Tire sizes

I just purchased two 235/40 Kuhmo Ecsta V700's to use on the track and auto X. I already have three slightly used 225/45's that I am going to put on the front. I mounted the tires on 17X8 wheels.

Last night I put on the new rear tires (235/40). They are only about 1/2 inch (or less) narrower than the stock 255/35-18's that came on the car. Do the different tire manufacturers have different measurements?

I will post pictures later today or tommorow of the two different tires lying flat next to each other.

Yes.

R tires, and tires like Azenis Sports and S-03s tend to run wide for their putative sizes.

Yes, all tires have different size footprints . . . but 1/2" difference is very close to what it should be . . isn't 20mm difference about 3/4 of an inch roughly !?

A good example is looking at a Bridgestone SO3 . . . that tire has a very big footprint . . .

Yes. 1inch =about 25mm

actual tire sizes vary slightly from one manufacturer to another. in fact, even different tires by the same manufacturer are slightly different. for example, in a size in 225/45/17, the potenza s03 is 9" section width and a potenza re750 is 8.9" section width and a michelin pilot sport is 8.8" section width. Tread widths vary differently too as some tires are more square shouldered than others. check out the specs for each tire on the tire rack website or on the manufacturers website.

s03
http://www.tirerack.com/tires/Spec.j...+Pole+Position

re750
http://www.tirerack.com/tires/Spec.j...=Potenza+RE750

pilot sport
http://www.tirerack.com/tires/Spec.j...el=Pilot+Sport