Just put on a set of Goodyear Silent Armor 285/70/17 in load D...what air pressure should I be running. The tire shop first put 35lbs in until I told them to bump it to around 50lbs. So right now I'm sitting at 50lbs but wondering if 40-45lbs would be better. They have a max of 65lbs. Thanks,

 

Not sure what you should be running. I run my Kelly TSRs (Good year similar to dura tracs) at 36 front 42 rear on my Expedition. I calculated this based on vehicle weights, versus max tire load, and pressures. I ran these numbers by an application's engineer at Kelly and they agreed. A good way to test for correct pressure is the chalk test. I attached a link below that discusses this. It also conatins math similar to what I used.

http://www.jeepforum.com/forum/f9/ti...-bfg-s-478109/

 

Those tires have a fairly decent load rating (3195# at 65). I would run them at 40. Maybe go to 45 if towing or carrying heavy. I would never go below 38.

 

chalk test x2

 

I have those tires, been maintaining 40psi for 5 yrs and zero problems. I actually think 40 is the highest you'd want to go for regular use.

 

BRAVO!!

The absolute best tire pressure response I honeslty believe I've ever seen. Guys are always quick to throw out a number or what you should or shouldn't do, but finally an approach that is spot on.

dkstone05, that 65 psi is the pressure you want to run when that tire is carying the weight it's stamped for; in your case 3,195 lbs. That means that tire is able to handle an axle weight of 6,300 lbs...your whole truck doesn't weigh that much. If you're applying 50-60% of that tires capability to it, there's no reason to run a pressure designed for 100%.

At least you have D's. When ever someone ask this question with E's, the response always seems to be "no less than 45 no matter what"...I don't get it?? I have E's, and based off my estimated axle weights, I use the same philosophy as Glen R; I run 42F and 36R (empty bed). My tires wear completely even, truck rides and handles flawlessly.

 

That number partly comes from doing the math, partly from the Federal Govt, and the partly from Ford.

Most LR E tires with a max of 80 have a max weight at that PSI of 3200 to 3600lbs, meaning at 40, at best they can handle 1600 to 1800 lbs. The GAWR of a 04 up F150 is normally around 4000lbs for the rear. At 40 those tires do not come close to that.

Second, the Fed reg for TPMS setups state that the the sensors should set a low pressure at 46psi.

http://www.nhtsa.gov/cars/rules/ruli...ule.html?name=
See the table about 1/4 the way down the page.


Finally, Ford does put LR E max 80 tires on some of the F150s. The recommended pressure for those trucks is 50psi.

As always there are some exceptions. There are a few LR E max 80 tires that have a max weight up around 4000lbs. On those I recommend a lower pressure, but not lower than 40. There are also LR E tire with a max of 65psi.
These require a different pressure on the F150.

There is no great problem finding a good tire pressure if you do the math.

PS - Using the chalk method I have seen people state they ended up with a pressure of 30-35 with a LR E max 80 tire. Very unsafe and an accident waiting to happen.

 

That's a ridiculous tire!! No idea why you'd ever need or want a tire like that on a 1/2 ton truck.

But curious...what exactly is the danger? Using your example tire, that's an axle capability of 8,000 lbs! No F150 I know is ever going to see that. If we play the percentages game; running 35 psi is 44% of the max. 44% of the weight capability is 1,760 lbs, or 3,520 lbs for the axle. A rear axle of an unloaded F150 is never going to weigh that much, nor is many loaded ones. I'm not arguing or disagreeing, I'm just very curious to know what the danger is? What would possibly happen? Cause I'd argue that tire is not overloaded nor will it run hot enough to ever create a safety concern in that configuration.

I'd argue that if it's such a safety concern as you make it out to be, then for nothing other than liability reasons some of these tire manufacturers better start putting a minimum pressure on the side; something I've personally never seen.

 

You would go at least 40 as the rear is rated at 4k. Also how many people do you know that because they loaded something in their truck they add air. I would be willing to bet that you don't add air just because you are hauling something. Have seen many trucks haul junk and the rear tires are near flat from the weight.
It is far easier to run what they should be and be safe.
I ran a set of LR E max 80psi BFG All Terrains on a 98 F150 for 40k and traded the truck in with them on and still plenty of tread using 50 psi all around. No excessive wear at all.

As far as a minimum pressure, there is know way to tell what it should be. If a P series on an F150 minimum should be 35, while it should not even be used on a super duty. A LR E max 80 in general would have a lower minimum when used on an F150 than if used on an F250 or 350.
That is partly what the Feds are trying with the TPMS, that and letting the GP a chance of checking before it gets too dangerous. Although the smart people check at least occasionally.

 

...and you would loose that bet. I absolutely do just that. Why? because I know where my tire pressure is and where it needs to be when loaded up. I like the way the truck rides and handles using my percentage methodology instead of bouncing around all over the place with a super light rear end and overinflated tires for no reason.

You still never answered my question about what the dangers are and what makes it so drastically unsafe.

 

Too low a pressure causes the tire to build heat, especially at highway speeds.. This will eventually cause tire failure, including blowouts, tread separation etc. Just look up about the Explorer and Firestone tires. The tires were under inflated by just a few psi.

Also at 40, the tire I mentioned would not be overinflated. It would not be squirrelly like an under inflated tire due to sidewall flex.

 

Another area of concern with too low a pressure would be bead seating. Although this would be a lot lower than we are discussing, and at lower pressures you lose teh internal pressure forcing teh bead against the sealing surface. This becomes worse with wider wheels narrower tires. With my 9" wide wheels and 285/ 70 s they have to use a tank bead sealer to set the bead.

 

Lots of information posted here. I checked my tires this morning and they were at 46psi...not the 50psi the shop put in. However the air temperature when installed was around 45 degrees and this morning it was 32 degrees. So I guess this explains the 4 psi difference but the shop uses nitrogen and I thought that nitrogen wasn't supposed the change that much with air temperature?

Anyway for giggles I took them down to 44 psi just to see what would happen on my 20 mile commute to work. Once I got to work they were just a shade under 50psi after the 20 mile hwy drive.

I'll try the chalk line as soon as I can but for the time being I'll stick to 40lbs to 45lbs. I don't plan on having to air up when I have to haul something...unless it is real heavy or making a longer trip than around town with a load.

If used the calculations I think I would be in the mid 30's psi but this is very rough as I'm not sure of the weight of my truck let alone weight per axle. I think I feel more comfortable with a minimum of 40-45psi for an general air pressure with out needing to air up for loads as an air compressor isn't always easily accessible. This unless I see excess wear in the center.

 

What tires do you have, max psi, max load at that psi, etc?

 

Too early in the morning....I'm the OP