[Tom D]

What is the size, width and offset of the BMW part# wheels that are specified in the challenge rules? What size and type of tyres are to be used?

Thanks,
Tom

[AndyW]

Hi Tom

They're the 15" 7-hole 175/65 R15 wheels that come as standard on the Cooper (here in the UK at least). The tyres were going to be the standard Pirellis as a control tyre, but Mike Cooper was saying on Friday that they've just struck a deal with Dunlop to sponsor the series, so we'll all be having those as our control now instead.

Offset? Dunno

Why do you ask?

Andy

[Tom D]

Thanks Andy. I am trying to decide what size tyres I will run here. I have a choice between 16 and 17 inch tyres and wheels. I'm trying to decide between 205/45/16 or 225/45/17. Our competition requires that we use factory wheel width with an offset no more than 1/4" wider (or narrower) than stock. I do not know if the 225/17's will clear the wheel wells and/or spring perches on the MINI, I presume that the 205/16's will fit. Do you know what the maximum tyre width is that will fit under a MINI on factory 16 and 17" wheels?

Tom

[AndyW]

Hi

I think the Challenge is being run on the basis of keeping costs as low as possible - hence no further mods are allowed after they've finished with prepping the cars, and the wheels/tyres are the smallest (and cheapest) they can be. So they're running it in a different way to your series - Autocross, is it?

So in, short, no idea what will fit - sorry.

A

[MINIAC]

Quote:

Originally posted by Tom D
I am trying to decide what size tyres I will run here. I have a choice between 16 and 17 inch tyres and wheels. I'm trying to decide between 205/45/16 or 225/45/17. Our competition requires that we use factory wheel width with an offset no more than 1/4" wider (or narrower) than stock. I do not know if the 225/17's will clear the wheel wells and/or spring perches on the MINI, I presume that the 205/16's will fit. Do you know what the maximum tyre width is that will fit under a MINI on factory 16 and 17" wheels?

Consider the numbers:

205/45-16 = 23.26" (590.9mm)
215/45-16 = 23.62" (599.9mm)
215/40-17 = 23.77" (603.8mm)
205/50-16 = 24.07" (611.4mm)
225/40-17 = 24.09" (611.8mm)
205/45-17 = 24.26" (616.3mm) [stock]
195/55-16 = 24.44" (620.9mm) [stock]
225/45-17 = 24.97" (634.3mm)

I think the two sizes you mentioned are too extreme. Since R83 (5-star), R84 (X-lite) and R85 (S-spoke) wheels all have 50mm offsets, any 205 tire will fit. I think you should be OK with a 215 on a lesser offset, but I don't know about 225.

I hope someone offers a 205/50-16 run flat tire for street use.

[Tom D]

Many thanks for the numbers MINIAC. I see that Hoosier makes a 205/40/17. What would be the diameter on that? I'm beginning to think that the only worthwhile way to go for now is with the 205/45/16. I plan on getting the 17" R85's to run on the street. Looks like I need to be looking for some very light 16" wheels to use for Auto-X. Any suggestions?

Thanks,

Tom

[MINIAC]

Given tire sizing as W/R-D, the formula for calculating overall diameter is:

(W * R / 100 * 2 / 25.4) + D ["] or (W * R / 100 * 2) + ( D * 25.4) [mm]

For a 205/40-17 tire, overall diameter would be:

(205 * 40 / 100 * 2 / 25.4) + 17 = 23.46" or
(205 * 40 / 100 * 2) + (17 * 25.4) = 595.8mm

You seem intent on getting the wheel/tire combination with the lowest overall diameter. Is this the best way to go in Auto-X?

This list of wheel weights may help you in your search for light wheels.

Don't know if you want to spend $315 per wheel, but 16" x 7" SSR Competition wheels weigh only 11 or 12 pounds each:

[Tom D]

The question you posed is a very difficult one to answer.
The best tire/wheel combination to run in Auto-X is the one that works best on your particular car and that suits your driving style. Generally, wider is better. The tire diameter helps to determine optimum shift points, depending on the transmission ratios. I usually look for the least amount of unsprung weight and the widest tires that will fit on the wheels and still give adequate clearance for maximum suspension travel. Any time a new car comes out it, there is a certain amount of experimentation involved to determine the optimum wheel/tire combination. I am trying to get some ideas. To some degree, economics also plays a part. For instance, there is a $58.00 difference in price PER TIRE between the two major manufacturers. That is a lot of money over the course of a season.

Tom

[minicoopersgirl]

IMO
I think 205 or 215 will be about the biggest you can go, and there’s more companies that make tires in 205.
My boyfriend had a Type R and it had crappy 205/50’s (about the same weight as the MINI) and it handled great! With GOOD 215/45’s on the MINI, it would be awesome!

[mike58]

I have fitted to my 911 the latest Michelin tyre it's the Michelin Pilot Sport Cup tyre and it is a road legal competition tyre. 5mm tread when new.
It's avail in many sizes and the tyre weighs substantialy less than a normal tyre.
The grip is close to a slick and is truly awesome,if you want the best this is it -- expect to get about 2-3000 miles from it