Tire pressures and light trucks.

Discussion in '4x4's, SUV's and P/U Trucks' started by melinuxfool, Jun 19, 2009.

  1. melinuxfool

    melinuxfool Well-Known Member

    I learned a valuable lesson in tire pressure today, after almost losing control of my truck. Let some air out when you anticipate traveling over bumpy roads.

    I hit a bad spot in the road at about 42 mph (speed limit 50) and realized that the "washboarding" effect that bumps can have on pickups was greatly magnified by having the tires up at max (50 psi vs 26 psi recommended). Fortunately I caught it and kept it from skidding, but the thought of "what if that had been above 60 on the interstate" came to mind. So I'm going to play with tire pressures a bit on my Nissan, to find a good balance between FE and safety, because max on this truck is not safe. I let them down to 36 psi hot for a noticeable difference in handling and pickup.

    Nonetheless, I still got over 24 mpg on the trip, with a ton of hills. DWL up the hills and NICE-On down the hills.
  2. my truck responds very similar based on the road surface and psi in the tire. If i'm off pavement for more than a couple miles I always get out and drop them to the suggested tire pressure (44 psi) but if i'm on asphalt I run up to 55 psi in them.
  3. Taliesin

    Taliesin Well-Known Member

    I noticed this as well, to a minor extent. But it is why my tires aren't going any higher.

    BTW: I live on back country roads, so I travel them every day.
  4. phoebeisis

    phoebeisis Well-Known Member

    I keep my large SUV at 41 front(31 called for on door) and rear 43 (42 called for) when traveling at speed on highways.This gives me good(relatively- 125% EPA hy (17 mpg vs 21 mpg) mpg but decent control.
  5. worthywads

    worthywads Don't Feel Like Satan, I am to AAA

    I've been running 55psi for over a year, 48psi for several years prior but have never driven on anything but paved road at any speed, no issues.
  6. melinuxfool

    melinuxfool Well-Known Member

    Biggest problem with Maine roads is the tendency to run into rough roads at random. Many paved roads here are in worse shape than most dirt roads because the state can't afford to maintain them all.
  7. npauli

    npauli Well-Known Member

    I've noticed something similar. The rear axle will lose traction a bit on some turns, presumably because the high pressure and light weight (unloaded) makes it too easy for a bump to throw the wheels up in the air.

    For mine, max sidewall = 80 psi. I've got them all around 72 or so. I probably aught to lower the rears a bit.
  8. R.I.D.E.

    R.I.D.E. Well-Known Member

    See if you can get Bilstein shocks for the rear (not cheap).

    They also make vibration dampners for many large pickups. These are weights that have fairly soft rubber mounting that alows them to counteract the forces you are experiencing. I know they use them om the Ford F150. Its located just inside the rear bumper outside of the drivers frame rail.

    The rubber is soft and you can twist them quite a bit with your hands. Maybe you could make one up, or find one at a salvage yard. I dont think they would ever wear out.

  9. kngkeith

    kngkeith Well-Known Member

    I concur with Gary re:suspension setup. Different shocks can make a big difference, and are usually overlooked.
  10. bluetwo

    bluetwo Member

    I still say yes, if you're going to be making a road trip go ahead and bring up the pressure a bit. I make anything from a two hour skip and a hop to 3,000 mile road trips, and all combinations in between, a lot more frequently that I would like and when I have to use my truck it's so much more than worth it to take a few short minutes to raise the tire pressure.
  11. zjrog

    zjrog Active Member

    I really don't think those dampers will help if you have no load in your truck. The only thing that helps over washboard is either lower tire pressure or lots of weight.
  12. phoebeisis

    phoebeisis Well-Known Member

    Bilsteins work well in my 98 Suburban, but it is just a 1/2 ton and it has more weight over the rear axle than a pickup. Pickups are generally really heavily sprung, and sometimes overdamped-some are so bad they act like hardtails when you hit a bump with no load.

    My 1986 Toyota was so bad I used to carry 50 1 gallon water jugs-400 lbs- strung in the back across the bed.It was like a buckboard.

    Still, good shocks might help a little if the stock ones are overdamped for the heavy loads they occasionally carry.

    The Bilsteins were about $220 on Ebay- for all 4.I got them to get rid of the extreme sway my truck had.Now I can take on and off ramps at higher speeds-no losing momentum because it cornered like a drunken sailor(so I had to brake too much too early).

  13. beatr911

    beatr911 Tightwad

    The weight of the tire/wheel/axle assembly can make a huge difference in the ability of the tires to stay in contact with the road and offer a smooth ride. In a tech seminar with our local Porsche club at Fikse (they make light, expensive wheels) the presenter as well as the the audience confirmed that light wheel/tire combinations are the single best suspension improvement one can make assuming everything else is in good shape.

    My Ranger was originally equipped with alloy wheels that weigh 17lbs and the 225/70R14 passenger tire weighs another 17lbs for a 34lb combination. I was getting lots of flats and had a hard time finding good used tires for this occasionally used vehicle. Fed up, I purchased some used alloy wheels and 6ply 30X950/15LT wheel/tires. The combination now is just about 50lbs.

    What a huge difference. Where the old lighter combination would track a rail road crossing butter smooth with as little as about 300lbs in the bed, with the heavier wheel/tire combo it hops all over the place even when fully loaded with more than 1200 lbs in the bed. The shocks are year old Bilstiens. The wheel/tire/axle combination is just plain too heavy for the shock/spring to keep it on the road.

    As mentioned in previous posts tire pressure can play a key role as well, so I'll play with that to see if it can make a significant difference. But I'm skeptical that it will smooth out as much as the lighter set-up.

    If you want that cool big tire look, or the puncure resistance of LT tires, or the off-road capabilities of a mud tire remember there is a price to pay in ride and handling. Lighter is better for ride and handling.

    As a side effect, the big and heavy wheel/tire combo REALLY rolls well. Coasting distance has increased probably 20-30% due to those 4 big flywheels at each corner. Of course it takes more energy to spin 'em up as well.
  14. phoebeisis

    phoebeisis Well-Known Member

    When I had my Titan,I decided to get light wheels for just the reasons you mentioned.The stock steel 17" 7.5 wheels were 31.5 lbs-the 17" OEM aluminum alloy wheels were 25.5 lbs.
    I finally got some Centerline forged aluminum wheels and they were 20.5 lbs.

    I was doing it mainly for FE purposes.I figured in pure city driving accelerating that extra 40 lbs-linear and angular-would eat up gas. I couldn't actually measure any difference in FE, but this was in my pre SG pre hypermiling days. I didn't P&G then either.

    Light is good for wheels and tires.


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