Tire Pressure Recommendations

[kdauto]

For the O.P., one thing we have not discussed is does your truck have TPMS? Not many GM duallies do, buut I think the upper level trims may have it on all 6 wheels.

If you DO have TPMS, then lowering pressure will be an issue. It will set a TPMS alert when it hits 60 psi and under. Only way to correct this is with an expensive TPMS tool and make a "placard change", IF it is available on your year,make and model.

[Kid Gloves]

Yet the unladen dually in this story has a rear axle weight of 3900lbs. Per the load and inflation table for a LT235/80R17E in a dual position, 35psi is the minimum recommended pressure to support 1570lbs per tire, or 6280lbs for the axle. At 45psi on the rears, the tires could support 7480lbs, nearly twice the unladen axle weight. At the placard recommendation of 80psi, the tires can support 11,340lbs, which exceeds the RAWR and is almost 3 times the unladen axle weight.

While I’ve made a habit of never recommending a specific tire pressure to anyone, I believe we can use the information available to us to determine tire pressures that are appropriate to our particular situation.

[FastEagle]

Originally Posted by Kid Gloves

Yet the unladen dually in this story has a rear axle weight of 3900lbs. Per the load and inflation table for a LT235/80R17E in a dual position, 35psi is the minimum recommended pressure to support 1570lbs per tire, or 6280lbs for the axle. At 45psi on the rears, the tires could support 7480lbs, nearly twice the unladen axle weight. At the placard recommendation of 80psi, the tires can support 11,340lbs, which exceeds the RAWR and is almost 3 times the unladen axle weight.

While I’ve made a habit of never recommending a specific tire pressure to anyone, I believe we can use the information available to us to determine tire pressures that are appropriate to our particular situation.

You must not forget that the vehicle manufacturer MUST provide a percentage of load capacity reserves above the GAWRs.

[Kid Gloves]

Originally Posted by FastEagle

You must not forget that the vehicle manufacturer MUST provide a percentage of load capacity reserves above the GAWRs.

The purpose of my previous post was not to delve into the alphabet soup of regulations, rather, it was to demonstrate that the rear tires on a dually might operate under a very wide range of load conditions. That being the case, a knowledgeable owner would be able to make an informed decision regarding tire pressures for their vehicle under a variety of conditions.

[Tireman9]

Originally Posted by wimpy

I can see potential tire rub on the dually tires at this inflation pressure. The tire mfgs. stopped doing recommendations due to our litigious society. Go by the vehicle mfg recommendations, if they say 80 as recommended, I'd not go below 65 psi.

Not quite. since the 70's, according to DOT Regulations, it is the responsibility, of the vehicle manufacturer to provide, on every vehicle intended for highway use, the tire inflation needed to support the rated load for each axle.
Tire companies follow industry published "Load & Inflation" tables and with the exception of a handful of unique sizes they all follow the same numbers.


RVs have Certification labels either on the driver door jam for motorized units with a driver door. Or near the left elbow of the driver when there is no driver side door, or on trailers on the outside, driver side toward the front of the trailer.


You should all have a picture of the information on the 'sticker" on your cell phone as this is important safety information.

[Tireman9]

Originally Posted by Ray,IN

I've since lost the reference, but back in 2002 when I towed with a Chevy Duramax dually with 16" LR E tires, the tire mfgrs. said to never run less than 45 psi in those tires. Their load/inflation charts did not display anything below 45psi.

Yes Ray is correct. This would apply to all DOT tires.


NEVER run inflation lower than the lowest number published in the tables.

[Tireman9]

Originally Posted by Kid Gloves

^^^As long as the +20% doesn’t put a tire over the Max sidewall pressure or over the Max rated pressure for the wheel, correct?

Yes. I would hope that people are not loading their tow vehicle tires to 100% of capacity.

[Tireman9]

Originally Posted by jadatis

Then I trew it in my made extra safe calculator, wich gives highest pressure, so reserve, with still acceptable comfort and gripp.
Front 73 psi
Rear 28 psi !!!!
4 tires on rear
If you had
2 of those on rear, 54 psi.

Suprising, I realise but
2 front carry 2x 3086lbs= 6172lbs
My calc adds 10% to the 5120lbs on front axle, is 5632lbs , so large portion of the 6172 for 80 psi of the tires.

Rear 4x 2833lbs= 11330lbs , axleload 3900lbs
Only 34.5% of tires capacity.
You determined from list front 65psi , but no reserve added probably.
Rear 35psi is probably the lowest psi the list gave.
35 for dual gives most likely 1580lbs in your list.x4= 6350lbs


When towing axleweight rear becomes much more
Mayby more then front , but devided over 4 tires.

The 5120 lbs on rear dual, would need 38 psi.

Edit: read back and saw the P/lc lists you gave and checked them to be calculated with the bad old american calculation, still used for LT .
The European calculation for every kind of tire would give for 35 psi dual 1460lbs a tire, 120 lbs less.

