Assuming the rolling circumference of the tyres remains the same, which it needs to for speedo calibration, the smaller the wheel then the more tyre there will be between the rims and the road and usually the ride quality will be better. Unfortunately, 'bling' has taken over and there is a marketing conspiracy afoot. Manufacturers are increasingly fitting big wheels with low profile tyres as standard equipment so every car looks like a racing car. I think tyre makers are sponsoring this, a bit like Hewlett Packard which virtually gives away printers in order to bind customers to its expensive print cartridges. Inevitably, replacement low profile tyres are much more expensive than deep profile tyres and that is where the money is made.