Finally weighed the whole rig

[VegasFlyer]

On 5/6/2017 at 7:06 AM, Jack Mayer said:

All of these comments have merit, especially NoDirectionHome's.  There is no one single measure that makes it "good" or "bad". and as pointed out above, the distance between the axle centerline and the kingpin location on the hitch is a significant factor. We snug the hitch as close as possible to the axle, which places it around 5' back from the centerline. Pins WAY back can provide for squirrely trailers, as can trailers with very light pins relative to their overall weight - no matter where the pin position is. So you have to look at the ENTIRE picture. Not just one element. 

That said, for most RVs with 18-25% pinweight you are not going to have handling issues induced by TRAILER balance. Certainly not with the pin placed where most HDT RV Haulers place it - pretty much as close behind the axle as you can. 

Move the hitch way back (cantilever it far) and then put a heavy pin weight on it - thus unloading the steers a LOT, and you will induce some issues into the equation.  But as Dolly said - none of this matters on most setups. They are well within bounds of "reasonable". 

The point of all this is to not ignore weight/balance issues if you have unusual configurations that you are considering. But for a hitch placed close to the axle,  even with the heaviest trailers, you should not have any issues at all. You will be within the load rating of your axles, AND you will have  a rational balance between them. AND you will not induce excess forces into the equation from a long cantilever if braking hard in a curve (for example).

We use the 35%  front number as a guideline. But you have to take into account the front axle rating and not exceed it under all loading conditions, AND you have to also consider the position of the hitch. LONG cantilevers are bad ju-ju. Even if you have good front weights. I'm not saying long cantilevers are impossible - just that you have to understand what you are doing, and the tradeoffs you are making. 

The effect that Jack is referring to in warning about an excessive cantilever, is quite simply, leverage.  Just like in a weight balance situation when someone uses the analogy of a teeter totter and how you balance a teeter totter with a 70 pound kid on one side and his fat 250 pound cousin on the other by moving the fulcrum of the teeter totter toward the fat kid until it balances out. 

The formula of weight x arm = moment is the foundation of determining what effect any item will have on balance or, in the case of a long cantilevered hitch, the effect on lateral stability of the truck.  Weight is the obvious, being weight of an object or side force applied by a trailer.  Arm is the distance from the fulcrum or hitch from the center of the rear axle assembly.  Moment is the resulting force.  The other simple analogy is how much easier a 24" breaker bar is to use than a 4" ratchet.

In our application, with a tandem truck, you can go back six to seven feet beyond the frame without having to do a lot of calculations on how the cantilever will effect the handling of the truck.  That statement is based on having done a lot of calculations on the effect of a 43' 24,000 pound triple axle trailer that is loaded with a pin weight under 4,200 pounds.  Anything longer that would put you way beyond length laws anyway.  

One other factor that a lot of folks do not think about, is that the distance between the hitch and the pivot point of the trailer have a big effect on how a cantilever hitch will effect the truck.  The same issue of the arm of the load comes into play with a longer trailer, versus a shorter one.  A much shorter trailer at the same weight would have a more adverse effect on the truck due to the reduced leverage the truck will have, thus possibly causing instability to the truck.

The overall common point here, expressed by several folks, is that it is worth frying a few brain cells to learn the effects on loading and pairing of a truck and trailer.  The one big safety valve is that with an HDT you have a much wider margin of error.

[NoDirectionHome]

Quote

A much shorter trailer at the same weight would have a more adverse effect on the truck due to the reduced leverage the truck will have, thus possibly causing instability to the truck.

VF,
     Are you assuming a greater pin weight to keep the same moment with the shorter pin to trailer wheelbase, or as you describe it, pivot?

[VegasFlyer]

6 hours ago, NoDirectionHome said:

VF,
     Are you assuming a greater pin weight to keep the same moment with the shorter pin to trailer wheelbase, or as you describe it, pivot?

