Actual Corner Loads?

[tireman9]

As a tire engineer I am interested in developing some statistics on the actual load on RV tires.

I have found a number of posts with axle weights but I know that very few vehicles have a 50/50 side to side load.

If you have had your rig weighed with individual scales for each position I would appreciate knowing the results.

I don't need info on the make or model RV or even the size tire as I am only interested in learning how much out of balance different type RVs are.

Your post or PM me with this basic info

Example

TYPE ( Class-C or Class-A)

RF - 3212#

LF - 3810#

RR - 8111#

LR - 9100#

If you have a Tag please include

RT - 3210#

LT - 3222#

Thanks in advance for your assistance.

[Guest BillAdams]

You are going to get such a small sample from the users that respond I suspect the data would not be meaningful. There are businesses such as RVSEF that have been compiling this information from thousands of actual weighings. You might want to contact them if you have some kind of a business interest and are looking for accurate information.

Also, the weight information that the user provide will only be accurate for that date. A year later, if the coach is not weighed again, the information may or may not be correct any longer.

[tireman9]

RVSEF data is not for sale. It is "owned" by the major sponsors of the Foundation.

I understand the likelihood of loads changing over time but since I am doing statistical sampling that should be no problem.

So far I have some answers from non FMCA folk.

[Guest BillAdams]

What is your goal?

[tireman9]

Bill

My goal is to develop statistical analysis to allow me to make a suggested adjustment for estimated load when individual corner weights are not known. I note that many folk do not know their actual corner loads and are unlikely to ge them as they do not attend large Rallies and Conventions where RVSEF or similar organizations offer the weighing service. However everyone can get to a truck scale and at least know their axle load.

I am expecting to be able to say something like...

If you do not know your side to side loads but only your axle load then

If you estimate a 50/50 load split you have a xx% probability of overloading one of your tires by yy%

If you estimate a 45/55 load split then....

and if you estimate a 40/60 load split then ....

Initial data suggests that if you estimate at a 45/55 split and then inflate all tires based on the 55% load when using the tables you have a 25% chance of still having one tire overloaded. Note the 25% figure is NOT based on a detailed analysis of the data but is provided here as an example based simply on eye-ball look at limited date.

To make the data analysis more reliable I need at least 25 more coach weights in Class-A plus 30 in Class-C.

On another forum I am also attempting to address the question of side to side and axle to axle variation for 5th wheel trailers.

Note I already have confirmed unbalance at more than 10% level for two Motorhomes out of 27 and confirmed unbalance axle to axle of more than 60% of 5th wheels in addition to side to side unbalance at about three times the rate found in Motorhomes.

This preliminary data clearly supports the need for developing reliable prediction statistics to encourage more people to get their real corner loads or at a minimum to stop estimation on equal distribution.

The above is a strong smoking gun for the probable root cause for the 18% tire failure rate seen in RV applications.

I find it interesting that FMCA people seem to feel this is not something they need to worry about.

[Guest Wayne77590]

This is something that I have been wondering about for some time. I'm in the group that cannot get a corner weight, but I can get an axle weight. I have weighed the coach, and I am within manufacture specs, and tire specs.

However, I do have a question. Since I do not know what the actual corner weights are I run my tires at their max load capacity, 110 psi all the way around. Is this a correct way when the corners are not known? So far my tires have been wearing exceptionally well and are still "looking" good for three years old.

[tireman9]

Wayne

If you can't get actual corner weights then your approach would seem to be the best you can do. If your wear is OK then you are probably not too far off.

You might touch base with RVSEF and ask what their schedule is. Never know if one of their guys will be traveling near where you expect to be. The only other option is to keep an eye out for a truck scale that has enough level space to allow you to do the multiple weigh that would allow you to calculate the individual corners.

I have seen scales with enough side clearance to allow this. You first get the full axle weight then drive through again with one side on the scale and one side off then do the math.

Hopefully there are some FMCA members who have had the corners weighed and are willing to share the data here. So far not so much.

[wolfe10]

RVSEF's Weighing Schedule: http://www.rvsafety.com/custompage7509.html?pg=weighing

But, as Tireman9 said, one of their guys may be on the road near you. Their phone number is: 321-453-7673.

