Tire pressure confusion...

[jlsworks]

I have a 2001 SuperDuty, and with every oil change the dealer airs down the front tires to 45psi and puts the backs at 70psi (and documents this each time on the reciepts). When I purchased the truck (new 6000 miles ago)It had 60psi in all four, I figure from the Factory. I was always taught to run tires hard, so I put the recommended cold pressure of 80psi. (Firestone Steeltex R45, Load range E, LT265 75/R16) The ride was rock hard and the wheel practically is jarred loose going over these great roads out here in Oklahoma. I tried 70psi and finally settled in at 65psi, maintaining some comfort. I tow about 30% of the time.
What is the dealer doing? I'm afraid to ask. Who's responsible for tire failures if the dealer is maintaining them that way, Firestone or Ford?
Any opinions on tire pressures, I've never had this Load Range of tire before and I'm puzzled as to how to maintain them.
Thanks, James

[MECHANIC88115]

All the srw pickups I have had with 16 inch tires, I have alway run my tires at 40 front, and 60 rear. I know that this is not what is normally recomended, but I have found that this was the best combo between ride and hauling capability. Hope this helps, Mason

[gossamar]

I have been running 70-80 psi all the way around with my 265's since I got my truck 1.5 years ago without a problem. The wear pattern with 14,000 miles is also very good. I do keep them rotated every 5,000-6,000 miles, this is also a key thing to remember. I tend to follow the tire manufactures rating for pressure that is embeded on the tire. Granted this is for maximum loads, but I think that the vehicle manufactures post pressures that give the best ride, not what the tires was designed to be ran at. I don't really notice any difference in ride, but I do have the "X" springs, plus if I want to swing by and pick up a few thousand pounds of mulch, gravel, dirt, etc. I don't have to worry about the pressure. just my $.49-cents

[TRK4]

Look on sticker in door jam it will tell you the proper pressure for your tires.

If I remember right mine calls for 50 psi front and 70 rear

[V10man]

The stickers on the door jam list the tire pressures to achieve the rated loads (for stock tires). These tire pressures will work, but if you are empty they can give you a very hard ride. When I had my stock tires I ran ~50 in the front and 45 in the rear when empty.

It gets even more complicated if you go to an aftermarket tire. It is best to get the load rating tables (that list psi for a given load)from the tire manufacturer for the aftermarket tires that you are using.

[jlsworks]

Thanks for the input, sure enough the sticker on the door jamb says 45psi front & 70psi rears, go figure. That is still odd to me, never heard of such a thing.
Would love some technical feedback from Firestone/Ford to explain that. Thanks again, James

[Wayne B]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by jlsworks:
Thanks for the input, sure enough the sticker on the door jamb says 45psi front & 70psi rears, go figure. That is still odd to me, never heard of such a thing.
Would love some technical feedback from Firestone/Ford to explain that. Thanks again, James<HR></BLOCKQUOTE>

The wieght list on the door is for a loaded truck. I would air down the back tires to 55 psi when runnig empty. Firestone does have a chart for the Steel X. It goes by wieght, you do then have to go have your truck put on the scale so you know the axle wait.
Here's the chart hope it posts correctly.

Here's the chart:
Load psi
1910 35
2100 40
2280 45
2470 50
2625 55
2790 60
3000 65
3105 70
3260 75

Note that this is load, per tire, and is for the 265 Firestone Steel-X tires.

Wayne B

[FMTRVT]

FYI, I weighed my PSD SC 4x4 and the tire loads with an empty truck with driver are:

LF 2,230 RF 2,145
LR 1,445 RR 1,500

Jack

[Harald]

The label on the door jamb is assuming a truck is loaded to the GAWR’s (Gross Axle Weight Rating). If you are operating at a lower weight, you can reduce the pressure for better tire wear, smoother ride and better traction.

Here’s the proper way to determine what pressure to run in your tires. Weigh your truck, getting individual weights for each wheel (or at a minimum each axle). Then consult the tire inflation chart for your brand/model of tire. You can view a chart at www.trucktires.com . The chart will tell you what pressure to run based on your weight. If you got individual wheel weights, use the heaviest wheel on an axle to determine what pressure to run on all tires on that axle. If you weigh your truck unloaded you’ll need to do this again with your normal load. If your load fluctuates all the time, it’s probably easier to just keep the tires inflated to handle the highest load you anticipate.

In my case, I carry a 4000 lb slide-in camper occasionally. I keep the truck tires inflated for unloaded driving most of the time. Then before I load the camper, I pump them up for the extra weight. That way the truck rides smoothly with good traction and even tread wear while unloaded. If I was loading and unloading the camper daily or even weekly, I’d probably just keep the tires pumped up. Changing tire pressure daily on a dually would get old real quick.

It's a good idea to read the footnotes and fine print in tire inflation manuals also. For instance, in the Firestone manual it says that if you are driving for long periods at 65 to 74 mph while at the rated max load for the tire, you should increase the tire pressure 10 psi (provided the wheels are rated to handle the pressure). In the case of the Firestone Steeltex 265/75-16 tire that would be 90 psi. This means that the 80 psi listed on the sidewall is not the max pressure. If you want to drive 75 to 84 mph , you still need those extra 10 psi, but you also need to reduce you max weight capacity by 10%.

You can view a tire inflation table for LT235/85-16 tires at www.trucktires.com .
Here’s the inflation table for the LT265/75R16 Firestone Steeltex tire

Weight Pressure
1910 35
2100 40
2280 45
2470 50
2625 55
2790 60
3000 65
3105 70
3260 75
3415 80

65-74mph add 10psi
75-84mph add 10psi & decrease load 10%

[jlsworks]

After hitting the scales today, I got some axle weights for my V10 SuperDuty. 3200# front axle, 3280# back axle and 3060# on my single axle trailer (w/ a 250# tongue weight).
That would mean roughly 1600# each front wheel, 1640# each back wheel.
Based on the Steeltex tire chart I should be putting in 27 lbs in each tire???
Is this correct?

[NoMo]

Personally, I wouldn't run them that low.

With 40psi (or so) in the stock tires, I felt that the truck "wallowed" too much. Usually kept 50 in front and 70 in back. Ride is a little more harsh, but handling was much improved.

[Harald]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by jlsworks:
After hitting the scales today, I got some axle weights for my V10 SuperDuty. 3200# front axle, 3280# back axle and 3060# on my single axle trailer (w/ a 250# tongue weight).
That would mean roughly 1600# each front wheel, 1640# each back wheel.
Based on the Steeltex tire chart I should be putting in 27 lbs in each tire???
Is this correct?<HR></BLOCKQUOTE>

You'll notice that the lowest value on the chart is 35 psi. I haven't been able to get a definitive answer on whether you can run less pressure. It's common practice to go real low pressure for driving slowly in sand, but for everyday use I wouldn't go below 35 psi. Too much risk of spinning a tire on the rim or denting a rim. My dually is a good example here. With 2800 lbs on the rear axle while unloaded, that's only 700 lbs on each tire. I still keep the rears at 35 psi unloaded.