It's not as much pin weight as it is in mass effect from the trailer.  Think lateral side to side versus weight in a vertical plane.  When you have a cantilever hitch on a truck and a trailer attached to it, you effectively have two levers, one being the truck, specifically the area hanging in space between the hitch and the pivot point of the rear axle(s).  The second lever is the area of the trailer from the pin to the pivot point of the axle(s).  The longer that either of those levers are, the more effect the opposing vehicle has on it.  That is why a long trailer will generally be far less erratic than a shorter trailer.

if you go back to the weight and balance formula of Weight x Arm= Moment and switch it to a vertical plane you can see it a little easier.  Using a the teeter totter analogy, if you had a teeter totter that was 1000" long and perfectly balanced with the pivot point right in the middle and put a one pound weight at the very end, five hundred inches from the pivot point, it would take five hundred pounds to balance that teeter totter if you were hypothetically put the the counter weight one inch on the opposite side of the teeter totter.  Now turn that to a lateral plane and that 500 inch lever will only require one pound of lateral force applied at one end to exert 500 pounds at the one inch mark on the other side.

Is that clear as mud?

[Dollytrolley]

Ok I am about to use..... BOTH thumbs to type this so hang on.....

If life was only this simple as far as we have come in this thread so far, but heck as the old saying the "Devil is in the details."

IF stability was so darn easy to capture and insure NASCAR would have two teams and 3 fans and a budget of 3 case of Dr Pepper but..........stability is tricky and fickle.

Fortunately we are blessed with and bunch of gifted darn-near--X-Perts here and one geezer that used to hang around a few ACTUAL for- real stability experts........(I was the gofer for pizza and drinks for the big-brain-stability-geeks)

Stekay should have chimed in here by now but I am sure he is hiding out waiting for me to trip over my own thumbs typing myself into a hole..........here goes.

 

Vegas Flyer said:

"The overall common point here, expressed by several folks, is that it is worth frying a few brain cells to learn the effects on loading and pairing of a truck and trailer.  The one big safety valve is that with an HDT you have a much wider margin of error."

So.......why do we "profess" to use a HDT to tow our trailers ? ? ?

Lots of different answers, but often if you throw all the answers in a big crock-pot and cook them a while it seems that the dish served taste a lot like........mass (weight)........you know..... Smart Cars...Hogs....Batteries.....Generators....TOOLS.....MORE TOOLS......250 Gallons of Fuel.......3,000 lbs of hay for Dolly.......Etc, Etc....

Now Henry has  photo album full of every tow rig ever to hit the highway and he always was able to hitch bigger and bigger trailers so that he could justify a bigger and bigger tow rig until he hit the mother-lode with a big red Volvo.....

The concept with a HDT is.... that so far 99% of the RV trailers are well within the rated TOWED-MASS of the HDT units that we operate......sorta..........maybe....

The "Devil" I am alluding to here is that the RV trailer is a very odd animal and is not much related  to any trailer that are utilized in commercial service. Many, many RV trailers are stability-marginal at best and become prone to unstable operations when not properly "Dampened".............in the Vegas Flyer statement underlined is basically referring the "Dampening" effect of the largely stable HDT attempting to impart a stable Dampener into the unstable RV trailer body.

Perhaps a few terms defined might help:

 

What is the dynamic stability?

The characteristic of a body, such as an aircraft, rocket, or ship (truck-trailer), that causes it, when disturbed from an original state of steady motion in an upright position, to damp the oscillations set up by restoring moments and gradually return to its original state. Also known as stability.

 

What is negative stability?

The center of gravity must lie ahead of the neutral point for positive stability(positive static margin). If the center of gravity is behind the neutral point, the aircraft (or trailer) is longitudinally unstable (the static margin is negative), and active inputs to the control surfaces are required to maintain stable flight (CORRECT steering wheel inputs).

 

DISCLAIMER.......sorta......the above Negative Stability  statement above refers to pitching (Z axis) but in our truck / trailer uses it becomes a factor in our  yaw axis (Swerve).

 

Now you may notice that I have copied the above definitions from fluid--suspended vehicles and this is true but the forces of mass don't really care.... our only advantage .....sorta ......is that we tend to have better POTENTIAL Dampening because our vehicles TEND to be SOMEWHAT better attached to the mother of all dampeners.... EARTH..........sorta......maybe...

 

Here id the dirty little Devil we have not talked about yet........sloppy-trailer-suspension........

