Airing PUP Down

Discussion in 'Taking Your Camper Off Road' started by Shuswap, Feb 19, 2012.

  1. phalynx

    phalynx Member

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    It will. Your springs will help with low frequency, high displacement bumps like speed bumps or bigger. Deflating your tires will help with the high frequency, low displacement bumps like wash board roads.
     
  2. cwolfman13

    cwolfman13 Active Member

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    Ditto!
     
  3. nhlakes

    nhlakes Well-Known Member

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    Lowering OHRV tire pressure is mandatory in some NPS areas.

    Take Cape Hatteras for example....

    16. What about tire pressure? What
    if my vehicle gets stuck on the beach?

    When driving on ORV routes, tire pressure must be lowered in order to keep
    adequate traction within the posted speed
    limit. Tire pressure of 20 psi is recommended for most vehicles. The softer the
    sand, the lower the pressure needed. Reinfl ate tires to normal pressure as soon as
    possible after you return to paved roads. If
    you get stuck and cannot get your vehicle
    out, your best bet is to call a commercial
    towing service. NPS rangers are not allowed to pull or tow your vehicle.

    http://www.nps.gov/caha/planyourvisit/upload/02-10-12-FAQ-Site-Bulletin-for-CAHA-ORV-regulation.pdf
     
  4. phalynx

    phalynx Member

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    Out in the sand dunes I usually air my truck tires down to 12 -14 psi, and I know some people who air down to less than 10 psi. It all depends on how soft the sand is and the type of hill climb you want to do. This was pre-popup, but if I were pulling one around on the sand, I'd probably go to 10-12 psi on the truck and maybe similar on the camper.
     
  5. roughin-it

    roughin-it New Member

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    I know ZERO about tires but I think with our EVO tires there is some sort of wide wall strength you have to consider. I'm thinking you could mess up the sidewall strength if you deflate them. again I'm not sure. I have the BFT T/A KO tires.
     
  6. huntero1975

    huntero1975 New Member

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    So if your running wash board roads drop the pup air about 5psi or so.. One guys said that will help avoid side wall tears yep he is right..If you allow the tire to flex over the rock, the rock will be less likely to go threw the tire tread or sidewall. running a tire at highway psi off road will prob result in a puncher sooner or later..

    but hey what do i know.. I only sold tires for 15 years and raced baja trucks as well..

    but dont under inflate the tire as well if you go to soft you will have smashed wheels real quick and bent wheels dont hold air.

    best way to get over wash board roads is to throttle down and start skipping your rig across the the tops of them. How ever this plan could pose high risk of crashing while towing a pup.
     
  7. Shuswap

    Shuswap New Member

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    Hunter, I would think that if you throttle down then you can't skip over the top of washboard because the tire has time to drop down.
     
  8. Unstable_Tripod

    Unstable_Tripod Well, there's your problem!

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    There was a Mythbusters episode on this point and a lot of people point to it as proof that driving faster on such roads is smoother. My response is that such a conclusion isn't necessarily valid. Scroll to the end of the linked page for the summary. In the first test at a State Recreation area, the suspension gauge deflected twice as much at 45 mph than it did at 15-20 mph and more water was spilled. In the second test on a road made bumpy by angle iron strips more water spilled at 40 mph than at 5 mph. The "confirmation" of the myth comes from the fact that the driver (Grant) felt that the drive seemed smoother at speeds in the 40 mph range than at lower speeds even though the objective date contradicted that. I give no consideration to the 70 mph runs because anyone who dives a washboarded dirt or gravel road at 70+ mph is asking for disaster because of loss of steering and braking control. Such behavior is reckless enough on the level but in the mountains, forget about it!

    There are two other issues at hand. First, these tests were not conducted with the tires "aired down." Everyone here who is talking about airing them down is also talking about operating the vehicle at slow speeds. Who is going to rock climb or drive deep beach sand at 40-45 mph? I think that trying to drive 45 mph on a badly washboarded road with deflated tires would be asking for wheel damage, especially when potholes are encountered and these roads usually have a lot of potholes. Finally, and this is the most pertinent point to us, these Mythbuster tests did not involve towing trailers. We can't expect that the objective or subjective results would be the same with a trailer.
     
  9. Shuswap

    Shuswap New Member

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  10. CREEPPINGCHARLIE

    CREEPPINGCHARLIE CAMPING RECHARGES THE HUMAN MIND

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    I have driven all the 4WD roads in the area of Ouray,Silverton and Telluride. Never once did I feel the need to air down my tires on my TV. At times I did pull my old Viking PUP over some trails. Again I never aired the tires down on the PUP. It did have the worst type of axle for off road,torsion. [8D] [PUC] [PUT]
     
  11. huntero1975

    huntero1975 New Member

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    I am just stating what I know from my real life experience.. the faster the ride the ride quality improves for the humans. now if your towing it may be a lot harder on the trailer but I am not 100% sold on this fact but I can see how high speed harmonics could damage many items. I have spent countless hours driving down dirt roads all over arizona most of my young life from about 8years old to about 27 years old most being on the western side of the state where it is nice and dry and hot.. Now most were not pulling a trailer, but some were.

    There are many factors that play a part in wash board running.. tire diameter, distance between the bumps, and how deep the bumps, are how fast your going, how much down force is your shock pushing back to the ground, and what kind of rebound it has set inside of it as well. guess what none of these matter when your going so fast your tire never has a chance to drop before hitting the next bump. that's the truth of the matter. you can put as much science it as you want.. that's why I said skip across it.. Is it safe to drive this way nope not even close. but practicing your dirt drifting when by our self is sure fun..

