I agree with Dave. The tyres on a 16" wheel will also be lower in profile. Fine on a race track but low profile tyres usually have a harsher ride and are more prone to damage to the tyre and/or rim when a pothole is hit.

I would be annoyed at the fee for changing the spec but now is the time to think seriously about it before the car goes in to production. In fact changing to narrower 15" wheels may not cost you much as the difference in price will balance, in good part, the fee for changing the spec. Certainly changing after you have the car, unless you can make a satisfactory deal with your dealer, will be more expensive and in the end may look odd because of the extra width of the mudguards which will be cut to cover the wider tyres.

Peter

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