Air pressure formula

[Okie-Go]

I am hoping someone can help me with the formula for air pressure. The one where you weigh the axle and divide by 2 then multiply something by maximum load of tire. In the next couple of weeks I plan on getting some mudgrips for the winter,they are in loadrange D and I want to know they will be safe if I have to haul a load or pull the 5er. I will leave them on till hunting season is over then put back on the michelins. I have two extra wheels so I can do this at home instead of paying the tire shop. Thanks

 

[SnoKing]

Owners manual has a tire pressure chart based on load. Check it! SNOKING

 

[Okie-Go]

Thanks, Snowking but that isen't the one I am after. I am referring to the one that has the formula thing.

 

[merryman]

Axel weight devided by 2 gives weight on wheel.

weight of wheel devided by tires max rated weight

result times max air pressure for tire



axel @ 4650 devided by 2 =2325 devided by tire rating of 3400 =. 68 X 80 psi = 55psi

Don't recall where I learned this, but have used it for years, but I add a little pressure on the theory that so long as the pressure is below the tires max. a little more pressure won't hurt anything.



Vaughn

 

[Loren]

Vaughn has the right idea. The tables I have seen from tire manufacturers say basically the same thing as what he said. Using round numbers may make it easier to understand.



If your tire is rated to carry 3000 lbs at 80 psi, then it can carry about 2000 lbs at 53. 3 psi, or 1500 lbs at 40 psi, etc. This is only good up to a point.



I would add a few extra psi as Vaughn does, just to be on the safe side. A little more pressure won't hurt, but too little pressure could kill you.



I can't get the entire table to copy here, but here's an example from one manufacturer's data, for one tire:



For a load range D tire, size LT 225/75R16:

35 psi = 1500 lb

40 psi = 1650 lb

45 psi = 1790 lb

50 psi = 1940 lb

55 psi = 2060 lb

60 psi = 2190 lb

65 psi = 2335 lb



Note that load range D tires only go to 65 psi.



For what it's worth, I have pulled a 14,000 lb fifth-wheel trailer with my 1995 truck for quite a while. Hitched up, the truck's rear axle is carrying 6050 lbs. This is well above the rated load for even most load range E tires. In spite of the load, my tire dealer fitted load range D tires after he couldn't get four Wranglers to run without vibration. He assured me that the D tires would handle the load, and they did.



I no longer pull that trailer with that truck, and would probably not accept load range D tires for that application again.



I guess the questions are:

Can you do it and get away with it? Probably.

Is it prudent? Definitely not.



I hope this is helpful.



Loren