 

Look at that second video that Nothome posted on page one of this thread......the trailer is doomed at the first swerve when the trailer roll axis went into a 30 degree heel and as the frequency and amplitude of the negative stability increased.....and the marginal Dampening limits of the tow vehicle was exceeded and the entire vehicle combo was reduced to .....bad juju.......

 

Australian: https://www.youtube.com/watch?v=_ix7ZgsWTMg

 

Rv trailers tend to have many factors that feed narrow stability margins.......large mass dampening tow rigs may aid to a measured extent but stability has limits and......... that's what makes NASCAR a big sport......

 

Drive on..........(Don't tease that RV stability too.....much)

 

 

 

 

 

 

 

 

 

[rickeieio]

3 hours ago, Dollytrolley said:

The center of gravity must lie ahead of the neutral point for positive stability(

There's a scene in "The World's Fastest Indian" demonstrating this with a cigar and a toothpick.

[Heavymetal]

On May 6, 2017 at 7:59 AM, NoDirectionHome said:

Weight distribution F/R alone is a really poor way of determining things, the way most of the haulers on the forum have their rigs set up.  Consideration should be given to the usually large distance from the hitch position to the rear axle AND that ratio to the wheelbase.  This is what determines your stability.  No not just going down the road where I'd expect almost everyone has large margins of safety.  It's in that emergency situation or limited traction scenario that you will discover the limits of your design.  Statics are a far cry from dynamics, and moments of inertia are the true determinant of your handling.  Weight distribution is a tool to "predict" but without multiplying by those moments, both vertical and lateral, you don't have a good picture.

Here is where I will commit heresy and state, "You can have good trailer stability with virtually  0 pin weight."  Not a practical trailer design, but it is theoretically possible.

Then there's the subject of "frequency" and how it effects your stability... but lets save that for another time -Steve

You are so correct here!!! When we bought our first HDT all I did was place my hitch between the rear frame rails, I added nothing to the length of the truck. We were towing our NH at around 25K total RV wieght and were towing down I20 when we came through Tuscaloosa, AL and started around the loop W to E I unloaded the front end and caused the traction control to come on and derate the truck it happened again on the same trip headed down a hill 5% grade "maybe" when the truck down shifted to maintain speed it derated again when the traction control over rode the truck. Granted the NH had a heavy pin and we did not have the weight of a bed or Smart on the truck but it opened my eyes to the risk on the pin behind the axles, and that truck the pin was only 12" back from the rear axle. 

[Heavymetal]

All I can say to this is the further back your pin is from the axle center might not make a big difference when towing straight down the road but when you place your pin 4-6' behind the axle it makes a huge difference when taking a curve and if you have to brake while making said curve with the weight so far back I don't care what your front axle weight is your rearend will meet your front end. This can happen with out a frame extension but it decodes more of a worry with every inch you add to your frame. 

[noteven]

In accordance with the gospel of rv forumsz, stability utopia is achieved with a dually / DRW / duallie aka a 'nuff truck with 4 hind wheels,  and 'nuff pin/tongue weight. 

None a this lever / cg / wheelbase / center of mass stuff...

Stability

Oh and good safety chains are a must...

[rickeieio]

57 minutes ago, noteven said:

In accordance with the gospel of rv forumsz, stability utopia is achieved with a dually / DRW / duallie aka a 'nuff truck with 4 hind wheels,  and 'nuff pin/tongue weight. 

None a this lever / cg / wheelbase / center of mass stuff...

Stability

Oh and good safety chains are a must...

Doesn't stability increase if lots of black smoke comes out when yer going up hills? And aren't tranny and brake life inversely proportional to stability?

[VegasFlyer]

13 hours ago, Heavymetal said:

You are so correct here!!! When we bought our first HDT all I did was place my hitch between the rear frame rails, I added nothing to the length of the truck. We were towing our NH at around 25K total RV wieght and were towing down I20 when we came through Tuscaloosa, AL and started around the loop W to E I unloaded the front end and caused the traction control to come on and derate the truck it happened again on the same trip headed down a hill 5% grade "maybe" when the truck down shifted to maintain speed it derated again when the traction control over rode the truck. Granted the NH had a heavy pin and we did not have the weight of a bed or Smart on the truck but it opened my eyes to the risk on the pin behind the axles, and that truck the pin was only 12" back from the rear axle. 

