Motor Cycle Tyre Codes

Load - Index: translator
Load Index	Weight kg
10	60
20	80
24	90
26	95
30	106
31	109
32	112
33	115
34	118
35	121
36	125
37	128
38	132
39	136
40	140
41	145
42	150
43	155
44	160
45	165
46	170
47	175
48	180
49	185
50	190
51	195
52	200
53	206
54	212
55	218
56	224
57	230
58	236
59	243
60	250
61	257
62	265
63	272
64	280
65	290
66	300
67	307
68	315
69	325
70	335
71	345
72	355
73	365
74	375
75	387
76	400
77	412
78	425
79	437
80	450
81	462
82	475
83	487
84	500
85	515
86	530
87	545
88	560
89	580
90	600
91	615
92	630
93	650
94	670
95	690

Motor Cycle tyres come in one of two coded descriptions
1) Imperial eg 3.00 S 18 4PR
2) Metric eg 110/80 17 54H

What does it all mean? Well use the following example and the following letter key.

Imperial

Metric

3.00 S 18 4PR 110 /80 17 54 H

A
D E
G

B
C E F D

A) tyre size in inches. I think this is the tyre width in inches...
B) tyre width in mm.
C) Tyre aspect ratio in percentage. 100% would have the tyre height the same as the width, 50% would have the tyre height half that of the width.
D) Speed rating (a letter code - see table below, left).
E) tyre diameter in inches, or more correctly tyre bead diameter.
F) Tyre Load Index (a number code -see table to the right).
G) the side wall ply rating (more plys the higher the load that could be carried).

Speed Letter Code - Translator
Code Letter	Speed km/H
B	50
J	100
K	110
L	120
M	130
N	140
P	150
Q	160
R	170
S	180
T	190
U	200
H	210
V	240
Z	over 240

Radials - on metric codes (just to confuse us) they sometimes put an R around abouts the Speed rating.

D.O.T. Number
The tire may contain a D.O.T. number. The last three digits show the year and week that the tire was manufactured. e.g., a tire stamped 324 means the tire was made in the 32nd week of 1994. Hopefully, it will not be too difficult to tell the difference in a tire made in 1984 from one made in 1994. Tires suffer from sunlight, ozone, and aging deterioration. You should choose the newer tire when the opportunity exists.

The ISO have several relevant standsards, 4249 and 5751.
They also have some on stablility with side and centre stands... and other things to do specifically with motorcycles.

Some people say that a tyre with a lower speed rating gets more mileage...
This is said to be due to the lower speed rated tyre having a deeper tread, the very high-speed tyres have to have a shallow tread or they heat up too much. Others say the high-speed tyres have a harder compound so last longer. Good luck with your choice.

A date of manufacture code may exit on your tyre. It is a 3-digit code, first two numbers indicate week of the year 1-52, last number indicates singles digit of year, i.e., 8 could be 1988 or 1998.

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back to my home page & start again Dated 6 November 2000