Brett

[Guest BillAdams]

Personally, with no insult meant to Tireman or anyone else, I think you are making dangerous choices if you use limited or inaccurate information to make your tire inflation decision. GET YOUR COACH WEIGHED ON ALL 4 CORNERS! If you are in the NW, Oregon (and likely elsewhere) leaves their scales open to anyone when the truck weigh station is closed. You can weigh the front, back, right front, right rear and subtract the difference to get pretty accurate numbers. If the scales are not busy at a Flying J or similar you can talk to them about doing the same thing by having your co-pilot direct you so the left tires are off the scales. It's not easy, but it is absolutely worth it. Your only other choice (IMHO) is to run the tires at the max. inflation rate until you can get accurate information. Anything else is just a guess and could leave you in a dangerously under-inflated situation.

[Guest Wayne77590]

I'm not sure who you directed your comments at Bill. That is exactly what i do - max all the way around,

I have recorded the phone number for later use. Yesterday I had the right rotators cuff repaired. Today is the first day towards recovery. I'll be in a sling for two weeks, then physical therapy for several weeks.

As soon as I get a chance I do want to get the corners weighed.

Thanks.

[Guest BillAdams]

Just a general comment. It was not directed at anyone in particular.

[tireman9]

Well so far I have received one PM with actual corner loads. Since I am presenting a seminar "Tire Basics for RV Owner" at Madison, WI Convention, I would really like some data from FMCA members and not have to depend on the other club members to provide actual data.

I am sure there must be a few here who have had their coach weighed by RVSEF at a convention sometime.

[mikev]

Hello Tireman9, don't see your name anywhere so I guess Tireman9 has to do.

Here are my corner weights for my coach, I took them myself, picked the most level spot I could find front to back and side to side, rented a digital wheel pad and did two separate weights, one loaded and one unloaded. Each time I took a corner weight I backed off and moved on again to get the weight twice-able to confirm and average the values. However the biggest difference was only 20 to 30 pounds. I did round up or down the individual corner totals as well.

When I was unloaded I did have full fuel, propane and all other required fluids at their running capacities. Otherwise the coach was stripped of anything that was not bolted down. No water in the fresh,waste or hot water tanks.

When the coach was loaded, I had it set as if we would be travelling for weeks at a time. Really not much else to add, filled the fresh and hot water tanks. Also had my wife in the copilot seat and my adult son in the drivers seat.

I was very glad to get these numbers, although it showed an imbalance of approx. 300lbs on my rear axle the percentage is negligible. Doing them also showed I could reduce my rear psi from 100 (which I was running with) to 95 and my front from 100 to 90, even with a 5 psi cushion. Lastly I was over my rear axle max load rating by 220lbs when fully loaded so I have shifted my loading pattern to match.

I'm still hoping to get to a rally to do a four corner weighing, just to check against what I found.

Hope these numbers help.

Class A 2003 HR Ambassador, front and rear slides both on the left side. Tire brand and size Goodyear 255/70R22.5 Load range "H"

Unloaded coach,

RF- 3990# .514%

LF- 3780# .486%

Total front axle weight- 7770#

RR- 7770# .479%

LR- 8420# .52%

Total rear axle weight- 16190#

Total coach unloaded weight- 23960#

Loaded coach,

RF- 4321# .503%

LF- 4275# .497%

Total front axle weight- 8596#

RR- 8470# .491%

LR- 8750# .508

Total rear axle weight- 17220#

Total coach loaded weight- 25816#

Cheers

[Guest BillAdams]

I am just a bit confused. Are you giving a seminar about tires and coaches and weights when you know nothing about actual tire/coach/weights? Shouldn't that be a job for someone who does like RVSEF? (I have no affiliation or relationship to RVSEF other than the fact that they have weighed my coach in the past.)

[wolfe10]

I am just a bit confused. Are you giving a seminar about tires and coaches and weights when you know nothing about actual tire/coach/weights? Shouldn't that be a job for someone who does like RVSEF? (I have no affiliation or relationship to RVSEF other than the fact that they have weighed my coach in the past.)

Bill,

I read this thread very differently.

I read it as someone who IS familiar with tires and tire safety (not only from posts on this thread but from his many other posts about tires and tire safety), but wants more factual data on actual coach weights.

Said another way, would like to add more current factual data to his presentation.

Presenting that XX percent of coaches surveyed in the last year were overweight could be used as a motivator to get more people to avail themselves of the RVSEF weighing.

