Motorcycle tyres have slightly different dimensions and features compared to
car tyres.
There may be numbers and letters on your motorcycle’s tyre sidewall that you might not understand, not being familiar with the ZRs or M/Cs scattered across the tyre.
We’ll be covering every motorcycle tyre dimension and explaining what each means to give you a better understanding of general motorbike tyre sizes.
Motorcycle Tyre Size
On the surface, motorcycle tyre sizes are confusing – but they don’t have to be.
As shown in our visual guide to motorcycle tyre dimensions below, the sidewall of your tyre will display key specifications for that particular model.
Tyre Width
This number indicates the tyre’s section width in millimetres, measured from sidewall to sidewall.
For example, in
120/70 R17 M/C (58W), the '120' refers to a width of 120mm. This is a nominal value and can vary slightly depending on the rim width the tyre is mounted on.
Aspect Ratio
This is the height of the tyre’s sidewall expressed as a percentage of its width. In our example, the aspect ratio is '70', meaning the height is 70% of 120mm – which is 84mm.
A lower ratio like 55 would result in a lower-profile, sportier tyre, while a higher ratio like 90 is typically found on touring or classic motorcycles.
'ZR', 'R', or 'B'
If your tyre has 'Z' on its sidewall, it indicates a high-speed rating, meaning the tyre is approved for speeds exceeding 149mph (240 km/h).
'ZR' means a high-speed rating and that the tyre has a radial construction – the 'R' standing for radial.
Many high-performance bikes use ZR-rated radial tyres, especially in sizes like 180/55 ZR17, whereas typical road bikes will tend to use standard radial construction tyres, such as 120/70 R17.
If a tyre has a 'B' marking (e.g. 170/80 B15), it indicates a bias-belted construction – a hybrid between bias-ply and radial – offering increased load capacity and improved ride comfort, commonly found on cruisers and touring motorcycles.
Rim Size
This indicates the diameter of the wheel (rim) the tyre fits, measured in inches. In 120/70 R17, the '17' means the tyre fits a
17-inch wheel.
Common motorbike rim sizes range from 10" on scooters to 21" on off-road bikes, but 17" is the standard for most sport and street motorcycles.