The most obvious piece of information is the big numbers and letters that usually look like this – 130/90 17, or MT90 17.
These numbers are a metric designation that indicates the size of the tire and the rim that tyre is designed to go on. The question is what do those numbers actually mean?
Let's start with the first series of numbers, 130/90 17 which in this case are a metric designation. This is the most popular nomenclature used in the motorcycle tire sizing world today. What do those numbers actually mean?
THE FIRST NUMBER – WIDTH
The 130 indicates the width of the tire in millimeters. This is measured as a straight line through the tyre from one edge of the tire's tread to the other edge.
THE SECOND NUMBER – ASPECT RATIO
The second number, the 90, represents how tall a motorcycle tire is in relationship to its width. This is the aspect ratio between the tire's width and its height indicated as a percentage. In simple terms this means the larger this number is, the taller the tyre will be. In the example the tyre is 90 percent as tall as its width which we could calculate to be 117mm.
THE THIRD NUMBER – RIM SIZE
The last number, 17, refers to the tire's rim diameter expressed in inches.
Inches
The width on some tires may be expressed in inches. In those cases the aspect ratio is usually not included.
Alphanumeric
An alphanumeric designation such as MT90 17, represents the same tire size as 130/90 17. It's just expressed in a different way. M means the tire is for motorcycle use, T is the tire width code, 90 is the aspect ratio and 17 is the rim diameter.
Tire Size Conversion Charts
You'll notice the tables do not go any further than 150/90 tyre sizes. Here's why.
The alpha numeric method of tire sizing is older than the metric system. Way back when … motorcycle tires didn't get much larger than an MV85 which is equivalent to a width of 150mm. Modern tires larger than 150mm wide now only carry the metric size designation.
Front | ||
| INCH | METRIC | ALPHANUMERIC |
| 2.50/2.75 | 80/90 | MH90 |
| 2.75/3.00 | 90/90 | MJ90 |
| 3.25/3.50 | 100/90 | MM90 |
| 4.00 | 110/90 | MN90 |
| 4.25/4.50 | 120/80 | MR85 |
| 4.25/4.50 | 120/90 | MR90 |
| 5.00/5.10 | 130/90 | MT90 |
Rear | ||
| INCH | METRIC | ALPHANUMERIC |
| 4.00/4.50 | 110/9 | 0 MN90 |
| 4.50/4.75 | 120/80 | MP85 |
| 4.50/4.75 | 120/90 | MP90 |
| 5.00/5.10 | 130/90 | MT90 |
| 5.50/6.00 | 140/90 | MU90 |
| 6.00/6.25 | 150/80 | MV85 |
| 6.00/6.25 | 150/90 | MV90 |
Understanding Speed Rating and Construction
It's likely you'll find other letters mixed in within these motorcycle tire sizing numbers. They'll look like: 120/70ZR17 or 170/60R 17V, or even in other combinations. The two extra letters designate the tire's speed rating and construction.
Construction
The letter R or B indicates the construction used to create the casing of the motorcycle tire. An R stands for radial construction and a B indicates the casing has a belted bias.
Speed Rating
The other letter refers to the speed rating and indicates the maximum speed a motorcycle tire can sustain under its recommended load capacity. For example, U is indicates a maximum speed of 200 kmh / 124 mph.
In the examples the Z and the V are both speed rating indicators.
| SPEED RATING | MAX SPEED – MPH | MAX SPEED – KPH |
| J Type | 62 | 100 |
| N Type | 87 | 140 |
| Q Type | 99 | 160 |
| S Type | 112 | 180 |
| T Type | 118 | 190 |
| U Type | 124 | 200 |
| H Type | 130 | 210 |
| V Type | 149 | 240 |
| W Type | 168 | 270 |
| Y Type | 186 | 300 |
| Z Type | Over 149 | Over 240 |