Over at the Campaign for Better Tyres, we have recently been hearing a few stories about tyre shops trying to talk their customers into changing their wheel size and/or their tyre size.
If you want to do this for atheistic or cosmetic reasons and can cope with the expense, then go ahead. But we maintain that there is little if anything to be gained in terms of safety or road handling from changing your wheel size from 16 to 18 inches etc; except for the tyre shop which will end up banking a good sale! Similarly, there is probably nothing to be gained from increasing tyre width from say 215 45 17 to 225 45 17 or even 235 40 17. Wider tyre widths are no guarantee of better road holding in wet weather, they may even reduce it.
Vehicle manufacturers put a lot of effort into determining the optimal rim and tyre size for a vehicle. Extensive road testing over many months will have highlighted the best wheel and tyre size which is unlikely to be bettered by some tyre shops off the cuff recommendation.
Sometimes a tyre shop will recommend a tyre size change because their tyre manufacturer does not make a size or because they do not have it in stock. Bettertyres recognises the financial and competitive pressures faced by tyre retailers but such pressures do not justify cajoling or pressuring their customers to buy anything but the optimal tyre size for their vehicle.