Picking tire pressure help

[RayH]

First you need to know what your vehicle weighs on each axle then look at the manufactures tire chart and adjust your psi accordingly.

And no you are not into a semi psi range...100 - 125 for my 22.5 lo pro on my Pete.

Exactly, the vehicle manufacturer helps you by putting a sticker in the door jamb. They have already weighed your vehicle so they know the proper PSI.

 

[jayhaitch]

100-125 psi for semis? OK, so I was little off How long does it take to fill up an empty semi tire? Me thinks my air compressor would wilt at the thought.

RayH: I understand your point: do what the factory says. But as I said, Ford spec'd P-series tires, evidently for soft on road ride and mileage. This is a half ton, not 3/4 ton. It's an F150 chassis, shorter but heavier. Curb weight is ~5400 lbs, so with me, a load, full tank, etc, I'm sure it's around 5900 lbs. But that's still only 1475 lbs per tire. At 80 psi, the sidewall says the ProComp All Terrains will hold 3195 lbs. No way should I approach 80 psi with my current loads.

Now, as an LT tire, and especially load range E, it's got a much stiffer sidewall and more tread belts. So I've got to increase the pressure from that of the P series. Thanks John Bud and Bird for reminding me about heat and side wall blowouts. I've never had a heat blow out. I've ran over nails, and had a slow leaking tire come off the rim hitting a snow rut in -30C weather, but never a high speed sidewall blow out, thank the Lord.

Wushaw: the Pro Comp web site doesn't have any chart for varying psi for varying loads. Is this something common in the OTR trucking world?

I've noticed a bit worse mileage on my trip computer since the tire changeover, plus the more rapid deceleration, so I agree 45 psi is too low. That's what got me thinking I needed to request the expertise of my TBN knowledgeable compatriots.

I'll try 60 psi, and see what happens.

I'm getting this vehicle ready for a 7.5hr trip in Sept. Four guys, a full load of gear. Driving to Thompson Manitoba (55.8 deg N latitude) then flying 3.5 hrs in a float plain to a hunting/fishing camp on the border of Nunavut and Manitoba. Caribou hunting. The trip of a lifetime!

Thanks everyone for your help.

 

[RayH]

You shouldnt be so quick to assume your mileage has decreased.
You went up in tire size, Im assuming you havent changed speedo gears, so the trucks computer doesnt know exactly how far youve gone now. Example, if you increased tire circumference by 10%, your speeoometer and odometer will be off by 10%. If it says youve traveled 100 miles, youve actually traveled 110 miles. Your computer knows your burning X amount of fuel in a given time but you are traveling further in that time than it thinks you are.

 

[jayhaitch]

I bought the same size tire as OEM. Original tire: P265/70-17 Goodyear RT/S. New tire: LT265/70-17 Pro Comp All Terrain. Speedo is reading the same.

 

[RobertN]

Bird,

Could you comment on air pressure vs rims? I seem to remember you talking about this before; putting E tires on rims rated for C tires, with rim failure from higher pressure.

I think it was a discussion on RV/5th wheel rims/tires.

It's been over 15 years now, so maybe some things have changed but . . . . this appears to be an old story.

Back about 15-16 years ago, some GM 3/4 ton vehicles, especially 4WD Suburbans and pickups came out with Uniroyal Load Range E tires, with 80 psi on the sidewall. But the sticker on the door post recommended as low as 45 psi. Well, a number of those tires developed "bubbles" when the rubber separated from the cords. Uniroyal did warranty them, and we replaced a few under warranty, but they also said, at that time, that it was GM's fault; that you should NEVER run highway tires lower than 80% of the maximum listed on the sidewall; i.e., if the sidewall says 80 psi, never go below 64 psi.

I still follow that rule; your mileage may vary.

 

[RayH]

I bought the same size tire as OEM. Original tire: P265/70-17 Goodyear RT/S. New tire: LT265/70-17 Pro Comp All Terrain. Speedo is reading the same.

