I'm just not sure if all ZR tires (eg 245 50 ZR 16) have the Z Speed rating or not. If anyone can help it would be greatly appreciated, thanks. I tried a couple searches in this forum without any luck.

 

If it has a "Z" in the tire size it is Z-Rated.

 

thanks for the help, i thought as much but wanted to be sure

 

Yep, You'd be right... 'Z' is speed rating 'R' means radial.

 

Additionally, there are 2(or 3) numbers and one letter after the (for example) P245/50ZR-16 - this is called the service description. The number corelates to a load rating, and the letter a speed rating. If the letter is a W, the tires are rated for sustained 168MPH, if the letter is a Y, the tires are rated for sustained 186MPH. If there's no letter, the tires speed rating reverts to the original Z spec, which is simply "over 149MPH".

 

Or otherwise called an "Aspect Ratio".... ex..245/50 ratio of the width of the tire to the height of the sidewall..

 

I wasn't refering to the aspect ratio. An example:

P245/50ZR-16 89Y

The "89Y" is the service description of the tire... the 89 means it has a load capacity of 1279lbs, the Y means it is rated for sustained 186mph.

 

[QUOTE=Dave '97 Z28 M6]I wasn't refering to the aspect ratio. An example:

P245/50ZR-16 89Y You can not have a tire with two different speed ratings on it. Your example "Z" & "Y".

 

The "Z" part means the tires are rated for 149+mph, the "Y" part clarifies it as 186mph.

Check it out, near the bottom of the page...

http://www.tirerack.com/tires/tirete....jsp?techid=35