Tyre Sizing

[shonen]

Ok this may seem like the most fundamental of things to the pros but ive always wondered why people go a lower profile on the rears when the rears are wider than the front ?

ie 235/40/R18 front and 265/35/R18 rears.

why is it that you go to a 35 profile ?

I mean the width doesnt affect the diameter.....so just wondering why this is done ?

Also can mismatched sizes have an affect on the handling of the car or perhaps trick the hicas or tcs systems ?

I used to have the above mentioned sizes on 8.5inch wide fron and 9.5inch rears. On my last tyre change I decided to get 275s on the rears and keep the same size at the front and for some reason the it doesnt handle as well.

It COULD be that something else happened at the same time as the tyre change that affects the handling but im yet to find what the problem is so hence im posting this here to find out if tyre sizing effects handling.

[Beer Baron]

the profile is a percentage of the width.

[Patto-]

The width does effect the diameter.

As Beer Baron said, the profile is a percentage of the width. So wider tyres may have a lower profile to keep the overall diameter the same.

[blind_elk]

The change in handling could be due to the wider tyres on the rear giving more grip. Also the brand / model / style of tyre may affect the handling (grip) characteristics.

[GTshortie]

http://www.miata.net/garage/tirecalc.html

This website will tell you have much a differene your speedo will be if you change to another tyre size.

For example put your standard rims/tyre sizes in R33 Gts25t is 205/55/16 then put in the size of the tyres of the rims you want to get like 18" so 265/35/18" or 265/40/18" and see the difference in diameter

my 2 c