Mazdaspeed MX5 Wheel Size

[Shadow2]

Hey ETR,

This upcoming Sunday will be my third ever autocross event and my second with my current car, my 2004 Mazdaspeed MX5. I'm running on Racing Hart 17"s that came from the factory, but I had a question about wheel size. As you can imagine 17"s are quite large on a NB Miata body and many of the Mazdaspeed owners end up stepping down to 16"s or even 15"s (can't go smaller than that, the brakes are too large). Currently, I'm registered to the Novice ES class, since I have no aftermarket modifications to it.
My question is, does reducing the wheel diameter place me into a different class? I've seen that pretty much as soon as any engine work is done to the Mazdaspeed, that it is thrown into BSP class, where I know that I certainly would become less competitive against the more experienced and better prepped cars. I plan on running the car as is for this season, but I wanted to start thinking about a longer term plan. Going down to a smaller, wider wheel like the 6UL (http://949racing.com/15x8-6UL.aspx) would be pretty nice, especially given the tire options there. However, if changing the wheels would change my class category, then I would probably prioritize the funds to go elsewhere on the car...

[steverife]

In the "Street" classes, you can run +/- 1 inch diameter, meaning a car with 17's could use a 16" or 18" inch wheel. You would also need to retain the stock wheel width and close to the stock offset. I think the rule now is +/- 7 mm in offset.

If you want a wider wheel, you could run BSP or our local STM class. STM is a really popular class and you can do whatever you want as long as your run 140 or higher TW tires (that number may change to 200 in the future).

[MARKP]

Welcome!

[Chuck629]

A local guy (Andrew Burt) does pretty well with his MSM in STM with 225's on a 15x9. The only con is you'll make the horrible MSM gearing slightly worse than it already is. Expect to use 3rd gear a lot if you're not changing the diff out for something else (3.63 would be ideal for the 6 speed) and bumping the stock 6500 rev limit way up.