What pressures are you running? (1 Viewer)

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Oct 14, 2020
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I have AMP M/T LT285/65R18 tires on my rig. Criticize if you want, but that is what is on it (bought it that way recently).

Before I owned it, it sat for a while so it has some flat spots. And no weights. At 30MPH you could feel the flat spots bucking. At 50MPH you started losing fillings.

I was running them at 50PSI (out of 80PSI max). Dont know where I saw that as a suggestion, but it seemed like a good idea at the time.

Today I went to the tire shop to have them balanced, knowing that I still need to ride out the flat spots. When I drove off, the truck was all over the place, wandering like a stray cat. I went back and asked them what pressure they pumped the wheels. They said 32PSI. I drove off with the thought that I might go home and do a chalk test and see where it puts me.

However, esteemed mudders, what do you run on the road? Also, any suggestions on the flat spots?
 
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I have AMP M/T LT285/65R18 tires on my rig. Criticize if you want, but that is what is on it (bought it that way recently).

Before I owned it, it sat for a while so it has some flat spots. And no weights. At 30MPH you could feel the flat spots bucking. At 50MPH you started losing fillings.

I was running them at 50PSI (out of 80PSI max). Dont know where I saw that as a suggestion, but it seemed like a good idea at the time.

Today I went to the tire shop to have them balanced, knowing that I still need to ride out the flat spots. When I drove off, the truck was all over the place, wandering like a stray cat. I went back and asked them what pressure they pumped the wheels. They said 32PSI. I drove off with the thought that I might go home and do a chalk test and see where it puts me.

However, esteemed mudders, what do you run on the road? Also, any suggestions on the flat spots?
 
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I'd check the dates on the tires. For the rubber to be so hard that it won't round out after a few miles, they must be pretty old. However, with no weights, they might just be way out of balance.

Also, to have an 80psi max, those must be some serious load-rated tires. Probably not what you want on an SUV. (I have no experience with or even knowledge about those tires though, so YMMV.)

32 psi is the factory recommendation, and I find it works pretty well with most tires. I've never tried that with 80psi-max tires though. I think mine are 55psi max.

As for the wandering, is there a lift on the truck?
 

cartercd

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The general method for finding the tire pressure for a new size tire is to determine the load capacity of the OEM tire and then "backing into" the proper pressure of the new tire using its load capacity. This is applicable if the truck is of similar weight as OEM.

Using the calculator at Tire Pressure Calculator I come up with below recommendation:



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mudgudgeon

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I would generally run anything between 30 and 36 psi, depending on the tyre and the weight of the rig.

Chalk test is a good way to set your pressures IMO.
 
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30-34 for normal on-road driving, 40 when towing the camper, 16 off road.

I've never even come close to 50psi let alone 80, yikes! Are you sure these aren't big rig tires? Never heard of the AMP brand.
 

mudgudgeon

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Zilch. Likely has to do with your overall suspension health.

I agree with this.

At 50Psi you'll feel every ripple and pebble on the road. Not surprised you think you're losing your fillings.

I've had trips where I've alternating between hours on forestry roads, then stretches of blacktop at 50-60mph before re-entering forestry areas.
Aired down to about 25psi, and the truck rides fine at 60, no wondering, just slightly vague in the steering.

Check wheel bearing adustment, tierod ends, general condition of suspension bushings etc
 
Joined
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Zilch. Likely has to do with your overall suspension health.
From under the truck I cannot see, nor hear, any movement when the wheel is turned left to right. I also used a pry bar to pull ever so lightly on all the joints. All look good. Shocks are brand new. What else should I check for suspension?

I do hear a "clack" on the right side every so often, but have not figured out what that is yet. Has been like that and didn't have the crazy wander before the lower tire pressure.
 
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San Diego, California
Does it feel fairly tight when stopped/at low speeds?

Wandering could be due to caster being off (unlikely without a lift) or more likely, the toe-in not being enough.

Maybe go under under the truck and widen the tie rod by 1/6 of a turn or so. You should be able to feel the difference in "tightness" of the steering at freeway speeds. Make sure you loosen the clamps at either end and hopefully the last guy to mess with it used anti-seize...

And mark where its at before you make any changes. The current alignment could be good.
 

mudgudgeon

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From under the truck I cannot see, nor hear, any movement when the wheel is turned left to right. I also used a pry bar to pull ever so lightly on all the joints. All look good. Shocks are brand new. What else should I check for suspension?

I do hear a "clack" on the right side every so often, but have not figured out what that is yet. Has been like that and didn't have the crazy wander before the lower tire pressure.

Clack could be from worn sway bar bushings.
Or loose suspension bolts in radius arms

Lower pressure will definitely high light an existing issue more than high pressure.
But lower pressure by itself should not have you wandering along the road
 

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