Truck tire pressure

[SPYDERLK]

Sorry to have to correct some misinformation here, but the EPA now pretty much sets the required pressure in all car and truck tires because of rolling resistance (fuel economy) demands. Requirements are set by a coast-down test which is then used to recreate the roadway conditions on a chassis dynomometer.

Stopping distance effects are not an issue because the tire construction recipe is then established by the tire manufacturer in order to meet dry, wet and sometimes snow traction requirements of the tire for braking and traction in order to meet MVSS105 stopping distance requirements.

The thing is, all of these parameters interact to affect rolling resistance. Hi traction tires have higher rolling resistance because they use a higher hysteresis rubber to improve traction. This has the effect of making the tire act like its always rolling up hill. Then I guess they crank up pressure to help offset it ... but that causes ever intensified pressure on the contracting contact patch resulting in tread heating. A mess of interelated factors.
larry

 

[pat32rf]

I was taught that (except for special performance vehicles) everything designed into a vehicle is a compromise aimed at what the general buyer wants in THAT vehicle at the best cost to the producer.
The OEM tires are the best choice for GENERAL usage. If your perceived needs are different, then you might want a different tire. The same applies to the pillar pressure.
I've run 4X4's on huge tires simply for the floatation they offered. At 12psi they still had a perfect profile, but EACH tire was rated to carry 75% of the total vehicle weight at the sidewall pressure. At sidewall pressure the 12" wide tire put 2" of rubber on the pavement.
My Dodge 1/2ton with OEM tires, but heavy suspension needed to be within 5psi of sidewall or they looked flat with NO LOAD. The truck rode like it had 12 ply tires. Now I have BFG's, I can run a little less psi, get a much better ride and traction, then load it up with 1000lbs and the profile doesn't change noticeably. When it does change, due to more weight, then I add more air....The oem tires looked flat at sidewall pressure if I had a load on, and the performance was just plain squirrely...

 

[ModMech]

Sorry to have to correct some misinformation here, but the EPA now pretty much sets the required pressure in all car and truck tires because of rolling resistance (fuel economy) demands. Requirements are set by a coast-down test which is then used to recreate the roadway conditions on a chassis dynomometer.

I am calling 'bs' on that.....

Just the facts folks....

1993 Grand Marquis = 32 psi
1999 Crown Vic = 32/35 psi
2004 Grand Marquis = 32/35 psi
2011 Fusion = 33 psi

Now, the technical details are: the '93 and '04 have "standard" passenger tires are within 300# of the same dry weight with full-sized spares. The '99 had performance tires, Z-rated in fact and I know for a FACT that GY does not endorse 35 PSI inflation pressures on that tire model! The Fusion is by far the lightest of the four and has Michelin XL tires for whatever reason with a sidewall rating of 51 PSI.

If the EPA had anything to do with requiring, mandating or pushing for greater inflation pressure it seems obvious that the Fusion would have a sticker pressure substantially higher than the '93, '99 or '04 cars. This especially given that the tire can take an "extra" 20 psi.

I would agree that the OEMs are pressured to increase suggested inflation to reduce rolling resistance and hence increase CAFE numbers, but that pressure is systemic and not directive as suggested.

 

[oldyellr]

It is my experience that OEM tires are not the absolute best available at all. They certainly aren't the worst choice and you could do a lot worse, but if you research you can do a lot better too.

Very true. It used to be widely known that manufacturers would buy their OEM tires from the lowest bidder, often at well below cost. The tire manufacturer would them be assured of future sales of replacement tires, where they made the big profits.

 

[ModMech]

Very true. It used to be widely known that manufacturers would buy their OEM tires from the lowest bidder, often at well below cost. The tire manufacturer would them be assured of future sales of replacement tires, where they made the big profits.

Correct, as an anecdotal example.....

Our '08 Taurus got 24k miles from the first set of tires and the second set, dealer installed BTW were no where near worn out after an additional 40k miles of driving. Hmmm.

I am sure that if I checked TireRack I would find out that the tires on our new Fusion should have 2 or 3 32ndths more rubber than they actually have.

 

[TheTrailerGuy]

It's the thread that won't die... someone drive a stake through it's heart... shoot it with a silver bullet.