Writings on the (side) wall

By Chris Aaron 15 hours ago

Ever wondered what all the text on your tyre’s sidewalls mean? How does it affect you? How does it influence your tyre-buying decisions? Read on to find out.

*Words by Nooralia Zaharin, brought to you by Michelin

First, the sidewall is exactly what it describes – the sides of the tyre wall, or the part which you see easiest and does not have treads. Look closely and you will notice a lot of text written onto it but what you would want to take note of is a sequence of numbers and letters such as this: 195/65 R 15 91H (the example here is based on a MICHELIN Energy X tyre).

The first set of numbers designate the section width of the tyre (195mm in this example). A tyre’s width plays an important part as it determines how large its contact patch is with the road. The larger the contact patch the better grip and traction the tyre will have and this is why sporty high-performance road tyres are usually built wide for maximum traction.

The second sequence refers to the aspect ratio or height of the tyre; and this is where it gets slightly complicated.

The aspect ratio takes into account of tyre sidewall’s height and width, with the number being its percentage. So, by reading it as 65, it means that the wall height is 65 per cent of the tyre’s width.

When you hear of people talking about ‘low profile tyres’, it means the type which you usually see fitted on sportier cars – these have very short sidewalls for better handling. However, ‘low profiles’ would largely compromise ride comfort.

The single alphabet advertises the fact that the tyre has a radial construction, which actually forms the large majority of road tyres (radial is the type of construction, as opposed to cross-ply which it replaces). The final number in that arrangement is for the tyre’s diameter (measured in inches), which informs you the diameter of the rim the tyre will fit into.

The irony and confusing nomenclature is not lost on the fact that it both uses millimetre (for section width) and inches (for diameter). But, you can be confident that it is a way that is accepted the world over.

Basically, it is not only important to know the tyre’s section width, its aspect ratio and diameter (usually for the car’s cosmetic reasons) but also the load factor and speed rating. 91H that comes after refers to the Load Capacity Index (91 here means 615kg) and the alphabet explains the Speed Category (H puts it capable to speed up to 210kmh).

The former, which corresponds with the maximum load carrying capacity of each tyre when properly inflated, goes from 62 to 126 in most passenger car tyres (62= 265kg, 126=1700kg). To know the maximum load your car can carry you would need to multiply this number by 4 tyres and subtract the car’s total weight from the result.

The latter refers to the maximum speed the tyres are built for, and not how fast your car can go when fitted with them. Most of the letters between J and Y are used in the speed rating (J=100kmh, Y=300kmh); with additional pairings namely VR (>210kmh) and ZR (>240kmh) are also used.