<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:<hr /><font size="1" face="Verdana, Helvetica, sans-serif">Originally posted by Wisrute B.:
<strong>Newer ZR rated tires have additional indicators like 91W (for example 225/50ZR17 91W) after the size indicator. 91 is the load index (weight), and W is the speed rating.
It simply means that the tire is good for 168mph, while Z indicating anything beyond 150mph. Y rating goes even further. wink
Secondly, you can fit VR-rated tires on your car, however you probably don't want to. VR-rated tires generally have harder compound than ZR, hence lower speed rating, harder ride, but less wear. This usually means less grip also. So, there is a trade-off for lower price VR-rated tires.</strong><hr /></blockquote><font size="1" face="Verdana, Helvetica, sans-serif">Wisrute I dont get it.
As I was looking for new tyres, I talked to two tyre "mechanics" and they both seemed to know what they were talking about. They both told me the same thing. That the optimum combination, is to get tyres that have the same speed rating, as the maximum speed of the car. Or at the maximum speed the driver drives (old men for example with cars that can go up to 240Km/h, if they never exceed 140Km/h, they should get Q rated tyres)
The lower the speed rating, the sooner the tyre gets to its working temperature conditions. In other words they get warmer more easy. Thus its not advisable to fit "Z" tyres to a 75bhp car, or Q rated tyres to a 200bhp car.
Does the speed rating has to do with the softness of the tyre? Does anybody really know? Or the speed rating depends on the chemical construction of the material, giving different temperature handling, but having the same softness/hardness ?
I thought that softness had to do with the tyre model ( different material for each brand ) and the speed rating ( lower speed rating, softer tyre )
From what Wisrute said, ZR tyres are softer than VR. Which one is true, or are they both true?
[EDIT]And another question: at a 215/45 ZR 17, is the ZR speed rating or a softness type indicator ? I thought it was a "Z" "R"adial..