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aftermarket tire psi question

218 Views 6 Replies 6 Participants Last post by  Uncle Douglas
Hi. I have an '83 110 that I run the wolf wheels on with LT255/85/R16 BFG KM2s on and for years, I've just put 50 psi in them all around. the Max is supposed to be 80.

However, is there an actual psi I should be running? What do you run? The truck is about 4000lbs for reference
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This gets in the weeds quickly, but run the truck empty and mark across the tire tread with a white tire crayon. Drive around the block and see how much crayon is missing. If it is not just edge to edge, you need less pressure, and if there is no crayon left, you need more pressure.

Not scientific but repeating this heavy and light will dial in your pressures for both scenarios.

I happen to run 50 in my tires as well, and that seems to work fine for me. I might increase pressure in the rears when heavy, however.
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Uh. Somewhere around 30-35. 50 is pretty high.
Find a scale. Weight each axle. Look at tire placard and adjust air pressure relative to actual load.

So say it is 3414 lb @ 80 psi. That is 1 psi for every 42.7 pounds.

I highly doubt your truck is 4000 pounds.
A vehicle's manual specifies tire pressure, front and rear, usually loaded and unloaded. This is where I run them, regardless of tire type, size etc. At the very least, it's where I would start before experimenting.
A Karmann Ghia is supposed to run 17 and 29. If you do like the typical tire store and fill them all to 32, see what happens the first time you charge a corner and turn in: Nothing - it keeps going straight.
Of course in low traction conditions with risk of getting stuck, cut psi up to half.
Most older Rovers run something like 29 and 40. I'd keep the factory front/rear ratio under most circumstances, although with a heavily loaded rear, e.g. when towing, add up to 5 to rears.
The max psi stenciled on the sidewall is, as a practical matter irrelevant, and certainly no guide for normal use.
Tires are the single most important variable when it comes to vehicle performance. Correct pres is what makes tires work.
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Here we are, in the weeds...

Tire pressure is a very important subject and should be more important to everyone since the root cause of the Ford "exploder" conspiracy was under-inflated tires, due to driver neglect.

Now, the suggested pressures are based on the OEM tire size and load range, for a vehicle loaded (or not) in a specific way (often just driver and a full tank of fuel- check the manual for specifics). If you are serious about your vehicle and doing longer trips loaded up with "stuff", you owe it to yourself (and more so anyone riding in your vehicle) to understand how load capacity is controlled by tire pressure, assuming the load does not exceed the maximum for the tire. Visit a local truck stop and you can easily get front, rear, and both axle weights in about five minutes.

One person in Africa ran mud terrains, but low load range "street" tires, v "light truck" tires. He had both spring and tire issues- at maximum pressure they looked to be aired down for rock crawling.

So, dig in, educate yourself, and relax knowing that once it's dialed in you have one less thing to worry about on your expedition.

And my truck is over 6000 pounds "heavy".
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As above depends on tire construction, weight load, & use. Typically 10psi softer in front than rear for best handling. I have run everything from Avon RangeMasters and Michelin XZL’s to Super Swampers on defenders. On 90’s typically 28 front 38-40 rear have handled best.
110’s where more weight is possible -I’ve had military trucks where tire pressure for the XZL’s was stenciled on the flares 38 frt 47rear. If running a tire with a soft sidewall like a BFG 30-32 frt & 38-40 rr.

A truck on over inflated tires will tend corner poorly and wander on the highway @ higher speeds.
When I say corner poorly I don’t mean body roll, I mean the tires don’t hold the pavement and tend to drift.

The tire crayon or chalk method is the only way to get it perfect for your individual vehicle.
If you are wearing the centers out of your tires you are over inflated. If you have cupping on your outer tread blocks you are under inflated.
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