Payload math / weight distribution hitch

[KevinFH]

OK, I'll point out wrongness again:

"If the trailer is alone, all the weight is on its axles." On my trailer, ~1000 pounds is on the tongue. It is this weight that is transferred somewhere (TT axles and front TV axles).

Too bad about convenience, but weighing is the only way to know what you are doing. Everything else you might do is guesses, rules of thumb and assumptions.

[Gene]

It is true that weight of a trailer is partly on the hitch jack, and that weight has to be accounted for in calculating weight distribution. To get a simple understanding of what is going on when you transfer weight thinking only of axles for the moment helps people understand where the weight goes with weight distribution. But, of course, not everyone sees things the same.

Laferic: You have the Tundra with the lowest cargo weight or payload. We have the extra cab, not the crew cab and thus have a few hundred more pounds to play with. We had a 25' Safari (same as Flying Cloud) and we were at the limits on weight with two passengers, tools, water and sewer hose containers, chairs, odds and ends like 12 v. compressor. Adding a bike, not good. We have a tonneau which weighs about 100 lbs.; I think a camper top weighs more, maybe much more depending on the model. Do the calculations and check how much everything weighs to see what you are facing.

Bob Cross: glad to see you back.

[Collyn]

There is a known correlation between tow ball mass and on-road stabilty. The lower that mass the lower the safe speed.

It is generally assume to relate to trailer mass - but more correctly should relate too trailer length (and of course loading along that length.

Collyn (in Australia - where we have major such issues)
(Am an ex Vauxhall/Bedford research engineer - working in this area. That company is owned by General Motors.

[Profxd]

Originally Posted by Collyn

There is a known correlation between tow ball mass and on-road stabilty. The lower that mass the lower the safe speed.

It is generally assume to relate to trailer mass - but more correctly should relate too trailer length (and of course loading along that length.

Collyn (in Australia - where we have major such issues)
(Am an ex Vauxhall/Bedford research engineer - working in this area. That company is owned by General Motors.

Welcome Collin! This site needs more people that understand towing dynamics, very few here do.

[ROBERT CROSS]

Originally Posted by Collyn

There is a known correlation between tow ball mass and on-road stabilty. The lower that mass the lower the safe speed.

It is generally assume to relate to trailer mass - but more correctly should relate too trailer length (and of course loading along that length.

Collyn (in Australia - where we have major such issues)
(Am an ex Vauxhall/Bedford research engineer - working in this area. That company is owned by General Motors.

KISS....

Bob
🇺🇸

[Gene]

When I was a student at Lehigh University over 60 years ago, there was a T shirt that said "Two months ago I couldn't spell ingineer, now I are one" (or something like that). Though Lehigh was known as an engineering school, it took me that two months of engineering classes to realize that I was not destined to be an "ingineer" and liberal arts was my future, and it wasn't because I could spell better than "ingineers".

[gypsydad]

Originally Posted by Gene

When I was a student at Lehigh University over 60 years ago, there was a T shirt that said "Two months ago I couldn't spell ingineer, now I are one" (or something like that). Though Lehigh was known as an engineering school, it took me that two months of engineering classes to realize that I was not destined to be an "ingineer" and liberal arts was my future, and it wasn't because I could spell better than "ingineers".

Lehigh? Didn't they used to use digital logic to call the plays on the football team, Gene? "1 0,000, 1, 0, 1; hut, hut!"

[Collyn]

Originally Posted by RussellG

I am hoping to buy an Airstream trailer in the future and I would like to tow it with my motorcycle in the back of my truck. (if this does not work, I need to find out before I get my trailer) So I can't do a physical example.

My truck, 2016 F150 with 3.5 ecoboost says I have payload of 2,170.

My Motorcycle is 700lbs (with full tank and bags loaded with normal items)
My self and passenger 400 lbs

That leaves me 1,070 pounds for the tongue weight and any other stuff I have in the truck. Also i'm worried about the rear axle load with the bike center of gravity just in front of the rear axle.