When those events occurred were you braking?  Was that a single or tandem truck?

[Heavymetal]

11 minutes ago, VegasFlyer said:

When those events occurred were you braking?  Was that a single or tandem truck?

Tandem and not braking. On the curve I had just turned the cruise off and was coasting, and on the down hill I was not breaking but did down shift to control the speed.  The traction control would flash a warning triangle on the dash and derate the truck for just a second and then give you control back. I will say that the curve on I20 loop around Tusscaloosa is not only to sharp for the speed limit but also very bumpy. I have not had this happen with the Western Star at all of coarse it is a heavier truck plus I have the weight of the bed. 

[VegasFlyer]

5 hours ago, Heavymetal said:

Tandem and not braking. On the curve I had just turned the cruise off and was coasting, and on the down hill I was not breaking but did down shift to control the speed.  The traction control would flash a warning triangle on the dash and derate the truck for just a second and then give you control back. I will say that the curve on I20 loop around Tusscaloosa is not only to sharp for the speed limit but also very bumpy. I have not had this happen with the Western Star at all of coarse it is a heavier truck plus I have the weight of the bed. 

It would seem that the weight differential of your 25k trailer pushing your truck that was most likely a whole lot less than 25k was more of the problem than pin placement.  Granted with a cantilevered hitch and that sort of weight difference, it would be worse, but that's why God invented the trailer hand brake....lol

[Heavymetal]

5 hours ago, VegasFlyer said:

It would seem that the weight differential of your 25k trailer pushing your truck that was most likely a whole lot less than 25k was more of the problem than pin placement.  Granted with a cantilevered hitch and that sort of weight difference, it would be worse, but that's why God invented the trailer hand brake....lol

I agree 100%. I will say that it opened my eyes to the fact that no matter what we tow with Things can and will go wrong. 

[Heavymetal]

Finally had a chance to weigh without the RV. So the truck with all souls onboard and the smart with 1/3 tank of fuel was, steer axle 11,100 drive 11,960 total 23,060. 

With RV steer 9,900 drive 18,440 rv axles 15,300 total 43,640. So i am unloading my steer by 1,200 lbs with 1/3 tank of fuel which is what I had both weigh ins and my pin would be 5,280 with these numbers correct?

[Dollytrolley]

4 hours ago, Heavymetal said:

Finally had a chance to weigh without the RV. So the truck with all souls onboard and the smart with 1/3 tank of fuel was, steer axle 11,100 drive 11,960 total 23,060. 

With RV steer 9,900 drive 18,440 rv axles 15,300 total 43,640. So i am unloading my steer by 1,200 lbs with 1/3 tank of fuel which is what I had both weigh ins and my pin would be 5,280 with these numbers correct?

Heavy,

Let me get back to you in a bit.

You have some basic numbers however the interaction of these numbers can be a bit muddled without some additional information........

I have been thinking about some "aids" that might be helpful in getting some better Weight & Balance solutions for the folks here on the forum.

Please stay tuned and I'll burn some midnite oil to see what I can do to make Weight & Balance a bit easier to get a handle on.

 

Drive on................(Weight & Balance is easy .....once we round up and get the "numbers" in "order")

[Heavymetal]

2 minutes ago, Dollytrolley said:

Heavy,

Let me get back to you in a bit.

You have some basic numbers however the interaction of these numbers can be a bit muddled without some additional information........

I have been thinking about some "aids" that might be helpful in getting some better Weight & Balance solutions for the folks here on the forum.

Please stay tuned and I'll burn some midnite oil to see what I can do to make Weight & Balance a bit easier to get a handle on.

 

Drive on................(Weight & Balance is easy .....once we round up and get the "numbers" in "order")

Standing by. 

[Dollytrolley]

Richard,

I would guess that your pin is as you calculated and for the most part you have utilized the “NORMAL-RV-METHOD” to obtain your pin weight FOR THIS MOMENT…...and only this moment.

