Inaccurate Speedo, Up one sidewall size?
 

Very quick question:

"New" 2017 Clubman S All4 (already autocrossed once!) and the speedo is pretty far off (speedo is fast) with the stock 225/45/17s. This is a mini-certified-used, so they put those low-grip Pirelli run-flats on it and they need replaced. Looking at the tire-size calculator I think replacing them with 225/50/17s will almost exactly fix the speedo offset, and I expect that will fit the car fine. Sidewall height is less than half an inch taller, so I think it will still look fine on the car and it looks to me like there is plenty of room for them to fit.

Thoughts? Anyone done this?

Thanks!