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Old 05-29-2015, 07:56 AM   #1
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Weighing Coach for Tire Pressure?

I have owned 6 or 7 Motorhomes and have never weighed them and always kept the recommended pressure in the recommended tires. I have never had an issue with the tires. The only blowout was in a friends coach that I was slow transporting for him for a free coast to coast 3 week vacation and he had just had it serviced and I did not check tire pressure as assumed the dealer did.

For those of you who weigh your coaches, how much difference have you found between the recommended tire pressure and the pressure that you end up putting into them? And did it make any noticeable difference in the ride?

Thanks
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Old 05-29-2015, 08:21 AM   #2
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I've weighed the three coaches that we've owned. First weighed each axle then one side of each axle to get an approximate load on each tire or pair of tires (duals on the drive axle). I'm running from 5 to 10 pounds under the coach maker's recommendation and still have a good margin of load capacity on each tire remaining according to the tire manufacturer's inflation tables.

I think it made a difference in handling for the shorter, non-tag 38' coaches but I don't know that it makes that much difference for the current 42' coach with tag axle.

One difference the lower pressure did make was reducing the "shock" or "bang" that occurs when you hit a sharp edge like a bridge transition seam or "well defined" pot hole.

On edit: The amount of load used to determine inflation pressure comes from the heavier side of the axle, not the axle weight divided by 2.

FWIW
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Old 05-29-2015, 08:37 AM   #3
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I've always weighed mine, at least once after getting the coach. More often if I know I've changed the loading much.

The recommended vs actual varies with the coach, but in most of them the rear axle is usually close to its max loading so the recommended psi is right-on. My front axles have been anywhere from well under to fairly close. In the current coach with a 14,600 lb fron axle, my actual weight is 12,600 so I can go with 10 psi less, and I feel that does yield a somewhat smoother ride on harsher surfaces. No difference on nice smooth roads, though.

The RV builder doesn't know how you will load your coach, so the recommendations pretty much have to assume a full load and psi to match. If you can run substantially less, then it does make a difference.
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Old 05-29-2015, 08:40 AM   #4
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I left the dealer with 110# each tire and a pounding ride down the road. After getting weighed in Oregon at road side scales and also at Cat scales, I have not had 4 corner weight done, I dropped the front to 95# and rear to 90#. Very different ride, a lot more comfortable also added Safe T Plus to the steering. This took away the push pull when a semi passed and also helped a great deal with cross winds, along with the peace of mind that it may help in case of a blowout. A lot more relaxing drive not having two hands tightly holding onto the wheel and constantly correcting.
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Old 05-29-2015, 10:34 AM   #5
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Much improved ride quality experience when having the tires set by weight.
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Old 05-29-2015, 12:07 PM   #6
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It's fairly easy to get your coach weighed if you pull into a Weigh Station on the interstate. Nice people will give you a printout, too.

Our coach differs from Gary's inasmuch as the front tires have more psi than the rears. Fewer of them to share the load.
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Old 05-29-2015, 03:30 PM   #7
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Quote:
Our coach differs from Gary's inasmuch as the front tires have more psi than the rears. Fewer of them to share the load.
I didn't say my fronts have lower psi than the rears. I said the front axle is carrying a less weight than its max load rating. That enables me to reduce the psi below the "recommended" value on the RV makers placard.
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Old 05-29-2015, 03:48 PM   #8
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So do you all lower the pressure when your fresh water tank is empty and you have less than half tank of fuel?
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Old 05-29-2015, 04:00 PM   #9
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Here is what I did;
Coach has our normal caravan of items
Full fuel and full fresh water, grey&black tanks empty
Weighed front and rear at the scale
Then weighed left and right
Did a spreadsheet with weights
Used the tire manufacturers suggested pressure for the load weights on the tires
Inflated (cold)and leave them there
Check inflation before each trip
Works for us
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Old 05-29-2015, 05:09 PM   #10
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Quote:
Originally Posted by DMTTRANSPORT View Post
So do you all lower the pressure when your fresh water tank is empty and you have less than half tank of fuel?
That is what I am wondering? Every coach I have owned has often had big weight differences based on what I am using it for. For example, taking a group to an out of town football game vs my wife and I going on a short trip. Or going to property we own in MT and coming back with the cargo boxes full of big rocks, etc. The weights vary so much so often that I have just gone with the posted Mfg's #'s as I would think they would be on the high side?
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Old 05-29-2015, 07:58 PM   #11
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Set it for the max weight less say 5-10% and forget it. You don't see L/H truckers changing their pressures every time the load changes or when they are bob tailing. I might get flamed, but I think too many people over think this issue on tire pressures.
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Old 05-29-2015, 08:27 PM   #12
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Originally Posted by Sky Pilot View Post
I have owned 6 or 7 Motorhomes and have never weighed them and always kept the recommended pressure in the recommended tires...
If you never weighed the coach, you don't know what the RECOMMENDED tire pressure should be! What you are doing is putting the MAXIMUM pressure allowed into the tire. 90% of the time, that max limit is far too much pressure.

Please go and get a good 4-corner weight. You will then know what pressure you should be running, and I'll bet it will be less than you are running now. Your ride and handling will improve markedly.

A personal observation...
When we bought our coach, the former owner was doing what you are doing, running the maximum allowed pressure - 120 psi - in all the tires. I got the coach weighed and was able to drop the pressure in the steer tires to 110 and the rears to 95! It was like driving a different coach! The ride improved, the oversteer in curves went away and the coach became a dream to drive.
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Old 05-29-2015, 09:19 PM   #13
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My tires say 110lb max yet the coach sticker says to inflate to 90lbs. I certainly am not maxing out my air pressure. I agree with some, I think some of you are too anal about a few pounds of air pressure.
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Old 05-30-2015, 09:07 AM   #14
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Originally Posted by Rich-n-Linda View Post
If you never weighed the coach, you don't know what the RECOMMENDED tire pressure should be! What you are doing is putting the MAXIMUM pressure allowed into the tire. 90% of the time, that max limit is far too much pressure.

Please go and get a good 4-corner weight. You will then know what pressure you should be running, and I'll bet it will be less than you are running now. Your ride and handling will improve markedly.

A personal observation...
When we bought our coach, the former owner was doing what you are doing, running the maximum allowed pressure - 120 psi - in all the tires. I got the coach weighed and was able to drop the pressure in the steer tires to 110 and the rears to 95! It was like driving a different coach! The ride improved, the oversteer in curves went away and the coach became a dream to drive.


Some good info here and thanks for all of the participation and thoughts.

I don't think I said I am putting the max tire pressure in my tires, I think (or meant) I said I have always run the Mfg's recommended tire pressure that has been posted in every coach I have owned. In my current coach it is 85 psi on the rear and 95 psi on the front, the max pressure on the tires is much higher than that. Since it is posted on the wall of the coach usually over the driver's seat, I assume the coach builder determines the pressure based on their calculations and probably uses the max weight the coach is rated for. Does anyone know if that is what they do? If so, and you are routinely running less weight than max., I would assume you would get a better ride when reducing the tire pressure.

In my coach the weight varies greatly based on how I am using the coach and always has, thus I could not see the point of weighing them. I sometimes tow a Wrangler and sometime put a Honda Reflex on the Hitch and often neither....in addition to carrying from one to eight people and no cargo to cargo bays full.

The reason I asked this question was to get an idea of how far off from Mfg recommendations people were getting when the weighed each corner of their coach. I don't think I saw any huge differences posted and did anyone, who has weighed their coach find they had to put substantially MORE psi in their tires than was on the Mfg placard? That was my main concern and I got some good info and thanks again.

Scott
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