Tire Ratings: Speed Rating and Load Index

All tires have tiny alpha-numeric characters engraved on its inner side. These engravings are specific codes that provide the user with the dimensions of the tire and its key limitations, such as load-bearing ability, maximum speed it can achieve, temperature and traction.

Tire Ratings: Speed Rating and Load Index
Since 1991, all service descriptions have to be marked on the tires manufactured. Following are the tables for speed rating and load index:

Load Index
The load index is the tire size's assigned numerical value, that identifies the tires ability to carry load. The higher the tire's load index, the greater will be its capacity to carry load. Most load indexes of the tires used on passenger cars and light trucks range from 70 to 110. Following is the table for Load Index, with its specified number and corresponding load bearing capacity:

Load Index	Pounds	Load Index	Pounds
71	761	91	1356
72	783	92	1389
73	805	93	1433
74	827	94	1477
75	853	95	1521
76	882	96	1565
77	908	97	1609
78	937	98	1653
79	963	99	1079
80	992	100	1764
81	1019	101	1819
82	1047	102	1874
83	1074	103	1929
84	1102	104	1984
85	1135	105	2039
86	1168	106	2094
87	1201	107	2149
88	1235	108	2205
89	1279	109	2271
90	1323	110	2337

Speed Rating
Speed ratings are the tire's capacity to move at high speed. Most of the ratings are based on laboratory tests, where the tire is pressed against a large diameter metal drum to reflect its appropriate load and determine its speed. However, no matter how high the speed rating of a tire, manufacturers do not recommend the use speeds that exceed the legal speed limits. The code is made up of one or two letters, or one letter and one number, and indicates the maximum permitted speed that the tire can sustain, without being damaged. Following is the table for Speed Rating with its specified code and corresponding speed limit.

Code	mph	km/h	Code	mph	km/h
A1	3	5	L	75	120
A2	6	10	M	81	130
A3	9	15	N	87	140
A4	12	20	P	94	150
A5	16	25	Q	100	160
6	19	30	R	106	170
A7	22	35	S	112	180
A8	25	40	T	118	190
B	31	50	U	124	200
C	37	60	H	130	219
D	40	65	V	149	240
E	43	70	Z	over 149	over 240
F	50	80	W	168	270
G	56	90	(W)	over 168	over 270
J	62	100	Y	186	300
K	68	110	(Y)	over 186	over 300

Most tires use the ISO Metric sizing system for their specifications. The European Tyre and Rim Technical Organization (ETRTO) and the U.S. Tire and Rim Association (T&RA), are the two major standardizing organizations for rating speed and load index of the tires.