Question about tyre ratings

[BHML]

Hi,

My existing tyres say ZR18 (and have a speed rating of Y). I want to replace these with the exact same brand (Kumho) but the website lists the same tyres as R18 (ie not ZR18). All the other specifications are the same.

I read on another forum that the Z designation is not used any more, and as long as the speed rating is the correct one (Y), then it doesn't matter if the tyre says R18 instead of ZR18. Have I got that right? Or should I keep searching for a tyre that says ZR18?

The car is a C63 AMG.

Thanks,

[TA14]

It sounds like you may have it right for the wrong reason.

Z was introduced as being 150mph and over. Two sub-groups of Z have now been introduced: w, up to 168 and y, up to 186. You'll see ZR on the tyre of each of these sub groups along with the W or Y. If the car can go faster than 186 you'll need a Z which is unaltered at over 150mph.

In short, just buy a Y.

[BHML]

TA14 said:

It sounds like you may have it right for the wrong reason.

Z was introduced as being 150mph and over. Two sub-groups of Z have now been introduced: w, up to 168 and y, up to 186. You'll see ZR on the tyre of each of these sub groups along with the W or Y. If the car can go faster than 186 you'll need a Z which is unaltered at over 150mph.

In short, just buy a Y.

Thanks - both the R18xxx and ZR18xxx were rated as a Y - I suppose I wanted to know whether a ZR18 and R18 tyre are the same, provided they both have the same speed index of Y.

To be more precise, the tyres that are on now are Ecsta LE Sport KU39 255/35 ZR (note the Z) 18 XL (Y rated) but I can only get Ecsta LE Sport KU39 255/35 R (note no Z) 18 XL (Y rated) from most places, like Blackcircles.