What is the largest/widest tires the stock R56S 2008 17" wheel alloys can take up to?

 

215-45-17

 

Are you just using it for street driving or for racing? For auto-x the stock class mini guys were squeezing 235 and 245 Hoosiers onto the stock tires. For street driving the 215/45/17 is a great option and I wouldn't look past that unless you have a real need.

 

I can guarantee you that autoX guys are not running 235 or 245 R-tires on stock 17x7" wheels with stock ET48 offset

Technically, you could squeeze 225/40-17 tires in there, but there aren't very many tires offered in that size.

It's not just a question of tire size fitting over a rim, but availability of the tire choices, prices, and limits of fit inside the wheel well.

Thus 215/40-17 size - lots of tire brands and models to choose from, most competitively priced. Will fit inside stock MINI wheel well on OEM wheels w/out any modifications.

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I have personally driven a 2009 Cooper S on stock class legal Enkei RPF-1s with 235/40/17 Hoosiers on it. Only some very slight rubbing on the rear trailing arm. However, r-compound tires are hugely different from street tires. I can imagine 235 street tires on a 7" rim being quite terrible.