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Old 04-23-2016, 09:32 AM   #1
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Tire pressure

I know this has been asked a million times but I own a 2016 Winnebago meridian 40r and would like a good base line for tire pressure. Both the front and rear state 120lbs max cold. I haven't had a chance to weight the rig so I'm just interested in knowing what others have set their pressure at.
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Old 04-23-2016, 10:22 AM   #2
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To be on the safe side , assume you are loaded to the max weights , on both axles and set your tire pressures to the chart from your tire manufacturer.
This may make for a rough ride to start ( until you have the actual weight ) but after you get your " loaded for travel " weight , it will be easier to drop the pressure ( cold ) than find a spot to raise the pressure if you start out, with the pressure too low.
Here are pdfs from the two big RV tire suppliers. Inflation charts are in the files.
Attached Files
File Type: pdf Goodyear tire-care-guide.pdf (1.70 MB, 40 views)
File Type: pdf michelin tires for RVs.pdf (1.58 MB, 56 views)
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Old 04-23-2016, 10:28 AM   #3
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Tire pressure

Quote:
Originally Posted by Trynforpar View Post
I know this has been asked a million times but I own a 2016 Winnebago meridian 40r and would like a good base line for tire pressure. Both the front and rear state 120lbs max cold. I haven't had a chance to weight the rig so I'm just interested in knowing what others have set their pressure at.

Somewhere on the coach Winnebago has placed a sticker that gives you recommended tire pressures. It is assumed that they, the manufacturer, knows the weight on the each axle, and that is what they recommend, to be tweaked as you add your stuff.
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Old 04-23-2016, 10:31 AM   #4
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The "base line" for your rig is its weight. Without knowing that, safety dictates that you should opt for the upper end of the spectrum... say, 110# psi or even maxing them out at 120# - which, by the way, isn't the maximum psi your tire can hold: It's the minimum psi required for carrying the maximum load capacity your tires are rated for, which you should assume you're carrying until you know for sure by weighing it.

It will likely be too much inflation for the load you're carrying, but without knowing for sure you really don't have much choice... these things are really easy to overload, especially side-to-side. A harsher ride and decreased braking distances from too much inflation are infinitely preferable to the probability of a catastrophic tire failure from too little inflation.

Inflation just isn't something you can guess at based on someone else's rig.
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Old 04-23-2016, 11:09 AM   #5
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There is a sticker on the sidewall by the driver seat that gives you a safe baseline psi for the coach weight, for both front and rear axles. This is what Winnebago has determined is the best (read: safest) pressure unless and until you get actual loaded weights. Using somebody else's weights/pressures is a recipe for early tire failure and/or ride & handling problems.

The max load psi shown on the tire sidewall is just that - the psi needed to support the maximum load the tire is capable of. It is not the "recommended' psi.
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Old 04-23-2016, 05:27 PM   #6
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If you really want to do it right it's all in the document provided below. Just scroll down to page #47 and read all about it.

Don't find your answer and stop, you may miss the real answer.

http://www.mcgeecompany.com/wp-conte...ete-manual.pdf
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Old 04-23-2016, 05:40 PM   #7
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Quote:
Originally Posted by FastEagle View Post
If you really want to do it right it's all in the document provided below. Just scroll down to page #47 and read all about it.

Don't find your answer and stop, you may miss the real answer.

http://www.mcgeecompany.com/wp-conte...ete-manual.pdf
Be aware that that document states that the maximum pressure is molded into the sidewall. This is incorrect for tire rated for vehicles of 10,000#'s or more.
The pressure on the sidewall of a Michelin RV truck size tire and many others is not the "Maximum" the tire should ever have (unlike car tires) it is the minimum to support the maximum rated carrying capacity of the tire. NHTSA defines a truck tire as those used on anything with a GVWR of 10,000#'s or more.

From the Michelin RV Tire Guide:
Quote:
"If you look at the tire's sidewall, you'll see the maximum load capacity allowed for the size tire and load rating, and the minimum cold air inflation needed to carry the maximum load."
From page 6 of the GoodYear RV Tire and Care Guide:
Quote:
"How much air is enough?
The proper air inflation for your tires depends on how much your fully loaded RV or trailer weighs. Look at the sidewall of your RV tire and you’ll see the maximum load capacity for the tire size and load rating, as well as the minimum cold air inflation, needed to carry that maximum load."
From TOYO:
Quote:
Q: What are the consequences of inflating the tires to accommodate the actual loads?
A: If the inflation pressure corresponds to the actual tire load according to the tire manufacturer’s load and pressure table, the tire will be running at 100% of its rated load at that pressure. This practice may not provide sufficient safety margin. Any air pressure loss below the minimum required to carry the load can result in eventual tire failure.
But then they go ahead and publish a weight/pressure chart allowing lower pressure for RV's!!

