[Pyrat 2]

A tried and true option for sure and one I've used time and again on my bimmers (see my signature). I never stay stock size when I replace tires. I've even replaced brand new stock tires using this approach.

Typically, I have upsized the tire by 1 or 2 sizes and ditched the run flat. This gives you more cornering grip plus a bit more rim protection both from curbs as well as from potholes (a big issue here in Chicago metro). For the X2 with 20" rims that strategy would be 235/40-20 or 235/40-20. However, 235-40 has very few tires available. Tire rack will show you noise vs grip tradeoffs for each tire. 245/40-20 opens things up a bit and gives you a lot more options. You can't really go larger than 245/40 because a 255/40 doesn't fit an 8" width wheel.

Both of these will change your actual vs indicated speed very slightly and interestingly towards a more accurate reading. Here's why. The indicated speed and the actual speed is intentionally different on most European cars. You may have seen the term 'corrected speed'. As an example your speedometer will read 60 mph but in reality you are traveling 58. Try it by setting your cruise and then reading actual with google maps. So what this means is that when you increase the diameter of your tire slightly by upsizing, your speedometer, which measures revolutions on your wheel, will be closer to accurate than stock (1 revolution will travel farther with a upsized tire).

Hope this helps and makes sense.