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How to Determine Tire Load Ratings

July 2007, Work Truck - Feature

by Mike Mavrigian

Paying attention to a replacement tire’s load rating is critical. The tire must be able to safely support a given amount of vehicle weight. If the tire’s load rating is insufficient, the tire may become overheated and can self-destruct.

For example, if a passenger car performance tire is selected to replace an original equipment light truck tire on an SUV, the new tire must meet or exceed the requirement for the specific vehicle weight.

In order to roughly determine the load capacity for each individual tire, take the vehicle’s gross weight and divide by four. If the vehicle gross weight is 4,500 lbs., each tire should be able to safely support at least 1,125 lbs.

However, the gross vehicle weight does not take additional load, such as the weight of the driver, into account. So you should never select a tire that only meets this minimum weight capability.

Always select a tire that offers a greater, or “reserve,” load capacity, which will help the vehicle handle and respond to higher-stress emergency situations when loaded.

The tire’s load rating, or “max load,” indicates the individual tire’s safe maximum load-carrying capacity when inflated to its recommended pressure. Never exceed a tire’s maximum load rating (the limit that is molded into the tire sidewall) or the maximum vehicle load limit shown on the vehicle tire placard, whichever is less. The tire is designed and constructed to handle a specific maximum load, and overloading will result in a buildup of excessive heat in the tire, which could lead to tire failure.

The load index number, which appears on the tire sidewall, is an assigned number that corresponds to the tire’s load-carrying capacity. Alphanumeric tires will display an alpha code that indicates maximum load. The letter can range from “A” to “N” (the higher the letter, the greater the load-carrying capacity at a given inflation pressure).

The max load and maximum inflation numbers found on the tire sidewall indicate the maximum load that can safely be carried and the maximum allowable tire pressure. The construction of the tire (belts, bead, carcass, liner) dictates the tire’s ability to withstand pressure. The stronger the reinforcements, the greater pressure the tire can hold.

Most alphanumeric tires feature a load range of B, which indicates that they are restricted to the load that can be carried at a maximum inflation pressure of 32 psi.

C, D, or E tires are capable of greater loads. Most load range C, D, and E tires are intended for light-truck applications.

The load-carrying capacity of Pmetric tires is rated as either Standard or Extra Load. Standard Load tires are limited by the load that can be supported with a maximum inflation pressure of 35 psi. Extra Load-rated tires are limited to the load that can be carried at a maximum inflation pressure of 41 psi. Generally, a Standard Load tire will not feature a special designation mark, while Extra Load tires will feature an “Extra Load” marking.

Extra Load tires will be branded as “Extra Load” and may be identified by an “XL” (for example: LT245/ 75R15 XL).

It’s important to note that a Standard Load tire (with a normal inflation pressure recommendation of 35 psi) may be marked with a maximum inflation pressure of 44 psi. This does not indicate an increase of the tire’s load carrying capacity, but indicates the tire’s ability to handle higher inflation pressure in order to accommodate special performance requirements.

Typically, the load indices of passenger car tires and light trucks range from 70 to 110. A speed-rated tire’s sidewall markings will indicate size, followed by the load rating index and the speed rating.

Comments

  1. 1. letters [ April 17, 2012 @ 12:23AM ]

    i would like to know that if a truck is fitted with a1200x20 tire, can it carry the same load as the one fitted with a1400x20 having the same sze of the loading buck.

  2. 2. Chris Miller [ April 26, 2013 @ 08:54AM ]

    I bought at Yokohama with Load rating of C1, how much weight do each of these tires old, they only told me the SI is 35 for each tire and they are 6 ply?

  3. 3. robert [ September 13, 2013 @ 03:05AM ]

    I need a taller tire not to wide load rate 4500lbs or higher load rate tire size 40x13.50 r24 for ftont if can use 40x15.50 for rear tire load canbe higest to use the same rim trailer being towed can carry 1700lbs but new rear tires makes nnough load and hight enough tire between rim and ground ok r24 n0w with was 40x15.50 high tire load rate in rear if able ford 8x170 load 7000lbs truck has 10 inch lift kit motor 6.0l worked out to close to 879 hp with trans and rears changed to heavyer rears all top of fabtec lift kit system parts price over 22,000 in10 in lift kit 250,000.00 dollars extra invested in lift kit done by a basket ball player Denver nugets CHRIS ANDERSON PLEASE FIND TOP OF LINE HEAVY LOAD RATING TIRES PRICE NO PROBLEM IF HAVE TO CHANGE RIMS OR TIRES PLEASE ADVISE TO BEST THANKS BOBBY FDNY

  4. 4. larry armstrong [ January 11, 2014 @ 10:55AM ]

    Here is something I haven't seen addressed in anything I've read. Say a tire says it will carry 1800 lbs at 44psi. If the vehicle weighs 4000lbs, should a person who may have say 700 additional lbs of weight besides himself be inflating those tires to 44psi or should the psi in the tires be calculated for the weight which is actually being carried on those tires? What I'm saying is if the total capacity of the four tires is 7200lbs (1800 times four) what pressure should the tires have in them for a gross vehicle load of around 4900lbs? Should a person calculate this out?

  5. 5. Biggy [ March 22, 2014 @ 01:42PM ]

    Why do they keep changing tire numbers and codes? It used to be easy. I ran 10 ply ties on my truck. Then they changed it up and the rating was for "E" rated tires. Now they changed it again to a number. 10 Ply was changed to equal a Load Range "E", but "E" now equals about a 120 rating?? Is there a chart somewhere?

 

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