**- Common Service Manual**

CLICK HERE TO PRINT.

Motorcycle Tire Sizes

Three different methods have been used for sizing motorcycle tires over the last half century, English sizing, metric sizing and American sizing. The oldest method is the English, while the metric sizing is the most common today. All rim diameters are measured in inches.

An example of an English tire size would be 3.50 H-18 4PR TT. In this case, the first number represents the nominal width of the tire at its widest measurement, which would be 3.5 inches. If the first number had been 3.00, the tire width would be 3.0 inches. However, if the first number ends in a .10 or a .60, this indicates the tire is a low profile design. For example, 4.10 would indicate a tire that is 4.0 inches wide and low profile, while a first number of 4.60 would indicate a low profile tire that is 4.5 inches wide.

If there is a letter immediately after the tire width, it indicates the speed rating of the tire. The speed rating is based upon testing the tire on a drum to determine the maximum safe sustained speed capabilities of the tire. If there is no speed rating indicated, the tire has an “S” rating and there will be a “-” or an “x” after the width. See the chart below for the most common speed rating letter designations.

Letter | Speed Rating |

S | 112 mph (180 kph) |

H | 131 mph (210 kph) |

V | 149 mph (240 kph) |

Z | over 149 mph (240 kph) |

The number after the speed rating (or the “-” or “x”) indicates the tire diameter in inches. This number will almost always be a whole number.

If there is a number followed by the letters “PR”, this indicates the load rating, in the example above the 4PR indicates a four ply rating. That doesn’t necessarily mean it has four plys, it only means it has the load capability of a four ply tire.

If the letters “TT” or “TL” follow the load rating, this indicates whether the tire has a “tube type” or “tubeless” construction. A tubeless tire can usually be run with a tube if necessary, but don’t ever run a tube type tire without an inner tube.

The most commonly used tire sizing method currently being used, it is actually a combination of metric and English measurements. An example of a metric tire size would be 180/60 VR 17. In this case, the first number indicates the nominal width of the tire in millimeters, which would be 180 mm.

The number after the “/” is the aspect ratio, which is the height of the tire from the bead to the outside circumference divided by the width and represented as a percentage. In this example, the tire height is 80% of the tire width. The lower the percentage, the lower the profile of the tire.

The letter immediately after the aspect ratio indicates the speed rating of the tire. The speed rating is based upon testing the tire on a drum to determine the maximum safe sustained speed capabilities of the tire. If there is no speed rating indicated, the tire has an “S” rating and there will be a “-” or an “x” after the width. See the chart below for the most common speed rating letter designations.

Letter | Speed Rating |

S | 112 mph (180 kph) |

H | 131 mph (210 kph) |

V | 149 mph (240 kph) |

Z | over 149 mph (240 kph) |

The letter “R” immediately after the speed rating indicates that the tire has a “radial” construction. If there is no letter “R” the tire has a bias ply construction. Never use bias ply tires on a motorcycle designed for radials or vice versa, and never mix bias ply and radial tires on the same motorcycle.

The number after the speed rating (or the “-” or “x”) indicates the tire diameter in inches. This number will almost always be a whole number, the exceptions being some GP road race motorcycle that use a 16.5 inch diameter rim.

An example of an American tire size would be MT90 V 18. The first letter “M” simply indicates that it is a “motorcycle” tire, while the second letter indicates its nominal width. See the chart below for the corresponding English and metric sizes.

American | English | metric |

MH | 2.50 or 2.75 | 80 |

MJ | 2.75 or 3.00 | 90 |

MM | 3.25 or 3.50 | 100 |

MN | 3.75 or 4.00 | 110 |

MP | 4.00 or 4.25 | 110 |

MR | 4.25, 4.50 or 4.75 | 120 |

MT | 5.00 or 5.50 | 130 |

MU | 5.50 or 6.00 | 140 |

MV | 6.00 or 6.25 | 150 |

The number after the letters is the aspect ratio, which is the height of the tire from the bead to the outside circumference divided by the width and represented as a percentage. In this example, the tire height is 90% of the tire width. The lower the percentage, the lower the profile of the tire.

The letter immediately after the aspect ratio indicates the speed rating of the tire. The speed rating is based upon testing the tire on a drum to determine the maximum safe sustained speed capabilities of the tire. If there is no speed rating indicated, the tire has an “S” rating and there will be a “-” or an “x” after the width. See the chart below for the most common speed rating letter designations.

Letter | Speed Rating |

S | 112 mph (180 kph) |

H | 131 mph (210 kph) |

V | 149 mph (240 kph) |

Z | over 149 mph (240 kph) |

The number after the speed rating (or the “-” or “x”) indicates the tire diameter in inches.

CLICK HERE TO PRINT.

Copyright © 2014 Common Service Manual. All rights reserved.