Mechanically connecting a trailer to a motorcycle - GL1800Riders
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post #1 of 38 (permalink) Old 08-20-2016, 03:24 PM Thread Starter
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Mechanically connecting a trailer to a motorcycle

This post will likely leave riders with more questions than answers. We have been really busy for a year in developing a new source for aerospace bodies for the Tailwind and this has resulted in my not having time to visit this really good board for several months.

For those of us accomplished in various fields, things seem obvious. However, how often do we think about a person that has never had a reason to be versed in our field and would not be expected to make correct decisions in that field. Like having problems with MS Excel and going to MS for help. Their answers always assume that you know almost as much as they do. So to get help in Excel it is best to go to a third party.

Pulling a trailer with a motorcycle is often assumed to be a non technical issue, like eating ice cream needs a spoon instead of a fork. Of course nothing could be farther from the truth. What brought this to mind was the thread about a broken Rivco receiver.

First off it was a broken ball plate. The receiver is what it plugs into.

I have been there and done that. I designed my first motorcycle pulled trailer and built it in 1957. I patterned it after a Wright auto camp trailer and just made it motorcycle size and out of aluminum instead of steel. Since that time I have had 40 years of aircraft structural, mechanical, and aerodynamic design experience and also several years in other fields. But the knowledge of baptism by fire in those early months in 1957 were deeply etched.

Making a trailer so it can be loaded nose light is like selling arrows with the feathers on the point end. (My first trailer was just that way.)

Riders that are not steeped in physics will almost universally think that a trailer on a bike should be loaded to have minimum down load on the hitch. This is as wrong as jumping off a building and flapping your arms to reduce the impact. Years ago when Hal Greenlee was kind of the owner/sponsor of this board, I read the post of a rider that had just crashed pulling his trailer with his wife as a co rider. He said he did not know why the rear tire of his bike failed because he had nearly zero tongue load. I cringe to see these kinds of stories over and over.

What happened was that he loaded his trailer near neutral and successfully pulled it in this highly unstable condition until he got a leak in his rear tire and as he tire started to be low, it reduced the lateral stiffness in the rear of his bike and the typical divergent oscillation happened and threw them off the bike. By the time he got out of the hospital and to his bike, the rear tire was all the way flat so he assumed it blew out.

I have posted information on this subject before but it has been years. When I see things like these ball plate failures and comments like the weight on the hitch was not very much, I realize that I need to bring this up again.

IT IS NOT THE WEIGHT ON THE HITCH THAT IS THE PROBLEM WITH BREAKING THINGS, IT IS THE INERTIA.

You can easily take a 2 wheel flat bed trailer and put 4,000 pounds of cement bags on it that are stacked in such a way to have exactly zero downward load on the hitch. You could sit there and hold this trailer level at the hitch with one hand. But, if someone paid you a thousand dollars to raise that hitch 3 inches and put it back down 3 inches 5 times in one second, you could not begin to do it because the dynamic force to do this would be in the thousands of pounds.

Postured another way, likely you can hold a 50 pound anvil in your hand. Also if you suspended this anvil with a bungee from your hand you could move your hand up and down very quickly while it was suspending this anvil, but if you had the anvil in your hand you could not move it up and down quickly because of its inertia. The Bungee would be relieving of the inertia.

Because of the dynamics of pulling a single axle trailer with a vehicle, the trailing vehicle must be nose heavy by at lest 10% and better if 15% to be stable. Dynamics are everywhere that things move. Airplane ailerons, elevators, rudders must be nose heavy or they will flutter and fly off the plane or take the surfaces they are attached to off the plane unless they are irreversible, meaning they can not be made to move as in transonic and supersonic aircraft.

People designing trailers and trailer hitches are not necessarily physicists, nor or the riders using them. Terms like notch sensitivity and stress risers are not in their vocabulary. Opinions will not make or prevent failures but there have always been lots of opinions.

If there is no inertial relief system in the mix, then the dynamic loads must be within the capability of the structure applying the loads including the fatigue spectrum.

