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Old 11-17-2021, 08:18 PM   #1
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Tire Pressures

Do you set your tire pressures according to the boiler tag located beside drivers seat or do you set your tire pressure according to the max cold listed on sidewall of tire.
Example: My tag on my diplomat says 115 psi front and 100 psi rear(dual).
Tires have 130 PSI (cold) on sidewall.
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Old 11-17-2021, 08:29 PM   #2
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130 psi? Semi tires are generally in the 105 to 110 range.
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Old 11-17-2021, 09:11 PM   #3
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Yep, that is on the sidewall of my tire.
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Old 11-17-2021, 09:27 PM   #4
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Quote:
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Do you set your tire pressures according to the boiler tag located beside drivers seat or do you set your tire pressure according to the max cold listed on sidewall of tire.
Example: My tag on my diplomat says 115 psi front and 100 psi rear(dual).
Tires have 130 PSI (cold) on sidewall.
Neither. I set it by measured weight and the load and inflation table.
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Old 11-17-2021, 09:33 PM   #5
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Neither. I set it by measured weight and the load and inflation table.
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Old 11-17-2021, 09:38 PM   #6
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Neither. I set it by measured weight and the load and inflation table.
We have a winner!
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Old 11-18-2021, 08:06 AM   #7
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Originally Posted by skitches View Post
Tires have 130 PSI (cold) on sidewall.
That is the air pressure at the tire's maximum load as set by the tire manufacturer. The max load will be listed right next to that air pressure number on the sidewall.

So, for example, if the tire was rated for 9,000 lbs at 130 psi, and you were carrying 9,000 lbs on that tire you would need to have 130 Psi in it. If you are carrying less weight then you can have less air pressure in the tire.

It would not harm the tire to have 130 psi in it, but the ride would be very hard. Worse case it might not wear the tire tread evenly.

You want to have the Coach weighed (four corner weighing) is best, from a place like SmartWeigh, next best would be a truck scale (CAT Scale) at one of the truck fueling places.

Then you go to the tire manufactures website and they will have a chart for the tire model/size with the air pressures to run in it based on the weight the tire carries.
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Old 11-18-2021, 05:12 PM   #8
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Can be that you need the full 130psi, but also even lower then 115psi is safe.

It all depends on the real weight on tires, and that is for every RV different.

So to determine which pressure can be used for your RV, determine first as acurate as possible the real weight on seperate tires.

Best way to do that is weighing fully loaded , as you go on trip, per axle-end, so also water and persons in it.

Second best is weighing per axle.

But in lack of that , you will have to go from GAWR's .

If you give me those , together with the tire, specifications( gamble on 9000lbsAT 130psi, but make me wiser) , I will put it in my made Motorhome tirepressure calculator, in wich I use an even safer formula then the European official used, and add 10% to the given loads for reserve.
Even recalculate maxload to that needed for 99mph ( OK, you never drive that speed) , yust for reason together with 10% reserve, to get highest pressure , with max reserve, but still acceptable comfort and gripp.

This then will give higher pressure then yust reading back the loads in an American list, even when first 10% added . So then if a115psi prescribed by RV maker, my calc could come to 130psi.
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Old 11-18-2021, 05:59 PM   #9
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Until you determine you need or want to do otherwise, start with the pressures provided by the RV manufacturer. If you think the ride too harsh, try the GAWR’s provided by RV manufacturer and look those numbers up in your tire manufacturers weight/pressure charts. If that is not to your liking get your unit weighed as you use it. All your stuff, full fuel, water, people and then look up those weights.
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Old 11-18-2021, 09:57 PM   #10
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Here in Oregon our truck scales (the official scales) are left turned on when the scales are closed.
I loaded up fuel and water and goodies and carefully weighed each axle. I went to the TOYO website and found the inflation chart for by 24.5 tires and calculated my pressures that way.
Better safe than sorry.
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Old 12-02-2021, 03:00 PM   #11
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Tire Pressure

I ran across this thread while researching tire pressure. My new to us 2006 Monaco Dynasty placard calls for 120 psi on the Steer Tires, 85 psi on the drive and 80 psi on the tags. I am running a brand new (DOT 2121) set of Toyo 295/80 22.5 M144 tires.

