Units of Measure
This is the standard for motorcycle tires. It depicts the most information of all the sizing styles and is the most current.
If your tire is a 120/70ZR17, the width of your tire (measured in a straight line from one edge to its opposite) is120 mm wide. It has an aspect ratio of 70%, which is how tall the tire is in relation to its width. ZR means it has a Z speed rating (149+ mph) and is of radial construction. The diameter of the tire is 17 inches.
The infographic to the right includes a breakdown of tire construction as well as an example of a tire measurement with detailed descriptions below each number or letter.
Older bikes, like Harley-Davidsons and some Honda Gold Wing models, use a method involving letters and numbers. We’ve included a conversion chart to make it easier further down the page should you need it.
If the tire is an MT90H16, it is designed for Motorcycle use (M) and it has a T tire width code. The aspect ratio is 90%, H is the speed rating, and the rim diameter is 16 inches.
Going hand-in-hand with the alphanumeric way of measuring, the service description is a combination of a tire’s load index and speed rating. For example, a tire with the sizing MT90B16 74H has a load index of 74 and a speed rating of H (130 mph).
Note: Newer tires that have a width of 150+mm will only use metric sizing. When the alphanumeric system was created, motorcycle tires didn’t get much bigger than an MV85 (150mm).
This measurement is most commonly found on ATVs and lawn tires. A few very old motorcycle tires may use it, but it’s unlikely to find many of these anymore.