Also, I only have 6.5 foot bed, so I would need to drive with tailgate down or off. So I would need to extend the hitch back a little

Questions.
1) Does the tongue weight go down with a weight distribution system? i.e. does it distribute the tongue weight to all the axles including the trailer?

2) If I extend the hitch away from the truck, what does this do to the calculations?

Forget the calculation - never extend hitch overhang. Extending overhang hugely increases the tendency for the trailer to sway.
Collyn

[ROBERT CROSS]

OMG...I'm 'gonna dye.


Bob
🇺🇸

POI...never say never.
15yrs apart

[Collyn]

In posts relating to WDH's (an Australian invention in 1950!) there is often confusion re mass and weight.

Mass is simply the amount of matter in something. Weight is a force - here the effect of gravity on mass.

Thus when we discuss the effect of a WDH that being moved is not 'matter' but that down force.

AL-KO once had a PR release that confused this (claiming its WDH moved mass) but doing that would need an angle grinder plus welding!

The downside of a WDH is that it reduces the weight downforce on the tow vehicle's rear tyres. That reduces their 'cornering power' and thus the vehicle's margin of understeer.

A major cause of trailer instability is length NOT weight (and loading along such length). Never have anything heavy at its rear. Is also speed related.

Much of that originally known re all this was originally from America - but appears to have been mainly read in Australia, UK and EU.

My own knowledge comes from working on this in a motor industry research capacity at the GM-owned Vauxhall/Bedford research lab and a great deal of actual on-road testing.

I have also written a book re this that is now seling well in the USA. I assume forum rules preclude my mentioning its title.

[gypsydad]

Originally Posted by Collyn

In posts relating to WDH's (an Australian invention in 1950!) there is often confusion re mass and weight.

Mass is simply the amount of matter in something. Weight is a force - here the effect of gravity on mass.

Thus when we discuss the effect of a WDH that being moved is not 'matter' but that down force.

AL-KO once had a PR release that confused this (claiming its WDH moved mass) but doing that would need an angle grinder plus welding!

The downside of a WDH is that it reduces the weight downforce on the tow vehicle's rear tyres. That reduces their 'cornering power' and thus the vehicle's margin of understeer.

A major cause of trailer instability is length NOT weight (and loading along such length). Never have anything heavy at its rear. Is also speed related.

Much of that originally known re all this was originally from America - but appears to have been mainly read in Australia, UK and EU.

My own knowledge comes from working on this in a motor industry research capacity at the GM-owned Vauxhall/Bedford research lab and a great deal of actual on-road testing.

I have also written a book re this that is now seling well in the USA. I assume forum rules preclude my mentioning its title.

Thanks for sharing your incite. Couple of observations on your comments above, from my limited knowledge. I surely agree with your comment regarding length/weight on rear, being important; especially on an AS. But your comment about WDH reducing force on rear tires causing "understeer" as a "downside" is confusing in your context. To my knowledge and understanding, that is the value of the WDH Weight Distributing Hitch...it re-distributes the tongue weight from the TT when hitched up, back thru the TV frame to the front wheels, improving steering and control (for cornering). You mention the WDH reducing weight on the rear "tyres" causing loss of cornering controll...

[ROBERT CROSS]

^
He's talking about when you are running a gymkhana while pulling the AS with max WD.

Ignore such foolishness...

Our Burb RA is 5000lb with no WD, 4140lb with MAX WD. and 4440lb with WD set...still corners 'on the rails'.😂

Bob
🇺🇸

[Collyn]

Bob

I am responding generally on the pros and cons of a WDH. Am not for one moment they be used unless essential - as they fix one issue (but introduce others).

In esence a WDH, by virtue of moving the downforce (that we call weight) increases the slip angle of the rear tyres - and deceases that of the front tyres. In an extreme emergency swerve that may cause the rear slip angles to exceed the front's. If that happens the tow vehicle oversteers. This has now created what engineers and physicists call a positive feedback loop resulting in that vehicle jacknifing.

There are many videos on the web showing just this happening.

