Size example: 225/55 R 17 97 W
225: this is the tyre width in mm. In our example, the tyre is 225mm wide
55: indicates the aspect ratio of the tyre, in other words the height of the sidewall expressed as a percentage of the tread width. In our example, the sidewall height is 55% of the tread width. The lower the figure, the lower the sidewall height
Remember: the lower the sidewall height, the better the grip when cornering; in this case, the ride is also less comfortable.
R: this refers to the internal construction of the tyre. R indicates it is a "radial" tyre construction. Almost all tyres in use today are of radial construction. This means that the plies of tyre cord extend across the casing from bead (also called "heel") to bead.
17: this is the inside diameter of the tyre, in other words the rim height. This diameter is given in inches. In our example, the diameter is 17 inches.
97: this is the load index. This index indicates the maximum load the tyre can carry when it is inflated to its maximum safe pressure. In our example, this doesn't mean that the tyre can carry 97kg, but that the index is 97; you then need to refer to a look-up table which determines the load in kg for each rating. For an index of 97, the maximum load weight is 730kg/tyre.
W: this is the speed rating, and indicates the maximum speed at which it has been certified that a tyre can carry a load safely. The speed ratings range from A (the lowest) to Y (the highest) with one exception: H is rated between U and V. As with the load index, each letter corresponds to an equivalent in km/h:
- Q: 160 km/h
- R: 170km/h
- S: 180 km/h
- T: 190 km/h
- H: 210 km/h
- V: 240 km/h
- ZR: > 240 km/h
- W: 270 km/h
- Y: 300 km/h
Please note: the speed rating is an indication linked to the capabilities of the tyre; in no circumstances does this authorise you to drive faster than the legal speed limits.
|Load index||Load in kg per tyre|
UTQG (Uniform Tire Quality Grading) is an American standard required by the US Department of Transportation (FMVSS: FEDERAL MOTOR VEHICLE SAFETY STANDARDS) concerning private car tyres.
It does not concern studded tyres (4x4, all-terrain), snow tyres, emergency spare wheels or tyres smaller than 12 inches.
This standard must be indicated on all tyres sold in the USA, and because almost all tyre manufacturers operate in the US market, it is also found on most tyres sold in Europe.
These codes indicate when and where the tyre was manufactured. In this example:
DOT - Department of Transportation (USA)
BP - Code relating to the factory where the tyre was made
M2 - Dimension code
P711 - Optional code
4008 - Week and year of manufacture. In this case week 40 in 2008.
Two specific winter markings can be found on tyre sidewalls:
This marking indicates that, in accordance with European regulations, it is a "snow" tyre. Nonetheless, its performances in winter conditions are not tested.
3 Peaks Mountain Snow Flake: tyres with this marking are designed for snowy roads and offer performance levels confirmed in tests.*
The symbol made up of three peaks and a snowflake (3pMSF) on M+S (Mud & Snow) tyres designates tyres designed for difficult snow conditions.
* Test of braking efficiency in winter conditions using the ETRTO (European Tyre and Rim Technical Organisation) method.