My mistake, I thought you had gone bigger in size.

 

[wushaw]

Jay here is Goodyears website on tire pressures and weights. It is not just big truck tires. And it depends upon which semi tire you have, it takes me longer to fill my rear tractor tires than it does to fill my 22.5 lo pro tires.

The vehicle manufacture sticker on the door jamb is a good place to start with the weight of the vehicle but a CAT scale will tell you exactly what it is.

http://www.goodyear.com/truck/pdf/databook/5113_Lsec_V.pdf

 

[Flywheel]

Jay here is Goodyears website on tire pressures and weights. It is not just big truck tires. And it depends upon which semi tire you have, it takes me longer to fill my rear tractor tires than it does to fill my 22.5 lo pro tires.

The vehicle manufacture sticker on the door jamb is a good place to start with the weight of the vehicle but a CAT scale will tell you exactly what it is.

http://www.goodyear.com/truck/pdf/databook/5113_Lsec_V.pdf

Yep - follow Wushaws advice.

weigh your axles and check the charts - then fill accordingly - remember to add about 10psi to the number for sustained high travel at 65plus.

Start with the chart plus the 10psi - these are the minimum pressures - then adjust up for comfort and control. I tend to like mine on the tight - maybe a little rough (still talkin' tires here) side.

You can throw out the recommended tire pressure on the door jamb now - and most rims can likely take the 80psi - if you ever need that. - you'll lprolly be ok between 55 - 65ps - prolly equal all the way around - unless your going to tow heavy - then bump the rears.

 

[jayhaitch]

Here's a follow up.

I weighed my Expedition on a truck scale: 2954 lbs front, 2825 rear, 5801 lbs total with full tank, otherwise empty.

Expedition front GAWR: 3500 lbs, or 1750 lbs per tire.
Expedition rear GAWR: 4128 lbs, or 2064 lbs. per tire.

In looking at the Goodyear tire chart (excellent resource, thanks!) LT265/70-17 single axle have a load rating of 1890 lbs at 35 psi, 2075 lbs at 40 psi. If I add 10 psi for 66-75 mph driving, I'm at 45 psi front, 50 rear, to reach GAWR's.

Now this chart has no load range E LT265/70-17 tires, only load range C. I'll need to run E's at higher psi due to stiffer construction with more plys. Even with load range C, at 50 psi the load rating is 2470 lbs per tire, or more than my GAWR's. So if I bump things a bit higher than this for the E plys, I've been using 55 psi all around. So far so good, but it's only been around 2000 miles.

I go on my caribou hunting trip in 2 days. I'll put another 1000 miles on in the next week, carrying a full load of guys and gear. I'll post back when I've returned.

 

[Rara Avis]

Here's a follow up.

I weighed my Expedition on a truck scale: 2954 lbs front, 2825 rear, 5801 lbs total with full tank, otherwise empty.

Expedition front GAWR: 3500 lbs, or 1750 lbs per tire.
Expedition rear GAWR: 4128 lbs, or 2064 lbs. per tire.

In looking at the Goodyear tire chart (excellent resource, thanks!) LT265/70-17 single axle have a load rating of 1890 lbs at 35 psi, 2075 lbs at 40 psi. If I add 10 psi for 66-75 mph driving, I'm at 45 psi front, 50 rear, to reach GAWR's.

Now this chart has no load range E LT265/70-17 tires, only load range C. I'll need to run E's at higher psi due to stiffer construction with more plys. Even with load range C, at 50 psi the load rating is 2470 lbs per tire, or more than my GAWR's. So if I bump things a bit higher than this for the E plys, I've been using 55 psi all around. So far so good, but it's only been around 2000 miles.

I go on my caribou hunting trip in 2 days. I'll put another 1000 miles on in the next week, carrying a full load of guys and gear. I'll post back when I've returned.

If you will be doing alot of offroading...then read the following...
Beefing Up Older Axles: Upgrade 'Em or Break 'Em - Ford at Off-Road.com