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Old 04-08-2008, 06:56 PM   #1
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Tow Vehicle Tire Pressure

I was just wondering what the correct pressure is. Is it the psi listed on the data plate on the door? Or is it the psi rating on the tire? My buddy suggests that I run 5 lbs less than the max psi stamped on the tire. I've always run close to the psi on the tire, but now I'm wondering. My tires have a max psi rating of 80. The truck plate says 70 psi in the rears, and 60 psi in the fronts. Right now I have them at 75 and 65 psi. I'm just wondering because the fiver puts a bunch of weight on the truck and I want to be safe. The tires are Firestone Transforce ATs and I have no complaints on these tires. I had a set of Transforce HTs on my 3/4 ton and they were great too, although a little slippy in the snow. Any suggestions, opinions appreciated.
Lowell
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Old 04-08-2008, 08:34 PM   #2
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Lowell

Here is what I have found. When towing TT’s with friction type sway controls, and friction meaning, friction sway bar, Reese DC, or Equa-I-izer type hitches, tires stiffness plays a major role in rig stability. In this TT towing setup the tires need to be inflated higher then actual load required to create a stiff side wall and not flex which can create towing instable from sway effects on the TT. A soft side wall tire even if inflated well to handle the weight can cause a true sway feeling as the TV is literally shifting on the soggy tire as the anti sway hitch try’s to hold the truck stable.

On your 5’er you have a slightly different setup. Sway effects of a TT are no where near the same. So you do not have that same anti sway need. But you do need tire capacity. The name plate pressure generally follows the TV GAWR’s. So the front psi = the front axle load rating and so does the rear. So when towing you need at least the name plate psi. I say at least as some day you need to hit the scales. If the actual scaled weight is more then the axle rating you may not have enough air in the tire. Not to mention you are over the axle rating. Your dual tires can handle more weight then the TV axle rating. But only if inflated properly.

What you do NOT want, is to run the tire at a pressure under the actual rated psi for the weight it is holding up. Then heat comes and soon tire failure. Tire manufactures do have psi charts per load ratings. Some are even on line on the tire brands web site. You can then look up the min psi for the load. But again you need to know the load and that is only done by a truck scale.

On the front end, the same load ratings apply. Need enough psi for the load. You can go above that PSI all the way to max side wall but you probably do not want to do that on the front. I have found on GM and Ford suspension that when approaching that max side wall in the front, to much bound and wander comes from it.

If you do go to max side wall, front or rear, make sure it is done cold. I personally doubt you will really need max side wall on the front.

Hope this helps

John

As a point of reference, on my 2500 Suburban, I ran 80psi (max side wall) in rear and 65 psi front. Name palte was 80psi rear/50 psi front. LT 75R16’s

On the F350, I run name plate in my case. 75psi rear, 65 psi front. That will take me to a full 11,000 GVW create enough tire stiffness for anti sway and not bounce the front end. But again now I have LT’s and 18” tires. You can’t just go by psi, it needs to line up with the weight rating and the anti-sway requirements. And in my case I’m using the extra load rating for tire stiffness not load rating. I do no come close yet to the 11,000# GVWR
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Old 04-08-2008, 09:17 PM   #3
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John,

Do you run 75 in the rear all the time? I run all four at 65. I'm thinking I should up the rears to 75.

On a side note, always check the tires and compare them to the sticker. My Ex originally came with D range tires, so they had a max pressure of 65. The sticker says 45 front, 55 rear, which was fine for those. But, since it was upgraded to E range, with a max pressure of 80, 45/55 is really flat and you get horrible mileage that way. The previous owner of mine ran the sticker pressures because he claimed they were "big tires and need to be left aired down" ( ).

Jon
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Old 04-09-2008, 08:24 PM   #4
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Quote:
Originally Posted by Sunline Fan
John,

Do you run 75 in the rear all the time? I run all four at 65. I'm thinking I should up the rears to 75.

Jon
Jon

On the F350, NO I do not run my 18" tires. (LT275/70R1 at 75 when non towing. I drop them down to 65. And if not the bounce on that 1 ton suspension is pretty bad. But towing not an issue. Again I can load 3000# cargo on my rear axle and still not hit the tire ratings. They are 3,630#/tire rated at 80 psi. I have larger capacity tires, so pressure is relevant to the tire.

On my 2500 Suburban, LT75R16 I went 80 psi towing and down to 65 psi non towing on the rear. The SUV would bounce hard on the back at 80 with no load in it. These are 3,042# / tire at 80 psi

Driving around empty on a harder tire will help with gas mileage. But there is a point where the bounce just is not worth it. So I find the middle ground. It comes out to be a tire pressure experiment. Just what ever one does, do not go below the tire pressure rating for the weight it is loaded to. Again the need to have scaled weights hitched and unhitched.

Hope this helps

John
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