Mike, question. Putting 15mm spacers on is, assuming the standard wheels are ET48, which most MINI wheels are, is effectively going to give you an ET equivalent of ET33. Which is pretty aggressive. 12mm would give ET36
So is fitting say a wheel like a TD 1.2 with ET37 the same with respect to the issues you raise above?
i'm not saying the issue what i'm saying is altering geometry of any car or bike by altering wheels offset needs to done correctly to have gains, when i was 17 years old a had and i know but it was cheap a datsun 100a for work hack but did glue alfa romeo 1.5 alfasud engine and gearbox in it on standard wheels and brakes and yes it was a death trap in the wrong hands,, but my point is because it had narrow tyres it would spin the front wheels a lot and because of this i could steer it more on the right foot,, ie power on understeer power off at 4000 revs and about get oversteer,, so all my mates back then had rs 2000s and gte's opel manta's and the only one that could live with this datsun was a mini 1275 with dcoe carbs and a nuts driver to be honest,,, the others messed around with wheels and tyres and all said made their cars worse to live with on the bendy roads, as with all that grip comes the dangerous part ie if a car can be forced at will to under steer or over steer its more controlled than one that grips right to that point with no warning lets go,, so adding grip means that car will be travelling fast at point of grip if the geometry is altered wrongly to remove all understeer, underteer is good keeps you safe warns you to if its creeps up on you and suddenly no grip,, and this is why i hate all cars without rack and pinion steering with no feel to them but thats another story. all newer cars are not really designed for driver input its A to B add some bhp and some seats and call them sports,,
most people would get more performance from doing grass tracking for a year or rally course so much fun at that understeer and over steer point in any car