Truck tire pressure

[Marveltone]

I hear what you are saying about ford lowering the door pressure, and im sure that was a big contributing factor but it isnt the whole story... Firestones tires were especially prone to tread separation which was possibly due to the run being made during a labor strike at the plant. Faulty tires played a roll as well which is why a bagillion were recalled and exchanged. If it were all an air pressure issue then why didnt they release a tsb with an air pressure change. Fact is it was a muddy situation noone wanted resposibilty for, but to use that as an example to tell people not to follow door recommendations is rediculous. Use common sense when loading your vehicle heavy, calculate the load and add air over the spec if nessesary.

I also heard that it was almost always the same side that failed. Apparently, there were three factors involved. 1. Firestone had a faulty batch of tires that were produced during a strike. 2. Ford posted an absurdly low inflation pressure on the pillar. 3. The tire that blew was very close to the exhaust, which added to the heat generated by the under-inflated, faulty, overloaded tire.

Three strikes, you're out!

That being said, I never run OEM tires, and as such, there is no way the vehicle manufaturer can know what I'm running on. Therefore, I look at the maximun load rating and pressure of the tires. Check the pressure cold and adjust according to the load. This is done purely by load estimation, as I live at least two solar systems away from the nearest scale. Empty usually equates to about 80% max pressure. When my tires eventually wear out, they almost always do so very evenly across the tread.

Joe

 

[TheTrailerGuy]

I'd never inflate past tire sidewall specs

Agreed. ALWAYS go by the tire and YES the recommend max inflation pressure is the RECOMMENDED pressure at all times. If the tire says 44lbs, put at 44lbs and keep it there.

Thanks
Craig
TheTrailerGuy
Stateline Trailers

 

[arsenix2001]

Agreed. ALWAYS go by the tire and YES the recommend max inflation pressure is the RECOMMENDED pressure at all times. If the tire says 44lbs, put at 44lbs and keep it there.

Thanks
Craig
TheTrailerGuy
Stateline Trailers

LOL really? I have to respectfully disagree I can see that for a trailer on max load but why in the name of god would you inflate to max rating on a vehicle. Most of the time the max rating on tires far exceeds the gvwr of the vehicle. I guess all the auto manufactures are stupid when they build a car, pick tires for it and then i guess they what, throw darts at a dartboard to pick inflation pressure?

 

[JasG]

I hear what you are saying about ford lowering the door pressure, and im sure that was a big contributing factor but it isnt the whole story... Firestones tires were especially prone to tread separation which was possibly due to the run being made during a labor strike at the plant. Faulty tires played a roll as well which is why a bagillion were recalled and exchanged. If it were all an air pressure issue then why didnt they release a tsb with an air pressure change. Fact is it was a muddy situation noone wanted resposibilty for, but to use that as an example to tell people not to follow door recommendations is rediculous. Use common sense when loading your vehicle heavy, calculate the load and add air over the spec if nessesary.

The tires could come standard on F-150's, Chevy 1500's, Explorers, and Blazers at the time. The only vehicle that had a problem was the Explorer. Which was the only one with the 28 PSI rating. There may have been a bad batch of tires, but the problem was documented over several years. I would think more than one batch was involved. There was also some claim that a layer was missing that firestone didn't put in the tire and a lot of finger pointing. I would bet, had the rating been 32-34 PSI, the issue probably never would have happened. Had Ford issued a update and change the air rating, they would have been admitting fault. Which would have left them wide open to class action suits.

I'm not saying don't follow the OEM, what I am saying is use common sense and reason, and don't take the door sticker as set in stone. Dealers can and do swap tires, so the tires the vehicle left the factory with, may not be the ones the sticker applies to. In the case of Ford, they were recommending a pressure, about 15-20% below the pressure on the side wall. So I think this is the perfect example of why to question the door panel.

 

[TheTrailerGuy]

LOL really? I have to respectfully disagree I can see that for a trailer on max load but why in the name of god would you inflate to max rating on a vehicle. Most of the time the max rating on tires far exceeds the gvwr of the vehicle. I guess all the auto manufactures are stupid when they build a car, pick tires for it and then i guess they what, throw darts at a dartboard to pick inflation pressure?

