Need a math teacher for tire pressure confirmation

[Mmnsc]

Ron
I looked at the Michelin RV tire chart for your size tire with the H rating and the front tires based on the weight you provided should be between 105 and 110 Psi. Are you sure about the weights you provided for the drive axle and the tag? The drive seems light and not even listed for dual wheel and the chart starts at 9080 lbs. at 75 Psi. When you take the 15020 and divide by 2 you get 7510 pounds for each side of the axle which is below the listed minimum for dual wheels. The same is true for the tag tires.
I would have the coach reweighed with 6 point weight readings before going further trying to figure out your proper tire pressure.
Marty


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[Campin Cajun]

Marty I noticed the same when I looked at my chart and assumed (bad idea) that a person would go with the minimum pressure rating listed.

[conceptumator]

Life is way too short to worry with these things, folks. Take a look at your tires. What does it indicate is the max pressure cold? Mine say 120 psi. Put that much air in all your tires and be done with it. It's an RV for pity sake, not a Rolls Royce. The ride may not be as smooth as you like, but you won't be blowing tires!

[DSQR]

"The vehicle manufacturer (not the tire manufacturer) has developed these numbers based on the axle distribution, gross weight and other oddball factors the tire maker could not foresee in a specialty application."

And assumes you are running the OEM tires. I use a tire only for the service for which the tire was manufactured, and inflate as per the tire manufacturer's guidance. The only time I consider the RV label as gospel is when it still has the original equipment tire - since this assumes the RV manufacturer has made the correct choice per tire manufacturer's specs)

Just imagine the liability issues the OEM would face if a serious accident due to tire failure occurred, and a sharp investigator determined the OEM label did not reflect the tire manufacturer's specification.

When I bought my dually, it had street-tread tires on it. These were replaced with BFG AT/KO tires. I know the inflation pressures on the door sticker are not correct for the BFGs. The BFGs would be significantly underinflated. (I have experienced this personally - having run BFGs on my trucks for over 40 years and experienced the rapid wear if I inflate to sticker pressure.)

[Phil57]

Originally Posted by conceptumator

Life is way too short to worry with these things, folks. Take a look at your tires. What does it indicate is the max pressure cold? Mine say 120 psi. Put that much air in all your tires and be done with it. It's an RV for pity sake, not a Rolls Royce. The ride may not be as smooth as you like, but you won't be blowing tires!

I really didn't want to comment but I can't stop. This is just not a good idea. It isn't hard to figure out the weight. In this case no one here is familiar with tag axle and psi. In any case it is well worth taking the time to set the psi correctly on you tires. Tires are very expensive and who wants to replace them before you need to? Also my life and my family's life is worth taking a few minutes to get it right. I know that most have never weighted their Moho. That's up to them but it is just not a good idea to run it up to max pressure and go.

[Phil57]

Originally Posted by DSQR

"The vehicle manufacturer (not the tire manufacturer) has developed these numbers based on the axle distribution, gross weight and other oddball factors the tire maker could not foresee in a specialty application."

And assumes you are running the OEM tires. I use a tire only for the service for which the tire was manufactured, and inflate as per the tire manufacturer's guidance. The only time I consider the RV label as gospel is when it still has the original equipment tire - since this assumes the RV manufacturer has made the correct choice per tire manufacturer's specs)

Just imagine the liability issues the OEM would face if a serious accident due to tire failure occurred, and a sharp investigator determined the OEM label did not reflect the tire manufacturer's specification.

When I bought my dually, it had street-tread tires on it. These were replaced with BFG AT/KO tires. I know the inflation pressures on the door sticker are not correct for the BFGs. The BFGs would be significantly underinflated. (I have experienced this personally - having run BFGs on my trucks for over 40 years and experienced the rapid wear if I inflate to sticker pressure.)

Remember that a Moho is built on a chassis. You have two manufacturers at work here. FR will give psi for max weight. fL also will give psi for max chassis weight. Neither of these manufacturers know what your Moho weighs so how would they know where to set the psi. Each owner must get a 4 point weight and adjust their tires to that weight. This is a Moho not a truck. Not a pick up and not a over the road tractor. They are different and need to be handled as such.
Sorry to the OP for all the side track.

[Boso]

The higher the psi the cooler it runs. The cooler tire is a much more reliable tire,and that means a safer tire. But not above maximum pressure. And you don't need to change according to climate. That is built into specs that are listed on your tire. Or on your coach.

