Rim to tire size question?

[Daryl Lane]

My son Adam and I have been auto-xing for about 5 years now - mostly with BWMCCA and we have done some SCCA events in the last 16 months or so. For 2012 we are going to give more effort to SCCA and have purchased points cards for 2012, numbers 201 me and 202 Adam.

My question is related to the best rim width to tread width for Auto-xing - how much to spread the tire? We run 225/45 x 15's with average tread width of 8.9", so would 9" rims or 10" wide rims be better? Currently we are running them on 7" wide Kosi K1's with 18mm offset, finding rims in our budget for our older 79 4x100 BMW is not easy. But I have found some cheap rims I can buy to test on before spending money on better rims - any help will be happily received, Thanks Daryl

Happy New year to you all!

[Robert Puertas]

When we were running the Hoosier 225/45-15 on the front of the Elise, the 9" wide wheel worked terrific.
However, the 10s are necessary to get the most out of the 275-15 Hoosiers if there's any chance you could upgrade to that wider rubber.

[Daryl Lane]

So would 10s be too wide for 225's so we could change later?

[Q V]

So would 10s be too wide for 225's so we could change later?

You can do it, it's just going to look stretched. 225's will fit fine on your 7" rims.

The best rim/tire size is usually whatever class you are competing in allows you to run.

[Robert Puertas]

If you can get 10's cheap, I'd give it a try.
It seems like 9's are actually out there at semi-affordable prices, so I'd go with that.

QV brings up a good point though...
Can you tell us more about the car and what class you are prepping it for?

[Daryl Lane]

We have the 79 bmw euro 320/6 2lt six we run in Hist 2 FP Car weighs 2130lb, but are are doing some more chassis work and putting in a 2.7lt six this winter.

Here a picture from a year ago BMWCCA San Diego -

[Daryl Lane]

So would 10s be too wide for 225's so we could change later?

You can do it, it's just going to look stretched. 225's will fit fine on your 7" rims.

The best rim/tire size is usually whatever class you are competing in allows you to run.

We currently run the 225's on the 7s, but was just wondering if a wider rim would be batter/make a positive differance.

[Mako Koiwai]

Bigger is Better ... even the Pikes Peak winning GT2 RSR that set the fastest production car run this year has over size wheels ... but wider rubber first, then wide(est) wheels:

[Robert Puertas]

Any reason you're not running real slicks?

You could run cantilever slicks on your current 15x7's.

Hoosier makes a 23x9.5x15 that's designed for a 7" rim.

The bias-ply cantilever might do a better job of putting down all your new found torque from the 2.7...

[Mako Koiwai]

I think Hoosier says that for every half inch of added wheel width you gain a tenth inch of tire width.

[Daryl Lane]

We bought a set of those hoosiers used for test fitting and could not get them you seat on our Kosi's, tire installer tried everything he could think of. The Kosi K1s have a really thick lip on them, not sure if this was the cause but they would not blow out and fully sit. Do cantilever slicks work that good in auto-x? What about the rim moving inside the tire?

We have a set of Hankook Z214 in C51 compound that are 225/45 - 15s that we really like and so does the car. This is way I was asking about wider rims wanting to know if they would get better? We also run Hankook 225/45 15 Rs3 to save on money at some events on another set of the same size 7" wide kosi's.

Sorry for not going into this from the start.

[Mako Koiwai]

Calling David Barrish !

[David Barrish]

Let's see...

Group 5, removable-to get the car on the trailer-flair's with 10" rims.

Opening up the front fenders is not the issue. The rear's are the challenge. But Daryl is amazing with a welder.

[John Coffey]

Make sure you are measuring the actual tread width, not the section width. Typically tread width is measures from point to point on the treadwear triangles. Jeff Speer years ago told me that for DOT-R tires you want wheel width to be 1/2" to 1" wider then actual measured tread width to optimize the tire.

[Robert Puertas]

Do cantilever slicks work that good in auto-x? What about the rim moving inside the tire?

Lots of prep & mod cars run cantilever tires to good effect. They are extremely forgiving and allow for lots of slip angle. It may come down to your car set-up and personal driving style, but my favorite set-up on the Elise was running cantilever slicks on the stock car. It was ridiculously fun.