Tire Specifications
By Jason Van Wyhe
Tires, tires, tires  every bike needs them, yet many bikers don't know the first thing about them. Here is what all those letters and numbers on the sides of your tires mean:
Tire Size
Your tire size will be formatted in one of three ways:
140/90 HB16
MU85 HB16
5.50 HB16
All three essentially say the same thing, but use a different numbering system. The first uses the Metric system, the second is the Alpha system, and the third is Inches.
Metric Tires
This is the most common system, and breaks down as follows:
(Tire Width) / (Profile Height) (Speed Rating and Tire Style)  (Rim Size)
The width is measured in millimeters, so a 140 tire is 140 mm wide (also known as the nominal section width).
Although we list it as profile height, the second number is technically the ratio between tire height and nominal width. The wider the tire, the lower this number tends to be. For example, on a 200 series rear tire, this ratio will be 50 or 60, while on a 90 series front tire it is 90, even though the profiles may be roughly the same height.
The letters refer to the speed rating of the tire, and the type of tire it is. If the tire is listed as HB, that means it is speed rated H (up to 130 mph), and is a belted biasply tire. Sometimes one or more letters are missing. If there is no letter for the speed rating, it is an H rated tire. If there is no letter for the tire type, it is a regular biased ply tire. The charts below detail the available styles and speed ratings.
The final number is the rim size, denoted in inches. The rim for the examples above is a 16" rim.
Alpha Tires
Alpha numbers mean:
(Width Letter Code) (Profile Height) (Speed Rating and Tire Style)  (Rim Size)
The Alpha system is identical to the metric system, except for the width. Rather than give the width in millimeters, a letter code is used. An MT tire is 130mm wide, an MU tire is 140mm, and so on. The size chart below details the various sizes available. This system is commonly used on OEM tires such as Dunlop 401's and 402's.
Inch Tires
Inches tires are a bit different in that they do not list profile height:
(Tire Size) (Speed Rating and Tire Style)  (Rim Size)
The tire size is denoted in inches, or sometimes a range will be given. The example given is a 5.50/6.00 inch tire, which is equivalent to a 140 or MU tire. The size chart below details the various sizes available. The speed rating/tire style and rim size are the same as with metric tires.
Load Rating/Exact Speed Index
The load rating of the tire will be a number code found along the side of the tires. This is a code for the amount of total weight this tire is rated for. A load index of 50 means the tire is rated for 419 pounds.
Sometimes there will also be a letter behind the load index. This is the speed index number. This is most commonly found on Z rated tires that end their speed rating at 149+. A W rated tire has an exact speed rating of 168.
More information on the load rating and speed rating can be found in the charts below.
Tube Designation
Along the side of the tire, it will state either "Tube" or "Tubeless". You must use a tube on a "Tube" tire, but you have the choice to either use a tube or run without on a tubeless.
Rotation Arrow
A directional arrow will be found on one or both sides of the tire. This arrow must point to the direction the tire rotates during normal operation.
Tire Charts
TIRE SPEED RATING 
SPEED SYMBOL 
MAXIMUM SPEED 
J 
62 MPH 
K 
68 MPH 
L 
75 MPH 
M 
81 MPH 
N 
87 MPH 
P 
93 MPH 
Q 
99 MPH 
R 
106 MPH 
S 
112 MPH 
T 
118 MPH 
U 
124 MPH 
H 
130 MPH 
V 
149 MPH 
Z 
149 MPH + 
W 
168 MPH 
Y 
186 MPH 

Construction Code 
LETTER 
TIRE TYPE 
No Letter 
Bias 
B 
Belted Bias 
R 
Radial 
Load Index (Select Sizes) 
LOAD INDEX # 
MAXIMUM WEIGHT (lbs.) 
35 
267 
40 
309 
45 
364 
50 
419 
55 
481 
60 
551 
65 
639 
70 
739 
75 
853 
80 
992 

Tire Size Conversion Chart 
FRONT TIRES 
REAR TIRES 
METRIC 
ALPHA 
INCHES 
METRIC 
ALPHA 
INCHES 
80/90 
MH 
2.50/2.75 
110/90 
MP85 
4.5/4.75 
90/90 
MJ90 
2.75/3.00 
120/90 
MR90 
4.50/4.75 
100/90 
MM90 
3.25/3.50 
130/80 
 
5.00/5.10 
110/90 
MN90 
3.75/4.00 
130/90 
MT90 
5.00/5.10 
120/80 
 
4.25/4.50 
140/80 
 
5.50/6.00 
120/90 
MR90 
4.25/4.50 
140/90 
MU90 
5.50/6.00 
130/90 
MT90 
5.00/5.10 
150/80 
MV85 
6.00/6.25 



150/90 
MV85 
6.00/6.25 

©2007 Chopper Surplus. This Article may not be reproduced without the express written consent of Chopper Surplus. It may not be reposted or redistributed on another web site, or any other form of media, or under a different author's name. Feel free to print copies for your personal use, however.