Steel is typically more tolerant in fatigue than aluminum but steel airplanes would not be able to carry much. So the aviation industry has had to establish and live by certain parameters relative to fatigue. There are a lot of very old airplanes flying, like B-52s.

It is probably well known that certain trailers have had lots of failures in certain areas and that is because there was no effort to reduce stress at these failure points. A 3/4 inch diameter shaft has a fair amount of strength but if you want it to fail, make it an extension of a large shaft turned down to 3/4" in a single sharp step or to put any kind of a stress riser in the design. If the dynamic load is high the shaft will break exactly at the step in diameters or other stress riser. History convinced one of the manufactures of this when my words could not.

Similarly, if you have a beam, say a foot long, and you apply a load of 100 pounds, the bending load at the root end will be 100 foot pounds and so its connection to resisting structure must be good for 100 foot pounds. If the beam is extended to 5 feet, then the bending load at the root is 500 foot pounds and so the joint receiving the load now must be 5 times as strong as it would be for a 1 foot beam. All of these of course must be good for the load applied when applied 1,000,000 times or however many cycles the life time of the joint needs to be. Armed with this kind of inquisition, it is obvious that many trailers are not prepared for long term use.

In similar thought, Honda did not do us any favors when they needlessly extended the plastic by almost half a foot aft. The most stable place to attach a trailer to the bike is where the rear tire touches the pavement. Obviously that is not in the cards. However, every inch aft and up from that point is going away from stability. Also, because the frame of the Wing was not changed, the hitch manufacturers kept their core mount structure and just made the ball plate longer. Remember the increase in bending moment on lengthening beams. Our Tailwind users have come up with a way of carving an arch in the rear fender so that the pre 2012 hitch ball location still works. This is low risk because there are so many center fender panels left from trike conversions.

Bushtec recognized that their rod end type hitch had limited travel when the bike was nose up compared to the trailer and recommended hitting steep drives at an angle. I do not know if some trailer/hitch combinations using a ball might run into a similar nose up limiting angle. The fact that some of these failures are at the ball end of the ball plate on Rivcos makes me wonder if that could be the case. Then too, when bending metal, when the plastic limit si reached granular separation starts. That gets into bend radius, hardness at bending temperature, etc..

My failure to convince those I wanted to buy trailers from on some of these issues, caused me to re enter the manufacture of trailers with the Tailwind in 2003. It has been very enjoyable with countless friends that I might not otherwise have, but I will admit that Aviation was more lucrative.

It is said that a person's wealth is measured by what he has that money can not buy. I would not think of trading anything for the friends I have in these motorcycle touring associations and particularly the Tailwind family. My longest lasting and best friends have mostly come from motorcycling. My friend Hilmer Merz and I have been riding together since 1959 and we each have great grand kids whose grand parents were our kids in diapers when Hilmer and I met.

Glen Kenny's enormously popular RTE is proof that Motorcycling families are naturally great friends.

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post #2 of 38 (permalink) Old 08-20-2016, 03:40 PM
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I actually did learn something from your words of wisdom. I knew that the tongue weight needs to be 10-15%. I just never knew why and how important it is.

Thank You, Tom



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post #3 of 38 (permalink) Old 08-20-2016, 03:54 PM
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So if i read this rite on newer 2012 n up with longer rear fender tallwind guys cut notch in fender ???? To accommodate new length of fender ? Any chace on a pic what they did. Old hitch works fine but issue as stated with length of bar.good rite up !!
.

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post #4 of 38 (permalink) Old 08-20-2016, 04:29 PM Thread Starter
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Have not posted a pix in a long time so here is trying. This is a photo of Len Ellis' bike and also shows where the six pin round socket was placed, since the 2012 and later bikes have a frail three piece bottom fairing of the trunk and will not support the six pin socket there.

This trim accommodates the screws in the bottom corners that attach to the saddle bags. The Rivco hitch ball plate is the ORIGINAL 6 inch drop ball plate, that is for 2001-2010 Goldwing models. Not the new stretched out ball plate.

