Tire Size Conversion Chart

Motorcycle Tire Size Conversion Chart

Street Tire Sizes - Front
Alphabetical Metric Std Inch
MH90 80/90 2.50/2.75
MJ90 90/90 2.75/3.00
MM90 100/90 3.25/3.50
MN90 110/90 3.75/4.00
MR90 120/90 4.25/4.50
MT90 130/90 5.00/5.10

Street Tire Sizes - Rear
Alphabetical Metric Std Inch
MN90 110/90 3.75/4.25
MP85 120/80 4.50/4.75
MP85 120/90 4.50/4.75
MT90 130/90 5.00/5.10
MU90 140/90 5.50/6.00
MV85 150/80 6.00/6.25
MV85 150/90 6.00/6.25


What do these terms alphabetical, metric and std inch mean? They are explained in a section below. The sizes in the above chart do not go as large as modern sizes (180/55 or 240/40) because new bikes are not made to use the Inch Format.

The above tire size conversion chart does not mean that these tires are universally interchangeable. They are to give you a point of reference when upgrading your older tires.  Consult your motorcycle's manual or manufacturer's customer service department for correct replacements for original equipment tires.

Critical clearances, motorcycle compatibility and stability, load-bearing capacity, speed rating, radial vs. non-radial, pattern and tread compound requirements, inflation recommendations, and front-to-rear tire matching will all vary with tire selection.

Wrong selection can result in tire failure, loss of control with serious injury or death.  You can also contact the manufacturer of the tires you want to put on your bike.  They have reps dedicated to this stuff.



Deciphering a Tire Size

Motorcycle and dirt bike tire sizes can be expressed in 3 basic formats: Alphabetical, Metric and Inch. Each format tells you the tire and rim size.

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Alphabetical Size Format


The alphabetical size format is mostly used on older bikes. Some current touring bikes still use the alpha size system.  Most tire manufacturers use the metric tire size designations now. The size we will use in our example is MU90-16 B.

M U 90 - 16 B
Motorcycle Code Tire Width Code Aspect Ratio (%) Rim Size or Diameter Load Range
 
The Motorcycle Code means exactly what it says.  Tires made specifically for motorcycles are coded with an M.  

The tire Width Code is just a letter to substitute for the width of the rim. The width codes below are for motorcycle tires with an aspect ratio of 80 or greater. A code of U means this tire will fit on a rim that is between 2.75 and 3.50 inches wide.   Please note that the values in this chart are the RIM width not the Tire width.

Width Code Rim Size Range
in inches
G 1.60 - 1.85
H 1.60 - 1.85
J 1.85 - 2.15
L 1.85 - 2.15
M 2.15 - 2.50
N 2.15 - 2.75
P 2.15 - 2.75
R 2.15 - 2.75
S 2.15 - 2.75
T 2.50 - 3.00
U 2.75 - 3.50
V 3.50 - 4.00

The Aspect Ratio is the tire section height divided by the section width (not tread width), multiplied by 100.  The section height is  measured at the center of the tire crown.  The tread width is usuallygreater than the section width.  The section width is measured from the middle side walls (above the bead, below the tread).  It is multiplied by 100 to give you a whole number for the tire.  So instead of .9 the tire is stamped 90.

Rim Size or Diameter is the outside diameter of the rim, also called the wheel size.

I have so far been unable to find a complete description and value set to explain the Load Range. When I find an adequate explanation, I will put it here.


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Metric Size Format


The vast majority of tires manufactured and sold today come with metric sizing.  The tire size we will use for our example isa 120/70ZR-17TL.  It can also be written as 120/70Zx17TL or 120/70ZR17TL.  

Some manufacturers put the speed rating at the end of the size and do not indicate if the tire is tubeless or not.  In that case the size would look like this 120/70-17Z.

120 / 70 Z R - 17 TL
Section Width (mm) Aspect Ratio (%) Speed
Rating
Tire Type Rim Size or
Diameter
Tubeless

The Section Width is the width of the tire measured from the middle of the side walls (above the bead, below the tread).  

