Tyre Size

[Mandy]

Can someone tell me the difference between the two please

[GT4 BOOSTER]

A common Trade-Off for higher Speed-Rating is reduced Ride Comfort. An "S" Speed-Rated tire will give a more comfortable Ride compared to "H" Speed-Rated tire, and a "H" Speed-Rated tire will give a more comfortable Ride compared to a "Z" Speed-Rated tire. The Ride Comfort Characteristics can be attributed to the tire's Overall Stiffness. A tire capable of running at High Speeds requires a more stiff construction, in order to provide the necessary high speed stability & durability. AN R RATED TYRE IS ONLY GOOD FOR 106 MPH

Tire Speed Rating Symbols:

S -- 180km/h or 112mph

T -- 190km/h or 118mph

U -- 200km/h or 125mph

H -- 210km/h or 130mph

V -- 240km/h or 149mph

W(ZR) -- 270km/h or 168mph

Y(ZR) -- 300km/h or 186mph

ZR -- Above 300km/h or 186mph

[Mandy]

Thanks Booster

I'm still a bit confused though. The Tyre has a W speed rating, I understand that. I assumed that the R infront of the 17 (size of rim) meant Radial.

Are you saying ZR means something different?

[GT4 BOOSTER]

Tyre Sizes

Tyre sizes are made up of a number of different numbers and letters. For example tyre size 175/70 R 13 82 T is made up of the following information:

175

The tyre section width in millimetres

70

The aspect ratio in % (the height of the sidewall divided by the tyre's width)

R

Denotes the tyre's construction type - in this case it's a radial

13

Rim diameter in inches

82

Load Index

T

Speed Rating

http://www.dashdriving.com/tutorials/tyre-markings.htm

[cfc1]

eg.. 185/65HR15

185

This is the width in mm of the tyre from sidewall to sidewall when it's unstressed and you're looking at it head on (or top-down). This is known as the section width.

65

This is the ratio of the height of the tyre sidewall, (section height), expressed as a percentage of the width. It is known as the aspect ratio. In this case, 65% of 185mm is 120.25mm - the section height.

H

This is the speed rating of the tyre.

R

This tells you that the tyre is a radial construction. Check out tyre construction if you want to know what that means.

15

This is the diameter in inches of the rim of the wheel that the tyre has been designed to fit on. Don't ask me why tyre sizes mix imperial and metric measurements. They just do. Okay?

There is also another way that the tyre size is displayed on the tyre..

1. 185/65HR15

2. 185/65R15 91H

Both of these tyres are the same size and the same speed rating.. the other number you see on the tyre in example number 2 is the Load Index. (a number which corresponds to the total weight that the tyre was designed to carry, multiplied by 4 = the total fully laden weight of a vehicle the tyre was designed to take)

Load Index table

There is a little more too it all than above.. it can get quite technical and VERY boreing (like this isn't?.. i here you say ) and just to confuse you even more.. the speed ratings for a tyre also depend in which way the speed symbol is stamped on the tyre.....

215/45ZR17

215/45ZR17 91W

In the first example the letter Z (after the number 45) denotes the speed rating of the tyre.

In the second example.. the letter W (after the load index) denotes the speed rating of the tyre.

215/45ZR17

215/45R17 91Z (very rare these days for Political reasons.. bringing Europe together etc... BOREING)

The second example above is a higher speed rating than the first example.. to simplify it a little.. the first one could be rated to a speed UP TO 156mph.... (the next line i am not 100% sure EXACTLY what the speed actually is.. it's been a good while since i have had to explain it to people.. so don't take the mph i am giving a correct.. it is just an example)..the second one would be slightly over and not exceeding 160mph

Mandy..

I assume you have at least a "Z" rated tyre on your car.. this is more than adequate for a Celica.. So if that is what was concerning you, don't worry, it's fine :)

[Mandy]

Davy

Thanks - Obviously thought out by a man!

Mandy