Now what I am about to say will cause some flames to come my way but I did not write one single Law of Physics…...I just abide by them (most days).

Here is a far better way to manage your complete RV combo Weight and Balance…….

The best method is to make ALL fluids are topped off including the fuel tanks on your truck. Next UNLOAD ALL cargo, tools, Dr Pepper is out of your truck…..unload the smart car.

Next unload your trailer and drain ALL liquid tanks, but top off your propane tanks…...UNLOAD ALL cargo and personal items, empty all cargo compartments.

Top off ALL fluids in the smart car but unload all other items from the car.

Now the best method to weigh each wheel position is to obtain a individual weight for each wheel patch however if this is not feasible you will need to obtain a weight for each axle position by itself.

Do this for the truck alone, and the Smart alone (each axle) and then hitch up the trailer and then weigh each axle of the truck again and then weigh each axle of the trailer alone…….get out of the truck each time you weigh a axle. Get out of the Smart each time you weigh each axle.

Now you have a baseline weight for each axle and will soon have a baseline hitch pin weight as well.

Next we will need to make “arm measurments” for each weight position.

Lets assume that the steer axle of the truck is datum 0” and all truck weight positions will be measured in inches from the steer axle datum.

Lets assume that the hitch pin of the trailer is datum 0” and all trailer weight positions will be measured in inches from the hitch pin datum.

Lets assume that the steer axle of the Smart is datum 0” and all Smart weight positions will be measured in inches from the steer axle datum.

Next:

Now get your tape measure out and measure and write down on the paper the following:

1M.  Measure from the steer axle to each drive axle and write on the paper.

2M.  Measure from the steer axle to the truck hitch pin, write it down.

3M.  Measure from the steer axle to: center of , each fuel tank, driver & pass seat, condo cargo compartments, drom box, each bed cargo box, write each set of numbers down.

4M.   Measure and write down from the trailer hitch pin to the center of the following; each trailer axle center line, each liquid tank, center of each cargo compartment, each propane tank, write it all down.

5M.   Document the capacity of each liquid tank and write it down.

Next email me the data at mmcdan3189@aol.com and then I will compose a BASELINE RV Combo weight and Balance and then we can ADD or subtract weights in the future WITHOUT having to weigh the RV again.

There will be loading's that will make your rig handle better and will likely help your tires become more reliable as well.

 

Drive on……...(Better the balance…..the better the ride / drive)

[Heavymetal]

Well I guess it's my fault for asking the question. Some things should just go unanswered. At least I don't have to worry about the Dr Pepper because I drink Cream Soda I only carry one Dr Pepper and we all know why that is. Thanks for  your input Dollytrolley but don't expect those numbers to soon. 

 

Richard

[Dollytrolley]

2 hours ago, Heavymetal said:

Well I guess it's my fault for asking the question. Some things should just go unanswered. At least I don't have to worry about the Dr Pepper because I drink Cream Soda I only carry one Dr Pepper and we all know why that is. Thanks for  your input Dollytrolley but don't expect those numbers to soon. 

 

Richard

Richard,

I understand that what I ask is for seems pretty anal and like a lot of detail however without the LOCATION of the variable loads (Smart, Trailer pin weight, Liquid tank weights, and heavy cargo) I simply have NO way to calculate the loads that your truck and trailer are burdened with.......

I have been doing Weight and Balance for +50 years but I am not good enough to do it without the numbers needed to calculate the solutions........

Now it is only a wild guess what some loading combinations will produce ...........

I suppose that HDT's have some advantage when the loading gets a little over the line but that's another story that yet to be written...

 

Drive on...........(some guess's are ok.........)

[Heavymetal]

8 minutes ago, Dollytrolley said:

Richard,

I understand that what I ask is for seems pretty anal and like a lot of detail however without the LOCATION of the variable loads (Smart, Trailer pin weight, Liquid tank weights, and heavy cargo) I simply have NO way to calculate the loads that your truck and trailer are burdened with.......

I have been doing Weight and Balance for +50 years but I am not good enough to do it without the numbers needed to calculate the solutions........

Now it is only a wild guess what some loading combinations will produce ...........

