how exactly do you read a tire size what does each number mena like in 325/65/18 i know the 18 is rim size, but what is the other and how do you knwo from that measurement how many inches the tires are.

thanks

 

http://www.discounttire.com/dtcs/infoSidewall.dos

 

First number is section width in milimeters. Second number is percentage of sidewall height to section width.

So, 325mm wide / 25.4 mm per inch ~ 12.8" wide
65% of 325mm = ~8.3" of rubber between the rim and road

There are two pieces of rubber on a diameter of a wheel so 2*8.3" + 18" wheel = 34.6" diameter tires, or what most people call a 35" tire.

Tirerack
s Tire Tech Page has a little more details. Remember, these are theoretical sizes as each tire brand/model will be slightly different.

 

Thanks a bunch

 

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