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Old 01-23-2022, 04:56 PM   #1
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Age old question tire pressure?

I have a 2003 Fleetwood Pace Arrow 37A about 20,940 lb loaded. Tires are Hercules 255/70R23.5. Sidewall states 120PSI. Camping World who I do not trust and will not go back to ( whole other story) set tire pressure at 80psi. I think they are way low. Am I right or wrong? Have not had each wheel weighed. Recent CAT weigh in: Front axle 6300 and Rear axle 14640. Any recommendations?
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Old 01-23-2022, 05:06 PM   #2
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Go on line to the Hercules tire website and get the recommended tire pressure based upon weight then add 5 or 10 pounds for safety. 80 psi sounds a bit low to me.
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Old 01-23-2022, 05:36 PM   #3
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Have you tried the placard pressure listed near the drivers seat? That's a safe pressure to use till you can fine tune it to the load inflation chart.
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Old 01-25-2022, 08:02 AM   #4
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The pressure stated on the side of the tire is the maximum cold inflation pressure the the should EVER be inflated. It is not directly related to the pressure that the tire should be set.

I don't have a load inflation chart for Hercules tires but I have found that most commercial truck tires have very similar or identical load/inflation charts. I do have a Firestone load/inflation chart.

You say your CAT scale measurements are 6300 for the front axle and 14640 for the rear. According to Firestone inflation chart for your tire size the minimum pressure recommended is 80 PSI. At 80 PSI your front tires can carry 4190 LBS each or a total for the front axle of 8380. The minimum pressure of 80 PSI your rear tires can carry 3970 per tire or 15880 on a dual tire axle.

80 PSI gives you a margin of 2080 lbs on the front axle and 1240 lbs on the rear axle. I think the 80 PSI is about right. It is definitely adequate for the front axle. Some might argue that you should increase your rear pressure a little to compensate for a possible side to side imbalance of load where one side of your rear axle has a heavier load.

Although I think you are fine at 80 PSI you might leave the front pressure at 80 PSI and increase your rear pressure to 85 PSI. This raises the rear axle capacity to 16440 lbs. 85 PSI on the rear raises your margin to 1800 lbs.

Both over inflation and under inflation is bad. Set your tires according to the load/inflation chart. Don't be tempted to increase your tire pressure significantly over the pressure on the chart.

Hopefully someone can point you to a load/inflation chart for your Hercules tires. I think you will find it the same as the Firestone chart.
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Old 01-25-2022, 09:17 AM   #5
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Hopefully someone can point you to a load/inflation chart for your Hercules tires. I think you will find it the same as the Firestone chart.
I was going to try and be helpful by finding a Hercules load inflation tire chart for the OP but didn't have any luck. Not sure why it's so hard to come by. I agree with you that another manufacturer's chart will most likely show the same or similar capacities to the Hercules brand.

With the OP's given weights, and even though the chart shows 80 psi as being satisfactory, I believe I'd experiment with a higher pressure at about 90 all around to see how the coach rode. That higher pressure would cover most any situation the coach might inadvertently end up in. Can always lower pressures if the ride is too firm.
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Old 01-25-2022, 09:28 AM   #6
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I have almost the same coach as the OP, and though I run Sailun tires, I run all tires @ 100#. We travel with 1/2 tank of water and a "few" grocery's. We have balance beads in all 6 tires and "Sumo's" all round, and she rides like glass.

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Old 01-25-2022, 10:13 AM   #7
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Quote:
Originally Posted by yeloduster View Post
The pressure stated on the side of the tire is the maximum cold inflation pressure the the should EVER be inflated. It is not directly related to the pressure that the tire should be set.

I don't have a load inflation chart for Hercules tires but I have found that most commercial truck tires have very similar or identical load/inflation charts. I do have a Firestone load/inflation chart.

You say your CAT scale measurements are 6300 for the front axle and 14640 for the rear. According to Firestone inflation chart for your tire size the minimum pressure recommended is 80 PSI. At 80 PSI your front tires can carry 4190 LBS each or a total for the front axle of 8380. The minimum pressure of 80 PSI your rear tires can carry 3970 per tire or 15880 on a dual tire axle.

80 PSI gives you a margin of 2080 lbs on the front axle and 1240 lbs on the rear axle. I think the 80 PSI is about right. It is definitely adequate for the front axle. Some might argue that you should increase your rear pressure a little to compensate for a possible side to side imbalance of load where one side of your rear axle has a heavier load.

Although I think you are fine at 80 PSI you might leave the front pressure at 80 PSI and increase your rear pressure to 85 PSI. This raises the rear axle capacity to 16440 lbs. 85 PSI on the rear raises your margin to 1800 lbs.

Both over inflation and under inflation is bad. Set your tires according to the load/inflation chart. Don't be tempted to increase your tire pressure significantly over the pressure on the chart.

Hopefully someone can point you to a load/inflation chart for your Hercules tires. I think you will find it the same as the Firestone chart.
Great answer Duster.

I couldn't find the load and inflation table for Hercules tires either but I did find a spec sheet for the 255/70/22.5 Strong Guard RA's and it confirms that at 120psi the Herc tires has the same load carrying capacity as the Firestone 255/70R22.5 Medium Truck tire. 5510lbs for a single and 5070 for a dual.

