225/45x15's on 15x7 wheels

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07-31-2007, 01:00 PM
leawil

Would like to run 225/45x15 tires on my ITA Miata, but am having trouble locating a tire in that size that works well.

Avon makes one, but its a cantilever sidewall design is thus very heavy - extra 6 lbs per corner of unspring weight and rotating mass compared to a 205/50. Don't think thats a favorable tradeoff for a low-power, momentum car like the Miata.

Hoosier makes the R6 in that size, but their engineers don't recommend it for road course use on a 7" rim (apparently concerned about sidewall flex and heating). They said the 205/50 R6 would perform better because of less contact patch deformation under load at racing temps. However, I recently heard about a guy who was using the R6 225/45x15 on a 15x7 wheel on his ITS Bimmer successfully.

So, I'm confused. :(

Anybody got any relevant experience on this question?

Are ya' out there, Andy?
07-31-2007, 01:05 PM
Greg Amy

Quote:

Hoosier makes the R6 in [225/45x15], but their engineers don't recommend it for road course use on a 7" rim.[/b]

Well, that's news to the literally dozens of their customers in ITA running that tire on 15x7 wheels.

Maybe we should all switch to Hankook's 225/45-15 instead...?

GregA
07-31-2007, 01:06 PM
DavidM

I'm sure everyone else will chime in as well, but most people in ITA and ITS run 225/45 R6s on 15x7 rims. They stick out a little over the rim, but not too bad. Not sure what Hoosier engineers you were talking to.

David
07-31-2007, 01:08 PM
JeffYoung

All ITS RX7s I know of run 225/45/15s, and I run 225/25/13s all on 7" wide rims.

Never had anyone say this would be a problem. In fact, the 225/45 or 225/50 is pretty much the de facto standard tire in ITS and ITA.
07-31-2007, 02:44 PM
cmaclean

I haven't done any testing on this but FWIW my co-driver used to drive a '99 Miata in Grand Am Cup and they were forced to go from 205/50 to 225/45 (rules). According to him the lap times suffered significantly. However, I would be very interested to hear what Andy has to say also :)
07-31-2007, 03:24 PM
JeffYoung

Gearing probably. I run 45s at some tracks, 50s at others. 45s at lower overall speed tracks, 50s at VIR and the Rovals. About 200-300 rpm difference in shift points.
07-31-2007, 06:18 PM
Harvey

I ran the 225/45X15 Hoosier on 15 X 6" wheels for years on the Volvo with NO problems.

Les Chaney
08-01-2007, 02:34 PM
924Guy

Quote:

I ran the 225/45X15 Hoosier on 15 X 6" wheels for years on the Volvo with NO problems.

Les Chaney
[/b]

I'm in my third year of the same; bit of a PITA to mount, but with the right equipment not a big deal... I've heard that it's perhaps sub-optimal for the tire, but when you've got no choices, and the 205/50 is known to be slower...
08-02-2007, 09:59 PM
Andy Bettencourt

They can certainly fit on a 7" rim but I would be surprised if the 225mm fit on the 90-97 Miata. I run a 205/50/15. No overheating issues...I think it's the right size for the car.