Brett

[mikev]

Yes I agree with Brett, Tireman9 has stated he is planning to use the values to try to demonstrate the variances existing in the coaches today. If this will help some people to become educated and get the real time values on their coach then I applaud his efforts. There can never be too much information available when safety is an issue. Which is why I added my coach information.

I was very concerned with my tire pressure shortly after purchasing the coach in 2009 and realized there was no definitive info on my particular coach. The manufacturers can be way out on real time weights and after I learned-through this forum- that my tire pressure was dependent on real time weights at each corner. I did a re-look at my factory spec sheet. It turns out they are approx 2080 lbs low on the UVW. Of course they add the proviso,

(.1) The UVW and CCC have been determined by weighing an exemplar motorhome with some but not all optional equipment available for each model year, make and model of motorhome. The result of the weighing of the exemplar motorhome is then used in calculating the UVW and CCC of other motorhomes of same model year, make and model. Your actual UVW and CCC may vary based upon options ordered. Please contact the manufacturer for the actual weight of each option.

After all the reading I have done concerning coach weights etc, I feel strongly the RV industry must take the lead and weigh every coach that comes off their lines. The cost is negligible, four wheel pads and ten minutes would do the trick. With the numbers of options available to buyers the weights they are listing are not only confusing but to some degree misleading to the uninformed. I would be very surprised if the options added to my coach turned out to be 2080 lbs....

At least the new owners would have a true starting weight at each corner of their coach. They could then at least do some basic computations to arrive at a reasonable tire pressure until they could fully load the coach and have the corners weighed again. Even if they could only get the axles weighed they would have some idea of the changes at each axle, if they are reasonably diligent they could weigh all the "stuff" they load on board and have a side to side idea of any changes until their next corner weighing.

As someone in aviation I am something of an expert in weight and balances, correct loading, cenrer of gravity-longitudinally and laterally so I have some understanding of the subject.

However I am not an expert on the issue of RV weights etc, I don't know if any coach manufacturers do "coming off the line" corner weights, I hope there are some. I have not found any RV dealers that offer the service either. I hope there are some...

One thing I do know- I will never buy another new or used coach unless the seller (private or dealer) agrees to provide a corner weighting while I am in attendance-full fuel, water etc. I'll even pay for the service if everything is correct. With all the concern over tire pressure etc I also want to know the coach is not overloading the axles. If you look at my numbers from my previous post you will see that I was 220 lbs over on my rear axle capacity when I was fully loaded. I have become much more careful about loading now to ensure my coach is as safe as I can make it, hopefully it will also save me time and money too if I don't over stress my tires, axles and chassis.

My gratitude to all of you for these forums, I was saved much time by simply reading what you all post here.

Great work Tireman9.

Cheers

[Guest BillAdams]

I did not mean to imply that Tireman knew nothing about tires but in re-reading my post I see how I may have implied that. I apologize. It just appears that he is trying to get an extensive database from a very small sampling of people for use at a seminar.

[tbutler]

If you get a chance, you should attend one of Tireman9's seminars. I attended his seminar in Bowling Green, OH several years ago and it was very enlightening.

He is a serious researcher with a long professional career in tire engineering. He is aware of research techniques and understands the statistical problems with a small sample. I've sent my data to him directly and I encourage others to do so as well.

I think an additional bit of information that would be useful is to do a survey at a convention to find out how many people had corner weights for their motor home. I'm afraid that this information would be shocking. Getting corner weights is difficult. Only those who are serious about tire safety and understand the need for knowing the weight on each tire position are going to take the time to locate a place to do this and then get it done. I would bet that the percentage of motor home owners who have corner weights is less than 5%.

MikeV I would like to know where you were able to rent the digital scales for weighing your coach yourself. That might help some people get their corner weights. How much did it cost and did they provide recent calibration information for the scales?

[rlking]

Class A, GVWR 20,500

Gross #17,080

Steer axle, #5,760

Drivers, #11,320

RF #2900, LF 2860

RR #6400, LR #4920

I don't understand the rear axle split unless the Weigh master made a mistake.He weighed the Front, Total and rear and then the left side, front and rear.

He was in a hurry as it was a commercial scale and trucks were waiting so I didn't wait to do the calculations. I went back to get it re-weighed but they

said that they don't weigh motorhomes anymore.