The aspect ratio is the same as for alphabetical sizes and is defined above.

The Speed Rating is explained in detail here.  For our example a speed rating of Z means this tire is rated for speeds exceeding 149mph.

The Tire Type can be either B for bias or R for radial.  Most newer bikes use radial tires. Bias are still available for older bikes if you are going for authenticity.

Rim Size or Diameter is the outside diameter of the rim.

TL is a descriptive abbreviation.  {See the sections below for more info.} It indicates that the tire is meant for a tubeless application.  The majority of modern motorcycles use tubeless tires.  If your bike has wire spoke wheels you need to use a tire designed for use with a tube inside.  All those spokes and nipples are not air tight. Not all manufacturers will add the TL to indicate that it is tubeless. It was used more when they were not as common as today.



Inch Size Format


The majority of modern motorcycles and dirt bikes do not use these tires. These were standard equipment on older machines. The Inch or Standard Inch Size Format does not include an aspect ratio.  The aspect ratio on these tires is 100. Meaning the section width and section height are equal. 

Also, inch size format tires are all bias type.  They do not come in radial. The size will will use for this example is 4.60x17H 4PR.  You may also see this written as 4.60H-17 4PR.

4.60 x 17 H 4PR
Section Width
(inches)
Rim Size
or
Diameter
Speed
Rating
Ply Rating or
Bias Casing Strength

The section width and rim size are defined in the same manner as described for the Alpha and Metric size formats.

The speed rating is explained in detail below, but in our example, a speed rating of H means this tire is rated for speeds not to exceed 130mph or 210kph.

The Ply Rating is a descriptive abbreviation.  It refers to the number of plys (layers) that make up the tire.  For more on descriptive abbreviations, see sections below.  For specific strength of the different ply tires, refer the tire manufacturers literature.


Dirt Bike Tires

Dirt bike tires are sold in both metric and inch sizing format but do not always have a speed rating. More often they are rated by terrain.


Descriptive Abbreviations

Sometimes a catalog will list a tire as TL, BL or RWL.  These have nothing to do with the size or handling.  They are strictly descriptive.  They describe the look or another feature of the tire.  

Abbreviation Meaning
B Belted
Blk Black
BW Black Wall
NWW Narrow White Wall
OWL Outlined White Letters
PR or Pr Ply Rating
RBL Raised Black Letters
RWL Raised White Letters
SW Slim Whitewall
TL Tubeless
TT Tube-type Tire
WW White Wall
WWW Wide White Wall

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Tire Load Index Ratings

In addition to the information listed above, tires can contain Load Index or Rating info on the sidewall.  This refers to how much weight a tire can safely transport.  It includes the weight of the bike and rider(s). Not all tire manufacturers make tires in all load indices. Dunlop, for example, starts at 33.

Load Index Rating = Carrying Capacity in Pounds
LI lb LI lb LI lb
20 176 42 331 64 617
21 182 43 342 65 639
22 187 44 352 66 661
23 193 45 364 67 677
24 198 46 375 68 694
25 204 47 386 69 716
26 209 48 397 70 736
27 215 49 408 71 761
28 220 50 419 72 783
29 227 51 430 73 805
30 234 52 441 74 827
31 240 53 454 75 853
32 247 54 467 76 882
33 254 55 481 77 908
34 260 56 494 78 937
35 267 57 507 79 963
36 276 58 520 80 992
37 282 59 536 81 1019
38 291 60 551 82 1047
39 300 61 567 83 1074
40 309 62 584 84 1102
41 320 63 600 86 1168


New Tire Break-in Period

All manufacturers warn that during the first 60 to 100 miles after new tire installation, the bike should be ridden cautiously with no sudden acceleration, hard braking or cornering.  The tires need time to wear-in (get scuffed and tacky).  Until the wearing in processes in over they will not grip as well as they should and not perform at their optimum level.

A rider also needs to get used to the new tire's ride and "feel." All tires will be slightly different, even from the same manufacturer.  When your break-in period is over allow the tire to cool completely, for at least 3 hours, before checking and adjusting the inflation pressure to the recommended pressure.

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