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Old 03-27-2015, 09:54 PM   #1
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Smile New MH owner, weight/tire question

We recently purchased a used 2010 Fleetwood Discovery. It needed new tires so I checked this forum before we decided which to purchase. I notice that everyone talks about weight and tire pressure. My husband says why not just keep the max pressure in tires and not worry about the weight? Can anyone tell me why you would adjust tire pressure based on weight?
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Old 03-27-2015, 10:07 PM   #2
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Tires that are overinflated will not ride well, and will not wear evenly. It is not difficult to have your coach weighed and adjust the pressures accordingly.

While every tire manufacturer has different parameters, this link will offer recommedations on Michelins.

http://www.rvtirepressure.com/assets..._Inflation.pdf

There are many threads on this subject. If you go to the search tab at the top of the page and type in tire pressures.
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Old 03-27-2015, 10:09 PM   #3
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Short answer is basically comfort of ride and handling. If you don't need max based on your weight lower pressure makes for a better ride and handing. There are charts you can refer to for proper inflation. Doesn't have to be exact but not too low. Sure makes a difference in mine.
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Old 03-27-2015, 10:10 PM   #4
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Quote:
Originally Posted by TRNewsom View Post
... Can anyone tell me why you would adjust tire pressure based on weight?
The short answer is ride quality. Nothing like driving on round rocks. LOL While over inflated tires are considered less problematic than under inflated ones, the will still have problems with excessive wear.

Part of the challenge in owning a MH is learning all of the best practices for operation and maintenance. Getting corner weights and then determining the proper tire pressure is one of those things you just need to do.

One other thing is also understanding tire pressure issues like the affects of ambient temps. If your tires are set at max sidewall PSI when it is 60* outside, what will happen when it is 90* or more?

Tires are just not a set-and-forget item. Failure to treat them properly is an invitation for disaster.
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Old 03-27-2015, 10:16 PM   #5
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The main reason is ride comfort. Those load/inflation charts show the absolute minimum air pressure required to support the load, not necessarily the optimum.
The Rubber Manufacturers Association =RMA, states to never run less than what the tire placard in your MH states. See ch 4, pg 55 for MH tires.
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Old 03-27-2015, 10:26 PM   #6
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Thanks for the information. I'm sure I will have more questions as we go but we are looking forward to using our "new" motorhome.
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Old 03-28-2015, 10:45 AM   #7
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Quote:
Originally Posted by Ray,IN View Post
The main reason is ride comfort. Those load/inflation charts show the absolute minimum air pressure required to support the load, not necessarily the optimum.
The Rubber Manufacturers Association =RMA, states to never run less than what the tire placard in your MH states. See ch 4, pg 55 for MH tires.
Not quite...

While I totally agree with you on charts and minimum pressure may not be optimum, the RMA item you quoted says, "Maximum tire load capacity can only be achieved utilizing the maximum inflation pressure molded on the sidewall of the tire." I think that could be a red herring if not properly read or misunderstood.

HOWEVER...(being fair and balanced) page 52 might be the more appropriate reference you meant. It says...

"Inflation pressure recommendations may also be determined based on the tire manufacturer's specifications, which define the amount of inflation pressure necessary to carry a given load. These inflation pressures may differ from those found on the vehicle tire placard or certification label.

However, never use inflation pressure lower than specified by the vehicle tire placard, certification label or owner’s manual. Nor should inflation pressure exceed the maximum pressure molded on the tire sidewall.
"

This is a bit of a circular argument since the pressure on the placard is the same as the pressure needed to carry the maximum weight for the axle. From my calculations and research, the placarded pressure specifications appear to also contain a "fudge factor" for an axle that is not perfectly balanced left to right thus minimizing the chance that an individual tire is overloaded. In other words, the placards (at least for Newmar) seem to add about 5 PSI compared to a perfectly balanced axle need based on tire manufacturer's loading charts. The exception to that is for the tag axle because the weight they carry is so far below the tire manufacture's loading charts that only the minimum pressure is required under any imaginable situation.

As to the OP's original post I took that to mean maximum pressure on the tire wall. OTOH, if they meant to run the placarded pressures then it would normally NOT be the maximum sidewall pressure but in some situation pretty close.

