glad you told me about all this. Would 225, 235 or 245 be better?

It all depends on what we are trying to do. Let's assume we are running STR class autocross...which is likely the class you will run. Class wheel width limit is 9 inches. So, 17x9 is the choice. Given that choice of 17x9, if we don't want to mess with fenders then the tire size is 235/40/17.

Brian wrote: Let's assume we are running STR class autocross...which is likely the class you will run.

Thanks Brian. Truth is, I'm not running in any class at the moment. All the HPDE I have participated in have been open to anyone in any arrangement. Honestly, I'm so new to this that I don't know the differences of the classes yet.

I'm looking forward to trying them. Unfortunately, I won't be able to get this in time before my next DE (this saturday at Auto Club Speedway), but definitely before the next. Thanks!

Brian wrote:Given that choice of 17x9, if we don't want to mess with fenders then the tire size is 235/40/17.

Actually, one more question. I was reading about the spacers and was interested. I know that they would pose no problem with my stock wheels against the fender, but what about with the 17x9? Is there a prefered offset with my setup with/without spacers?

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.

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.