I've been reading a bunch of different articles and stuff. I understand how to use tables to calculate what my tire pressure should be for me truck based on the label on the truck and the LT truck tire size.

But for the life of me, I'm not understanding why the LT tires for the same size should be a higher pressure than p-metric tires (that came with the truck stock).

Can someone explain in simple English why this is? I would have thought that stiffer sidewalls meant less pressure needed. But seems like dramatically more is advised (ie - 33psi for stock, 43psi for LT in the same size).

Perhaps due to the weight they think you might be carrying with the LT tires? I have Load Range E LT tires on my K2500. I was carrying gravel for a retaining wall project I was doing. Routinely put 2,500+ lbs in the bed. I upped the tire pressure to 65 PSI. I also plow with the truck and I up the front tires to 65 PSI when I hang the plow on it.

Probably heat issue. The lower tire pressures cause the carcass to flex more generating more heat. More heat could cause the layers of the tire carcass to lose their bond.

I'm no truck expert, but I believe Truck tires are for trucks larger than regular 1/2 ton pickups. Like F250, Chevy 2500 and larger. P series passenger tires aren't strong enough for real truck work. If you're running a truck for commercial work and hauling stuff, you need a LT tire. That's my understanding. I inquired about putting LT tires on my F150, and was informed it would kill the nice ride. So I'm sticking with P tires, since I like the smooth ride and that's what my truck calls for. But if you have a F250 or larger, you can't use P tires, you have to use LT tires, as the P tires would be destroyed.

First, the air carries the load.
Second, the tire holds the air.

In a given size tire of the same type, lets say LT, the one rated for more pressure will have a higher load rating. It has more air in it at the higher pressure. With two LT tires rated for the same pressure, the larger one will have a higher load rating. Again, it has more air in it.

Now, same size tire and same pressure rating, but one is an ST tire and the other is an LT tire. They have the same amount of air, but the ST tire will have a higher load rating than the LT tire. Seems to go against what I said above, right? The testing for LT tires is much more stringent than the testing for ST tires. Also, LT tires generally have a higher speed rating than ST tires.

I don't know why a p-metric tire of the same size as an LT tire will have a higher load rating at a given pressure. I suspect the testing is different.

LT tires have more plys 6, 8, or 10 for example. The more plys the more air pressure a tire can take with a load over P tires. Air pressure is necessary and a huge factor for upping the load rating.

quote:

Originally posted by trapper189:
First, the air carries the load.
Second, the tire holds the air.

Trapper’s pithy response answers your question.

quote:

Originally posted by sigcrazy7:

quote:

Originally posted by trapper189:
First, the air carries the load.
Second, the tire holds the air.

Trapper’s pithy response answers your question.

Also to some degree, the additional rubber (plys) takes more air to properly shape.

Running LT tires under inflated will shorten tire life. Those that complain of a stiffer ride are simply princesses who would feel a pea. Is it stiffer, sure a bit, but most make it out to be bone jarringly stiffer and that just ain't so.

So, the curiosity continues - maybe only tire manufacturers understand why LT tires need higher pressure than the same size p-metric tires for a given load capacity. They just can't explain it well.

Another thing to keep in mind is what wheel they go on. Wheels suited for P-Metric may not be OK for LT's at a higher pressure.

My Rubicon is on D rated LT's, I run 33 psi, rides fine.

Here is an explanation:

http://www.tirereview.com/tire...s-and-load-capacity/

Thanks, that helped. Although I still have questions of interest:

1) LT requires higher pressure because of p-metric de-rating AND LT inherently requires more pressure? Or only because of de-rating?

2) If also because LT inherently requires more pressure (and this is the original question), why does it require more (ignore the de-rating for p-metric)?

Not critical as I know what to buy and what pressure to use. Just curious on the why.

Let's talk hammer (air pressure) and nails (tires).

Drive in a small nail (pmetric) using the hammer then drive in a very large nail (LT) with the same hammer. Which one took more hammering (air)?


Similar basic concept. There is more rubber to move/shape in a LT tire (higher air pressure).

LT tires are able to take a higher pressure and load. However, they require a higher pressure to run the same load. So (just examples) if a P rated tire could carry a max load of 2800lbs at 50psi a LT tire could also easily carry 2800 lbs (not at max) but it would require a higher pressure to do so, say 65lbs.
But that would not be the max load for the LT, the LT could carry say 3250lbs max load but only up at its 80PSI max range which the p rated tire could never be inflated to.