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Thread: Recommended tire pressure?

  1. #1
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    Recommended tire pressure?

    Doing a little vehicle upkeep and got to wondering. The recommended tire pressure on the door post is 30 psi front and back. The Max recommended is 44 psi. Vehicle is 2001 Ranger supercab 4.0L 4X4 automatic. Tires are 245 75R 16 Goodyear Wrangler RT/S. I think running higher tire pressures should yield better mileage, probably ride rougher. Any downside to running 44 psi except for the ride?

    Thanks for any info.

    Curt

  2. #2
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    I don't think I'd even consider running even close to the max. A couple pounds probably wouldn't matter much and that's not uncommon given inconsistencies in various "filling" mechanisms, but any real deviation upward not only changes the "ride comfort", but also the handling, cornering and braking of the vehicle. Keeping the tires properly inflated is the best way to get the best mileage without compromising safety.
    --

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  3. #3
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    Kurt, while I generally agree with Jim, I must then say that I run about 50# in my F-150. We have been buying dirt, sod, mulch, and other ca ca for the yard. A front bucket on a Bobcat will hold a half yard, and that will weigh about 1000#. For my use, the extra air is a requirement to keep the rear rims off the road.

    If you do a lot of highway driving at highway speeds, then add about 5# to the recommended pressure, at least that is when M/Benz recommends.
    Best Regards, Ken

  4. #4
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    In addition to the concerns that Jim noted, I would add that using maximum tire pressure will cause the center of the tread to wear prematurely. DAMHIKT.

  5. #5
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    What Jim said. When you raise the pressure you lose traction, especially in the rain. Even if you punch them up for a heavy load, you should put 'em back when that's done.

    Click n Clack did a column on this recently and while I can't remember all their arguments, it was a persuasive case for running the factory pressure.
    Cheers,
    Bob

    I measure three times and still mess it up.

  6. #6
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    Recommended tire pressure?

    Remember too that heat expands air, so when you are at the max and running on the freeway, especially on a hot day, the pressure will be over the max. I'd go with maybe 2-3 lbs over the recommendation at most.



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  7. #7
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    The tire pressure number on your door post was put there at the factory based on the original tires that were on the car. That number is determined as I understand it based on their tests for the best compromise between handling and comfort. It all goes out the window when you change tires unless you buy the same exact tires that were on the car.

    The tire manufacturer makes recommendations for each tire. They also stamp a maximum pressure for maximum load on every tire. You need to stay below the maximum pressure rating.

    If you have aluminum wheels, chances are you will lose about 1-2 pounds of pressure per week. The older the wheels get the more pressure they will lose due to corrosion and due to greater flexing on corners. Clip on tire weights in northern climates are the biggest corrosion problem due to dissimilar metals. My mechanic friend says that 90% of the tires he sees are underinflated by more than a few psi. Any car he services he checks the tires while the oil drains and doesn't chage extra for doing it.

    I would stay some where between the pressure on the door post and the maximum pressure, keeping all tires the same pressure for best tracking and handling. I check my tire pressure weekly and more often on my Ford Explorer since it loses air more quickly.
    Lee Schierer
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  8. #8
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    Great info!

    Thanks All. I hadn't considered the braking and handling consequences or wear issues. Lee, interesting info about aluminum wheels. I have one wheel that seems to lose air faster than the others, I wonder if there's something going on with it. Now if somebody'd produce a drop-in diesel kit.....

    Curt

  9. #9
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    Click and Clack say to stay with tire sizes and pressures reccomended by vehicle manufacturer. Max tire pressures are warnings so you don't blow them up in your face. For optimum performance under normal driving conditions, stay with makers reccomendation.

  10. #10
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    I run an F-350 with 460ci, 5-speed manual and 4:10 rear end. When hauling a heavy load (loaded to the gills with hay) or my 9,000 lb. 5th wheel I punch the tires up. When not loaded, I run much lower. I use load range E tires. A number of years ago I was doing some major landscaping in my back yard and bought 225 of the 65# wedge shaped concrete blocks to make some raised beds with. My youngest son had dropped out of dental school and was waiting to go into the armed forces. I bought the blocks at a local concrete manufacturer and had to go back to pick them up. My youngest was driving the truck as his transportation to and from work. The 1st day he drove up after work and had the guy put 113(x 65#) of the blocks on the truck. 2 pallets of 50 and 13 singles. I asked him how it drove....a little mushy in the corners. I asked him if he'd put any air in the tires. NO? I aired the tires up to 65# and the next day he brought home 112 of the blocks. I asked how it drove....."Didn't even know they were there." These are load range E tires and will take more than 65 # but normally I run about 45 and when I've got a load on I air them up a little.
    Ken

    So much to learn, so little time.....

  11. #11
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    Odd man out again...