If you were an actual tire design engineer you would know to never suggest running a pressure lower than the published tables.

[Tireman9]

Originally Posted by wolfe10

This can be viewed one of two ways:
Lawyer speak.
Engineer CYA, knowing that most Americans don't check their tires (hence the now standard tire pressure monitors/alarms that up the cost of every vehicle built) and wouldn't reinflate when going from empty to loaded.


So, IMO, they are correct in what they say, but a smart owner can do better.

Yes that is a key point. The regulations are written to address the "lowest common denominator" vehicle owner. Hopefully many of the readers here pay more attention to the maintenance of their vehicles and do not do the bare minimum necessary. Ensuring a reasonable Reserve Load capacity is always a good practice.

[Kid Gloves]

Originally Posted by Tireman9

Yes. I would hope that people are not loading their tow vehicle tires to 100% of capacity.

To clarify, allow me to ask a specific question. If we weigh a vehicle and the chart recommends 70psi for a LRE tire, should we add the 20% (14psi) that you have recommended and inflate to 84psi?

Same question if the chart recommends 75psi. Should we add 15psi and inflate to 90psi?

In either case the tires are not being loaded to 100% of potential capacity. I use the word potential, as a tires capacity varies based on the pressure to which it is inflated.

Additionally, while one can hope that certain conditions don’t exist, you, of all people, must certainly be aware that some, less than desirable conditions do exist.

[jadatis]

Answer to post #66.
Apart from that I determine the reserves different.
But if calculation with reserve comes above reference-pressure, I would use that pressure up to 10 psi.
If calc comes higher, you should ask yourselfes if not overloaded, or tires with poor reserves.
In your example , E- load tire AT 80 Psi.
If pressurevwithvreserve comes to that 84psi I would fill to 84 or rounded 85psi.

The reserve is needed for next.
inacurate reading of pressure, even a digital device has its inacuracies.
Unequall load R/L .
Pressure loss in time.
And what I forgot.


Its better to be in the clear with laws of nature, then rules decided by organisations.

[Texas Sooner]

Originally Posted by kdauto

For the O.P., one thing we have not discussed is does your truck have TPMS? Not many GM duallies do, buut I think the upper level trims may have it on all 6 wheels.

If you DO have TPMS, then lowering pressure will be an issue. It will set a TPMS alert when it hits 60 psi and under. Only way to correct this is with an expensive TPMS tool and make a "placard change", IF it is available on your year,make and model.

Yes it does, but I set my front tire pressure at 70 lbs and the rear four tires at 65 lbs for our trip down to the SmartWeigh program. Once I get the TV and the trailer weighed tomorrow I will be able to adjust accordingly.

I was not aware that the TPMS would go off under 60 lbs and if that's the case then I will probably make sure that everything is set at 65 lbs, even though the back four will probably be able to go lower.

[kdauto]

Originally Posted by Texas Sooner

Yes it does, but I set my front tire pressure at 70 lbs and the rear four tires at 65 lbs for our trip down to the SmartWeigh program. Once I get the TV and the trailer weighed tomorrow I will be able to adjust accordingly.

I was not aware that the TPMS would go off under 60 lbs and if that's the case then I will probably make sure that everything is set at 65 lbs, even though the back four will probably be able to go lower.

OEM TPMS will set off when pressure drops 25% from the OEM placard (door jamb sticker). This can be reprogrammed on many pickups with the proper tooling. Since your placard reads 80 psi (from memory here), then the warning lamp and associated trouble codes will set when tires hit 60 psi. There's a few psi variation in sensors, so it could hit at 58 or 62psi.

[FastEagle]

Originally Posted by Kid Gloves

The purpose of my previous post was not to delve into the alphabet soup of regulations, rather, it was to demonstrate that the rear tires on a dually might operate under a very wide range of load conditions. That being the case, a knowledgeable owner would be able to make an informed decision regarding tire pressures for their vehicle under a variety of conditions.

Your method may be acceptable for a motor coach. It depends on the vehicle certification. If the chassis was certified as the primary source for tire fitments the FMCSA methods may apply. However, the tire industry will still not recommend inflation pressures below what was recommended on the vehicle certification label, in the vehicle owner’s manual or on the tire load information placard.

I’ve taken the time to provide a verbatim statement from the RV section of a USTMA document. It can be found on page 44.

https://www.ustires.org/sites/defaul...uckTires_0.pdf

“Inflation pressure recommendations may also be determined based on the tire manufacturer’s specifications, which define the amount of inflation pressure necessary to carry a given load. These inflation pressures may differ from those found on the vehicle tire placard or certification label. However, never use inflation pressures lower than specified by the vehicle tire placard, certification label or owner’s manual. Nor should inflation pressure exceed the maximum pressure molded on the tire sidewall.”