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4xMike's avatar
4xMike
Explorer
May 22, 2013

Adjusting tire pressure for load

So my tires on my dually are wearing heavily in the center indicating over inflation. I typically run 80 psi loaded (load range e) and 65 empty. Judging by the wear, I should be running significantly less


Beware: math ahead!!!

I haven't weighed mine, but found someone with a nearly idenical setup and got their weight.

Empty is 4500 front, 3000 rear
My camper weighs between 3000 and 3500 wet, and his weight bias was nearly 100% of the camper weight on the rear axle.

My tires are range e and rated at 2850 in dual or 3050 in single at 80 psi

Would it be proper to deflate my tires in a linear fashion to match the weight on them?

Example. 4500 lbs divided by 2 is 2250. The tire is rated at 3050 at 80' or 38 pounds per psi. By this theory the front tires should be correctly inflated a t 60 psi

On the rear they are at 35 lbs per psi ( 2850/80). 6500 lbs across 4 tires is 1625 lbs per tire. Divided by 35 lbs/psi is 46.4 psi.

This would explain my overinflated wear pattern, but it seems crazy to run my tires at 45 psi in the rear while loaded. One one hand it makes sense as I am only running st 1/2 the tire capacity, but at the same time I'm afraid of the loss of tire stability (specifically lateral stability) by running at almost 1/2 of pressure

Any insight? Thoughts? Input?

Thanks,
Mike
Truck Campers

15 Replies

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  • jadatis's avatar
    jadatis
    Explorer
    May 23, 2013
    Using my spreadsheet i come to 64F and 49 back, and I use my own formula that gives a bit lower pressure then linear math. This is higher then your linear math because I add 10% reserve to the load first.
    These pressures wont give damage to the tires, assuming your given weights are right, and thats the tricky point here, but you realise that , I make of your story.
    The tires stability is yust how you feel it, a little swaying wont say that the car is dangerously unstable, is my opinion.
    Nowadays cars are made that stiff, that we have gotten used to the discomfort, wich a stiffer tire gives, but before 2000 the tiremakers also gave minimum advices.

    Here a picture of the spreadsheet but will also give the link to the map where you can download the spreadsheet, search for 4xMike,
    Then you can chanche things or add in dark blue the GAWR's and to use reserve % , wich is now set on 10% standard.

    Now the link to the map.
    The examples map with the spreadsheet 4XmikeRVetc.
    See what you can do with it.
  • Lowsuv's avatar
    Lowsuv
    Explorer
    May 23, 2013
    srw 2002 duramax with 9200 # gvw
    replaced my stock 245 with LT 265/75R16E tires on an 8 inch wide wheel
    tires rated 3415 each so 13,660 capacity in the tires .
    i run 50 psi year around except when towing when i go to 70 psi.
    the charts say 50 psi is good for about 2470 # each
    65 psi good for 3000 #
    stock 245 were rated 3042 # at 80 psi
    i have about 55,000 miles on my 265/75r16E michelin highway tires.
    i anticipate another 10,000 miles or so before replacing .
    they seem even across the tread
  • ChooChooMan74's avatar
    ChooChooMan74
    Explorer
    May 23, 2013
    Look up the load chart and go from there. I almost never tan my old dually at full pressure.
  • wintersun's avatar
    wintersun
    Explorer II
    May 22, 2013
    In my own experience I have never been able to rely 100% on the tire manufacturers' load and tire pressure charts. They are designed to insure the tire stays on the rim and not to insure maximum tread life. The tread contact area with the road does not change in a linear manner with tire pressure as a lot of the change is in the action of the sidewall and not the tread section of the tire. When I have used the charts to determine the air pressure the end result has been underinflatted tires and tread wear on the edges.

    With 4 x 2850 at 80 PSI the tires are set to carry 11,400 or nearly doubly the actual load at the rear with the camper in the bed. I would forget about a linear adjustment and go down to 70 PSI at the rear after rotating the tires and then go another 5k miles to see what the tread wear looks like. You may get enough wear to see what is happening after only 3K miles or you may not. Most likely the rear tire pressure should be in the 65-70 PSI range but only time will tell.

    Some people suggest using chalk on the tread or some other trick but I have never seen this work with a truck tire. Monitoring the tread wear as you are doing is the best way even if it takes more time and you lose some tread life in the process.

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