I suppose that HDT's have some advantage when the loading gets a little over the line but that's another story that yet to be written...

 

Drive on...........(some guess's are ok.........)

No I understand why it's needed. I was just thinking of the reaction in the park when if I started pilling stuff up on my site and then drove away. Since we full time I'd have to unload a lot of things my neighbors would not want to see. Lol. I was the unit load master during deployments in the army so I understand needing a empty weight but I think I will just take a running series of weights and shift items until I reach my balance point. 

[Dollytrolley]

4 hours ago, Heavymetal said:

No I understand why it's needed. I was just thinking of the reaction in the park when if I started pilling stuff up on my site and then drove away. Since we full time I'd have to unload a lot of things my neighbors would not want to see. Lol. I was the unit load master during deployments in the army so I understand needing a empty weight but I think I will just take a running series of weights and shift items until I reach my balance point. 

 

Ok Heavy……..one more time…...maybe…...this damn new “forum software” just ate my last response to your last post so now I a reverting to Open Office Writer so that I don't lose this posting…….hope they did not pay any $$ for the software because it is junk…….on the other hand maybe most of my posting should go…….poof…..some days…..

So back the “weighty-subject” at hand.

Perhaps we might consider a ……..”reverse-Calc-Weight & Balance”…….often in accident investigation a Weight & Balance of the accident vehicle is needed however the lack of many items surviving the accident will make a physical Weighing impossible so…… the investigators will often take items known and through “calculate” additions or subtractions of items to arrive at the needed weight & balance for the investigation……

Now by now maybe you are truly regretting asking for my “help” and if I am a bit too anal about this matter I am sorry to bother you and I'll understand if you call uncle at this point ….

Now IF you might want to give this “project” one more shot you might consider what I propose……

TRUCK:

Since your truck is New it is likely that the dealer might be able obtain a weight slip for the truck from the factory for the Basic Truck as it was delivered……..(Scrap just sent me 3 New KW weights from the Kwopper factory so KW weighs each unit as it leaves the factory) …….Now of course you have a hitch installed (ET I assume?) and so we know the weight as well as the location and it appears you have a bed so we would likely “Guesstimate” the bed weight and bed C G, then you would need to take each cargo area on your truck and weigh and record the cargo and then replace the cargo and move to the next location and do the same. IF you do not want to fill both of your truck fuel tanks you could “dip-stick” each fuel tank and calculate the weight of the fuel in each tank.

Once you have all of the various weights and locations as noted above send the data to me and I will enter all of the data into the Weight & Balance calculations and simply enter “Negative” values into the calculation to remove the unwanted cargo from the truck in a fashion that will keep the balance pure since the subtracted weights are also accounted with “negative-moment-values”…...is this as clear as mud?…….Don't worry it sounds a bit more complex than it is…..

TRAILER:

Obviously stacking your cache of 200 Gold bars on the pick-nick table at the RV park is bad form so…...just do as you did with the truck and just bathroom scale weigh each cargo area one area at a time and then replace the cargo and move on to the next area and just record the weight and location data. Next before you leave the RV park for the Trailer weigh drain the Grey, black, and fresh water tanks and fill the propane tanks. Next weigh the truck and trailer and try to obtain each axle weight separate if you can (some gravel or redimix or grain elevators will allow RVs to weigh for a case of beer or whatever) When you get the data send it to me.

SMART CAR:

Fill the fuel tank and then weigh each axle or if to much trouble just weigh the car empty without no one in the car…..send me the data.

This sounds like …….work at this point and it is…... sorta ……..however it is less work that running your rig to the scales several times and still not getting a descent idea of where your true Weight & Balance really is……..

Once we are able to obtain your new BASELINE RV combo calculated empty weights then the easy part is calculating various loading's for your future adventures ……

The final finish would to consider getting the rig weighed on each wheel position and then the lateral weights could be considered for tuning your loads for better tire life…..

Sorry again that I have so little skills at divining weight and balance without thin air but I need some numbers to crunch to make something that makes sense…….

The better the quality of the numbers going into the calculations the better the solution ……..

 

Drive on……….(Gold is…...heavy)