Using the Firestone Load and Inflation table I agree that 80psi is perfect for the front tires and 85 would be perfect for the rear. If the OP wants to add 5psi to those numbers he surely can but 80 and 85 respectively will carry the load with no problem.

https://www.herculestirescommercial....fications=true

https://commercial.firestone.com/con...s_web_2014.pdf
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Old 01-25-2022, 10:56 AM   #8
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Quote:
Originally Posted by yeloduster View Post
The pressure stated on the side of the tire is the maximum cold inflation pressure the the should EVER be inflated. It is not directly related to the pressure that the tire should be set.
Just a slight clarification: the sidewall pressure is the MINIMUM pressure required to carry the MAXIMUM weight that the tire is rated for, and it actually states that, right on the sidewall.
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Old 01-25-2022, 11:00 AM   #9
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Originally Posted by Alan_Hepburn View Post
Just a slight clarification: the sidewall pressure is the MINIMUM pressure required to carry the MAXIMUM weight that the tire is rated for, and it actually states that, right on the sidewall.

Absolutely correct.


But, HOPEFULLY, that will be well more PSI than is needed to carry the axle loads on his coach.


Said another way, you do not want the tires loaded to their maximum capacity-- better to have a safety reserve.
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Old 01-25-2022, 09:02 PM   #10
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Calculating Proper PSI for motorhome home tires (video)

Quote:
Originally Posted by Reuscher View Post
I have a 2003 Fleetwood Pace Arrow 37A about 20,940 lb loaded. Tires are Hercules 255/70R23.5. Sidewall states 120PSI. Camping World who I do not trust and will not go back to ( whole other story) set tire pressure at 80psi. I think they are way low. Am I right or wrong? Have not had each wheel weighed. Recent CAT weigh in: Front axle 6300 and Rear axle 14640. Any recommendations?
Ya, my recommendation is axle weigh doesn't cut it nor sidewall stated pressures.You have to do a 4 corner weigh b/c the heaviest corner is where you start. Knowing the proper PSI according to your weight for any brand of tires is math not guess work. I found a great video awhile back that explains step-by-step how to calculate proper PSI after you have done a 4 corner weigh if your interested.
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Old 01-26-2022, 08:35 AM   #11
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Originally Posted by mr.tommy View Post
Ya, my recommendation is axle weigh doesn't cut it nor sidewall stated pressures.You have to do a 4 corner weigh b/c the heaviest corner is where you start. Knowing the proper PSI according to your weight for any brand of tires is math not guess work. I found a great video awhile back that explains step-by-step how to calculate proper PSI after you have done a 4 corner weigh if your interested.
I'm going to have the tire pressure police all over me!

Four corner weight and corresponding tire pressure is nice...nice but overkill! For every Motorhome on US highways there are several thousand OTR trucks. You can be assured that OTR truckers don't weigh "four corners". Most of them don't even have the ability to do an individual wheel weight. The conscientious ones do axle weight and set tire pressure accordingly. Most of them don't even go that far. They set tire pressures for GAWR of the vehicle. Those that do that much rarely have tire pressure related tire problems.

The vast majority of motorhome drivers do even less than that. They treat their motorhome like a car. They get in and drive! They only think about tire pressure when someone points out that a tire appears to be low! Bless modern tires for their ability to survive abuse. Motorhome forums represent a tiny percentage of motorhome owners. Most of them don't think like us! It is a miracle that there aren't more motorhome tire disasters!

So, be as obsessive as you want about tire pressure or not, as long as you are paying attention to your tire pressure and inflate according to actual weights or GAWR you will be fine.
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Old 01-26-2022, 09:58 AM   #12
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Originally Posted by yeloduster View Post
I'm going to have the tire pressure police all over me!

Four corner weight and corresponding tire pressure is nice...nice but overkill! For every Motorhome on US highways there are several thousand OTR trucks. You can be assured that OTR truckers don't weigh "four corners". Most of them don't even have the ability to do an individual wheel weight. The conscientious ones do axle weight and set tire pressure accordingly. Most of them don't even go that far. They set tire pressures for GAWR of the vehicle. Those that do that much rarely have tire pressure related tire problems.

The vast majority of motorhome drivers do even less than that. They treat their motorhome like a car. They get in and drive! They only think about tire pressure when someone points out that a tire appears to be low! Bless modern tires for their ability to survive abuse. Motorhome forums represent a tiny percentage of motorhome owners. Most of them don't think like us! It is a miracle that there aren't more motorhome tire disasters!

So, be as obsessive as you want about tire pressure or not, as long as you are paying attention to your tire pressure and inflate according to actual weights or GAWR you will be fine.
Nailed it again Duster.

I've weighed both my coaches many times, both 4 corner and just the individual axles. I've never seen more than a 200# difference between the left and right side tires.

It's pretty simple even if you don't do a 4 corner weight measurement.

1. Weigh your coach per axle.
2. Divide axle weight by the number of tires.
3. Multiply that number by your own desired safety factor.
4. Find that number on the Load and Inflation table.
5. Air up your tires according to the pressure recommended on the table.
6. Monitor your tire pressure regularly, preferably with a TPMS system.

The more complex you make it the bigger chance for a mistake.
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Old 01-26-2022, 11:10 AM   #13
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Paralysis by analysis.

Just read post #4. That answers your question.


The GoodYear RV tire inflation table also agrees. I think most of these tables are the same.
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Old 01-26-2022, 11:57 AM   #14
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Originally Posted by Alan_Hepburn View Post
Just a slight clarification: the sidewall pressure is the MINIMUM pressure required to carry the MAXIMUM weight that the tire is rated for, and it actually states that, right on the sidewall.
I see these posts correcting people from time to time but imo, it's not that big a deal. A person reading the pressure on the sidewall knows it's the pressure needed for the tire to carry the maximum load it can. I really can't think of any reason why someone would say to themselves "hey, I know I'm not gaining any more capacity but for grins, why don't I just add more than the tire specifies."
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