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Motorcycle Tires 101


Decoding the numbers and letters on your motorcycle tire sidewall can be a bit of a head-scratcher. Most modern tires use metric measurement, but older motorcycles may size alphanumerically.

Our guide breaks it down with infographics to simplify.


tire infographic

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.


speed rating

Speed Rating

This notes how fast your tire can go at its recommended load capacity. This is the letter found immediately after the aspect ratio. The letter next to that will perhaps be an R. This refers to tire construction, which tells you how the belts and plies are laid when the tire is created. Radial has a belt with plies that overlap at different angles to make it longer lasting. Bias tires are softer and can handle higher loads thanks to their plies criss crossing over each other. 

This system generated from Europe, so these increments are in 10s of kilometers.

Note: When Z speed ratings were first introduced, the tire industry expected that to represent the highest speed possible (at the time an excess of 149 mph or 240 km/h). As the industry and technology evolved, even greater speeds were possible, which is when W and Y were added to note where the speed actually reaches a threshold instead of the more vague Z rating. W = 168mph or 270 km/h).


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. 

load index chart

size conversion chart

Size Conversion and Date

The size conversion chart for understanding Metric vs Alphanumeric can be found to the right. 

Born On Date and Tire Wear

How old is that tire? Does it really matter?

Yes, it does. Older tires are susceptible to dry rot, cracks, or damage from UV rays. They’re sensitive to temperature changes, as well. The manufacturing date can be found on a raised block. It will have 4 digits, usually found by the US DOT ID number.

First two numbers = week of manufacture (out of 52 weeks of the year). Second two numbers = year of manufacturing.

EX: 1702 = 17th week of 2002** Prior to 2000, 3 digits were used, with the last one indicating the year.

Some tires have raised triangles or the letters TWI to mark where the tire wear indicators exist. When these are parallel to the rest of the tread, it’s time for new tires.

You may see TL or TT on your sidewalls. This means you have a Tubeless or tube type construction.

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