I'm not trying to argue, but unless all of the tire store owners, factory tire reps and everyone else were all full of it. They contended to me the maximum inflated pressure was also the OPTIMUM pressure to run that tire at for durability and mileage, for both the tire and fuel.

End of story. Said what i was always told to be true. Take it or leave it at that.

 

[ModMech]

I'm going to ask what should be an obvious question...do I go by the tire pressure rating inside the door panel of my truck, or do I go by the rating on the tire itself? The door rating says 32 front/35 rear, the tires say 44lbs max cold. Since that's a difference of nearly 10lbs I'm kind of curious as to what number should be used, mostly for fuel savings and to prevent premature wear on the tires. I bought the truck used so I'm not sure if the tires are factory or not (they appear fairly new and the truck has less than 20k miles on it).

I try not to ask dumb questions but since this truck is not very kind on the wallet at the gas pump, I want to squeeze as much mpg out of it as I can, but I don't want to over or under inflate the tires.

Thanks.

VERY wise question!

Unless the tires on the vehicle are the ones it was BORN WITH, the pillar chart is WORTHLESS (I would argue it is worthless in any event, re: Explorer).

What inflation pressure do I need? That's a loaded question and is deterined by data that is difficult to obtain for automotive tires. To KNOW the correct inflation pressure for ANY tire you need three things:

1) The tire manufacturer's "load inflation chart" that covers the EXACT TIRE MODEL you are using
2) The LOAD on the tire (or axle/2 on the rear of a SRW truck and axle/4 for DRW)
3) The SPEED you will be driving

Items 2 & 3 are relatively "easy", but #1 is very challenging unless you happen to have an awesome tire dealer that actually does their job!

In ANY event, you are UNSAFE if the measure inflation pressure is less than 75% of the "COLD MAX" embossed on the sidewall.

Heat is the enemy, low inflation, high speed and high load all INCREASE HEAT.

BTW, this is a "trick" question.... What is the PRIMARY deciding factor in the pressures listed on the pillar charts supplied by the OEM?
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NVH - Noise, Vibration and Harshness. aka, Ride "quality". I for one, do not consider it to be good ride quality when you flip onto the roof because the tire failed from under inflation by the TIRE manufacturer's recomendations.

 

[ModMech]

Wonder if all those folks with the Explorers and exploding Firestone tires followed the door tag for inflation pressure?:

Probably had a very nice ride till they heard the bang.

If one researches carefully, it was discovered that Ford demanded Firestone supply the tires with one belt LESS than Firestone engineers suggested (4 vs 5 as I recall) for the inflation pressures FORD wanted to use.

The Firestone folks were trying to do the right thing, more belts = stronger tire. But when you run tires very low on air, about 50% of the sidewall "MAX COLD", you are well into the danger zone regardless.

Add to that the fact the the highway speeds increased 15-20 MPH from the time the vehicles were built to the first failures and we can see it was a failure caused by multiple factors.

In the final analysis, I do not *believe* Firestone got a fair shake, nor that Ford was responsible either. Operator's need to be aware of many factors and not to ignore basic maintenance practices and routine checks.

BTW, OSHA rules are that any tire inflated to "less than 80%" is considered "underinflated" and MUST be dismounted for repair and reinflated in a CAGE. The devil is in the details of those OSHA regs, no where is it established what the basis for the 80% rule is. Is it the "MAX COLD", "OEM inflation sticker", or the Tire Mfgr "load inflation table"? I have always concluded that it MUST BE based upon the Tire Mfgrs L-I tables or nearly every car, truck and SUV leaves the factory in voilation of the OSHA rules.

 

[zzvyb6]

Here are the simple facts from a vehicle manufacturer engineer in the tire and ride and handling field: ME.

The door placard pressure label has the set of front and rear pressures that represent the overall best compromise for ride, fuel economy, durability, treadwear, comfort and handling. For GVW and trailering loads, alternate pressures are usually listed. These pressure recommendations are for the size(s) listed on the placard. Tires are given a max pressure rating by the tire manufacturer based on Tire & Rim Association (T&RA) design guidelines for a load vs. size range. The tires themselves are actually good to hold up under many more times this pressure. You could probably put 100 psi into a tire without anything happening. That's because we know that there are some people out there who put air in until the compressor stalls, or because the regulator is cranked up, that's line pressure. This is called foreseeable misuse and has been reviewed by all our lawyers as well as trial (plaintiff) lawyers.


When you put tires on of a different size (both up and down), you need to reexamine the useage pressure. There's actually not much point in putting larger tires on a vehicle except for looks because the driveline, brakes, springs and shocks will be the same. OK bring on all the "expurts" who think they know better. I've written a few SAE papers on this and been on SAE committies and been in courtrooms for this, too. What are your qualifications?

FYI, though, I routinely put 45 psi aire pressure in my tires because I want a different set of compromises to be biased towards fuel economy and tire wear. Ride and handling are diminished and I accept that. When the centers wear out, I replace them with the same size tires.

In the case of the Ford Explorer, the desire was to have superior ride over Chevy and Chrysler and Toyota when they had a leaf spring disadvantage and that was done by a pressure released at 26 psi. A tire design change to give better fuel economy compromised tire durability when the pressure dropped to well below 26 psi. That's a common problem with tires. It's called "permiability" and amounts to how much leakdown per month or year occurs because air molecules pass through the carcass materials. That's why you find your spare tire flat if its not checked regularly: In 3 years a tire naturally goes down to about 1/2 its installed pressure. In the Ford case, customers who never checked their tires started out at 26 cold and bled down to below 20. They got hot and a tread sep. occurred. Note that GM had a tire pressure monitoring system based on the ABS sensors which counted wheel revs. When a tire showed an abvnormal wheel rev increase, it was probably going flat. But it couldn't tell what the average pressures were. Nope the govt' demanded radio sensors in the wheels to report out actual pressure at all times at a huge cost for design, manufactire installation and replacement burden.

So that's the real story. BTW, don't fall for the nitrogen in your tire scam. In 6 months the permiability leaks the excess nitrogen out and lets the standard atmospheric chemical brew rebalance to your local mixture. Yes NASCAR uses straight nitrogen for a number or reasons (air guns run better as well), but I don't know of any of you from my NASCAR Team support days. I dougbt whether you could pass a blind test experiment to judge the difference in a set of tires. (Actually a few teams run carbon dioxide in their tires. Can you explain why???) I can !

 

[ModMech]

^^^^ Yup, yup.

Nitrogen is used in Aviation and racing for one reason and one reason only, it is DRY Nitrogen. Having NO moisture in the tire helps with corosion of the wheel (aircraft) and pressure changes are more predictable w/o moisture as a factor.

The delta in the leakage rate between N2 and air is so meaningless as to be a pointless discussion for automotive uses.

 

[oldyellr]

I'm not trying to argue, but unless all of the tire store owners, factory tire reps and everyone else were all full of it. They contended to me the maximum inflated pressure was also the OPTIMUM pressure to run that tire at for durability and mileage, for both the tire and fuel.

End of story. Said what i was always told to be true. Take it or leave it at that.

No, you're not trying to argue, much less debate. You're merely repeating what you've heard as if it were fact. Since you're TheTrailerGuy I'm assuming a lot of your experience pertains to trailers. All my life I've seen U-Haul rental trailers with big signs on the fenders like "Inflate tires to 60 psi" or something like that. That's if you're hauling the trailer empty or loaded to maximum. The reason is that U-Haul doesn't want to see a tire fail from underinflation. They don't really care if the trailer bounces and rattles when empty or if the tires wear out the centre of the tread from overinflation because they'll probably die of old age before that.

However, this thread is about truck tires. "Trucks" can be a variety of vehicles. If you drive one of those yuppie Porsche Cayenne SUVs, don't want to be inflating your tires to the maximum sidewall number because some redneck in a Ford pickup will be able to outdrive you as you go skittering off into the weeds on a twisty road. Generally, trucks used for personal transportation carrying just the driver should have their tires inflated to the door jamb pressures for best comfort and roadholding. 18-wheelers, however, would probably run the maximum sidewall pressure just to be safe. If they're never carrying a load, they should be in a different line of work.