HOW TO DETERMINE TIRE LOAD CAPACITY

The amount of air a tire is capable of holding determines the amount of weight the tire can carry. Therefore to achieve a higher tire load capacity, a tire must hold more air. In addition, the tire must be strong enough for it to hold more air volume and pressure.

Consulting the original equipment tires and manufacturers’ suggestion for tire load ratings will ensure the correct tire load capacity.

Tires continue to improve, especially with the use of steel ply materials and radial construction. This makes the Ply Rating Number less effective in determining a tire’s load carrying capacity. Load Index, on the sidewall of a tire, is a newer guide that more accurately provides the tire’s load carrying capacity.

Tire LOAD INDEX is a number that corresponds to the maximum weight a tire can support with proper inflation. The higher the tire’s load index number, the greater it’s load carrying capacity. So, choosing a tire with a lower load index than the original equipment specifications means that the tire will NOT carry the load capacity of the original.

In this example 94 is the load range. Referencing the Load Range Chart below, the 94 equates to a load carrying capacity of 1,477 lbs.

Light truck tires have two load indexes on the sidewall of the tire, unlike passenger tires, which onlyhave one. This is because you may find light truck tires on vehicles with dual rear wheels.

In this example, the light truck tire has a load index of 117/112. Using the Load Range Chart, the 117/112 load index equates a load capacity for a single tire of 2,833 pounds and a load capacity of 2,469 pounds for two tires.

The reason the capacity for two tires is lower than a single tire is to make sure that the vehicle can continue to carry the load should one tire fail.

Most passenger car tire load indexes range from 75 to 100, but some are higher. The chart shows how load indexes translate to weight.

1 102 31 240 61 567 91 1356 121 3197
2 105 32 247 62 584 92 1389 122 3307
3 107 33 254 63 600 93 1433 123 3417
4 110 34 260 64 617 94 1477 124 3527
5 114 35 267 65 639 95 1521 125 3638
6 117 36 276 66 639 96 1565 125 3748
7 120 37 282 67 677 97 1609 127 3858
8 123 38 291 68 694 98 1653 128 3968
9 128 39 300 69 716 99 1709 129 4079
10 132 40 309 70 739 100 1764 130 4189
11 136 41 320 71 761 101 1819 131 4289
12 139 42 331 72 783 102 1874 132 4409
13 143 43 342 73 805 103 1929 133 4541
14 148 44 353 74 827 104 1984 134 4674
15 152 45 364 75 852 105 2039 135 4806
16 157 46 375 76 882 106 2094 136 4938
17 161 47 386 77 908 107 2149 137 5071
18 165 48 397 78 937 108 2205 138 5203
19 171 49 408 79 963 109 2271 139 5357
20 176 50 419 80 992 110 2337 140 5512
21 182 51 430 81 1019 111 2403 141 5677
22 187 52 441 82 1047 112 2469 142 5842
23 193 53 454 83 1074 113 2535 143 6008
24 198 54 467 84 1102 114 2601 144 6173
25 204 55 481 85 1135 115 2679 145 6393
26 209 56 494 86 1168 116 2756 146 6614
27 215 57 507 87 1201 117 2833 147 6779
28 220 58 520 88 1235 118 2910 148 6844
29 227 59 536 89 1279 119 2998 149 7165
30 234 60 551 90 1323 120 3086 150 7385

As highlighted in the image above, standard tires will indicate the standard tire size. The tire size markings on the sidewall are as follows:

Overall Diameter Height in Inches - 35” in this example

Section Width in Inches - 12.5” or 1250 in this example

Rim Diameter in Inches - 17” in this example

A letter on the sidewall of a tire represents the load range. This letter provides a comparative value of a tire’s strength, helps gauge how much air a tire can hold and the weight carrying capacity. The higher the Load Range, the more weight carrying capacity of the tire.

Load range comes from an older measurement known as ply ratings. Tires are made up of rubber and cord layers also known as plies. Historically, more plies gave a tire a larger load carrying capacity, so manufacturers would count the tire’s plies and use this number to denote carrying capacity.

However, today’s tire construction uses fewer, stronger plies. Therefore, Load Range basically defines the tire’s toughness and maximum allowable air pressure and not the specific information about its composition. For example, a C Load Range specifies that a tire is equivalent to a 6-ply construction tire. This tire is not actually built of 6 plies, but rather one or two plies of equivalent strength.

Check the tire sidewall to find the letter that indicates the Load Range. Passenger tires do not have markings because they have a standard 4-ply rating. However, you may find Standard Load (SL) or Extra Load (XL or Reinforced). Both these types have a 4-ply rating, but the Extra Load can support additional load at up to 42 PSI, vs. the Standard Load’s 36 PSI.

Ply Rating is on a tire to provide the load carrying capacity at specific tire pressures. Ply Ratings are alphabetic ranging form for A – N with the absence of I and K to prevent confusing with the numeral 1 and a Kilogram (Kilo) respectively.

Refer to charts below for Load Range and Ply Ratings comparison.

A 2
B
(SL, XL)
4
C 6
D 8
E 10
F 12
G 14
H 16
J 18
L 20
M 22
N 24