I'm still trying to find a scale somewhere that I can get new weights. I run 80# all around. May be a bit high but have had no problems.

Bob

Thanks for the heads-up Brett.

It's a Ford F-53 and the Fresh water tank and Generator are on the street (lite) side.

Bob

[wolfe10]

Class A, GVWR 20,500

Gross #17,080

Steer axle, #5,760

Drivers, #11,320

RF #2900, LF 2860

RR #6400, RR #4920

I don't understand the rear axle split unless the Weigh master made a mistake.He weighed the Front, Total and rear and then the left side, front and rear.

He was in a hurry as it was a commercial scale and trucks were waiting so I didn't wait to do the calculations. I went back to get it re-weighed but they

said that they don't weigh motorhomes anymore.

I'm still trying to find a scale somewhere that I can get new weights. I run 80# all around. May be a bit high but have had no problems.

Bob

Bob,

What chassis are you on?

Looking at the location of tanks, heavy gear, slides, etc. would you expect that the heavy side of the rear is that much heavier? If on a spring suspension, is the ride height lower on that heavier side?

We can't comment reasonably on the tire pressure, as we don't know what tires you have.

Brett

[Guest BillAdams]

Class A, GVWR 20,500

Gross #17,080

Steer axle, #5,760

Drivers, #11,320

RF #2900, LF 2860

RR #6400, RR #4920

I don't understand the rear axle split unless the Weigh master made a mistake.He weighed the Front, Total and rear and then the left side, front and rear.

He was in a hurry as it was a commercial scale and trucks were waiting so I didn't wait to do the calculations. I went back to get it re-weighed but they

said that they don't weigh motorhomes anymore.

I'm still trying to find a scale somewhere that I can get new weights. I run 80# all around. May be a bit high but have had no problems.

Bob

It's fairly common for someone doing a weighing the way you describe to get it wrong. It sounds like that's what has happened here. If you can get to an RV rally where they actually put an independent scale under each wheel you will get the critical information that you need.

[rlking]

It's fairly common for someone doing a weighing the way you describe to get it wrong. It sounds like that's what has happened here. If you can get to an RV rally where they actually put an independent scale under each wheel you will get the critical information that you need.

Thanks Bill. We are going to the FMCA Rally in Perry, GA, and will sign up for the weighing when I get there.

Bob

[akadeadeye]

Tireman9,

Here is my information.

Newmar Allstar, Class A, 42 ft., Spartan Chassis, mid engine Cummins ISL 400

Empty gray tank, empty black tank, 40 gals. fresh water, fuel tank full (100 gals.), no humans, empty frig., empty closets, but the basement has the usual assortment of folding chairs, 2 tables, weber grill, bag of tools (30lbs.), etc. In other words, stocked but not fully loaded for a trip.

RF---5,740

LF---6,330

RR---9,150

LR---9,070

CAT scales

Don

[mikemopar]

Tireman9,

Here's my data for your needs. Got the four corners weighed a while back but it should be all the same today. It was done by a vendor called "A'Weigh We Go" which gave me a good idea of my weight distribution. All the capacities were at about 80% to 90% and all the personal gear was on board.

Class A, 18,000 GVWR (1999 Ford F53)

Ratings

RF= 3,640#

LF= 3,640#

RR= 6,830# (2 x 3,415#)

LR= 6,830# (2 x 3,415#)

Load Measurements

RF = 2,810#

LF = 3,100#

RR = 5,110#

LR = 5,240#

16,260#

Although not really a part of this subject I have always had a question regarding the rear air bags on my rig. The way they are set up is each bag has a it's seperate air pressure (Air stem). Is there a benefit to connect them together where the air pressures are equal?? Maybe someone can shed light.

Thanks

Mike

[wolfe10]

Although not really a part of this subject I have always had a question regarding the rear air bags on my rig. The way they are set up is each bag has a it's separate air pressure (Air stem). Is there a benefit to connect them together where the air pressures are equal?? Maybe someone can shed light.

Thanks

Mike

Mike,

You will have slightly better handling if you keep them separate. If connected, when you go around a corner, rather than the bag on the outside of the corner resisting leaning, the air will rush from that outer side's bag to the other bag. So it will lean more and sway more when other side to side forces affect the coach.

Brett