I am thinking about selling/trading my 16" X-Lites for some 15's or lighter 16's.

What are people running on the track? I really love the look of 15's with big thick tires, but does such a large sidewall flex too much for the track?

 

The issue is tires. If you can find the tires you want in 15" sizes, then go with 15" wheels. If not, go up to the next size.

 

I run 225/45/15 R comps on the track. No problems with flex, but these are a smaller diameter than stock, and relatively stiff sidewalls. I also ran 205/50/15 in the past, Falken Azenis, also smaller than stock diameter, no problems with the sidewalls rolling on those either, that tire would work as an everday driver as well, but there are better choices for dual duty.

Some people do complain that the turn in isn't quite as sharp with 15's; I went from 17's to 15's and much, much prefer the 15's--the smaller diameter shortens the gears nicely, I'm faster on 15's....

 

+1

 

Most Extreme Summer, R-Comps, etc don't offer too much sidewall flex.
15x7-8 inch wheels with 225/45-15 tires is likely the best set-up for a MINI, but nothing wrong with 215/45-16 Kumho XS or Falken RT615 on your X-Lites, then later trying the Kumho V710s on your X-Lites as you get to Red Group/Advanced/3rd level. Then you could keep your 16 X-Lites for street tires and have a dedicated set of 15s with Hoosier 225/45/15 tires or "streetable" R888, NT01s, or RA1 type tires.