How to read a car tyre
The numbers on the side of your car tyre detail your tyre’s speed rating, load index, service description, and more – here’s how to read a car tyre.
WHILE THE HISTORY BOOKS show that Mr R.W. Thompson was the first person to ever wrap a wheel in a strip of rubber, it was Charles Goodyear (1855) and James Boyd Dunlop (1888) who produced the first workable pneumatic tyre. It was fitted to a push bike.
It wasn’t until 1895 that the first car tyre was introduced. From then until 1925 most car tyres had beaded rims and had to be held in place by Clincher Rims. These were binned when Dunlop introduced Well-Based Rims. Dunlop was also the first company to produce bullet-proof tyres in 1917.
Without getting too nerdy, a car tyre consists of an outer carcass made from plies (which can be made of metal, rayon nylon, polyester, or fibreglass) encased in rubber. Steel wire beads hold the tyre against the wheel rim. In typical driving conditions a tyre will last around 50 million revolutions before needing to be changed.
There are many different systems of marking tyres but in Australia the most common form is the P metric system and a typical marking would be: P 215/65 R15 89H. P suggests the tyre is indicated for a passenger vehicle, 215 is the tyre (or section) width in mm, 65 indicates the aspect ratio, R means the tyre is a radial-ply and 15 is the wheel rim diameter in inches. 89H refers to the load and speed rating of the tyre, in this case H means the tyre is indicated for a maximum speed of 210km/h.
TYPE OF TYRE
As mentioned above, the letter P (and sometimes no letter, as in the case of the pictured tyre) denotes the tyre is indicated for use in passenger vehicles. LT, on the other hand, means the tyre is rated for Light Truck use.
This number usually follows the letter P or LT and it means the width of the tyre, measured from sidewall to sidewall. In the case of the tyre pictured the width is 205mm.
This is the next number along and, in the case of the tyre pictured which is showing 55, means that the height of the tyre is equal to 55% of the tyre’s width.
This tells you how the tyre has been made. So, in the case of the pictured tyre, the R stands for radial-ply which means the plies run radially across the tyre from bead to bead. An B indicates the tyre is of a bias construction which means the plies run diagonally across the tyre from bead to bead, with plies alternating in direction for reinforcement.
This is indicated by the R (and a number) and, in the case of the pictured tyre R16 suggests the wheel rim is 16 inches. If you’re buying a new set of tyres for your car this is the size you’ll need.
LOAD AND SPEED
This tells you the maximum speed at which the tyre can carry its load (the load is indicated in pounds – elsewhere on the tyre sidewall you’ll find the load rating in pounds and kilograms). In the case of the pictured tyre which shows 91V, the tyre has a speed rating of 240km/h. Despite this rating, you should, of course, always drive the sign-posted speed limits.
Z: more than 240km/h
This number means the tyre is compliant with applicable safety standards established by the US Department of Transportation, or DOT. Adjacent to this is a tyre identification or serial number.
PLACE OF MANUFACTURE
On the sidewall you’ll notice a reference to where the tyre was made.