Motorcycle Tire Size Meaning Explained

Motorcycle Tire Size Meaning Explained

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Motorcycle tires have size codes, a set of numbers and letters, which represent different factors like width, aspect ratio, speed rating, rim size, construction, type of the tire, load and speed indices, type of tube and the like. These sets of numbers and letters may either be measured in Metric, Alpha, or using the rare Standard Inch. These are called measurement systems, and they help you know the size of your tire. There are three major systems and each has a different format, which is why it is important to have the motorcycle tire size meaning explained, so you can learn – in order to buy the right tire for your bike.

Metric System

This system measures the size in millimeters. It is the most commonly used system for motorcycle tires, which is a set of three numbers and letters implying the width of the tire, the aspect ratio of the tire (ratio of tire‘s height to the width) and lastly the rim size given in inches. Immediately after the speed rating, you will find a letter or two letters used to signify the speed rating and the radial construction of the tire consecutively.

Let us look at an example of this rating from a Shinko motorcycle tire 190/50 ZR 17:

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  • 190 =width of the tire,
  • 50 = aspect ratio which is the percentage of the height of the tire to the tire’s width,
  • Z = speed rating which is above 149mph,
  • R= Radial construction
  • 17= size of rim which is 17 inches

However, the speed rating and the construction of the tire may not be indicated. In this case you will have a set of number in this manner: 100/90 – 19. This Shinko tire reading means it is 100 mm wide, with a 90% aspect ratio and can be mounted on to a rim of 19 inches.

In short, Metric measurement takes either the Width/aspect ratio-rim size format or Width/aspect ratio-speed rating-Tire Construction-Rim size format.

Alphanumeric system

This is the standard system used in the United States. The measurements are given in inches and the measurements are straight forward.

Let us look at this format used by Shinko on one of their touring tires; MT90 – 16.

  • M is used to denote that the tire is a motorcycle tire
  • T denotes the width of the tire. In this case you have to refer to a chart to find out the width dimensions. Shinko always provide a chart on the website, so you can easily access the reference chart online.
  • 90 denote the aspect ratio. In this case it is 90%
  • 16 denote the size of the rim.

There are 3 key differences between the Metric reading and the Alpha reading:

  • A· The format of alpha readings always starts with letter “M”
  • A· The width of the tire is denoted by a letter
  • A· The speed rating is usually preceded by letter “S”

The wheel construction is denoted by letter “B” otherwise it is assumed to be bias-ply.

Standard Inch System

This is an outdated system and is only found in classic motorcycle. It is usually given in inches, hence the name Standard Inch measurement system. The aspect ratio of these tires is 100%; and it may or may not be indicated. Another thing to note is that these tires are not belted and are of bias-ply construction.

An example is 3.25H-19

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  • 3.25 symbolizes the width,
  • H symbolizes the speed rating, and
  • 19 symbolizes the rim diameter in inches

The aspect ratio, though not indicated, is 100% meaning the height of the tire is 100% the width of the tire

Low Profile Inch System

This is almost similar to the standard system; the difference is that the aspect ratio is 82% instead of 100%. However, on some tires the aspect ratio may be specified as 85%. This system is no longer in use.

Next time you are out shopping for new tires, make sure you have the right size now that you have the readings explained to you.

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