wheel and tyre profile

[jonbrown]

There is probably a really sensible or obvious answer to this, but was out looking at cars with the other half over the weekend and came across a clio that has had the wheels changed on it, no big deal I thought but they just looked really small in the arches, on closer inspection the wheel size was fine, but the profile on the tyre was rubber band thin, making the overall diameter of wheel and tyre smaller than standard.

With the exception that the tyre has to rotate more to reach maintain the a speed, thus in theory using more rpm and petrol and the lower profile making the ride a touch more choppy are there any other down sides and negative effects that this could have on the car?

 

[Dash]

I believe you should maintain a diameter that is as close as possible to the original so that the gearing of the drive train is not adversely impacted. (speedo reading incorrect) From what I read on the web, a difference in diameter +/- 2.5% is a general rule.

Cups with tiny tyres get to 60 in 2 secs where normally this would be 3 secs.