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Old 05-13-2016, 07:22 AM   #1
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Weighing rv for tire pressure setting.

I need to set my tire pressures. Last time I had my class c on the road, it was a very rough ride.
As I understand it's best to weigh each tire independently. Problem is all the scales in my area only allow you to weigh the front axle and rear axle separately. Can I just use the front axle weight for each of the front two tires? Or is there a significant weight difference from side to side?
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Old 05-13-2016, 08:18 AM   #2
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There can be a significant difference between the left and right sides of the same axle. A conservative (higher safety margin) approach may be to use the max cold inflation pressures on your tire sidewalls to set your pressures until you get a true 4-corner weight. A less conservative approach is to use your axle weights and set the pressures about 5 - 10 pounds over the chart recommendation to help cover if one of the tires is significantly more loaded (but no higher than the max cold inflation pressure) until you can get the 4-corner weight.

Recommend you talk with the scale folks - they will often know who might have a scale with your needs. A call to local RV dealers may also be helpful. You're on the right track by paying attention to this issue. Safe travels...
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Old 05-13-2016, 08:31 AM   #3
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I think the best, in the middle choice, is to use what the sticker on the door recommends. Mine are 80 rear and 65 front. Not a bad ride.
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Old 05-13-2016, 08:39 AM   #4
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There some advice mentioned here:
Weighing your coach

Are the scales you mention the ones you drive UP onto? Like a bridge? If they're even with the road you straddle left or right to get individual weights.

Do you have double wheels in the rear? Remember to divide!

We don't carry anywhere near max capacity and there is a world of difference between cold tire inflation as seen on the sticker inside the driver's door and what you actually only need based on weights. You will definitely feel the difference when you hit some rough asphalt!!


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Old 05-13-2016, 08:46 AM   #5
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Quote:
Originally Posted by tmaxx View Post
I need to set my tire pressures. Last time I had my class c on the road, it was a very rough ride.
As I understand it's best to weigh each tire independently. Problem is all the scales in my area only allow you to weigh the front axle and rear axle separately. Can I just use the front axle weight for each of the front two tires? Or is there a significant weight difference from side to side?
tmaxx
Although "axel weights" MIGHT get you close to the "corner weights" required to accurately determine the correct tire inflation pressures for your RV... inflation pressures based on axle weights might not be correct because there can be a significant weight difference from side to side.

That's why independently weighing the individual left and right, (on both the front and rear axles), is recommended.

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Old 05-13-2016, 08:51 AM   #6
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Yes, I have dual tires on rear. Not sure what you mean by divide? Can u elaborate?

Quote:
Originally Posted by RogerRoll View Post
There some advice mentioned here:
Weighing your coach

Are the scales you mention the ones you drive UP onto? Like a bridge? If they're even with the road you straddle left or right to get individual weights.

Do you have double wheels in the rear? Remember to divide!

We don't carry anywhere near max capacity and there is a world of difference between cold tire inflation as seen on the sticker inside the driver's door and what you actually only need based on weights. You will definitely feel the difference when you hit some rough asphalt!!


2010 Winnebago Aspect 28B
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Old 05-13-2016, 09:02 AM   #7
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I'm just being silly. Most inflation charts you'll find will show the pressure for rear duals, and of course both tires of a dual must be at the same pressure!

I just meant if you have the weight of one corner in the rear, that weight is supported (divided) by two tires.


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Old 05-13-2016, 09:07 AM   #8
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Truck stops with CAT scales can do the job for you, but expecting help from them might be a stretch. The counter help know how to get you a weight slip, but beyond that, you generally get a blank stare when it comes to RV's.

4 corner weight involves getting a weight slip as you normally would - producing axle weights. To get the 4 corner weights, you need to ask to be re weighed. It's cheap, like 4 bucks. Pull off the scales, drive around, but this time put one side or the other off to one side of the weight tables as you pull on. There's always a safety area on each side, but they do vary in width, so pay attention when pulling up with one side of the coach off the tables, or have somebody watch/guide you. Then ask for your weight with just one side on the scales.

You'll get a second slip, just like the first one. To get the corner weights, just subtract the one side results from the total.
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Old 05-13-2016, 09:14 AM   #9
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Ok maybe I'm confused. I thought the entire axle would be set the same based on the heaviest side. Same thing on the front. Run both sides at the same pressure based on the heaviest side.


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Old 05-13-2016, 09:34 AM   #10
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Harleyjt, that's what you should do when you only have axle weights.

Remember, it's not "bad" to run with tires slightly over-inflated (within the max rating of course). I think that is better than under-inflating. It comes down to tire wear life and road comfort. I find inflating individually makes you more likely to load all your stuff more evenly.


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Old 05-13-2016, 10:14 AM   #11
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So you are saying to inflate each side based on weight on that particular corner? I can't believe anyone would inflate the fronts differently.


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Old 05-13-2016, 10:23 AM   #12
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I wouldn't either, but I might make an attempt to equalize the loads if I found excessive side to side differences. As can be imagined, these can be caused by load, but can be caused by broken parts or wimpy springs just as commonly. For instance, a heavy front reading might be trying to compensate for a weak rear on the same side...

Once that's settled, then I would inflate per the requirements of the heavy side.
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Old 05-13-2016, 12:05 PM   #13
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Quote:
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I can't believe anyone would inflate the fronts differently.
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It is not unusual for the fronts to be inflated to a different pressure than the rears.
However all tires on the same axle should be inflated to the pressure recommended for the tire, (or tires), on that axle that is/are carrying the most weight.
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Old 05-13-2016, 12:11 PM   #14
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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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