Tyres are the unsung heroes of car safety. While they may not be the most exciting part of your car, they are vitally important for keeping your car on the road. As you dutifully and regularly check your tyres for ware and pressure, you may have noticed a bunch of numbers and letters on the sidewall. Ever wonder what they all mean? Well, today we’ll find out, and the best way to do this is to look at an example.
225/55 R 16 91V DOT XBFU XJJX 1315 RFT NO REF
This jumble of numbers and letters above may look confusing, however it’s a typical example of what you would see on a tyre’s sidewall. Each one means something, though some are more important to us as drivers than others.
Let’s start with tyre size. The ‘255’ in the above sequence is the width of the tyre in millimetres across the thread. The ‘55’ is the ‘Aspect Ratio’ which is the profile height of the tyre as a percentage of the width. In this case, the aspect ratio is 55% of 255mm.
Next in the sequence is the ‘R’ which stands for ‘Radial’. A Radial tyre is constructed with the plies running at a 90 degree angle to the direction of travel. A ‘B’ would indicate a Bias construction where the plies run diagonally across, however most new tyres these days are Radials.
The ‘16’ in the above example is the size of the rim in inches that the tyre fits and is effectively the size of the hole from one side to the other.
The next number, ‘91’ is the load index. It is a code which tells you what weight the tyre can carry. For example, 91 equates to a maximum load of 615 kilograms when a load index is consulted.
The Speed Rating is next: S= 180km/h; H= 210km/h; V=240km/h; Z > 240km/h; W= 180km/h; Y 300km/h. So for our example, our tyre’s speed rating is 240km/h which is the maximum speed the tyre is capable of.
After the speed rating will be the letters ‘DOT’ followed by a series of eight letters and numbers. DOT means the tyre exceeds the safety standards laid down by the Department of Transport in the USA. The series of eight letters and numbers is a serial number used by the manufacturer.
The ‘1315’ tell us when the tyre was made. The first two digits is the week of the year and the next two is the actual year. So in this case, the tyre was made in the 13th week of 2015.
‘RFT’ in our example denotes these are Run Flat tyres. The symbol does change though according to the manufacturer. For instance, Pirelli use ‘RFT’, but Michelin use ‘ZP’.
Tyres that are specifically designed to be used on certain car makes occupy the next space in the form of a code, depending on the car manufacturer. In this example for instance, the ‘NO’ tells us that this tyre has been specifically designed for Porsche.
Last but not least is a code to show whether or not a tyre has been reinforced to carry extra weight. This code will change depending on the manufacturer. For our tyre, it’s ‘REF’ but it could be XL, RF, RFD, etc. depending on which company made the tyre.
This list, while not exhaustive covers most of what you will find. Red dots, rotation arrows, whether the tyre can handle mud and snow, mountain snowflakes and the like can be found, along with the basics like maximum tyre pressure. Who would have thought a tyre’s sidewall would provide so much information?