    My truck is a '96 Dodge Ram 2500 with the Cummins diesel and we have a slide-in Lance camper (weighs ~3000 lbs empty). I always run 80 lbs in the rear and 65 lbs in the front, all year long with or without the camper. Never had tires wear out in the middle or noticed braking or cornering trouble. My tire guy said it's best to fill them to what ever pressure you need and keep them there. It must work 'cause i get ~70k from a set of Michelin's and never rotate them.

    YMMV

    Brian
    Last edited by Brian Hale; 06-23-2006 at 10:21 PM.
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  12. #12
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    A little trick I learned from a cheap aluminum wheel company is if you get a leak in the aluminum casting of a wheel, (not real common on good brands, but does happen), pull the tires off, scuff the insides (the part between the beads-inside the tire when mounted) and paint them with a couple thick coats of spray paint. Seems to fill the voids in poor castings! Jim.
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  13. #13
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    Quote Originally Posted by Ken Fitzgerald
    I run an F-350 with 460ci, 5-speed manual and 4:10 rear end. When hauling a heavy load (loaded to the gills with hay) or my 9,000 lb. 5th wheel I punch the tires up. When not loaded, I run much lower. I use load range E tires. A number of years ago I was doing some major landscaping in my back yard and bought 225 of the 65# wedge shaped concrete blocks to make some raised beds with. My youngest son had dropped out of dental school and was waiting to go into the armed forces. I bought the blocks at a local concrete manufacturer and had to go back to pick them up. My youngest was driving the truck as his transportation to and from work. The 1st day he drove up after work and had the guy put 113(x 65#) of the blocks on the truck. 2 pallets of 50 and 13 singles. I asked him how it drove....a little mushy in the corners. I asked him if he'd put any air in the tires. NO? I aired the tires up to 65# and the next day he brought home 112 of the blocks. I asked how it drove....."Didn't even know they were there." These are load range E tires and will take more than 65 # but normally I run about 45 and when I've got a load on I air them up a little.
    You're a '60's gear-head aren't you, Ken?

  14. #14
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    Doggone it Joe..........you keep making my age public!........Yeah....I was a Chevy man 'til I got burned by an uncaring Chevy Company when I bought a new 83 full sized Blazer. Haven't had a Chevy or GM product since.........
    Ken

    So much to learn, so little time.....

  15. #15
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    [QUOTE=Bob Childress]What Jim said. When you raise the pressure you lose traction, especially in the rain. QUOTE]

    Sorry, but I have to Respectfully disagree with this statement. There is a thing called "Hydroplane Speed" for tires in Aviation that is VERY Important, (but the same principles apply to land vehicle tires, although due to tread design, the formula "may" differ slightly from brand/model to brand/model of tires). The formula for the Hydroplane speed of an aircraft tire, is 9 x the square root of the tire pressure. When a tire pressure is reduced, it allows more area to touch the ground, thereby reducing the pounds per square inch of the surface of the tire touching the road, and will actually push a small wall of water up in front of the tire because the grooves between the treads cannot funnel the warter away quickly enough, and the tire will then ride up onto the water and will hydroplane, much like a waterski riding on top of water, (and braking is NIL).

    The same reduction in braking/handling performance will also be noticed between a New tire, and a worn,(SLICK) tire on a car or pickup, because the Slick tire has more surface touching the ground, AND the tread grooves are no longer there to funnel the water away and allow the treads to grip the pavement, and again hydroplaning will occur at a much slower speed than with the newer tire .

    Another easy observation of this is to replace the normal sized tires with a size or two Wider Tires, (especially on pickup trucks, which already have a light rear end load when empty), and you will quickly discover that in wet conditions, the tires will spin out easily, braking deterioriates considerably and even the steering will tend to skid/slip if you aren't very careful. These facts I have personally observed from transporting cars, pickups and trucks over a million miles professionally, and 16 + million miles flying.

    I always use a higher tire pressure than the "Soft Ride" pressure on the vehicle door, (how much higher,...depends on the load, but NEVER more than that Max Pressure stamped on the tire), and have NEVER worn out the middle tread of a tire. I get more miles from my tires than they are rated for, better gas mileage, and better handling too. The most common detrimental thing about underinflation, is that the sidewalls have to flex more, causing more heat buildup, thereby shortening the life of the tire and many times causing a blowout or failure long before the tread is gone.

    If one changes the orig equip tires, but uses the original wheels, you should make sure that those wheels are rated for the higher pressures that may be allowed by the pressure markings on the replacement tires. This used to not be a factor, but NOT ALL wheels today, are of the same strength as they used to be, and that is especially true of "some" of the cheaper brands of aftermarket wheels that are available, as well as "some" of the orig equip wheels, especially on the smaller/lighter vehicles.

    Some tread designs are much better than others in wet conditions, because they disperse the water better and contribute to the most important safety factor, which is "PSI......where the tire meets the road".

    Sorry to be so long winded, but I hope it helps to understand the theory.
    Last edited by Norman Hitt; 06-24-2006 at 5:39 AM.
    "Some Mistakes provide Too many Learning Opportunities to Make only Once".

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