[Campin Cajun]

Twice, after doing some research on other Motohome forums here the best I gathered.

I couldn't quote or copy paste the link but it is basically said if your weights are less than what is listed on the tire charts then you should run your air pressure at 75% of the Max pressure listed on the side wall of the tire. So if you max is like mine at 120psi you should run no less than 90psi on any given tire.


Also, you have a FL chassis, a non adjustable pressure regulator is installed for the tag axle. If you want to you can drill out a pop rivet on the regulator that locks the ability to adjust the pressure of the air bags on the tag axle. This gives you the ability to use less pressure on the tag axle air bags which in turn will add more weight to the drive axle and takes some weight off the steer axle.

Adding pressure to the air bags on the tag will have the opposite effect.

I hope this info helps you.

[TwiceTheIce]

Originally Posted by Mmnsc

Ron
I looked at the Michelin RV tire chart for your size tire with the H rating and the front tires based on the weight you provided should be between 105 and 110 Psi. Are you sure about the weights you provided for the drive axle and the tag? The drive seems light and not even listed for dual wheel and the chart starts at 9080 lbs. at 75 Psi. When you take the 15020 and divide by 2 you get 7510 pounds for each side of the axle which is below the listed minimum for dual wheels. The same is true for the tag tires.
I would have the coach reweighed with 6 point weight readings before going further trying to figure out your proper tire pressure.
Marty


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Marty, the weights are correct. Had them weighed on two different cat scales. My weights on drive are approximately 1200# heavier than empty weights from factory. This equates to full water and clothes, etc. Remember gvw for coach is 43000# and we are now only at 35200# shipped weight was 32495#.

[TwiceTheIce]

Originally Posted by Campin Cajun

Twice, after doing some research on other Motohome forums here the best I gathered.

I couldn't quote or copy paste the link but it is basically said if your weights are less than what is listed on the tire charts then you should run your air pressure at 75% of the Max pressure listed on the side wall of the tire. So if you max is like mine at 120psi you should run no less than 90psi on any given tire.


Also, you have a FL chassis, a non adjustable pressure regulator is installed for the tag axle. If you want to you can drill out a pop rivet on the regulator that locks the ability to adjust the pressure of the air bags on the tag axle. This gives you the ability to use less pressure on the tag axle air bags which in turn will add more weight to the drive axle and takes some weight off the steer axle.

Adding pressure to the air bags on the tag will have the opposite effect.

I hope this info helps you.

CC: I had 85# floating around in my head. But, just for argument's sake, if 75% of 120 is the minimum, why does Michelin have 75psi in the chart?

I don't believe I want to start messing with suspension pressure in tag, because the stability on the road is phenomenal. Seventy mph in 20-35 mph winds and steady as a rock.

Thanks for the input.

[RKNOLA]

Originally Posted by conceptumator

Life is way too short to worry with these things, folks. Take a look at your tires. What does it indicate is the max pressure cold? Mine say 120 psi. Put that much air in all your tires and be done with it. It's an RV for pity sake, not a Rolls Royce. The ride may not be as smooth as you like, but you won't be blowing tires!

Life's going to be a whole lot shorter with that type of reasoning. Go on the internet and search Motorhome Tire Blow Out. Then tell me it is no big deal.
I am not willing to take the chance with my MH.
(While you are online search the price of a 2016 Berkshire XLT, then search the price of a 2016 Rolls Royce. Which amount would you rather see turned over in a ditch from over/under inflated tires?)

[Campin Cajun]

Originally Posted by TwiceTheIce

CC: I had 85# floating around in my head. But, just for argument's sake, if 75% of 120 is the minimum, why does Michelin have 75psi in the chart?



I don't believe I want to start messing with suspension pressure in tag, because the stability on the road is phenomenal. Seventy mph in 20-35 mph winds and steady as a rock.



Thanks for the input.

That 75% I mentioned was from an RV tire expert on the Tiffin Forum. He worked for Michelin in the past. He is very knowledgable on RV tires.

I do agree with you on not wanting to mess with the air bags pressures. And I am glad to know she handles so well down the road, I will probably upgrade to the XLT next year.

