Tyres are the only contact your two-wheeler has with the road while in motion. It is, thus, extremely important to ensure that the tyres installed on your two-wheeler are of the correct specification, or there may be some very undesirable consequences. For example, a tyre which is too wide, if installed on a commuter bike would reduce not just its acceleration and efficiency but also make it dynamically unstable despite having a wider contact patch. On the other hand, a slim tyre installed on a high performance machine would get shredded to bits before you know.
In order to ensure that the specification of a tyre could be clearly defined by a manufacturer, and understood by the end consumer, there’s a well defined nomenclature for tyres. All tyres made by credible manufacturers come clearly marked with codes denoting details about all the critical parameters defining their capability. In this guide we’ll tell you everything about how to read two-wheeler tyre markings, and why they are important.
Size, load and speed rating
Let’s take this tyre image as an example. The size, load and speed markings on the sidewall read 180 / 50 R17 71 W
Tyre width – the first two or three digits of the marking represent the section width in millimetres, measured from the widest parts of sidewall to sidewall (not the contact patch) with the tyre inflated to its correct specification. So the number 180 in our example represents a 180mm wide tyre. This is followed by a forward slash ‘/ ‘ for separating the next number.
Aspect Ratio or profile – The next digits denote the aspect ratio. This represents the height of the sidewall or the ‘profile’ of the tyre. Aspect ratio is typically denoted as a percentage of the section width of the tyre. In our example it’s 50, which means that the height of the tyre’s sidewall is 50% of its nominal sectional width or less.
Tyre construction – Sometimes (but not in all cases) the aspect ratio is followed by a code indicating the construction type of the tyre. The code is represented by a letter from the alphabet, and this is what it means
- B – bias belt or bias ply construction
- D – Diagonal tyres made of nylon cords placed diagonally across each other in the tread and sidewall.
- R – Radial tyres
The next set of digits represents the diameter of the wheel in inches. In our example it’s 17, which means that the tyre is meant for 17 inch wheels.
The next set of digits represents the load index, which denotes the maximum mass, or weight the specific tyre could carry. Here’s a part of the load index table for reference. Some tyre makers also specify the maximum load a tyre can take separately in kg.
|Load Index||Load in kg|
From slow moving mopeds to superbikes which could hit the triple ton mark, tyres are made for all varieties of two-wheelers. The fastest speed a tyre can travel at is denoted by the speed rating. Speed rating is indicated by either a single letter, a combination of a letter and a digit, or a letter in brackets. As in case of load, some manufacturers provided the speed limit of the tyre specifically in miles per hour (mph) or km/h separately.
The complete list of speed rating codes and their respective speeds is provided below:
|Z||over 149||over 240|
|(W)||over 168||over 270|
|(Y)||over 186||over 300|
Date of Manufacture
The date of manufacture of a tyre is typically enclosed in an oval and may be preceded by a code, which represents the facility where the tyre was manufactured. Last four digits of this code tell you the date of production of the tyre. The first two digits represent the week of the year when the tyre was produced from 1 to 52. The last two digits represent the year. So, basically a tyre marked 4513 was manufactured in the 45th week of 2013. This is a good way for consumers to ensure that the tyre they’re buying is not too old, as tyres turn hard over time and don’t perform optimally.
Other common markings
Direction of rotation – Represented by an arrow with the head denoting the direction of rotation
Air pressure – in some cases, the tyre will have explicit markings indicating the maximum pressure in PSI or kPA. This isn’t necessarily provided on all tyres though.
TL – Tubeless
TT – Tube-type, this tyre must be used only with an inner tube
Made in ‘Country’: Depicts the country of manufacture
TWI: It’s the tyre Tread Wear Indicator which lets you know when the tread has worn out and the tyre needs replacement.