A load index is an assigned numerical value that signifies a tire's maximum load carrying capacity. They're useful to help compare load carrying capacity of different-sized tires, and as you might expect, the higher the tire's load index number, the greater its load carrying capacity. Using the image below of a P195/60R15 87S tire, the load index is the 87 near the end. The 87 identifies the tire's ability to carry approximately 1,201 pounds.
Typically, the load indexes of the tires used on passenger cars and light trucks range from 70 to 126.
Load Index
Pounds
Kilograms
Load Index
Pounds
Kilograms
Load Index
Pounds
Kilograms
70
739
335
89
1,279
580
108
2,205
1,000
71
761
345
90
1,323
600
109
2,271
1,030
72
783
355
91
1,356
615
110
2,337
1,060
73
805
365
92
1,389
630
111
2,403
1,090
74
827
375
93
1,433
650
112
2,469
1,120
75
853
387
94
1,477
670
113
2,535
1,150
76
882
400
95
1,521
690
114
2,601
1,180
77
908
412
96
1,565
710
115
2,679
1,215
78
937
425
97
1,609
730
116
2,756
1,250
79
963
437
98
1,653
750
117
2,833
1,285
80
992
450
99
1,709
775
118
2,910
1,320
81
1,019
462
100
1,764
800
119
2,998
1,360
82
1,047
475
101
1,819
825
120
3,086
1,400
83
1,074
487
102
1,874
850
121
3,197
1,450
84
1,102
500
103
1,929
875
122
3,307
1,500
85
1,135
515
104
1,984
900
123
3,417
1,550
86
1,168
530
105
2,039
925
124
3,527
1,600
87
1,201
545
106
2,094
950
125
3,638
1,650
88
1,235
560
107
2,149
975
126
3,748
1,700
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When looking at Light truck tires (LT) or newer Special Trailer Service (ST) tires, there are two load indexes branded on the sidewall, separated by a forward slash. Using an LT235/75R15 104/101S Load Range C tire as an example, the load index is 104/101. 104 corresponds to 1,984 pounds, and 101 corresponds to 1,819 pounds. So what is the true load carrying capacity of the tire? The answer changes depending on the situation in which the tire is being used.
Since LT tires are commonly used on trucks with dual rear wheels, they are branded with two load indexes. The first number indicates the load carrying capacity if the tire is installed on a truck with a single-wheel rear axle, and the second number applies when the tire is used in a dual rear application.
Though it may seem counterintuitive that a tire is rated to carry less weight when working in tandem with another tire in the dual pair, the purpose is to build in additional reserve capacity should one of the two tires fail, leaving the sole remaining tire to carry the load normally handled by two tires.
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