Tire pressures

[flynnwalter]

Jeepoholic
While admittedly unusual, the passenger rear corner on our RR4R Monaco chassis is 2700 lbs heavier than the driver's side rear. There is little that can be done about it as far as moving things around to balance the load. That is what happens when the 'pillow arrangers' hold sway over the engineers. Without a four corner weighing our only choice would be to weigh the whole rear axle. Dividing this axle weight by the four rear tires and then referring to your tire chart for the proper psi would, in our case, leave the two tires on the heavier passenger side dangerously under inflated. Over time that frequently leads to a blowout. I shudder to think of us having a blowout with injury or worse because I did not perform my due diligence. It is our responsibility.
Frank W. 09 Cayman
Lake City, Florida

[usinvestment]

Originally Posted by Crasher

Your company was doing the same thing we are doing. 90 psi was below the max pressure on the tire, but they have determined that 90 would carry the load and wear evenly. That also insured the best control and handling when loaded. That is exactly what I and others have done. Once the tire pressures are set for the maximum load each will carry, that's where they stay. Same as what your company did.

90 PSI cold? Here in AZ the ambient temp is over 100 during the day and a cold tire at 82-84 PSI cold will run at 93 to 95 PSI hot.

[Gordon Dewald]

As I understand your chassis is air ride. If the passenger rear is substantially heavier than the drivers rear does the drivers front weigh more than the passenger front?

If it does there may be an issue with the ride height. If it is it should be quite easy to fix by having the ride height adjusted.

On the tire pressure it appears that the difference in tire pressure is about 10 lbs for 1000 carrying. If you divided by 4 and added 10 lbs one side would be right on and the other side would be 20 lbs overinflated. Rough math. 2700/4

This would get you through until the corner weighing and any corrective suspension adjustments.

[flynnwalter]

Gordon
I assume you are replying to my post? If you put a name in the subject line, it would be clearer.
Yes, the driver's front is a bit heavier than the passenger, but we don't believe it is transferred weight from the rear--which as you state is a possibility. The air suspension will automatically level the coach side to side. Josams in Orlando did the four corner and also re-aligned our coach after we had Source trailing arms installed. While the 2700 lb difference is certainly not good, Josams assured me it was not a critical issue. Josams stated there are many coaches not balanced well side to side. I believe we have this problem under control on our coach, and was simply trying to explain to Jeepaholic why at least one four corner weighing is critical. Unless a major change is made there is really no reason for more 4 corner weighings. You really are just guessing what the psi should be in your tires without a four corner weighing and then hoping for the best. That 'hoping' doesn't stand up well in court, and since MCC went bankrupt prior to our purchase of the coach, that doesn't leave a lot of folks to blame, other than me. Heaven forbid that we cause an injury to anyone else, if we could have reasonably prevented it. Thanks for your concern about our coach.
Frank W. 09 Cayman
Lake City, Florida

[Crasher]

Originally Posted by usinvestment

90 PSI cold? Here in AZ the ambient temp is over 100 during the day and a cold tire at 82-84 PSI cold will run at 93 to 95 PSI hot.

That's true. If you are checking pressures in the morning before a trip and it is warmer than 60*, just add 2% for every 10 psi above it. That becomes your "cold" pressure. The temperature range from 30* up to 90* is absorbed within the 10% above recommended that I carry. Once set that way, I can go a year or more without adding or releasing any air.

[Crasher]

Originally Posted by flynnwalter

Gordon
I assume you are replying to my post? If you put a name in the subject line, it would be clearer.
Yes, the driver's front is a bit heavier than the passenger, but we don't believe it is transferred weight from the rear--which as you state is a possibility. The air suspension will automatically level the coach side to side. Josams in Orlando did the four corner and also re-aligned our coach after we had Source trailing arms installed. While the 2700 lb difference is certainly not good, Josams assured me it was not a critical issue. Josams stated there are many coaches not balanced well side to side. I believe we have this problem under control on our coach, and was simply trying to explain to Jeepaholic why at least one four corner weighing is critical. Unless a major change is made there is really no reason for more 4 corner weighings. You really are just guessing what the psi should be in your tires without a four corner weighing and then hoping for the best. That 'hoping' doesn't stand up well in court, and since MCC went bankrupt prior to our purchase of the coach, that doesn't leave a lot of folks to blame, other than me. Heaven forbid that we cause an injury to anyone else, if we could have reasonably prevented it. Thanks for your concern about our coach.
Frank W. 09 Cayman
Lake City, Florida

Frank,

An incorrect ride height "Will" affect the opposite corner. On our first six position weigh, the front right was 8100# (above the tire rating) and front left was 7100#. They found that the left rear was also heavier than the right rear. They found that the left rear ride height was set 1/2" too high. Once corrected, the front right dropped to 7600 and the front left went up to 7550#. On my chassis, there is a 1/4" above or below range from the recommended height. Since then I have lowered the front steer weight to 14,600# by adjusting the tag suspension, but that's another issue.