I recently weighed my coach essentially unloaded with a full take of diesel. Obviously when I add potable water and all our creature stuff I will add weight. I plan to re-weigh in the loaded condition. However, I have questions based on the weight data I do have.

The actual front axle weight was 12,260 lb vs the placard GAWR of 15,160 lb). For the front axle, 120 psi seems high. My previous coach (2003 American Eagle) had the very same actual front axle weight and only called for 110 psi. The Toyo table load at 120 psi is 7,575 lb and at 110 psi 7.065 lb. I choose to run at 110 psi based on my current actual weight.

In the rear I only have a combined actual weight for both the drive and tag axles. The combined actual weight was 24,260 lb. The GAWR for the drive axel is 20,000 lb and 10,000 for the tag axle. Table load rating at 85 psi for dual use is 5,095 lb. For the tag, rated load for single tire at 80 psi is 5,475 lb. I don't understand why the recommendation is for lower pressure on the tag vs drive tires. I left the tire shop with all six rear tires at 100 psi.

Am I making a mistake running 110 psi on front and 100 psi on all six rear? Should I quit over thinking and simply run the pressures recommended on the coach placard?


Doug
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Old 12-02-2021, 03:36 PM   #12
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Placard pressures will almost always be the recommended minimum pressure for the tires on each axle, when the axle is at GAWR.

Dual positions will have different pressure recommendations than single positions.

80psi is likely the minimum recommended pressure for the tire, which is why that psi is given for the tag, even though that pressure is sufficient to support nearly 11,000lbs.

85psi on the drive axle is sufficient to support 20,000lbs.

The 120psi and 7575lb load for the fronts is actually 10lbs less that your FAWR.

I wouldn’t compare anything to your previous coach unless it had the same size tires. I’ve made a practice of not recommending specific pressures to anyone, or saying “you’ll be fine”. You’ve weighed the coach, you know the axle ratings and you’ve checked the load and inflation table. Ideally, it would be beneficial to have separate drive and tag weights, but you have enough information to make an informed decision.
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Old 12-02-2021, 03:46 PM   #13
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Quote:
Originally Posted by Kid Gloves View Post
Placard pressures will almost always be the recommended minimum pressure for the tires on each axle, when the axle is at GAWR.

Dual positions will have different pressure recommendations than single positions.

80psi is likely the minimum recommended pressure for the tire, which is why that psi is given for the tag, even though that pressure is sufficient to support nearly 11,000lbs.

85psi on the drive axle is sufficient to support 20,000lbs.

The 120psi and 7575lb load for the fronts is actually 10lbs less that your FAWR.




I wouldn’t compare anything to your previous coach unless it had the same size tires. I’ve made a practice of not recommending specific pressures to anyone, or saying “you’ll be fine”. You’ve weighed the coach, you know the axle ratings and you’ve checked the load and inflation table. Ideally, it would be beneficial to have separate drive and tag weights, but you have enough information to make an informed decision.



"I’ve made a practice of not recommending specific pressures to anyone, or saying “you’ll be fine”"


I totally respect your position. And yes my old coach did have the same size tires. I hope to find a weight station that can accommodate at minimum separate drive and tag axle weights and ideally individual tire position weights. Then after getting fully loaded coach weights I will study the tables and come up pressures for each axle.


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Old 12-03-2021, 12:39 PM   #14
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If the scale is on same level as the ground before and behind it, you can first drive front on it and weigh, then upto drive axle, so the tag not on scale.
Then if front still on scale, you substract front from total to get weight on drive-axle.
Then drive on untill front is off the scale, or even also drive, then you have tagweight , or if drive still on scale, substract that from total to get tagweight.
You can also write it all down first and do the calculations at home.

If also beside the scale, the ground is on same level, and no obsacles beside, you can do the same trick with only one side on the scale, then substract those weights from axleweights to get the other side.
If the ground is only halve inch lower or higher, this wont work.

But write down what you weigh, for instance next.
F 12500LBS
F+D 27000lbs
D+T 26000 LBS

THEN Left F, F+D, D+T, if left side drives over the scale.

If one side can be weighed, dont be surprised if weightdifferences R/L is crossed between the axles, chance on that is 50/50.
For instance F left more heavy, D right more heavy, T left more heavy.
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