    But back to the original posters question airing down 5lbs when driving slow offroading will help prevent tire damage and not really risk the rim damage. but when you return to the highway back up. load rating is a equal part of psi in the tire.
    think ford exploders back in the day that was all due to under inflation of the tire getting to hot and blowing out. Good luck enjoy your offroad trips.
     
  12. phalynx

    phalynx Member

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    I may be able to shed some light on the mythbusters seemingly contradictory data, but keep in mind, this is just an educated guess without seeing the details of the test. I do remember seeing this episode, but there's a lot of things that go into testing that they aren't going to show on TV. Also, I'm not trying to be argumentative, just trying to further this conversation.

    When the suspension showed increase travel despite a perceived smoother ride, this tells me the suspension is doing exactly what it's supposed to do. That is, isolate the cabin from the road. Ideally, the suspension would completely follow every nook and cranny of the road, keeping the tire completely in contact with the road, but allowing the rest of the car to glide along in a steady line.

    What keeps this from happening is the frequency of the bumps and the dynamic response of the suspension system. At some slow speed, the tires will follow every bump, but as the speed increases, the tires start to catch air. At some other faster speed, the frequency of the down side of the bumps will coincide with the natural drop of the tires. In other words, the tires go up the front side of one bump, but come down on the back side of the next one. At this speed, the suspension displacement will be significant, but will still isolate the rest of the car.

    Alternatively, what else could be happening, is that the tires really are skipping across the tops, but when the tires impact the bumps, the tires kick up the suspension at the natural frequency of the suspension, but 180 degrees out of phase from the car, thus increasing travel but still isolating the rest of the car.

    As for the wine glasses, the glasses are much lighter than a human and they're sitting on the seat cushions, which have their own natural frequency. Now, because of vehicle dynamics on a road, a specific type of vibration is created, and this is called random vibration. Random vibration will excite all frequencies and thus, can excite the natural frequency of the wine glasses and causing more water to spill. There is one problem with this theory, however, and that's if random vibration excites all frequencies, then why doesn't the water spill out no matter what speed the car is traveling. One reason is that the frequency of the bumps in the road concentrate a greater proportion of the random vibration near the wine glass natural frequency, and that is speed dependent.

    Out of all that, the proof is in the pudding, as my boss likes to say. It's a commonly accepted fact in the off road world, that the faster you go, the smoother it gets. The high speed camera is further proof of what is going on.

    As for driving at 40+ mph on washboard roads and in the sand? Yes it's done and done a lot. Just ask the people at pismo beach and glamis sand dunes about the sand drag races where some people race normal trucks and SUVs. Just ask the people who live in the desert southwest where there are hundreds if not thousands of miles of washboard roads. 40 mph isn't that fast on a dead straight dirt road that goes for miles. Mind you, this is all without a trailer.

    Whether airing down a trailer will give the same comfort benefits as a vehicle, the answer is undoubtedly yes. The physics are the same. Obviously, there's nobody inside a trailer, but there's lots of flimsy cabinets, electronics, etc that could benefit from lowering of this high frequency wash board roads. Now going fast down a washboard road with a trailer attached, that's a whole 'nother ballgame, one that I can't comment on.

    Keep in mind that within this thread, at least four types of terrain have been mentioned. Mountain gravel roads, sand, rock crawling, and desert running. Every one of these conditions call for different driving techniques and different tire pressures. Even the type of tire and the vehicle dictate different tire pressures. For example for 38" bias ply boggers on a light weight jeep and beadlocks, you can literally take out the valve and run 0 psi on sand and boulders. For my 4runner, I'd run maybe 20-25 psi on a long desert run.

    Another benefit to airing down, is that since you have better traction, you do less damage to the trails. This is especially important in high profile states like California and Colorado where people are trying to close down the trails we all love. Tread lightly my friends.
     
  13. phalynx

    phalynx Member

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    By throttle down, I think hunter means to push down the throttle and go faster.
     
  14. Shuswap

    Shuswap New Member

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    As in peddle to the floor - oh yeah!
     
  15. RobertGreenlee

    RobertGreenlee Member

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    I was thinking about doing the mod to add shocks to my PUP this summer.. We hit some washboard roads last year that were so bad it was knocking drawers out inside. Would the shocks help much to reduce stress on the PUP.
     
  16. bearman512

    bearman512 Well-Known Member

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    Tire size will be the best at smoothing out the washboards. If you are running the small tires washboards will be killer. A larger diameter 13" tire or a 30 x 9.50 x 15 will have a larger contact area and thus smooth the ride.
    I have shocks on mine and really all the shocks do is slow the rebound of the axle.
     
  17. huntero1975

    huntero1975 New Member

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    yes sir thats what I mean.. glad to see someone finally understands what i was trying to say..
     
  18. RobertGreenlee

    RobertGreenlee Member

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    I've got ST205/75R14 tires on my PUP. Don't think it bigger ones would fit. So what benefits are you seeing from having the shocks?
     
  19. bearman512

    bearman512 Well-Known Member

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    I have the offroad type with a 30" mud terrains factory stock and I air down to 20 PSI (I will run 45 mph on the long open stretches but generally run 35-40). The only time the shocks come to play is if and when I go through dips or large bumps in the road. Shocks keep the axle from rebounding and oscillating on dirt washboards causing it to jackknife when you try to slow down or descending a grade in the mountains. Potholes will do the same. This is just my experience, been driving dirt roads in the mountains of NM, AZ, UT, and CO for 40+ years.
     
  20. phalynx

    phalynx Member

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    I'll probably be doing shocks at some point in the future as well.
     

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