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Tyre Markings

 

What's all that stuff on the side of the tyre? All tyres are required to have the size clearly marked on the side wall of the tyre. It will look something like this:
195/65 R 15 91H
So what does it all mean? Well first is the tyre width. In the example above the width is 195mm. This figure refers to the tyre width not the tread width.

The next two numbers are the tyre aspect ratio. In plain terms it would be called the height to width ratio. The above example has a hight of 65% of 195mm. ( 126.75mm) If the tyre was a 195/70R14 it would be 70% of 195mm (136.50mm). This two digit figure is referred to as the tyres series. For example "65 series Tyres"

Next is usually the letter "R" This identifies the tyre as having a radial ply construction. If it was the older style cross ply construction it would be identified with the letter "D"

Next is the rim diameter. Our example size was a rim diameter of 15 inches. That's right, "inches". They measure diameter in metric measure and rims in imperial measure!! There have been some attempt to start using rims measured in metric measure but for some reason it never seams to catch on! A tyre with a metric rim has a size that looks like this 220/60 R390.

Finally, comes the load and speed index. This refers to the maximum load and speed the tyre is designed for. Below are two tables explaining the various ratings. Our example is 91H so it is designed to carry 615kg per tyre at a maximum speed of 210kmh.


Speed indexes
The following is a list of speed indexes as found on passenger car tyres. The speed rating is the maximum speed the tyre is designed to work at. A similar set of speed ratings applies for commercial vehicle tyres.
R 170kmh 106mph
S 180kmh 112mph
T 190kmh 118kmh
H 210kmh 130mph
V 240kmh 150mph
W 270kmh 169mph
Y 300kmh 187mph
ZR over 240kmh over 150mph


Load Indexes
Remember these are the maximum load for each tyre with the car fully loaded.
75 375kg 88 560kg
76 400kg 89 580kg
77 412kg 90 600kg
78 425kg 91 615kg
79 437kg 92 630kg
80 450kg 93 650kg
81 462kg 94 670kg
82 487kg 95 690kg
83 487kg 96 710kg
84 500kg 97 730kg
85 515kg 98 750kg
86 530kg 99 775kg
87 545kg 100 800kg