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View Full Version : Tire Tech.What do those numbers/letters on the side wall mean?



sailsmen
02-06-2004, 07:41 AM
I have been researching tires and I thought I would share some 411.

As an example our front MM stock tire is 235/50ZR18 97W.

This means;
1) the first number is the tire width from sidewall to sidewall in mm, 235 mm is the width of the stock MM front tire
2) the second number is the aspect ratio, the ratio of the sidewall height to the sidewall width, 235X.50=117.50, the sidewall height is 117.50mm
3) the letter is the speed rating, ZR for speeds over 149 mph
4) the next number is the wheel diameter, 18 for 18" wheels
5) the next number is the load index which indicates the tires load carrying capability, 97 has a load index of 1,609 lbs.
6) the next letter, W is for ZR rated tires and indicates how far over 149 mph the tire is rated for, W is up to 168 mph.

Our MM has a Gross Vehicle Weight of 5,240 lbs.

When looking for replacement tires, particularly in a non-stock size, it is very important to note the load index number. A tire with a load index number lower than the stock tire's 97 for the front and stock tire's 103 for the rear should raise additional questions to determine it's suitability for the MM.
Here are links for additional info;
http://www.tirerack.com/tires/tiretech/general/speed.htm
http://www.tirerack.com/tires/tiretech/general/size.htm

Paul T. Casey
02-06-2004, 08:44 AM
Thanks, I can never remember all that, so I copied it.

Thomas C Potter
02-06-2004, 01:11 PM
A reputable tire company will not sell you a tire that is load rated lower than stock. I was thinking about 275/35/18 on 10" front wheel, but no can do!! I would work around this, but for my daily driver, gotta play it safe.

TP

jgc61sr2002
02-06-2004, 04:28 PM
sailsmen - Thanks for the 411. :up:

MapleLeafMerc
02-08-2004, 09:26 PM
Thanks salesmen. It's always sounded like Professor Irwin Corey and the Caramilk secret to me! :up: