12 Inch Tire Pressure

[littlecar]

Pu241...I just say what I know. Not trying to come across as anything, let alone a know it all. I think a run down would be good, I'll try to write something up by the weekend and PM it to for your opinion if you'd like.

Let me know.

[Pu241]

That would be appreciated!
I'm not the final say on what is a good writeup or not.
Please rough it out or refine it as much as you like, then post it under a new thread and let the member ship make suggestions and ask questions.
Then update it as you see fit for a second round to get all of the detail needed for new member as well as old.
Then we can re-post it as a sticky or maybe an article depending upon how it ends up!
Fair enough?

[jrbauerjr]

Tire Pressure

Just a couple of additions.

Why I would ask such a silly question if I know everything...

Because I didn't want to take the time to weigh the axle loads as I don't own a thousand pound scale........

Secondly, while I don't hold myself out to be the absolute authority on tire pressures or tires, I will defer to someone that is...

From the National Highway Traffic Safety Administration, those people who are responsible for writing the regulaions:
__________________________________________________ _______________
Understanding Tire Pressure and Load Limits
Tire inflation pressure is the level of air in the tire that provides it with load-carrying capacity and affects the overall performance of the vehicle. The tire inflation pressure is a number that indicates the amount of air pressure– measured in pounds per square inch (psi)–a tire requires to be properly inflated. (You will also find this number on the vehicle information placard expressed in kilopascals (kPa), which is the metric measure used internationally.)

Manufacturers of passenger vehicles and light trucks determine this number based on the vehicle's design load limit, that is, the greatest amount of weight a vehicle can safely carry and the vehicle's tire size.The proper tire pressure for your vehicle is referred to as the "recommended cold inflation pressure."

Remember, the correct pressure for your tire is what the vehicle manufacturer has listed on the placard, NOT what is listed on the tire itself.

Because tires are designed to be used on more than one type of vehicle, tire manufacturers list the "maximum permissible inflation pressure" on the tire sidewall. This number is the greatest amount of air pressure that should ever be put in the tire under normal driving conditions.
__________________________________________________ _______________

[Pu241]

NTHSA - Are those the same people who permited the underinflation of Firestone tires on various SUV's to provide a better ride?
Or was that a manufacturing issue with either Firstone or the vehical maker?

Re-reading it, exactly how does the above NTHSA pronouncement tell us what is the "recommended cold inflation pressure?"
Because few of us are actually running the 145 80 12's or 165 70 12's that are OEM equipment.
Do you still use the placard specs when running 155 80 12's?
What should it be when running 13's or even 14's or 15's of various width's and profiles?

[festyxfi]

I run 45 PSI all the time. It's a rough(er) ride, but awesome MPG.

Helps to have LX seats.

[milehighbear]

bhazard, i hope you know what year those tires were made if your running 50psi in them and they are not too old

[jrbauerjr]

Inflation Guide

Well PU241,

Just on the off chance that you really are interested, here is a reference published by Toyo that will take you through the steps of recalculating the manufacturer's recommended tire size pressures to a replacement size pressure....

http://marktg.toyotires.com/file/loadinflationtable.pdf

Comparable data is available from all tire manufacturers.

By the way, most of the Ford accident investigations seemed to indicate that the vehicle owners weren't bothering to make sure that their under tired vehicles were even maintained to the recommended pressures..


Happy reading,

Jim Bauer

[Safety Guy]

I have read somewhere long ago that back in the eighties and maybe early nineties, car manufacturers preferred to recommend inflation pressures which made their cars ride softer for comfort, instead of recommending harder pressures for better handling and mpgs.

More modern cars should have recommended pressures that are more economical and not so "luxurious."

I don't exceed the sidewall pressure of my tires, but I do run them at around 32 to 35 psi. My new 155/80-12 National Metric tires are rated at 35 max. I have them at 33 now. For my 175/70-13 Nokians, however, I've gone up to 36 or so, since their limit is higher (at 45 psi, IIRC).

Karl

[Levitan]

I use to own a tire shop in the early '90's. That being said I refuse to be labeled a know it all and the things mentioned in my post are strictly MY opinion.

I think most of us can agree that everything is about the all mighty dollar. For example, seat belt laws. I don't think for one second that lawmakers really care about saving lives as much as they like the police to hand out thousands of $93 no-seatbelt-tickets daily.

Anyways, remember, the placard inside the car is issued by the company that is trying to SELL you a car.

I would bet a dollar to a donut that if you do "proper" vehicle requested tire pressure and rotations, when you do a tread depth test across the tread, you will find that the edges have worn more than the center. You will have lost money in gas mileage and tire wear, but will have gotten a better ride.

Same bet. Using a tire with a max psi of 35psi. You fill your tires to 35psi, cold, and rotate properly. I guarantee you will see better tread wear and better gas mileage, thus saving money. You will sacrifice a little on the ride, but I don't think any of us bought a Festiva because it rides like a Caddy and handles like a Porsche.

To expand on this a little further. When looking at the tread of the tire, the center grooves, usually wrapping vertically around the circumference(sp?) of the tire are for traction on wet roads, preventing hydroplaning. The horizontal cuts on the edges are for traction. ANd the little cuts, known as sipes(I believe thats the name), are for traction on ice. Using my above tests, wearing the edges down due to under inflation per the placard, is more unsafe than putting the air pressure at the max cold inflation labeled on the tire.

