Proper tire inflation

The vehicle manufacturers tire placard is a recommendation only. They have no idea how much weight the truck owner will carry on the trucks front or rear axle.

Hell my 2500 Dodge/Cummins came with a 50 psi for the the front and 75 psi for the rear on LT265/70-17 E tires.
The front tires at 50 psi were rolling on the edges empty or loaded. I use the chalk line method and found 65 psi worked best. I found 45 psi works best when the truck is empty and 70-75 psi when carrying a load.
Thats why the tire placard says see your owners manual.

Owners manual says to adjust the tires pressure according to the load carried or accordingly.

I have a 1500 4x4 truck and a older one ton DRW 4x4 truck and they all require different tire pressures that are different than their tire placard pressure recommendations.

IMO the tire placard is a good place to start. Then fine tune them from there. I generally run my LT tires up to 115k miles on 3/4 ton trucks. DRW trucks around 75-80k and 60-65k on the 1500 trucks by using the chalk line method when empty and carrying a load.
Learn to read your tires and of course having a large air compressor at home to quickly air up helps.

I have found that the truck handles better with the tires inflated more than the manufacturer recommends for the given axle weight. This seems especially true for Michelins, which have a true radial sidewall which is quite flexible. Therefore I run the pressure a bit higher than the chart, knowing that I am probably trading a small amount of wear for better handling. On a dually, the tires last until you are tired of looking at them anyway.

Car tire pressures are higher front or rear to handle the weight of the engine and a full load of passengers at freeway speeds for extended periods of time. Uninflatting is likely to cause a tire to overheat and suddenly fail.

With trucks the tire pressures recommended are for a full payload in the bed and with a full load of passengers in each of the available seats in the cab. Heavy duty truck tires are not the same as car tires by any stretch of the imagination. The idea of adjusting the tire pressures to match the load is a stupid one at best and actually dangerous as the end result will be underinflatted tires.

With my tires that are 3750@80 PSI and no load in the bed they each support 2400 lbs. so according to a tire chart I would inflate them only to 55 lbs of pressure. If I do that the tire wear will be much greater on the outer edges of the tire and there will be less contact area on the pavement so longer braking distances and there will be more sidewall flexing which also affects road handling.

Start with the sticker pressures recommended by the truck manufacturer and monitor the tread wear on the front and rear tires. If it is uniform from edge to edge then it ain't broke and no need to fix it.

Tires are designed to allow for increases in internal pressure as the heat inside the tire warms the air and causes it to expand. When the tire pressure is measured with the tires "cold" all it means is that the air temp inside the tire is the same as the air temp outside the tire which is the baseline.

Tire pressures do increase with speed which is part of the reason why tires have a speed rating. Tires for my coupe are rated for 125 MPH and I could buy ones for a lot more money rated for 140 MPH and that is sustained driving speed. The tire dealers will not sell me a tire for my particular car that is rated at less than 125 MPH even though the speed limit is at most 70 MPH in my state.

not to further confuse the matter.. but i'm going to further confuse the matter ;)

door sticker PSI is for the ambient air we breath (lots of nitrogen, some oxygen, CO2 etc. and, depending upon where you are, possibly lots of water vapor in the form of humidity)

its the water vapor that expands the greatest when heated and that is why race teams use nitrogen or desiccant filtered ambient air.
They want their optimal x psi to remain as such throughout the race even as the tires heat up.

so if you want to control for temperature affects on psi, use dry air or nitrogen.

gitpicker2009 wrote:

If you set the pressure at 80psi, cold, then you can bet it's going to be closer to 90 at actual road temps.

If you check, the tires have COLD stamped behind that max pressure. Unless you have a massive change of altitude or ambient temperature during the drive, set the pressure cold and allow the pressure to increase as the tire warms from driving. The manufacturer knows that will happen and included that in the specification.

BurbMan wrote:

Lynnsr wrote:
How quickly we forget the Firestone and Ford tire controversy.

Actually Ford spec'd a tire inflation in line with the GVWR of the truck as indicated on the door sticker. The tires were perfectly safe at that psi if the Explorer wasn't overloaded.

Investigations found that all of the Explorers involved in blowout incidents were loaded way beyond stated capacity. Folks figured if it fits inside, it's OK. That resulted in tires being overloaded because the truck was overloaded, not because they were underinflated.

The main issue here was not Ford spec'ing a tire psi that was too low, it was Ford spec'ing a GVWR that folks didn't realize was so low, and led to folks overloaded their vehicles without realizing it.

Hey BerbMan

I think we agree 100%.