From the August 2010 Motorhome Magazine "Tread Carefully" tire article:
Quote:
The maximum load capacity allowed for the size tire and load rating and the minimum cold air inflation needed to carry that maximum load are located on the tire’s sidewall.
From our owners manual:
Quote:
Federal law requires that the tire’s maximum load rating be molded into the sidewall of the tire.
If you look there, you will see the maximum load allowed and the cold air inflation pressure required to carry that stated maximum load. Less air pressure restricts the tire to carry a lighter load.
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Old 04-24-2016, 01:56 AM   #8
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Before anyone fools around with their RV tire inflation pressures they should learn the basics.

Recommended tire inflation pressures for your RV trailer and Motor Home tires are set by their manufacturer’s. Tire industry tire inflation charts developed by tire manufacturers and approved by the tire and rim association are primarily intended for usage by the tire industry.

When the Original Equipment tires are replaced with tires of a different size or design the recommended tire inflation pressures will have to be adjusted. It is the installers responsibility to make those adjustments. The primary target is to provide a load capacity with the replacement tires to equal or exceed the load capacity of the OE tires. That is accomplished with inflation pressure. Once the adjustment has been determined a notation in the vehicle owner’s manual should be made and also adjacent to the tire placard/certification label. Auxiliary tire placards are authorized by NHTSA.

Tire industry standards are not going to recommend using inflation pressures below that recommended by the vehicle’s manufacturer. If you cant balance your cargo load to safely accommodate a usable and safe tire inflation pressure within the industries standards your vehicle is probably overloaded.

One thing to become aware of is there are two sets of regulations in play for larger tires such as those used on large Motor Homes and RV trailers with 7 or 8 thousand pound axles. Only one of those regulations applies to all vehicles in the RV industry, that’s the FMVSS. The regulations for the trucking industry tires does not have recommended inflation pressures. Their pressures are good as long as they have a cold inflation pressure to carry the load on the tires. We see the results of that method on every major highway in the country.

As the owner of your vehicle you’re responsible for it’s safe operation. IMO tires for RVs should always have a reasonable amount of load capacity reserves when rolling down the highway. You have to have tires installed that can provide those reserves via inflation.
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Old 04-25-2016, 08:20 AM   #9
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Quote:
Originally Posted by Gary RVRoamer View Post
There is a sticker on the sidewall by the driver seat that gives you a safe baseline psi for the coach weight, for both front and rear axles. This is what Winnebago has determined is the best (read: safest) pressure unless and until you get actual loaded weights. Using somebody else's weights/pressures is a recipe for early tire failure and/or ride & handling problems.

The max load psi shown on the tire sidewall is just that - the psi needed to support the maximum load the tire is capable of. It is not the "recommended' psi.

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Old 04-25-2016, 01:37 PM   #10
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This method was posted to me from another member "lovlabs". I used his method and my coach drives WAY BETTER. Especially in wind conditions. It was hard for me to let a bunch of air out of my tires but like I said, big improvement. Here's what he sent me. Hope it gets you right.

"Individual wheel weights are hard to get but axle weights are available at just about any truck stop. Look for the CAT scales (big yellow and black signs with a stylized cat face on them).

So, load your MH as it will be when you travel and drive it to the nearest CAT scale and get the front and rear axle weight. That is one trip to the scale and your axles on the 1st and 2nd weighing pads. Pay the person your $10 bucks (could be $12 now) and get your weight certificate.

With your Michelin RV weight tables in hand and your calculator, you are going to do some math.

Front axle weight + 5% of that weight / 2 = your front wheel weight. Look that number up in the table for tire inflation pressure. Add an extra 5 psi to it as a safety factor.

Rear axle weight + 5% of that weight / 2= your rear wheel pairs weight. Look that number up in the dual wheel section of the chart and add 5 psi to that.

You now have your front and rear tire inflation numbers, your side to side difference has been estimated (that's the 5%) and you are ready to go. When you can, get individual wheel weights and fine tune the numbers.

Yes, your front and rear wheels can be inflated differently. No, what someone else uses for tire pressures is not OK to use on your rig.