Running placarded pressures would seem very wise and safe for those that don't feel comfortable with using tire pressure charts. There is nothing wrong with that approach to the subject. But that would not relieve that same person from getting proper corner weights. They need to ensure they are not over loaded or extremely out of balance in weight distribution which might cause them to exceed the weight bearing limits of an individual corner.

All that a being said...thanks for that very informative item. While the pressures I use are at or above the placarded specifications I found it to be helpful in this discussion. I would just like them to expand on the placard vs tire manufacturer's weight charts a bit more.

HOWEVER...lawyers who may vet such articles are not normally engineers and engineers that review these articles may be more concerned about lawyers too.
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Old 03-28-2015, 11:14 AM   #8
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RV's and tire pressure's.........WOW(https://www.google.com/search?q=tire...com&gws_rd=ssl 6,710 results on irv2). The bottom line here is weight on the tire's and inflation pressure per manufacture's charts to achieve the best ride on the tire for the weight one carries. I have read, where some check their tire's everyday! Are there tire/charts for auto tire's? So one can achieve the "Best" ride in their auto? Heavy duty trucks, semi's, tri-axle dumps, rental trucks, and on and on ...........the tire's are aired up to carry the maximum weight of the licensed registration, and spend a fair amount of the tire's life traveling empty..........is it a harsh ride? You bet, but they do not take the time to adjust the pressure's every time their weights change, not practical, and most do not run empty long enough to affect the wear pattern, but do a lot of miles empty. Weigh your coach axles(fully loaded), look up and find your recommended pressure for that weight, adjust pressure, and good to go. If weighing on a 4 corner scale, adjust for the greatest weight.
Add-on: When I weighed our Coach, adjusted tire pressure's, it did not handle good, wandered.......tire's felt mushie........weighed again, same results........started playing with tire pressures.......ended up running a higher pressure than the charts recommended.......handles great now, I monitor/watch tire wear........
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Old 03-28-2015, 11:39 AM   #9
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Quote:
Originally Posted by palehorse89 View Post
RV's and tire pressure's.........WOW. The bottom line here is weight on the tire's and inflation pressure per manufacture's charts to achieve the best ride on the tire for the weight one carries. I have read, where some check their tire's everyday! ...
I try to check my tire pressure every day I travel. If weather is reasonably stable I generally do it the night before we travel when the sun has been down and tire temps are not as affected by solar heating. Otherwise I get up early enough to do it the next morning.

While in theory setting tire pressure is easy, properly setting them is not so simplistic. Taking tire pressure readings and adjusting after being driven or heated by the sun could be disastrous. Relying on yesterday's settings after a major cold front passes overnight can be disastrous.

No device/system on our RVs has such a huge and sometimes immediate impact on safety while moving than our tires.

EDIT...I see you edited you post about beating a dead horse. The OP has 1 posting on IRV2 and says they are novices. This may be a dead horse to many of us but we also need to welcome new posters without being too frustrate by saying something we may have said dozens of times before. I certainly didn't understand the IRV2 search capability at first.
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Old 03-28-2015, 11:57 AM   #10
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You are right Don, I am sorry, I did not welcome the OP as I always do..........Welcome to the forum! My post was , with the search, was cased( ) for reference, not directed at the OP, the "Dead Horse" is about all the different comments that are always posted(As above) referring to the poster's personal methods when it comes to tire pressure threads..............Tire pressure is not a science.........but I see now, to some it is, which is also OK. I use to drive OTR, I do not check pressure's everyday..........and do not agree that it is needed. One thing for sure, there is a lot of reading, if one needs/wants to read up on this subject on here is why I posted the link.
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Old 03-28-2015, 12:03 PM   #11
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Welcome, and great question!
My understanding is that slightly overinflated is way better than underinflated.
Chances of me getting it "just right" isnt going to happen.
But thats just me!
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Old 03-28-2015, 11:11 PM   #12
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Ok Arkie, here is what you need to do. Click on my avatar and when the options pop up select Send Private Message. This sends a message directly to me, also an Arkie, and introduce yourself. I don't know all the answers but I too have a Discovery 40x!
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Old 03-28-2015, 11:57 PM   #13
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I did search this site before we purchased tires and read all the posts concerning tire pressure and weight. I just didn't know WHY you would adjust the tire pressure. I just knew it seemed to be a big deal.
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