However, you're using "if" in a Truck Camper World, where I can tell from the blogs that everyone is running well below GVWR. :W

Lynnsr

One last comment, the scale may show that you are carrying less than the max on the front axle, and maybe 50 psi is OK, or you may be heavier and find that 60 is better.

The door sticker for my Suburban when loaded is recommended at 50F/80R. Obviously 80 rear for max load capabiltiies. I upgraded from the stock 245/75-16 to 265/75-16 on wider rims, and I find that 60 psi in the front gives me the best handling and ride combination. It took me a while to get it dialed in, 50 was too soft for the bigger tires and 65 was like it had no springs LOL, so 60 seems to be the sweet spot.

Your rig obviously will be different...you never want to be below what the tire mfr specs for the load on the axle, but waaay over is no good either.

I would start 55F/80R with the camper on take it to a scale and see what you've got. If not happy with the ride/handling, some adjustment may be in order.

Happy camping, and always set tire pressures cold! :B

gitpicker2009 wrote:
...if you want to run the tires at 80psi, you should fill to about 70 or 75 cold....I'd suggest slightly lower, and let them come up to the desired pressure/temp/volume during driving.

While this approach seems logical, it is not the case with tires. The pressure increase due to heating has already been accounted for by tire/wheel manufacturers.
Always set tires to the correct inflation pressure when they are cold. Always!

It's actually Charles law which lays out the relationship of temperature and volume, and it can be stated, simply, that most gasses have a direct relationhip between volume and temp.

IMO, the relationship between tire temperature and pressure is best described by the Ideal Gas Law (PV=nRT), or perhaps Ammonton's Law (P/T=k).

Boyle's Law assumes constant temperature. Charle's Law assumes constant pressure.

gitpicker2009 wrote:
Actually, at least in my opinion, if you want to run the tires at 80psi, you should fill to about 70 or 75 cold.
As the tire warms up, the actual pressure will increase.
Often explained as Boyles law, that's actually not correct. Boyles law is more concerned with pressure, though the two are related.
It's actually Charles law which lays out the relationship of temperature and volume, and it can be stated, simply, that most gasses have a direct relationhip between volume and temp.
Increasing temp results in an increase in volume.
If you set the pressure at 80psi, cold, then you can bet it's going to be closer to 90 at actual road temps.
I'd suggest slightly lower, and let them come up to the desired pressure/temp/volume during driving.

Just my humble opinion. My background was engineering, though I don't use it much anymore:)

anthony

For the other engineers out there:

Charles's law (also known as the law of volumes) is an experimental gas law which describes how gases tend to expand when heated. A modern statement of Charles's law is:
The volume of a given mass of an ideal gas is directly proportional to its temperature on the absolute temperature scale (in Kelvin) if pressure and the amount of gas remain constant; that is, the volume of the gas increases or decreases by the same factor as its temperature.
This law explains how a gas expands as the temperature increases; conversely, a decrease in temperature will lead to a decrease in volume. For comparing the same substance under two different sets of conditions, the as absolute temperature increases, the volume of the gas also increases in proportion. The law was named after scientist Jacques Charles, who formulated the original law in his unpublished work from the 1780s.

I guess what people are saying is that the tire is engineered with the knowledge of the fact that the 80 psi cold will turn into 90 psi hot and that's OK.

Actually, at least in my opinion, if you want to run the tires at 80psi, you should fill to about 70 or 75 cold.
As the tire warms up, the actual pressure will increase.
Often explained as Boyles law, that's actually not correct. Boyles law is more concerned with pressure, though the two are related.
It's actually Charles law which lays out the relationship of temperature and volume, and it can be stated, simply, that most gasses have a direct relationhip between volume and temp.
Increasing temp results in an increase in volume.
If you set the pressure at 80psi, cold, then you can bet it's going to be closer to 90 at actual road temps.
I'd suggest slightly lower, and let them come up to the desired pressure/temp/volume during driving.

Just my humble opinion. My background was engineering, though I don't use it much anymore:)

anthony

For the other engineers out there:

Charles's law (also known as the law of volumes) is an experimental gas law which describes how gases tend to expand when heated. A modern statement of Charles's law is:
The volume of a given mass of an ideal gas is directly proportional to its temperature on the absolute temperature scale (in Kelvin) if pressure and the amount of gas remain constant; that is, the volume of the gas increases or decreases by the same factor as its temperature.
This law explains how a gas expands as the temperature increases; conversely, a decrease in temperature will lead to a decrease in volume. For comparing the same substance under two different sets of conditions, the as absolute temperature increases, the volume of the gas also increases in proportion. The law was named after scientist Jacques Charles, who formulated the original law in his unpublished work from the 1780s.