Post your weight certificate and I'll walk you through the steps on how to calculate it correctly."
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Old 04-25-2016, 01:55 PM   #11
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I did a 4 corner the other day and came up with this:

LF 2780 RF 3080 Front axle GAWR 5,500

LR 5300 RR 5460 Rear axle GAWR 11,000

Total 16620. Freshwater and fuel tank full, black and grey empty. That's 120 lbs overweight. I'll travel with 1/4 tank freshwater (about 500 lbs less than full) and I moved some weight from RF to LF to make them more equal.

I'm going to run 80 PSI in my Cooper 225/70R 19.5 G rated tires. Fed Cert tag calls for 65 PSI in F rated tires.

Sound right?
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Old 04-25-2016, 07:09 PM   #12
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Quote:
Originally Posted by DrDaveMA View Post
Somewhere on the coach Winnebago has placed a sticker that gives you recommended tire pressures. It is assumed that they, the manufacturer, knows the weight on the each axle, and that is what they recommend, to be tweaked as you add your stuff.
Quote:
Originally Posted by Gary RVRoamer View Post
There is a sticker on the sidewall by the driver seat that gives you a safe baseline psi for the coach weight, for both front and rear axles. This is what Winnebago has determined is the best (read: safest) pressure unless and until you get actual loaded weights.
Just a note concerning the placard that the manufacturer has installed near the driver's seat: the tire inflation pressures listed on the placard are based on the GAWR of the front and rear axles - not on an actual weight of the vehicle. If you follow the placard's recommendations you can safely carry the maximum weight that each axle is rated for.

But, until you actually weigh your rig you won't know if you are below, at, or above the ratings for the axles.
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Old 04-25-2016, 07:26 PM   #13
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Quote:
Originally Posted by TS192 View Post
This method was posted to me from another member "lovlabs". I used his method and my coach drives WAY BETTER. Especially in wind conditions. It was hard for me to let a bunch of air out of my tires but like I said, big improvement. Here's what he sent me. Hope it gets you right.

"Individual wheel weights are hard to get but axle weights are available at just about any truck stop. Look for the CAT scales (big yellow and black signs with a stylized cat face on them).

So, load your MH as it will be when you travel and drive it to the nearest CAT scale and get the front and rear axle weight. That is one trip to the scale and your axles on the 1st and 2nd weighing pads. Pay the person your $10 bucks (could be $12 now) and get your weight certificate.

With your Michelin RV weight tables in hand and your calculator, you are going to do some math.

Front axle weight + 5% of that weight / 2 = your front wheel weight. Look that number up in the table for tire inflation pressure. Add an extra 5 psi to it as a safety factor.

Rear axle weight + 5% of that weight / 2= your rear wheel pairs weight. Look that number up in the dual wheel section of the chart and add 5 psi to that.

You now have your front and rear tire inflation numbers, your side to side difference has been estimated (that's the 5%) and you are ready to go. When you can, get individual wheel weights and fine tune the numbers.

Yes, your front and rear wheels can be inflated differently. No, what someone else uses for tire pressures is not OK to use on your rig.

Post your weight certificate and I'll walk you through the steps on how to calculate it correctly."
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I realize this was info sharing and away to help you, and now your playing it forward.

But IMO, this could be dangerous for some coach owners. Read the post that follows yours, with actual weights, and do the math on the 5% / 2 on the front axles. You will find that the weight is below the 'actual' weight of one of the tires. Yes, the extra 5 PSI may have covered this, and brought it to the 'minimum' PSI for the weight. But then there is not contingency PSI in the tires.

If going to a Cat scale, and they have the room, pay for the extra drive down the scales, to get the left or right (Does not matter.) single axles weights. Then you can do the math to subtract the single axle from the full axle's weight.

If you do not have four corner weights, IMO, your better off running the coach manufactures placards PSI's. Which are usually just the max axle rating weight PSI's.

-----

With so many coaches carrying significantly more weight on one side then the other, this method could be far enough off to be dangerous. Thus my opinion of a potential safety concern by using the tire manufactures charts without true 'four corner weights'.

My best to you, and to all. And advance apology if this was not worded diplomatically enough to come across in the positive way it was intended!

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Old 04-26-2016, 09:36 AM   #14
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This inflation question is always on my mind when I'm traveling. I used the info sent by "lovlabs" because that's all I can do. I would love to weigh the individual corners on my MH but according to anything and everything I have found searching the internet, there is a better chance of finding an albino unicorn than a 4 way weigh scale. As far as I can tell there is only one East of the Mississippi River in Florida. If anyone who reads this post knows of one of these illusive scales in the state of Tennessee, please post it here. I totally agree it could be dangerous to do it the way "lovlabs" described it, but what else is there? I always appreciate good advice so keep it coming. Thanks to all.
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