dual rears a problem at low psi

[charlieaarons]

I just thought of the best reason why DRWs are a problem in a vehicle that goes offroad a fair amount:
If the pressure in the rears is significantly lowered the bulge in the tires will rub, potentially causing rapid heating. Does anyone have a duallie pickup and does the owner's manual proscribe pressure lowering because of this reason?
Typically there is only 5-10mm of clearance between properly inflated dual radial tires. Large radials can squash out up to 35mm at decreased pressures which are "OK" with the mfg in a low speed offroad SRW application. According to my Michelin data sheets.
Does anyone actually have personal experience running dual rear radials at 35-40% highway pressure?

Charlie

 

[Rhode Trip]

Hi Charlie,
I don't claim any expertise, but I've got a Dodge Cummins 3500 with dual rears and a NL TC. There is more than 10mm clearance between my rear tires.
I've had it out on the beach, and talked with other dually owners out there. General consensus is to drop the pressure until the wheels just barely touch, or slightly before. I'd estimate the pressure at this point to be 30lbs or so, less than 50% of the normal pressure, but this is eyeballing them, I never actually checked with a gauge. In my experience, its more important to drop the front pressure more so the truck rides up on top of the sand, the rear is for providing more traction. Obviously, the speeds you can drive are very low anyway, so the heat buildup is not the concern that it would be at higher speeds. No question that you can air down a SRW further, and it sure is easier to do 4 tires than 6!

 

[michaelgroves]

I'm not even sure there is a problem with the tyres touching. They shouldn't rub a huge amount, I wouldn't have thought.

Bear in mind that the increase in footprint when you deflate a tyre is mainly in the length of the footprint, not the width. So when the outer tread areas touch, they won't be doing so under a lot of pressure - the distortion will be transferred to the places they are not touching.

NB: I don't know this for a fact - just what seems likely to me!

 

[ntsqd]

There shouldn't be very much relative motion between the tires since they're bolted together, but they could interfere with each other's shape change at the 'bulge'. I think that if they are going to touch in the bulge that it is crucial that they be at the same pressure. Otherwise one will dominate and then the potential for relative motion between them, though still minor, does exist.

Perhaps paint the inside sidewall of one tire, and then observe how the paint is worn away?

 

[ExploringNH]

I recently had to operate a loaded dump truck on some rough trails and had some thoughts about the DRWs. What I found while off road was that in rocky areas, I would often have one of the dual rear tires off the ground while the other was on a rock, leaving that one tire to support the weight that was previously carried by two. If running near the load limit of the tires, I would think that this could cause a problem. This problem, I think, would intensify if running a lowered psi (effectively reducing the load capacity of the tires).

Has this proven a problem to anyone on here?

 

[madizell]

Tire heat is caused by flex, not by contact, and heat transfer between contacting sidewalls is likely more an issue of lack of cooling rather than excess heat or heat transfer. Watch for duals to pick up debris, especially when aired down, which might lead to tire failure. Hopefully your rims have safety beads which allow for aired down operation to start with.

 

[rambrush]

In the wildland fire arena which I was a part of this was a major problem. We had to keep them aired up to a point where they did not rub unless we were in a slow running situation. Going down the highway was where the heat would build up the worst.

 

[86cj]

Tire heat is caused by flex, not by contact, and heat transfer between contacting sidewalls is likely more an issue of lack of cooling rather than excess heat or heat transfer. Watch for duals to pick up debris, especially when aired down, which might lead to tire failure. Hopefully your rims have safety beads which allow for aired down operation to start with.

I agree on the debris comment, I have a Chevy dually and a 12' truck camper and have had rocks stuck between my tires when off road. I was not aired down but could see it being worse aired down. It seems if rock was sharp and spent some time there it would not be good for the sidewall, on or off road.

I know I am glad I saw the rock and did not have it hit the inner fender at 50MPH.