I am planning to do a track day in my R56 Cooper which has OEM 16" R94 Bridge-spoke ET48 20.9lb (9.5kg) alloys
http://www.mini2.com/galleries/data/572/R94.jpg
with
Dunlop SP Sport 01 DSST RF tyres fitted for daily road use
I also have a spare set of 15" R81 7-hole (aka Imola) ET45 12.0lb (5.45kg) alloys
http://www.mini2.com/qt/r81_silver_wheel.mov
fitted with
Pirelli P3000 Energy non-RF tyres
I fancy using the 15s because:
- saves tyre wear on the daily use tyres
- lighter weight of 15s wud mean better acceleration / speeds
- non RFs would corner more progressively than RFs ?
- smaller 15s cud give lower centre of gravity & so improve handling ?
BUT, am concerned about the tracking, wheel alignment being set up for 16s and causing handling problems if I drive on the 15s ...
Am I better swapping to the 15's or keeping the 16's on ? 
probably take both a do a few laps on each to find the answer but appreciate people's advice ...
