Just wondering if anyone has successfully run a wheel smaller than 15" at the autocross. I know this wouldn't fly in stock classes and fitting over the brakes (and potentially around rear control arms) would be a concern, but I was curious if someone has found a 14" or even a 13" wheel that does the job.

Wilwood's brake system (according to Helix website anyway) claims that they will fit under some 13" wheels. Running 13" or 14" wheels opens up some interesting R-comp tire size options - 215/50/13 and 225/40/14 V710s for example. Wide, yet short and light sounds good to me. Wheels and tires should be cheaper too.

Or is this just an impossible task? Thanks.

 

The 225/50/14 V710 looks interesting. It has good tread width and the overall diameter is just about the same as the 215/40/16 which would give you a second gear top speed of around 55 mph.

The Hoosier 245/45 ZR16 might work also. Craig Wilcox was looking at putting those on his DSP MINI. I haven't heard how that is working out for him. The overall diameter is the same as the stock 16" tires.

 

I have an MC, so lack of power at the autocross is a problem. I think a wide, light tire with a lower diameter would really help.

Based on the specs provided by tire rack, a V710 in 225/50/14 would give a ~5% reduction, be 3 pounds lighter and cost less while being as wide as a 225/50/15. Even the 215/50/13 looks interesting - pretty nice tread width, light and major reduction in gearing. This might be a little bit extreme, but local autocrosses here rarely get over 50mph. Or maybe its just me who rarely goes over 50mph cause the MC is so low on power .

 

This has been discussed before. 15" rims are the smallest that will fit.
Limiting factor is the size of the stock MINI brake calipers.
Forget 13" and 14" rims, it's been tried.

For an MC stick to the stock 15x5.5" holey rim if in stock class or if in any modified class then look at 15x7 or 949racing.com's 15x8 +36mm offset rims.

205/50-15 tires will fit stock or 15x7" rims while 225/45-15 will fit 15x8 rims. Both will give you 22.9" outer tire diameter favorable for autocross or track with reasonably low weight and decent tire width/traction.

For autocross you don't really need to change the brake calipers, just the brake pads and fluid. For track, upgraded brakes can be helpful. Basic Wilwood brakes will fit 15x7 or 15x8 rims.

 

I currently run 15x7 40et wheels with 225/45/15 and I know they work fine, but it doesn't mean I should stop exploring other less orthodox wheel/tire sizes. Fitting 14" or even 13" wheels on the MC introduce some very interesting tire sizes from the diameter/weight/price/width perspective.

I understand that stock brake systems don't allow much room for smaller wheels. This is why I didn't consider anything other than the 15x7 when I bought the Slipstreams last year, but then I read a blurb on Helix webpage saying this about Wilwood brakes: "The pad radius matches rotor diameters 9.45" - 12.19", and the caliper fits easily inside many 13" wheel applications."

The V710s in 215/50/13 for $140 sounds pretty good to me...especially at the bmwcca events where I never go faster than 50-52mph. Oh, and being stock is not a concern for me.