[Paulie Boy]

Twice, if their is a Freightliner Oasis service center anywhere near you I would recommend you take the rig to them. They are capable of the six corner weigh, adjust the air bags and set your tire pressures to the recommended inflation. I did that last year at the Gaffney, SC facility and the coach handled and road like it was floating on air. No pun intended.
I crack myself up sometimes✌️


Paul
2015 XL 40QL-60
2015 Jeep Wrangler Unltd. Sahara
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[TwiceTheIce]

All of this knowledge (and lack thereof) has caused my I-pad to die, so I have to move to the computer.

As Julius Caesar said as he crossed the Rubicon, "The die is cast."

I am now going to go to the toy barn and install my tire monitor for 110 front and 90 for all the rest (35 psi Ford Edge toad). Once I get done with that, I will probably return and create more havoc with additional questions.

What I should do is wait for Frog Bob to get off his lily pad and move into his XLT. Since he has the finest of advisers at his beck and call, I can just do whatever he does.

[conceptumator]

Originally Posted by Phil57

I really didn't want to comment but I can't stop. This is just not a good idea. It isn't hard to figure out the weight. In this case no one here is familiar with tag axle and psi. In any case it is well worth taking the time to set the psi correctly on you tires. Tires are very expensive and who wants to replace them before you need to? Also my life and my family's life is worth taking a few minutes to get it right. I know that most have never weighted their Moho. That's up to them but it is just not a good idea to run it up to max pressure and go.

Sorry, but not following you here. Not a good idea why? Tires blow when they overheat due to excessive flexure caused by overloading or decreased pressure, for the most part. The way some folks talk about calculating their tire pressure down to a gnat's behind they must stop and adjust it every time they burn a few gallons of fuel up. It's simply not that critical so long as you maintain adequate pressure. The safety factor comes into play when people try to lower tire pressure to maximize ride comfort based on perceived vehicle weight. If you want to get that picky, you better allow for the effect of the crown in the middle of the roadway, too.

[wmtire]

The site team has had to do some editing and deletions in this thread that had extremely rude initialisms, and/or follow up comments.

We take the Play nice rule seriously. Post accordingly.

This has been a fairly good informative thread, please keep it that way.

[Phil57]

No one is concerned with getting the psi that close. There is a huge difference between not giving a crap what your rig weighs and being responsible and setting your psi to the weight of the Moho. Sorry you don't " get it" but you are wrong. On your Moho it might be right but on Berkshires it is not. The OP is trying to get his new tag axle Berkshire set up safe and comfortable. Why would you give such irresponsible advise when you don't even set yours correctly? Sorry you were upset by my response but it's just not how things are done.

[Paulie Boy]

Originally Posted by conceptumator

Sorry, but not following you here. Not a good idea why? Tires blow when they overheat due to excessive flexure caused by overloading or decreased pressure, for the most part. The way some folks talk about calculating their tire pressure down to a gnat's behind they must stop and adjust it every time they burn a few gallons of fuel up. It's simply not that critical so long as you maintain adequate pressure. The safety factor comes into play when people try to lower tire pressure to maximize ride comfort based on perceived vehicle weight. If you want to get that picky, you better allow for the effect of the crown in the middle of the roadway, too.

Well; we all have a choice now don't we. We can follow the tire manufacturer's recommended pressures or think we're smarter than the manufacturers engineers and fill the tires to whatever pressure you think is best. It's not that most of us are picky, just doing what recommended.


2015 XL 40QL
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[conceptumator]

Originally Posted by Paulie Boy

Well; we all have a choice now don't we. We can follow the tire manufacturer's recommended pressures or think we're smarter than the manufacturers engineers and fill the tires to whatever pressure you think is best. It's not that most of us are picky, just doing what recommended.


2015 XL 40QL
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Again, I simply don't get your point here. I AM following the tire manufacturer's recommended pressures. What you're looking at in those tables is the MINIMUM allowable pressure for the load you are estimating on each wheel. If you want to do that then more power to you. I'm just saying it's just as safe to simply use the max rated pressure and move on. That way if the actual load is underestimated somewhere, all is well, assuming the max loads are not exceeded. No one us saying you're wrong, but I'm not wrong in the alternative approach, either.

[Mmnsc]

If all the opinions were taken with a grain of salt we would never get to real way to set the tire pressure. For those who have attended Camp Freightliner you know how to properly set the tire pressure. Big Mike from Camp Freightliner spent hours teaching us the proper way to set the tire pressure and using the tire manufacturers tables for each tire size and type and using the actual individual wheel weights.

I know how to set mine and so does Phil. Everybody should do it what ever they think is right and best way.


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