Motorcycle Tyres: Sizes, Markings and Construction

While most bikers can use a tyre size guide to find the right tyres for their motorbike, not everyone understands the wider extent of the tyre markings found on the side of a motorcycle tyre.

Aside from explaining the tyre sizes, these markings contain numerous pieces of highly useful information. To help you, we’ve compiled a breakdown of what they mean, as well as some useful information on the wider nature of a tyre’s construction.

What are the most important elements of a motorcycle tyre?

Tyres are very complex objects, with a lot of key components going into their design. There are actually numerous key areas apart from the rubber, including:

• The carcass. This is a combination of steel belts and ply layers, providing the main building frame for the tyre itself.
• Plies. These are made of strong fabric and help define the tyre’s shape. As such, they are responsible for coping with dynamic deformation and heavy loads.
• Treads. This is the part of the tyre responsible for traction, as well as how the motorcycle handles. It is also where water, mud and dirt are channelled away from the tyre, to reduce the risk of aquaplaning.
• Sidewalls and shoulders. These are the thinnest elements of the tyre, yet offer some of the highest resistance to tyre deformation.

 A crosscut of a motorcycle tyre, highlighting the various construction components.

Dividing tyres according to their construction

Generally speaking, tyres can be constructed in three completely different ways. These are:

• Bias tyres, which are indicated by a “-” on the tyre markings
• Bias-belted tyres, indicated via a “B” on the tyre marking
• Radial tyres, indicated by “R”

Each type has its own unique properties and each type is worthy of a lengthy article. Yet, for the sake of convenience, here are the key characteristics of each.

Bias tyre

• This type features a cross-ply pattern in relation to the tyre’s centre line.
• The simple construction and high external resistance make this tyre ideal for off-road use.
• When it comes to the speed rating on tyres, this construction method allows speeds of up to 149 mph.
• This type is most commonly used for chopper tyres, cruiser tyres and enduro tyres.

Bias-belted tyre

• Extra ply layers reduce the deformation of the tyre, and lower the working temperature.
• This extra play also reduces friction within the tyre structure, giving it better stability.
• This design choice is ideal for heavy motorcycles.

Radial tyre

• In this type, the ply layers from radial patterns, which is where the name comes from.
• Additional ply layers sit just below the tread, offering better stability.
• This design makes the best choice for fast motorcycles.
• Thanks to the extra ply layer, the friction within the radial tyre is lowered, making it more resistant to high temperatures and centrifugal forces when travelling at high speeds.

Motorcycle tyre sizes explained

These days, the markings on a motorcycle encode a lot of useful information. Other than having the tyre size explained, this includes information on the tyre’s age, construction type, date and place of production. A better breakdown of this information can be seen here:

The tyre marking example above is for a bias motorcycle tyre - we know this thanks to the dash (“-”) seen between the profile and diameter of the tyre. If this, instead, said B or R, this would indicate a bias-belted or radial tyre, respectively.

However, sometimes a tyre size can be described with another system, such as 2.25-16, where both the tyre width and diameter are given in inches.

Here are some other useful tyre marking information.

How to find the production date on a tyre

If you want to know how old a tyre is, you need to look for the DOT number. DOT stands for Department Of Transportation and will be followed by four digits. The first two numbers are the week and the second two numbers are the year.

For example, if your motorcycle tyre has a year of DOT 2312, this means it was produced in the 23rd week of 2012.