What tire pressure to use.

[Tigerstripe40]

I run 35x12.50 MT/R's (old tread) a 30PSI on the street
10 PSI on the trail.

 

[cuencanolenny]

Years ago Armstrong tires published a PSI chart based on vehicle weight . Their Norseman tire ( now a Dick Cepek Fun Country ) in a 31" tire on an FJ40 was optimal at 27 PSI highway. Off road 12~18.
The lower tire pressures will promote tread separation so save the 12 PSI for when you really need it.
Nowadays the advertised pressures are generic and conservative in the manufacturers best interests

I found a link that discussed tire size, weight and inflated appropriately. Then Coen & Karin of Landcruising Adventure stopped by about a year or so ago and Coen looked at my rig and stated I was over inflated. That was at 28 lbs. In the last year that the rig has been on the road I have found that my Hankook M/T 235-75/R15 tires ride best at 25 front and 20 rear. When I have passengers in the rear I revise to 28F/25R. This seems to be stable and the handling okay. If I run them around 28 all around it is like a buckboard and very twitchy.

 

[tyama]

I do the chalk method and found out that my pig with the winch up front and a heavy duty bumper in the back needs 35 psi, but the 40 with no winch and a lighter bumper needs about 25 psi on the same BFG 33x10.50's.

Best, ty

 

[cuencanolenny]

Sounds like we are on the same page. It doesn't figure that a given psi, say 32, would apply to all vehicles. Different weight would be the primary factor. I know that Coen & Karin with their FJ45 loaded the way it is on tall skinny tires runs like 60 psi. I think my rig would touch ground about every twenty feet with that pressure.

 

[lcwizard]

there's a lot of factors including sidewall stiffness and profile, We ran 15 lbs regularly in a 38 x 14.5 -15 TSL Swamper on a softtop 40 on pavement. We could air down to 4 lbs on the trail without looking excessively low. With TSL's on a Samurai we drove 20 miles home on a flat. With virtually no pressure It had about the same profile as 18 lbs in a Goodyear MTR on a 60

 

[65swb45]

I had a run-in with Armstrong 30 years ago that apparently I have not shared online before.

I bought a set of 33x12.5s for my 76K5 at Price Club, the predecessor to Costco. Ran them at 32 cold, which was what the guys in my 4wd club were telling me was normal. After 12 months, all 4 tires had horrible scaling.

I drove to Price Club to ask them about it. The manager took one look at my lifted K5 and matter-of-factly pronounced I had alignment issues.

I was prepared for this.

I said "So let's suppose you're right about having an alignment issue. Let's also assume I'm a lazy MoFo and haven't bothered to rotate the tires for the year since I got them. That doesn't explain why the rear tires are as badly scaled as the front!"

He was not amused.

He called Armstrong, spoke to the factory rep for a couple of minutes, then said, loud enough for me to hear, "That's what I told him. You explain it to him." Then he put me on the phone with the rep.

The rep immediately asked me what the GVWR was for my truck. Since I knew this, I immediately replied "6200lbs." Startled, he said hang on a minute, then came back on the line and said "According to my spec book, that tire is not rated for a vehicle that weighs LESS than 7000 pounds."

I scanned my brain as fast as I could, and after about 5 seconds I said, "You know, I can't think of a 15" wheeled vehicle that weighs 7000lbs. So it sounds to me like you've designed a tire for which there is no correct application in order to avoid all warranty claims, and I wouldn't be surprised if this is the kind of thing that class action lawsuits are based on."

He said, "Let me speak to the store manager."

I handed the phone back to the manager, and watched as he slowly turned beet red. He hung up, turned to me and said "I am authorized to issue you a 100% non-prorated refund on the tires and let you keep them."

While it was comforting, it didn't 'solve' my problem. I went home and calculated the difference between the 7k reference and the ACTUAL weight of the truck as a percentage, then lowered the tire pressure from 32 cold by the same amount. Within 6 months, all the scaling was gone!

On all tires since then, I have used the contact-patch method.

 

[65swb45]

Aris @HKforte , time for a bump!