How To Read A Motorcycle Tire Size

The Basics

Your tire size is written like this: 180/70 R 17 M/C 75H. Seems like an encrypted message, right? However, each component has a specific meaning that contributes to your understanding of the tire’s specifications.

Width & Aspect Ratio

Starting with the first digits: ‘180’ represents the tire’s width in millimeters. The width is measured from the widest point of the tire’s sidewall to the widest point of its inner sidewall. Imagine it as a hip-to-hip measure – important for the tire’s grip on the road. Then there’s the aspect ratio, the ‘70’ in our example, which shows the height of the tire’s cross-section as a percentage of its width. A ‘70’ implies the height is 70% of the 180mm width, shaping the tire’s comfort and handling.

Tire Construction

• Radial Tires ®: These tires are constructed with layers of fabric known as plies that run radially across the tire from bead to bead. The layers are placed perpendicular to the centerline of the tire. Additionally, radial tires have steel belts running beneath the tread, providing stability and enabling better heat dissipation. This construction allows for greater flexibility, improved ground contact, and a larger footprint on the road. As a result, radial tires offer better traction, especially in various road conditions, and typically provide a smoother ride.
• Bias-Belted Tires (B): In contrast, bias-belted tires have plies of fabric that run diagonally from bead to bead at alternating angles. These plies crisscross each other, creating a sturdy, overlapping structure. Bias-belted tires often have fewer plies compared to radials. This construction type tends to make the tire stiffer and less flexible. While they may not offer the same level of traction and road contact as radial tires, bias-belted tires are known for their robustness and durability, making them suitable for certain types of heavy-duty applications or off-road use.

The key differences lie in their flexibility, road contact, and how the layers of fabric are positioned within the tire. Radial tires generally provide better performance in terms of traction, handling, and ride comfort due to their design, while bias-belted tires are favored for their toughness and resistance to damage, making them suitable for specific types of rugged terrain or heavy loads.

Wheel Diameter & More

The number ‘17’ in our example represents the wheel diameter in inches, basically, the size it fits. Matching this with your wheel size is vital, plus it's important for top performance and safety too. ‘M/C’ simply stands for Motorcycle.

Load Index & Speed Rating

Finally, ‘75H’ is the load index and speed rating. The ‘75’ here does the heavy lifting, it is the maximum load the tire can carry at speed indicated by its speed rating, which in this case is ‘H’. An ‘H’ rating allows for speeds up to 130 mph. Different letters allow different speed ratings.

Tubeless or Tube-type

‘Tubeless’ or ‘Tube-type’, indicate whether the tire is designed to be used without an inner tube or with one, respectively. Tires can be tube-type, which aren’t airtight themselves, and need an inner tube to hold the air in, or tubeless type, which have an airtight lining so they don’t need a tube. The tire will be marked on the outside to tell you if it’s a tube-type or tubeless. The distinction between the two is also closely related to the design and compatibility with the wheel structure. When selecting tires for your motorcycle, it's essential to match the tire type with the corresponding wheel type to ensure optimal performance, safety, and longevity of the tire. The compatibility between the tire and the wheel is crucial. Using a tubeless tire on a wheel designed for tube-type tires (or vice versa) may result in poor performance, air leaks, or even safety hazards. Additionally, the rims need to support the specific tire type to ensure proper sealing and air retention.

Rotation Arrow

The arrow on the tire’s side is a guide – ‘front’ or ‘rear’ – to ensure you fit it the right way. Avoid mixing the front and rear tires, it’s like getting shoes for the wrong feet!

Production Date & Approval Marks

Checking the production date (those four digits in an oval) helps you know how old your tires are. The date is made up of four digits, the first two digits represent the week, and the latter two, the year – so ‘2118’ would be a tire made in week 21 of 2018. The letter ‘E’ with a number is like a stamp of approval, signifying it’s passed all the required safety tests in Europe. DOT, on the other hand, tells you it’s road-legal in the US.

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