Tire Tips 101: Load Range vs weight rating and more (LOAD)Posted in How To: Wheels Tires on November 11, 2016
If you are like us, the first thing you might do with your new rig is add a leveling kit or suspension lift and larger tires. But when you do this, are you actually decreasing the towing capacity of your truck? If you don’t pay close attention to what you are purchasing, that is certainly a possibility.
Some trucks, like the current Toyota Tacoma and Chevrolet Silverado 1500, come with P-metric tires instead of LT (light truck) tires. In this situation there is nowhere to go but up. The P-metric tires have lower load ratings than LT tires, and the sidewalls are not nearly as tough. So why do manufacturers use them? For starters, they cost less, but they also generally weigh less. For manufacturers trying to meet strict fuel economy requirements a lighter tire can help them reach their targets.
A tire's load rating is the maximum weight the tire is designed to carry at a given pressure. The maximum load range (rather than rating) of an LT tire is designated by a letter that corresponds to the maximum pressure the tire is designed to hold. In contrast, P-metric sizes aren’t load-rated.
Common Light Truck (LT) Load Ranges
|Load Range||Max Load Pressure (psi)|
Note that if a Load Range E tire is only inflated to 50 psi, it will likely be able to safely carry the same load as a Load Range C tire at the same pressure. Less pressure will decrease the amount of weight the tire can safely carry and generate more heat going down the road. Heat is the true killer of tires, which is why you always want to reinflate your tires to the proper pressure when you get to the end of the trail. Less air pressure is a conscious decision that off-roaders make to allow the tire carcass to conform to the terrain, but this should only be done at crawling speeds.
We can compare four different 265/70R17 tires to illustrate our point. One is a P-metric Michelin LTX A/T 2, one is an LT Michelin LTX A/T 2, one is a Load Range C BFGoodrich All-Terrain KO2, and the last is a Load Range E BFGoodrich All-Terrain KO2. The P-metric Michelin is rated at 2,535 pounds at 44 psi and weighs 43 pounds. The LT Michelin is Load Range E, rated at 3,195 pounds at 80 psi and weighs 49 pounds, despite having less tread depth than the P-metric tire (12/32 inch versus 14/32). The Load Range C BFGoodrich tire (manufactured by Michelin) is rated at 2,470 at 50 psi and weighs 44 pounds, while the same tire in Load Range E is rated at 3,195 pounds at 80 psi and weighs 52 pounds.
In the road racing world, a heavier tire is universally considered as a bad thing. More rotating mass means poorer acceleration and braking, and is harder on parts. These are true in the off-road world, but can you have such a thing as too light of a tire? A heavier tire means that there is more rubber, which translates into deeper lugs that provide better traction and thicker, stronger sidewalls. Keep weight in mind as a factor when you look for your next set of tires.
There is no need to run down the road with your tires at the maximum inflation pressure unless you have the payload to require it. The Nitto Exo Grapplers on this Duramax are rated at 3,195 pounds each at 65 psi for a total of 12,780 pounds, but the truck only weighs 6,500 pounds unloaded.
Over-the-road truck 19.5-inch and 22.5-inch wheels have become popular conversions on 1-ton trucks that do a lot of towing. These tires are available in Load Range G and wear like iron. The tradeoff is that the ride quality suffers since the tires are so stiff, and they do not conform at all to terrain, making them a poor choice off-road.
Light Truck (LT) tires will be marked with the load range, along with the load rating and the maximum pressure. The load rating is always at the maximum pressure for a tire; lowering the pressure lowers the amount of weight the tire can support.
If you air your tires down off-road (and you should), remember to air them back up when you get to the pavement. Heat is the biggest killer of tires. That heat can come from low air pressure, excessive weight, or high speeds. All of these factors result in friction that is converted to heat.
Dual rear tires are common on trucks dedicated to towing. The extra set of tires not only increases stability but also spreads the load across an extra set of tires in the rear, to share the workload.
The ply rating is just that, a rating. It does not imply that the sidewall actually has eight plies (in this case). Ply rating comes from older bias-ply tires that actually did use these many plies. Modern radials typically have sidewalls with two or three plies.
On a fullsize truck used for backcountry travel, load rating can be critical: Particularly if the truck is loaded heavy, like this Super Duty. A Load Range E tire is recommended, and we would be very careful about airing down too much if traveling at more than crawling speeds.
There is still value to running a Load Range E tire on a lightweight off-road vehicle. While the carcass will not be as flexible as an equivalent tire in a lower load range, the air pressure can be lowered to account for this. The reason the carcass is less flexible is because of heavier construction that fends off punctures off-road.