[Gordon Dewald]

Originally Posted by Crasher

Frank,

An incorrect ride height "Will" affect the opposite corner. On our first six position weigh, the front right was 8100# (above the tire rating) and front left was 7100#. They found that the left rear was also heavier than the right rear. They found that the left rear ride height was set 1/2" too high. Once corrected, the front right dropped to 7600 and the front left went up to 7550#. On my chassis, there is a 1/4" above or below range from the recommended height. Since then I have lowered the front steer weight to 14,600# by adjusting the tag suspension, but that's another issue.

Thanks Crasher. I should have been clearer in my post.

Also if the ride height was correct and the two corners were heavy you may be able to adjust the ride height to compensate for the heavy corners and still remain within ride height spec. The 1/4" tolerance can add up to 1/2" of play to bring things closer to even.

Won't go into the details of adjustments but it appears the passenger rear is too high.

[flynnwalter]

Crasher
I am only vaguely aware of the 'workarounds' available to tag axle owners and it is pretty cool. A friend in the trucking business briefly explained how he handles different weights with his tag axle coach. But my situation, having measured the ride height quite a few times and finding it level, is probably not being affected by it. Notice I write probably as the more I delve, the less I am sure about. But we do believe our coach's main problem is the 'upstairs' that we immediately fell in love with is supported below in the basement by heavy batteries, etc placed inappropriately mostly near the passenger rear. Not much we can do, except realize what extra stress there is on those tires and figure a way to relieve the tires. Going up two tire sizes to 295/75R Bridgestones hopefully has done that. With a little over 300 miles on the Bridgestones, I can say the ride has smoothed out more than we even hoped it would. But thanks for reminding me about the weight transfer issue.
Frank W. 09 Cayman
Lake City, Florida

[Crasher]

FWIW, what Gordon mentioned could apply. My chassis manufacturer told me that if getting all ride heights correct still did not correct all of my unbalance problem, I could lower a heavy corner up to 1/4" and/or raise a light corner 1/4". That would not stress the frame, but could transfer unwanted weight to another area. Just something for you to consider when you get bored.

[JEEPOHOLIC]

just another thing to add to my "worry list" dang it

[JEEPOHOLIC]

I remember a time when I was younger, I drove half way across this country in an old beat up motor home with a leaky exhaust manifold, a transmission that was on it last leg, the rims were split rims, we had fun back then, not a care in the world, what happened to me ?

[Crasher]

Originally Posted by JEEPOHOLIC

I remember a time when I was younger, I drove half way across this country in an old beat up motor home with a leaky exhaust manifold, a transmission that was on it last leg, the rims were split rims, we had fun back then, not a care in the world, what happened to me ?

Yep, with our first MH, I was always happy when it started. I knew then it was going to be a good day. Then my analytic brain kicked in and I discovered a whole new world of information. Much of which I did not need or have any use for. At least it has kept me out of the bars and out of trouble.

[Ray,IN]

Originally Posted by oildriller83

The reasoning for doing the four corner weighing of your coach, is to make sure you're running enough psi in each tire for the weight on that corner, right?

If this is correct, why not fill your tires to maximum air pressure for maximum weight rating per tire manufacture specs? Wouldn't this eliminate the need for constant weighing, if you change your load? I don't for see running them this way to take away life, since motor home tires time out anyways?

I agree. Goodyear also agrees; note the "important" paragraph.
All tire load/inflation charts reflect the minimum acceptable pressure for the corresponding load, not necessarily the optimum.

[Gordon Dewald]

Most of this is due in part to having more information closer at hand.

In the old days you bought a vehicle and perhaps you put overloads on it and pumped the tires up to carry a larger load. I recall Dad putting side boards on the 1/2 ton truck to take a load of grain into town. The tires looked "squashed" but we drove the 15 miles at 30 mph and always got there safe. Back home he took the sideboards off and let some air out of the tires.

Now days we have much more complex systems able to take higher loads at higher speeds. Part of the issue is the new systems come with adjustments. This is part of the technology improvements developed by folks who thought they would make things that could be could be customized for unique situations. Not only engineers but practical people who see a need and tinker until they come up with a good solution.

We are the beneficiaries of those custom adjustments. You do not have to make the adjustments unless things are really out of whack - and even then you have to be aware that something is not as it should be. A lot of us with no experience have nothing to use as a base line so accept whatever we have until we talk to someone who says "Mine does not do that".

IMO the example of a rear axle being 2700 lbs heavier on one side than the other makes me think something is not right. I expect the MH manufacturer did not design or build the MH with a weight difference that large. I could find no information on the net to confirm that but that is about 10% of the coach weight.

Bottom line - if the coach handles the way you expect and the tires are wearing evenly is there anything to worry about?

Just saying!