I may be the only feller that doesn't know this stuff, but why is it so hard to find the normal unloaded tire pressure for LT tires?
I bought myself a set of Hercules Load Range E LT 275/70R18's and the MAX pressure is 80psi. Now, I'm not normally under a load, so I wanted to know what the optimal PSI is for running empty. My google-fu must have bee weak. I called Hercules home planet up on the phone and the guy said to add 15psi to what the factory non-Lt tire recommendation says. So, we settled on 50psi for unloaded Load Range E 10-ply casings.
Where have you folks been getting your tire pressures from on these matters?
Why don't somebody make this info easier to find?

I've always just used what is recommended on the door jamb sticker. 65 front and 80 rear for my F250. seems to work fine.

Because there are quite a few variables. The best way to know what tire pressure to run is to send your tire pressure manufacturer a picture of your door jamb sticker, what model tire, size, and what your intended purpose is.
They’ll send you the proper PSI with no guess work.

After some body repair, I no longer have the handy door jamb sticker, and I upgraded from a P-series to a larger LT-series tire. I'm not real keen on running 80psi and rattling my gizzard out at this point in life. Max PSI is recommended for full load, but pressuring down is recommended for every day unloaded use, but nobody seems to be eager to let a guy know how much to pressure down.

80psi unloaded is entirely not needed. There's only one variable: how much weight is on the rear tires?

What you are looking for is called a Load Inflation Chart or Table: https://www.google.com/search?...sclient=gws-wiz-serp

For your tire size:
35 PSI: 2,095 lbs
40 PSI: 2,270 lbs
45 PSI: 2,470 lbs
50 PSI: 2,680 lbs
55 PSI: 2,840 lbs
60 PSI: 3,020 lbs
65 PSI: 3,195 lbs
70 PSI: 3,330 lbs
75 PSI: 3,530 lbs
80 PSI: 3,640 lbs

That happens to be the same size I have on my F350. Unloaded, my F350 has only 3,300 pounds on the rear axle. According to the chart, 35psi will be enough to carry the load. I run 55psi as I didn't like the handling at 50psi.

Amazingly enough, the chart shows us the difference between an F250 and an F350 SRW; 15psi. The axle on the F250 is rated for 6,200 pounds, while the axle on the F350 SRW is rated for 7,200 pounds. The minimum pressure for this size tire that carry 6,200 pounds is 65psi while the minimum pressure for 7,200 pounds is 80psi. This why the door sticker on an F250 says 65psi while on the equivalent F350 it says 80psi. Used to be there was no actual differences in the axles themselves. I don't know about the post 2016 trucks.

This message has been edited. Last edited by: trapper189,

I’d still shoot them an email with year, make, model, and what tire size and rating came on the truck and tell them what you have switched to.

Browse this link and the inflation charts. It’s way more math than I enjoy but maybe you can figure it out.

https://www.toyotires.com/tire...and-inflation-tables

Page 27 from Black's link:



One variable, no math calculations needed; 35psi to 80psi in 5psi increments.

What year make model truck?

What I do is start at recommended psi and experiment. I like lower psi and set mine just above the tire pressure monitoring system triggers a dashboard alarm.

When I had a 3/4 ton truck I’d keep it near 40 psi front, 50 or so in the rear unless towing a heavier load. This is with 80 psi max, load range E tires.

I may go a little higher, but virtually never the full 80 psi.

quote:

P-series to a larger LT-series tire

P-series is Load Range B. That's quite a jump to Load Range E. No wonder it rides hard. I'd go down to the OEM recommended pressure, maybe 5 or 10 psi over that, but not more. It will still ride a lot firmer than the originals, but not bone-jarringly.

Don't forget about all of the flipped Ford Explorers caused by under inflated tires. Tires are created with heat.The sidewalls are the weakest link. Under inflation causes flex and heat in the sidewalks increasing the chances of failure.

Door stickers only matter when replacing like for like. When changing to different, then it's time to go with tire manufacturer's recommendations.

The trend to switch from Pmetric to LT was likely spawned by off-roaders looking for heavier duty tires to rock crawl etc.. There is also a chance it was spawned by sellers or buyers hearing "Light Truck" (what LT stands for) and miss purchasing/selling.

If all else fails, what does the sidewall say?

I have used this resource before when going up in load range. Pretty self explanatory to use.

Tire PSI Conversion Calculator

Assuming the empty truck probably has less weight on the rear tires than would ever be on the front tires when fully loaded, I use the recommended front PSI when empty. Easy to remember and less work when rotating. On my Chevy 2500HD I believe that is 55 PSI.

I settled in at 46 with a set of Wildpeaks E load range. This on an F-150 supercrew. Tire wear has been excellent, ride and handling is good and fuel economy is acceptable.

2022 Chevy 3500HD here. E-ply 275/70/18 here. 65psi up front and 80 in rear. We haul a Fifth wheel during the summer. I don't change the psi at all in the "off" season.

I’ve had good luck using the load range tables. In a pinch, you could always do the old chalk test, but some tires don’t sit flat so well.

Not to low, not to high.

quote:

Not to low, not to high.

Sourdough, By-Golly- that's the best darn answer I've had in 30 or 40 years!

Think I'll go with 50 and call it good.

with year make and model, and trim level, it can be figured out.

In related news, in Short Pump VA a local repair facility performed an alignment on a truck with LT tires. Prior to the repair, the owner dialed in his soft riding tire pressure. Without thinking, this nearly senior citizen rode two thousand miles after the repair cursing the ride quality. He found his old 100 psi gauge and thought “wonder what changed?” With some disgust he discovered the evil repair shop had set the pressure to 65 front 80 rear. He set pressures to 57 front 68 rear to return the ride quality. A federal class action lawsuit has been filed against all evil repair shops that change tire pressure without owner’s permission.