Although we have not tried it yet, I believe the ORIGINAL short flat ball plate for the Bushtec Hitch will also work here. It is all but impossible to get someone at Bushtec to find and ship the original short Flat ball plate. Nevertheless, some of our customers have been successful in getting them to do it.
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Help downsize Government! Encourage private industry!
Make things here, sell them in the Mid and Far East!!
Ship goods out. Bring dollars in. Strengthen America!!
Texan since 36, Rider since 52, Bike/Trailer riden' since 57. Passed 1,000,000 motorcycle miles 6/16/08.
'10 GL 1800A '04 GL 1800A, '04 Tailwind XTc (We make 'em), '75 TEFCO Streamliner




Last edited by Tom Finch; 08-20-2016 at 04:35 PM.
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post #5 of 38 (permalink) Old 08-22-2016, 09:40 PM
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Quote:
Originally Posted by Tom Finch View Post
Have not posted a pix in a long time so here is trying. This is a photo of Len Ellis' bike and also shows where the six pin round socket was placed, since the 2012 and later bikes have a frail three piece bottom fairing of the trunk and will not support the six pin socket there.

This trim accommodates the screws in the bottom corners that attach to the saddle bags. The Rivco hitch ball plate is the ORIGINAL 6 inch drop ball plate, that is for 2001-2010 Goldwing models. Not the new stretched out ball plate.

Although we have not tried it yet, I believe the ORIGINAL short flat ball plate for the Bushtec Hitch will also work here. It is all but impossible to get someone at Bushtec to find and ship the original short Flat ball plate. Nevertheless, some of our customers have been successful in getting them to do it.
It was a simple phone call for me to get the flat ball plate.
When I called, I was told that it would be a week or two because it took time to get them back from the chrome shop. I told him I did not want it chromed and got it in two days.

<font size=3><font color=#333333><font face=Verdana>If you don't watch the news or read the newspaper, you're uninformed; if you do.... you're misinformed.</font></font></font>
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post #6 of 38 (permalink) Old 08-25-2016, 03:30 PM
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Originally Posted by moh58 View Post
It was a simple phone call for me to get the flat ball plate.
When I called, I was told that it would be a week or two because it took time to get them back from the chrome shop. I told him I did not want it chromed and got it in two days.
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I sure miss the old days when you could call and talk with John Preston and get all your questions answered. Now when you call, you get a very nice lady, who I am sure tries to get you with the right person. But, that person never returns your phone call...

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post #7 of 38 (permalink) Old 10-26-2016, 04:44 PM
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So came across this and wanted to share as Tom's original post to this thread touched on this issue.
And in my recent trip I noticed quite a number of trailers (mostly attached to cars and trucks) that were suffering from lack of understanding...
I think this makes it VERY clear why a forward bias in weight distribution is highly desired

Mitch

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post #8 of 38 (permalink) Old 10-26-2016, 04:45 PM
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and oh yea... Hiya Tom, good to see ya back 'round these parts.

Mitch

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post #9 of 38 (permalink) Old 05-16-2017, 10:45 PM
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Very important stuff !!!

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post #10 of 38 (permalink) Old 05-16-2017, 11:19 PM
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I know this is reviving an old post but hope Mr Finch sees it. I take everything he says about trailers as gospel. I used his directions to have the bearing spacers on my Bushtec trailer custom made to fit the individual wheels to prevent possible bearing failure. Just as he predicted, the ones from the factory were a few thousands too short and resulted in the bearings seating improperly. Also had a spare wheel done to be safe. One day I hope to have a yellow Tailwind in my garage.
Tom, I saw you at Glen's RTE this year but unfortunately I received a call from my wife about a family emergency and had to leave soon after I arrived and didn't get a chance to shake your hand which was one of my main reasons for finally making the trip. One day I hope to meet you and take delivery of a new trailer in Spring Branch.
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