"a Question About Tire Pressures "

Discussion in 'Towing, Vehicles, Maintenance and Repairs' started by BankShot, Sep 9, 2014.

  1. BankShot

    BankShot
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    Just wanted to bounce a question to the forum for some feedback. We recently installed six brand new tires on our 31 foot HR Admiral, size 245/70x19.5. All the calculations done show that we should be carrying 92 lbs pressure in all six tires for the load and load distribution we carry. The coach has been stationary for just over 10 weeks now except for moving it a few feet every two weeks to prevent the tires from flat spotting, since our last trip. The outside temp has been all over the board fluctuating between lows at night of 51 degrees to highs during the day of up to 106 degrees. Pretty typical for our area. I just checked the pressures yesterday and found them to be at 79 lbs pressure. I know that RV tires do lose pressure from just sitting and that any major loss usually means bad valve stems or improperly mounted tires however we had all new valve stems installed as well as special stem caps, etc. Does a drop in pressure as described prior seem normal over a 10 week period under the temps mentioned? I've heard of tires losing up to a couple of pounds a month but never over a pound a week as I am measuring. I am taking it in tomorrow morning to have the tires all aired and will check the shop's tire gauge against my own to make sure mine is not giving a bogus reading but it shouldn't be as it is one of the better gauges, or at least it is supposed to be. Any feedback is welcomed here and thanks to anyone ahead of time who does chime in.................

    Regards, BankShot
     
  2. Fitzjohnfan

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    So when you weighed your coach, was the weight equal on each corner? Are you determining the 92lbs psi from the inflation tables for your type of tire?

    Also, when you checked the pressure, were the tires completely cold, or warm. Warm tires will show higher pressures.

    I would guess that the loss of pressure is natural for your new tires, and as they become better seated on your rims during regular use, you will get less pressure loss.

    When you get them aired up, will you wait while they do the work or will you leave it with them overnight? If they air them up while you wait, the tires will be warm, and the pressure will have to be higher than 92psi.
     
  3. BankShot

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    QUOTE(Fitzjohnfan @ Sep 9 2014, 11:22 PM) [snapback]38260[/snapback]

    So when you weighed your coach, was the weight equal on each corner? Are you determining the 92lbs psi from the inflation tables for your type of tire?

    Also, when you checked the pressure, were the tires completely cold, or warm. Warm tires will show higher pressures.

    I would guess that the loss of pressure is natural for your new tires, and as they become better seated on your rims during regular use, you will get less pressure loss.

    When you get them aired up, will you wait while they do the work or will you leave it with them overnight? If they air them up while you wait, the tires will be warm, and the pressure will have to be higher than 92psi.



    The weight loaded is almost the same at each whee and I have also checked the weight chart to determine the pressure I should be running. So yes to both of your questions about that. And I always check the pressure when the tires are cold or at ambient temperature for that day, etc. I wasn't aware that new tires lose pressure quicker than after they have had some mileage put on them, thanks for that piece of info. I am very fortunate to have a mechanic's shop less than a quarter mile up the road from where the coach resides when not being used. Driving a quarter mile at very slow speed early in the morning will not warm the tires up at all in my way of thinking. But as a precaution I will check them prior to leaving and then again at the shop and adjust the pressure levels accordingly if needed..............

    Thanks for the info, I really appreciate it. Safe future travels to you and any others traveling with you...............

    Regards, BankShot
     
  4. docj

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    Won't comment about the concept that new tires lose pressure faster than older ones, but I've sure never heard that before. As for your varying pressures, I often see swings of 2-5 lbs depending on the ambient temperature, but I've never seen a drop as large as you're stating. Of course, it is rather difficult to get an accurate pressure measurement on high pressure truck tires using a hand-held pressure gauge; is that what you're using or are you looking at the readout of a TPMS system? I always use my TPMS for accurate pressure readings. If you are using a handheld gauge, I bet you haven't fully mastered the art of using it.
     
  5. BankShot

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    QUOTE(docj @ Sep 10 2014, 08:48 AM) [snapback]38263[/snapback]

    Won't comment about the concept that new tires lose pressure faster than older ones, but I've sure never heard that before. As for your varying pressures, I often see swings of 2-5 lbs depending on the ambient temperature, but I've never seen a drop as large as you're stating. Of course, it is rather difficult to get an accurate pressure measurement on high pressure truck tires using a hand-held pressure gauge; is that what you're using or are you looking at the readout of a TPMS system? I always use my TPMS for accurate pressure readings. If you are using a handheld gauge, I bet you haven't fully mastered the art of using it.



    I use a handheld gauge we bought early on from CW and it is supposed to give accurate readings. I plan on checking it this morning against the gauge the shop uses to see if there are any variances. I've used a good handheld gauge for many years on my vehicles and several motorcycles but this is a horse of a different color using one on a motorhome, I do realize that. Again thanks for the added info. Sure glad we joined this forum a while back, wish I had done it sooner...................

    Happy & safe travels, BankShot
     
  6. Skymessenger

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  7. Fitzjohnfan

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    The last time I weighed my motor home, it was at a local truck stop, and the charge was $9.00. This was for a motor home with two axles only, so your tow vehicle and trailer may be more depending on how the scale charges.

    I wasn't able to weigh each corner independantly, but weighing each axle was the next best thing. I found I was 400lbs overweight in the rear, but I was testing the "worst case scenario". Both holding tanks full and fresh water and fuel full.
    Since then, I drive with the fresh water only full enough to get me to the next full hook up location, and try to empty the tanks when they are 3/4 full.
     
  8. BankShot

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    As a side note here, when I first became the "Captain of our Coach" I did some calculations to get some idea of how much weight we might be carrying along with us when we did travel. Give or take a pound or two here and there I think I came pretty close to how much all our "stuff" weighed. Afterwards as I was sitting back feeling proud of myself for all my math skills it hit me right between the running lights, what did all that fuel, water and waste weigh that we would be carrying along in back, tucked away, out of sight and out of mind. So using the old scale of so much per gallon for gas and so much for water and adding a tad for the "sludge" I came up with a total of just over ONE TON that would be pressing down on the rear axle area............... :eek:. Holy crap, that's like carrying one of those mini cars in the rear bedroom. I have to wonder how many folks forget to add in those weight figures when calculating their axle/corner weight? Probably a few because I was almost one of them. Even leaving with empty grey and black tanks, it's amazing the total weight of gas and fresh water we take along with us when you take the time to do the math and add it up.................... ;)

    Happy travels, Bankshot
     
  9. mdcamping

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    Check your local town gravel yard, they should have a weigh station

    Mike
     

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