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Old subject….Tire Pressure
I had never had my coach weighed at every tire location….had it done today. I guess a few pressure adjustments will be in order….but a couple of interesting points came out of this!
1. My front axle is about 1000 lbs overweight with the door-side being the chief culprit. According to the weights provided me, the door side is 9000 lbs. That is, first of all, right at the limit of the tire weight-rating, and combined with the driver side adds up to a 1000 lb overload of the front axle……..anyone got any thoughts on this?
2. Based on the weights provided me, the drive (differential/drive) pressures should be 85lbs. Does that (85 lbs) sound correct? 85 lbs strikes me as somewhat low….although I’ve been running only a little more than that @ 95 lbs.
3. I was running the tag about right….95 lbs.
I’m always reminded that a “Consultant” is someone from out of town with a briefcase….or maybe a set of scales….
What’s your take on all this? ty
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15 Replies
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Some conversions are known to be over the axle weight limits. You can address the tire issue by converting to larger tires but that does nothing to deal with the other components that were sized for the axle weight limits. I know that is not what you might want to hear.
The 85 PSI pressure for the drive sounds very reasonable and I suspect the tag could be less. The lowest pressure for the 315 tires listed is 80 and if it is calculated the needed tag axle pressure could be as low as 70. But with the 80 PSI being the lowest listed weight it is probably best to use that pressure.
Your steers definitely need to be inflated to the specified limit because the weight is at the limit.
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BTom,
You know those storage compartments under your steps? That’s that not the place to store all of those gold bars, you will have to move them (I have some extra space).
I was wondering if you have the big box TV up front? Switching to flat screen would reduce a little weight. You could also reduce weight of anything in the first bay and put lighter stuff there.
We are also near the max weight of the chassis with our weight being toward the drive axle. I can control it by taking out the junk we don’t need or not carrying max water (189 gallons).
I’ve started to take out things we just don’t use.
Good luck,
Mark
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Don’t know if right or wrong but run 100 psi in my 12R 22.5’s.
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That’s the reason I went to 365’s on my H, I’m right at gross, but not over. With 315’s on the front I had to run 125 psi, the max pressure.
Btom may not be able to move much weight, he probably has the generator in the first bay driver side maybe Cruiseairs on the curb side.
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The book says 115-F, 90-D and 100-T. Last time I weighed the coach, I was 420 pounds over on the front. I relocated some stuff further aft, haven’t weighed it since, but I run 120 on the front for safety. I did not like the way the drive tires looked at 90, so I run the drive and tag at 100. I’d rather go high on pressure.
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Per,
I don’t know what book you’re talking about; however the following Prevost link is the “Tire Pressure Calculator” Prevost uses, supplied by Michelin.
“Tire pressure recommendations based on Michelin OEM tires. The coach should be weighed fully loaded, all tanks full.”
https://www.prevostcar.com/parts-and-services/tools/tire-pressure-calculator
If I used the chart, 365s on S/T and 315s on D, using my current weights 16,277 S / 20,169 D / 13,738 T, I would be at 90 S / 85 D / 80 T.
But I like running a little more air so I have them at 105 S / 95 D / 85 T.
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Tim,
The book is the one supplied by Marathon for our coach, and the Prevost book for the chassis gives the same pressures. Since you are running 365s on steer and tag, you should be in good shape running the pressures you stated.
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For coaches it was not unusual for tire pressures to be listed. Except how does whoever writes the book have a clue about how much personal stuff was going to be in the coach and how that would affect weights?
The only way to know how much tire pressure is required is to have each axle or tire weighed and use the charts provided by Prevost or Michelin to calculate the proper tire pressue.
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Thanks, Guys…
The fact that the worst over-weight was at the door corner is perplexing because there just isn’t much I can do. I might have 10lbs of a pressure gauge, rags, rubber gloves, etc in the under-step box, but thats about it. The first bay (door-side) is a bank of (factory) speakers, plus the four, very handsome, chrome plated, embroidered Marathon folding chairs, with cruise-airs behind…I might have another 10 lbs of junk there….so as far as the door corner, there is just not much I can do.
So….I think I’m going to start running MAX pressure in the fronts and the recommended on the others. And….rather than checking my Pressure Pro every 5 minutes…I’ll change to every 4.
See y’all at ClawFest…ty
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Btom,
Are you positive you got the right steer axle weight reading? Mine has the same setup as yours, assuming your gen is in the 1st bay driver side and my max steer is 17,200. Full of water and fuel, I’m 16,901 on the steer.
1999 XLV X-6872, liberty #440 -
Jon,
The Prevost owner’s manual is written based on maximum allowable axle weight, although it states you can run lower pressures if actual weight is below allowable. In that case it refers you to tire manufacturer’s tables for inflation pressures. If you are over on the axle weight, you can compensate with higher tire pressures up to a point. Marathon just copied the tire pressures recommended by Prevost.
Some interesting points on weight; I asked Marathon if they weigh their new coaches–they don’t. I’m wondering if any other Prevost converters weigh their new coaches, or they just let the customer hang out there? Production coaches come with a weight sticker–haven’t seen that on a Prevost yet.
On our coach (1999 shell), if you add up the axle weights, you get 900 pounds more than the gross allowable weight. Just curious!
Just for the record, I am not a fan of reducing tire pressures. Less pressure, more heat, which is bad for tires.
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Per,
Who at Marathon told you they don’t weigh their coaches? I would think they would be open to huge liability if they didn’t have out the door weights given it is a converted motor vehicle. When we purchased ours I spoke to someone at the factory that had the weights on mine. As I recall they didn’t tell me what it was but indicated it was less than what I was getting. Just curious who told you that.
Bill
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Per,
Our GVWR is 54,000 lbs.
When I add up all my axle weights, I’m at 50,184 lbs.
So to clarify, you’re at 54,900 lbs.?
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Per, when Marathon indicated tire pressures how did they know before you bought your coach and loaded it with personal stuff how much weight each axle would be carrying?
There is low tire pressure which is less than the amount specified in the charts. Then there is high tire pressure which is greater than that specified. Then there is the correct tire pressure that takes into consideration by the manufacturer braking, economy, tire life, ride, handling etc. If you choose to deviate from the specified pressure it is always better to go higher.
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Bill,
That would be the salesperson at Marathon in Coburg when we made the tour two years ago. Also, I asked when I was there last year if they could weigh our coach–I wanted to get individual wheel weights–and they told me they don’t have scales. I did get individual wheel weight at Jeff’s, which were very close to the CAT scale numbers. Jeff’s scales also showed I am 500 pounds heavier on the driver’s side steer, which makes sense since the generator is on that side.
Tim,
Our actual weight from the CAT scale in January was 50, 720, very close to the 50,935 I read on Jeff’s lifts last November, so you and I are close on total weight. Gross allowable weight on our coach is 52,060, adding total axle weight comes out to 50,960.
Jon,
Like I mentioned, all the Marathon owner’s manual does on tire pressures is to copy the Prevost recommendation at gross weight. They leave it up to the owner to load the coach responsibly.
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