All this was explained by (the USA's) Richard Klein in the 1970s. There many videos showing this on the Internet.

Oversteer/understeer was explained in the mid 1930s by ex Rolls-Royce chief engineer and later GM engineer (Maurice Olley) in the mid-1930s. I had the great fortune to study with him (in the mid-1950s) when he visited the GM-owned Vauxhall-Bedford in the UK.

Collyn

[BayouBiker]

Collyn, raising over steer as a general issue, I think, only provides a small part of the story. For a set-up with significant under steer gradient at highway speeds and through its range of cornering capability what is the harm in bringing cornering response closer to neutral? It's hard to argue more under steer is better than minimal under steer, as the vehicle would certainly corner more safely, holding the desired curvature at higher speed with reduced under steer, so I, like gypsydad am struggling with your use of the word "downside" when describing the consequence of weight distribution. For one set-up it may well be a downside, but for another it may be an advantage, so in reality it seems WD tension should be optimized as opposed to minimized.

What do you say is the ideal under steer gradient while towing? The SAE collectively has decided any amount of under steer right up to neutral is acceptable.

For lightweight vehicles with performance tuned suspension, and near neutral steering when not towing, your caution to manage weight distribution tension carefully when towing to avoid over steer makes perfect sense.

Likewise, the inertial moment of the trailer (you described it as the length and the load distribution) represents a trade-off also does it not? High trailer inertia contributes to sway damping but also increases rear axle lateral force, tire slip and over steer so like WD tension it to should be managed and optimized.

Hitch length seems like a third item to be managed. Here though we agree that shorter is always better. Sometime though there are good reasons to extend it a bit. The Hensley type hitches extend it to accommodate the cam type physical sway control. Others accept extensions to provide some clearance even though they sacrifice some stability margin and suspension performance. Would like to hear you talk about that as well.

[rmkrum]

Hensley design hitches flat out DO NOT use cams of any sort for anti-sway, period.

They use a trapezoidal linkage and a set of simple tapered roller bearings on the pivots. There are no cams involved in the geometry of the linkage. Their sway prevention action is applied to the full range of the possible angle between the trailer and the tow vehicle.

Effectively the linkage projects the apparent pivot point to a spot very near the TV rear axle. It makes the trailer track like a fifth wheel setup. It’s real obvious in a turn when the front of the trailer shifts to the inside of the turn much more than towing on the ball. Something that a Hensley design hitch owner needs to be very much aware of.

There are very clear videos on how the trapezoidal linkage works. Links are on the Hensley Manufacturing site, ProPride site, and YouTube. Watch and understand them before you make erroneous assumptions on how Pivot Point Projection works.

Cam-type systems tend to have the most sway control applied in a very narrow range of angle, mostly straight in line. That’s why they don’t provide full angle sway prevention.

Friction based systems are even less effective compared to the Hensley designs.

[Collyn]

Originally Posted by BayouBiker

Collyn, raising over steer as a general issue, I think, only provides a small part of the story. For a set-up with significant under steer gradient at highway speeds and through its range of cornering capability what is the harm in bringing cornering response closer to neutral? It's hard to argue more under steer is better than minimal under steer, as the vehicle would certainly corner more safely, holding the desired curvature at higher speed with reduced under steer, so I, like gypsydad am struggling with your use of the word "downside" when describing the consequence of weight distribution. For one set-up it may well be a downside, but for another it may be an advantage, so in reality it seems WD tension should be optimized as opposed to minimized.

What do you say is the ideal under steer gradient while towing? The SAE collectively has decided any amount of under steer right up to neutral is acceptable.


For lightweight vehicles with performance tuned suspension, and near neutral steering when not towing, your caution to manage weight distribution tension carefully when towing to avoid over steer makes perfect sense.

Likewise, the inertial moment of the trailer (you described it as the length and the load distribution) represents a trade-off also does it not? High trailer inertia contributes to sway damping but also increases rear axle lateral force, tire slip and over steer so like WD tension it to should be managed and optimized.

