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 > Dually tire pressure?

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TxGearhead

Texas

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Posted: 06/24/19 05:46pm Link  |  Quote  |  Print  |  Notify Moderator

36psi this morning. Rain all last night and this morning. Cool air and cool roads. Ambient air 68F. Ran to Lake Charles for about 1 1/2 hours at 65-75 mph. Tires stayed at 36. Back home in 78F temp and dry roads. Tires aired up to 38. I'll leave them at 36 until something says otherwise.


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TxGearhead

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Posted: 06/24/19 05:54pm Link  |  Quote  |  Print  |  Notify Moderator

ryoung wrote:

Quote:

80 front
65 rear

When the truck is empty a fair percentage of the total weight is on the front tires, particularly if it's a diesel.


What difference does the front tire pressure have to do with whether the truck is loaded or unloaded. Obviously by simple mathematics, the front will be carrying the greater percentage of total weight when unloaded as opposed to when the truck is loaded, which now has the greater percentage of the total truck weight.

I'll bet the sticker on the door pillar doesn't recommend 80 psi for the front tires.

On the '04 Dodge 3500 dually that I previously owned the recommended tire pressures were 55 front and 65 rear. And that 65 psi pressure for the rear was the recommended pressure at the maximum GAWR of a little over 9,000 lbs.

So why do you put more air in the front tires than you do in the rear tires, when the front tires are carrying lesser weight than the rears?

This is not the manufactures recommendation. And as I said before you are degrading the tires performance.


I run 80 in the front at all times. My yellow sticker says 80 front and 65 rear.
My camper adds only 200# to the front.
This IS the manufacturer recommendation.
How much you wanna bet?

Grit dog

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Posted: 06/24/19 11:48pm Link  |  Quote  |  Print  |  Notify Moderator

Ryoung, you're completely off base. % of total weight is irrelevant. Actual load on the axle is what matters.
Empty truck, any truck, drop a big load in the bed, centered on the rear axle and the front sees the same weight as unloaded regardless of the %.
55psi on the front of a stock tire size dually (215-245 wide tires) is LOW unless maybe it's a gas motor. 50-55 psi in a wider tire like 285 wide is about min before it starts detracting from handling with a diesel.
As well, too much pressure for the weight does also detract from handling and braking. Harder tire = smaller contact patch and less compliant and greater rebound rate than a softer tire (less pressure). Ever see drag cars with a lot of air in the back tires? Nope, poor traction. Air up for more traction, nope, the opposite.
However, with a high CG load like a camper, the advantage of a bit harder front tire, even though the static load is the same or slightly more or less than empty, is less sidewall flex when the load is transferred laterally when the camper/truck gets body roll.
Think about it before replying.


"Yes Sir, Oct 10 1888, Those poor school children froze to death in their tracks. They did not even find them until Spring. Especially hard hit were the ones who had to trek uphill to school both ways, with no shoes." -Bert A.

jimh425

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Posted: 06/25/19 07:22am Link  |  Quote  |  Print  |  Notify Moderator

Funny that this thread is comparing DRWs to drag cars now. [emoticon]

Any way, the effect of air pressure on traction depends on a lot of factors. More contact patch can lead to more float and less traction or more traction depending on if the road is dry or not and the material surface, and of course, tread compound. In any case, I don’t think anyone probably thinks DRWs have good traction in rear either way.

Also, if the harder front tire has less sidewall flex, the harder rear tire (with more air) will as well.

As noted, I have 19.5s, so I’m not going to be airing down much past 70 in any case. I’d prefer my beads to stay in place. [emoticon]


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ticki2

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Posted: 06/25/19 07:23am Link  |  Quote  |  Print  |  Notify Moderator

TxGearhead wrote:

ryoung wrote:

Quote:

80 front
65 rear

When the truck is empty a fair percentage of the total weight is on the front tires, particularly if it's a diesel.


What difference does the front tire pressure have to do with whether the truck is loaded or unloaded. Obviously by simple mathematics, the front will be carrying the greater percentage of total weight when unloaded as opposed to when the truck is loaded, which now has the greater percentage of the total truck weight.

I'll bet the sticker on the door pillar doesn't recommend 80 psi for the front tires.

On the '04 Dodge 3500 dually that I previously owned the recommended tire pressures were 55 front and 65 rear. And that 65 psi pressure for the rear was the recommended pressure at the maximum GAWR of a little over 9,000 lbs.

So why do you put more air in the front tires than you do in the rear tires, when the front tires are carrying lesser weight than the rears?

This is not the manufactures recommendation. And as I said before you are degrading the tires performance.


I run 80 in the front at all times. My yellow sticker says 80 front and 65 rear.
My camper adds only 200# to the front.
This IS the manufacturer recommendation.
How much you wanna bet?
what is the stock tire size and what is the front GAWR ?


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TxGearhead

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Posted: 06/25/19 04:03pm Link  |  Quote  |  Print  |  Notify Moderator

LT 235/80 R17 LR E 10 ply rating. 3085# Single at 80psi.
Front GAWR 6,000
CAT Scale empty: front: 5260. Rear: 3540
Cat scale with Bigfoot ready to camp: front: 5460. Rear: 7520.

TxGearhead

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Posted: 06/25/19 04:18pm Link  |  Quote  |  Print  |  Notify Moderator

jimh425 wrote:

Funny that this thread is comparing DRWs to drag cars now. [emoticon]

Any way, the effect of air pressure on traction depends on a lot of factors. More contact patch can lead to more float and less traction or more traction depending on if the road is dry or not and the material surface, and of course, tread compound. In any case, I don’t think anyone probably thinks DRWs have good traction in rear either way.

Also, if the harder front tire has less sidewall flex, the harder rear tire (with more air) will as well.

As noted, I have 19.5s, so I’m not going to be airing down much past 70 in any case. I’d prefer my beads to stay in place. [emoticon]


DRW traction...why wouldn't a DRW have good traction?

jimh425

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Posted: 06/25/19 06:09pm Link  |  Quote  |  Print  |  Notify Moderator

TxGearhead wrote:

DRW traction...why wouldn't a DRW have good traction?


I’m sure you probably noticed how a pickup is light on the rear and spins pretty easily compared to a car for anything but dry pavement is very noticeable. A DRW is worse than a SRW because it has double the tires and tends to float compared to even a SRW.

Of course, once you put 2 tons in the bed, that all changes, but it seems like this discussion is about empty. Which means more air, more tire on the ground and more floating.

That doesn’t even count that the DRW tires don’t line up with the fronts so they always make at least part of their own track. In any case, I don’t think any of us buy DRWs for traction, but hey, maybe someone did.

Kayteg1

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Posted: 06/25/19 07:13pm Link  |  Quote  |  Print  |  Notify Moderator

jimh425 wrote:

Which means more air, more tire on the ground and more floating.

Laws of physics say other wise.
[image]





jimh425

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Posted: 06/25/19 07:20pm Link  |  Quote  |  Print  |  Notify Moderator

Kayteg1 wrote:

Laws of physics say other wise.


Your picture doesn’t represent any laws of physics.

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