Motorcycle Tires 101

Units of Measure

Metric

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. 

Alphanumeric

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.

Service Descriptions

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).

Inch

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.

Load Index & Direction

Load index refers to the weight a tire can carry when properly inflated. This is listed on the tire wall next to the maximum air pressure. DO NOT overfill the tire. Many think overinflating is okay, but this leads to premature wear and poor handling. Measure your tire pressure when your tire is cold, as a warm tire skews the accuracy of your reading.

Rotation and Balance

Many of today’s modern tires require operation in one direction only.

Why?

During manufacturing, the tread is cut to length in a flat strip at an angle and spliced together with the ends overlapping. This creates a hoop that adds to tire longevity and stability. When a rear tire is mounted backward, under acceleration, it will peel back the splice, leading to blowouts. For front wheel tires, braking will peel back the splice.

In some cases, using a rear tire for the front is applicable, but you must remember to reverse the rotation. Never use a front application on the rear, and always consult with your manufacturer before reversing positions.

Our best recommendation? Use the front on the front and the rear on the rear. There will be an arrow on your tire noting the direction the tire must turn.

Finding the correct balance is incredibly helpful, and most tires feature painted balance dots to make it easier.