Hitch length seems like a third item to be managed. Here though we agree that shorter is always better. Sometime though there are good reasons to extend it a bit. The Hensley type hitches extend it to accommodate the cam type physical sway control. Others accept extensions to provide some clearance even though they sacrifice some stability margin and suspension performance. Would like to hear you talk about that as well.

There are several problems with neutral steer. The main one is that very minor change will swing it to oversteer and if that happened while towing you will a positive feedback loop fuelled by the rig's momentum. It will almost instantly jacknife.

Re hitch overhang. Re shorter the better (but is less of an issue with long wheel base tow vehicles). That important is the ratio of hitch overhang to tow vehicle wheelbase.
Also, that known as the radius of gyration - in effect the distance from the tow hitch to the laden trailer's centre of gravity. Here, the greater the better.

Am well aware of the Hensley hitch (and bump) but cannot really comment as they are not used ever in Australia or Europe. To some extent the Dexter/AL-KO ESC does much the same job (but in a different manner). I suspect however, in borderline situations adding that extra length creates the need to have it!

Often overlooked is using 7-10 psi (50-70 kPA) higher tow vehicle rear tyre pressures. Helps high speed stability. Also overlooked is that friction damping is totally useless at speed. If doubting this check Coulomb damping (and Isaac Newton).

Am interested to know what speed people tow at in the USA.

Re WDHs - like truss that supports a hernia they are a device that attempts to correct a condition that is better avoided. The inevitably reduce 'cornering power' by a typical 25%.

Collyn

[Bruce B]

I love these threads! My problem is that I know just enough to be easily confused by these arguments...
Still, it is fun to read them!

[ROBERT CROSS]

Originally Posted by Collyn

Bob

I am responding generally on the pros and cons of a WDH. Am not for one moment they be used unless essential - as they fix one issue (but introduce others).

In esence a WDH, by virtue of moving the downforce (that we call weight) increases the slip angle of the rear tyres - and deceases that of the front tyres. In an extreme emergency swerve that may cause the rear slip angles to exceed the front's. If that happens the tow vehicle oversteers. This has now created what engineers and physicists call a positive feedback loop resulting in that vehicle jacknifing.

There are many videos on the web showing just this happening.

All this was explained by (the USA's) Richard Klein in the 1970s. There many videos showing this on the Internet.

Oversteer/understeer was explained in the mid 1930s by ex Rolls-Royce chief engineer and later GM engineer (Maurice Olley) in the mid-1930s. I had the great fortune to study with him (in the mid-1950s) when he visited the GM-owned Vauxhall-Bedford in the UK.

Collyn

WADR...there are NO cons to towing with a properly set-up weight distribution rig.

What do you tow and with what?

BTW... I do not trust the British Automobile Enginers.
It took them way too long to determine that engine oil was a liquid.
And they never did figure out how to keep the smoke from leaking out of their Lucas Ekectrical Systim's.

Bob
🇺🇸

[BayouBiker]

Originally Posted by Collyn

There are several problems with neutral steer. The main one is that very minor change will swing it to oversteer and if that happened while towing you will a positive feedback loop fuelled by the rig's momentum. It will almost instantly jacknife.

We have already agreed, over steer is undesirable, though I hope you're aware experienced drivers perceive the onset and easily counter by steering into it. Though under steer does not compound with positive feedback, there is no correction possible and the set-up will dangerously fall out of the desired trajectory and into the other lane or worse. Though insurance experience indicates most drivers handle over steer more poorly than under steer, they are both undesirable.

Since you say neutral steering is a problem because the risk of over steer is too great, then what is optimal? Why is it the SAE specifies the full range of under steer right up to neutral? It seems they would make the lower limit near this elusive optimal under steer gradient. When trailer tests are performed, the engineers give themselves a margin to avoid failing. I can agree a small margin could be appropriate, something close to neutral. You also implied there are other "problems" with neutral steering. Curious what those would be.

