So with the 8" front and 8.5" rears

Should I go

245/40 255/45
or
245/40 265/35?

Anyone still got that handy dandy formula lying around?

 

Track wheels come with 225/45 on the front and 245/45 on the rears, just an FYI.

 

Here's a useful calculator that will show how off your speed will be

http://www.miata.net/garage/tirecalc.html

 

265/35, to small an outer diameter. Go with your first choice. 245/40 and 255/45/18s.

Lou

 

I used 245/40-18 front and 255/45-18 rear and the rear tires looked like truck tires... and the car was slower down the front straight at Texas World Speedway. I'm guessing the slightly taller sidewall altered the rear gear ratios enough to make the car a little slower.

I have since changed the rear to 255/40-18 and they look much better and the car is faster down the front straight.

just my $0.02 worth.

PeteH

 

Okay heres the deal Stock is f225/45 r 245/45

I didnt like the huge sidewall height on the rear tires so I went to 255/40 on the rears. Looks much better now. I havent changed the fronts yet so VDC goes a little screwy with the break in stagger. When I get my new fronts i will go 235/40 and the car will be back to normal. Smaller sidewall but just enough that I dont have to worry about fudging up my wheels

The point is The tire size you want depends on the look you want. You can do a taller sidewall or a shorter sidewall. An easy way to avoid screwing up vdc dynamics is to take the stock tire specs and whatever you add to the width and aspect ratio of the rears you add to the fronts.
I learned the hard way! First I went with 255 by 45. My vdc was off and the rear wheels looked like those of a tractor. so I went with 255 by 40. VDC is still a little screwy but at least it looks better. once I get my 235/40 fronts the fronts and rears will be back into proportion.

 

Thanks Jules, I think the 235/40 255/40 seems like a good match with the rears being .6 bigger than the fronts. Should look nice on the already lowered car. $$

Thanks to All.