I believe a tire is safer, evenly worn across the tread than a tire that has good tread in the middle and worn down on the edges.

This is where somebody will be a weisenheimer and go extreme and say, "well then, 50 psi is better! Or 60 or 70psi!" I never said that. If you over inflate, then you risk wearing the center tread down, thus causing hyroplaning.

Like somebody said, tires are tested for way more than 35psi...probably double that, so I don't think there is a safety issue 5 or 10 psi either way. Buy a tread depth gauge and monitor your results. If you typically run 32psi and you notice the front tires wearing down on the edges a bit, rotate the tires and bump the pressure up on the "new" fronts a couple psi, and monitor.

Notice I mentioned the fronts and not the rears. The rears don't really do much other than follow, so there shouldn't be much wear on the rears, unless you have a rear alignment problem.

Bet you find all tires wear differently and you start to see things going wrong with other suspension parts sooner, saving you money in the long run.

And isn't that why we really bought Festivas anyways!?

Strictly my opinion.

[Mike McKown]

[QUOTE=By the way, most of the Ford accident investigations seemed to indicate that the vehicle owners weren't bothering to make sure that their under tired vehicles were even maintained to the recommended pressures..



Most?

Under tired?

Recommended pressure? Do you know what it was?

Really?

Is this why they traced all these problems back to one Firestone plant in Illinois that had just had some labor problems?

[FB71]

By the way, most of the Ford accident investigations seemed to indicate that the vehicle owners weren't bothering to make sure that their under tired vehicles were even maintained to the recommended pressures..



Most?

Under tired?

Recommended pressure? Do you know what it was?

Really?

Is this why they traced all these problems back to one Firestone plant in Illinois that had just had some labor problems?

ok, I was a Ford Service Training Instructor during this investigation. Many of us STI were tapped for our expertise, to do some of the field investigation. We retrieved the tires from the vehicle, and examined all other aspects of the vehicle, if permitted (some were being investigated by local/state authorities). Here's the results as tabulated by NHTSA, and I concur, based on my experiences;

The tires that failed all came from one Firestone plant in IL, manufactured during a labor union strike. However, not all the tires from that plant at that time failed. The ones that failed were grossly underinflated, typically less than 20psi, many less than 15psi. Nearly all the failures occured in high temperatures/hot climates. The most catastophic failures occured on vehicles that were grossly overloaded, or operated at excessive speeds (in excess of 80 mph). One cited crash resulted in the death of three of the seven occupants in a 1998 Exporler Sport. Mind you now, both the 1998 Explorer and Explorer Sport only seat five people. Why were seven people in a vehicle that seated five? The vehicle also had about 500lbs of luggage strapped to the roof, and experienced tire failure at a highway speed in excess of 90mph. All of this was well documented by the investigating state police agency (Louisianna, I think).

Now, Ford did admit to one thing; asking Firestone to sign off on a lower tire pressure than orriginally recommended by Firestone. In 1989/90, when Ford was finallizing the Explorer, they aske Firestone to sign-off on 26psi rear/28psi front to improve ride quality. Firestone was adamant (reportedly) that they did not want the tire operated below 32psi. This was because that was the pressure the tire was tested and certified at. Eventually, they conceeded to the request, without retesting. This was because both Ford and Firestone engineers calculated that at 26psi, the ATX tire still had reserve load capacity. Basically, the tire could handle more weight than vehicle could place upon it. The Firestone ATX tire performed on the Explorer without significant incident from 1991 to 1998. 1998 saw about a 1000% increase in failures of the ATX tire, not on just the Explorer, but the Ranger, the F150, the Chevy Tahoe and GMC Yukon. The reason the other vehicles did not receive as much attention was because they were optional tires on those vehicles, while the ATXs were standard on the Explorer. There were literally hundreds of thousands of ATX tires in service on Explorers, while there may have been about ten thousand ATX tires in service on each of the others.

The final result of the investigation revealed this; the Firestone plant in IL sat idle for 7-8 months during the labor dispute. When an impass was reached in negotiations, Firestone brought in non-union labor, in order to fulfill their contractual obligation to supply tires to the Ford SLAP (St. Louis Assembly Plant), where the Explorer was built. In the time the plant was idle, the vast quantities of steel wire that had been delivered to manufacture the steel belts, had sat outside, unprotected from the weather. What happens to bare steel when it sits outside in rain and weather for 8 months? Rust, of course! The wire was sent thru an acid bath to clean any surface corrosion from the wire, but this determined to be insufficient. The remaining embedded iron oxide acted like a barrier between the steel wire and the rubber of the tread. Basically, it's like trying to glue a patch of rubber to a dirty piece of steel. The glue adheres to the dirt, not the steel, and the rubber can be lifted off. This is what happened to the ATX tires.

I personally still have faith in Firestone products. The ATX tires were great, as were their Steeltechs. I had FR680s on my TBird, and they were indestructible. They wore like iron, gripped great dry, ok in wet.

Hope this helps clear up a few things.