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Old 04-25-2019, 10:37 PM   #1
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Tire Air Pressures?

I have a 2013 4318 Dutchstar,trying to determine whether the recommended air pressures of 130lbs front and 85lbs rear cold is realistic and should be abided by? Right now I have 115lbs frt and 80 lbs rear,under inflated? I am concerned,as when the running,the pressure will increase with the heating up of the tires? Just wondering what others out there are doing?
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Old 04-25-2019, 11:50 PM   #2
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Tire Air Pressures?

Quote:
Originally Posted by Bruexx View Post
I have a 2013 4318 Dutchstar,trying to determine whether the recommended air pressures of 130lbs front and 85lbs rear cold is realistic and should be abided by? Right now I have 115lbs frt and 80 lbs rear,under inflated? I am concerned,as when the running,the pressure will increase with the heating up of the tires? Just wondering what others out there are doing?


Hi there!

What is the source of your pressure “recommendations”?

130psi is way up there! Without knowing your scaled weight I can say that the number you have cited are way off.

Generally, your steers would be close to 110 and your drives including tag at around 95. These numbers are not accurate for you, just a generalization. It’s what I am running based on my scale weight and what is exactly what you need to do.

Tire pressure is relative to weight and 5-10psi +\- won’t be he end of the world but if clocking a lot of miles you will wear those tires poorly. 20-30+\- can be dangerous. Both for handling and potential failure and should be inspected.

Load your rig, hit the scales at a truck stop and get an understanding of your loaded weight. It doesn’t cost much and takes a few minutes. Most drive on to the scales and stop your window but the hung speaker. The attendant will speak with you. Make sure your toad is connected too (if applicable)

When you have that info you can set your pressure correctly. In fact I recommend you get your weight and post it here. I am sure you will get lots of insight.

For the interim, here is some general info from Goodyear but it could be from any manufacturer as the info is universal. Browse ‘RV tire inflation guide’

https://www.goodyearrvtires.com/tire...n-loading.aspx

Good luck!
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Old 04-26-2019, 02:19 AM   #3
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We stopped at a weigh station on our way home after picking up our new coach. It took a little discussion with the clerk to get the rig on the scales correctly - but even for a newbie it was easy enough. Once we got home (500 mi) I pulled out the tire manual (Michelin in our case) that came with our coach and got familiar with our specific tires. The manual helped me identify the specific tires on our coach and provided a weight vs. tire pressure for each axel. The dealer had the pressure 10 - 15 lb over the manual recommendation so I have adjusted accordingly. We ended up close to Miramichi's estimate. I'll re-do the weight once we load up our coach and re-check the pressure for the tires on each axel. I'll get a four corner weight when I can - but axel weights are better than not knowing.
BTW, stumbled onto a couple of CAT scale mobile apps that make it easier to get your weight. The first is 'CAT Scale' that tells you where the nearest CAT scale is and the second is 'Weigh My Truck' that allows you to get the weight without going inside and it emails the weight results to you.
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Old 04-26-2019, 06:24 AM   #4
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You really need individual corner weights to set your tire pressure.
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Old 04-26-2019, 06:33 AM   #5
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Hi Bruexx,
Every year DS is different. Sometimes same year with different model is different. The rear seems to always be the same. This is because the rear of a coach is usually very near gross axle weight.

The front is a different story. That can range from 110 to 130 easily. It just depends on how Newmar built the coach and model. Consider stopping at a PFJ for fuel. They have CAT scales at all truck locations. Get the coach weighted. This will give you axle weights, which is better than nothing. When you determine the steer axle weight you can go to the tire manufacturer's web site to get the correct PSI.
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Old 04-26-2019, 08:12 AM   #6
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What tire pressures does the sticker inside your coach list? (It is usually located near the driver seat) That's your starting point. Once you get fully loaded corner weights, you can adjust per the tire manufacturer chart.

As for the pressure increasing as the tires warm up, that is already included in the cold pressure calculations. Tire engineers know that tires warm up and pressure increases; it is nothing to be concerned about. A search of this forum for "tire pressure" will turn up a bunch of threads where this has been discussed at length.

Are you using a Tire Pressure Monitoring System? If not, it is a very wise investment. Not very expensive and it will give you individual tire pressure and temperature readings in real time. Very instructive too! You quickly learn what is normal and what is not.

TJ
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Old 04-26-2019, 12:28 PM   #7
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Quote:
Originally Posted by Ernie. View Post
You really need individual corner weights to set your tire pressure.
Absolutely agree -
But where do you get corner weights? From my reading here and other sites their are few places I can do this, mostly at a few rallies (FMCA and others) each year. I will get corner weights as soon as I don't have to go 500+ miles to get them. In the meantime axel weights are way better than nothing.
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Old 04-26-2019, 12:50 PM   #8
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Quote:
Originally Posted by Nildecaf View Post
Absolutely agree -
But where do you get corner weights? From my reading here and other sites their are few places I can do this, mostly at a few rallies (FMCA and others) each year. I will get corner weights as soon as I don't have to go 500+ miles to get them. In the meantime axel weights are way better than nothing.
On scales with no restrictions on the sides, you can get corner weights by making two passes through with one side on the scale on the first pass and all wheels on the scale on the second pass. A little simple math will get you actual corner weights. That procedure usually requires some discussion with the scale operator/clerk, they can usually accommodate you with two sets of weight tickets.

And, yes...axle weights are better than nothing. Don't simply split the axle weight in half, however; use 55% of the total axle weight as the weight for each side. That gives you a bit of a safety factor. Its not as good as actual axle weights, but it probably the next best option.

TJ
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Old 04-27-2019, 08:26 AM   #9
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We have a 2013 4338 DS and after the 4 corner weighing with full fuel and water, our pressures are 115 front, 80 rear and tag.
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Old 04-27-2019, 09:42 AM   #10
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This sticky has a thread explaining how to determine your correct tire pressures.
One thing you do not want to do is have low air pressures in your tires that are posted on a plac-card posted on wall beside your drivers seat, your inviting a blow out on one of your steer tires for sure.
Read the thread link get your coach weight at a scales and using the tire pressure tables for your MFG of your tires.
You may load your coach differently than some other owner.
When driving on road your tires will increase in tire pressure 10 to over 20 PSI and you adjust tire pressure in the morning when tires are cool.
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