Originally Posted by Collyn

Re hitch overhang. Re shorter the better (but is less of an issue with long wheel base tow vehicles). That important is the ratio of hitch overhang to tow vehicle wheelbase.
Also, that known as the radius of gyration - in effect the distance from the tow hitch to the laden trailer's centre of gravity. Here, the greater the better.

Am well aware of the Hensley hitch (and bump) but cannot really comment as they are not used ever in Australia or Europe. To some extent the Dexter/AL-KO ESC does much the same job (but in a different manner). I suspect however, in borderline situations adding that extra length creates the need to have it!

I Agree with these points, though it seems a bit unfair for someone with no hitch experience to trash a hitch for an issue that is addressed with proper set-up.

Originally Posted by Collyn

Often overlooked is using 7-10 psi (50-70 kPA) higher tow vehicle rear tyre pressures. Helps high speed stability. Also overlooked is that friction damping is totally useless at speed. If doubting this check Coulomb damping (and Isaac Newton).

I too nearly always advise higher pressure on the rear tires to increase cornering stiffness, improve suspension response and reduce tire heat buildup.

I 'm confused about your reference to Coulomb damping vs. velocity, as the relevant relative velocity is that of the friction material sliding past each other. Given that sway has typical frequencies of .2 to 2 hertz and the friction distance is at most 6 inches velocity remains quite low. I wonder what friction material speed you consider excessive.

Originally Posted by Collyn

Am interested to know what speed people tow at in the USA.

The most common towing speed in the US for major highways is 65-70 mph.

Originally Posted by Collyn

Re WDHs - like truss that supports a hernia they are a device that attempts to correct a condition that is better avoided. The inevitably reduce 'cornering power' by a typical 25%.

I'm not following this statement at all. Towing a trailer with the hitch point significantly behind the axle reduces 'cornering power' in the range cited for any and all vehicles, addition of WDH always recovers some of that lost cornering (unless the vehicle is previously tuned for performance handling and immediately experiences over steer with addition of a trailer). I'm curious, given that one is towing with the hitch point behind the axle, what measures in your mind can and should be taken to avoid reduced cornering power.

[gypsydad]

Originally Posted by Collyn

Bob

I am responding generally on the pros and cons of a WDH. Am not for one moment they be used unless essential - as they fix one issue (but introduce others).

In esence a WDH, by virtue of moving the downforce (that we call weight) increases the slip angle of the rear tyres - and deceases that of the front tyres. In an extreme emergency swerve that may cause the rear slip angles to exceed the front's. If that happens the tow vehicle oversteers. This has now created what engineers and physicists call a positive feedback loop resulting in that vehicle jacknifing.

There are many videos on the web showing just this happening.

All this was explained by (the USA's) Richard Klein in the 1970s. There many videos showing this on the Internet.

Oversteer/understeer was explained in the mid 1930s by ex Rolls-Royce chief engineer and later GM engineer (Maurice Olley) in the mid-1930s. I had the great fortune to study with him (in the mid-1950s) when he visited the GM-owned Vauxhall-Bedford in the UK.

Collyn

Collyn- Not sure if your a troll here or your serious? Your telling the "experienced" folks here, who have been towing AS's with WDH and antisway control for 30+ years on the road we are unsafe with our set ups. (many with mechanical engineering and physics training also) It's the actual "real" sway and emergency stopping experience, while pulling 25-30' AS's with various size TV's, that counts; not the hypathetical BS which is never accurate since there are so many factors that contribute to towing safely. All conditions are affected by one thing or another and could easily be an argument, as your trying to make.

I just know, the system I use works great at sharing the load with my 3/4T TV providing positive steer and control. 4 AS's and 3 different WDH- I like the BO SC system. The TV brakes are synched with the AS brakes, and in an emergency maneuver (swerve) or stop, the system with anti-sway bars works as it should; control is there and slow to a stop with no issues. Occasionally, we will see someone who claims to "know it all", even more than the manufacturers of the WDH's., even claim "you don't need a WDH"...you do as you wish, Collyn...just hope you don't take someone out if you do get into a situation where the WDH with Sway Contol could have helped your situation... Argue all you want...I am happy with my system...