[Pa Pa's Hack]

Trailer hitch placement, I always planned to install a aftermarket trailer hitch. no preference as I've not looked into them much. In other research I come across what seems to be more Hack rigs choose to install a trailer hitch more to the center line of the rig. Most use the sidecar to bike hardware as a attatchment point for the trailer hitch.
So this has caused me to question? Anyone have a preference? Any reason one way or the other, why one is better or worse?

Thank you Pa Pa's Hack

 

[Unkle Krusty]

With the side car on the right hand side, and assuming that the rig goes straight down the road at 50 mph. Any drag on the car, will cause the rig to turn right. Drag can be from wind, extra weight in the car, or a hitch attached anywhere to the right of the bike. This changes if the car has a driven wheel. Then it would depend if it is of a locked diff type, pozzy traction type ( limited slip ) or differential type. I have not studied driven wheels, but the commie models have them.
A road with more slope to the right, will also cause the rig to turn right.
So I think a hitch should go behind the rear wheel of the bike. But I have never tested this idea, and probably will not.
On a decent pick up truck, it is okay to tow will the ball a few inches off center.

UK

 

[hogcowboy]

Just thinking out loud but I'd think you would want the trailer hitch more or less in line with the drive wheel or wheels in the case with some hacks like the Ural that does drive that outside wheel as well. So on those I could see moving the hitch just slightly to the right of the motorcycle if there is a good attachment point. And attachment points might be the driving factor anyway. As well as available hitches. So without major changes, you might not have a choice as to where the hitch goes. But I'd still think pulling inline with the drive wheel as the best place for the hitch.

 

[johnnyvee]

Just FYI, Ural has no differential, and mfg warns against engaging the drive on pavement. It's strictly an off-road thing, where you rely on the mud or dirt or snow to provide the slip to be able to turn.

Just my 2 cents. I would think that for optimal pulling purposes, the trailer mass would want to be behind the center of pull, i.e., the rear wheel. For braking purposes however, the resulting force would want to be in line with the center of the combined braking effort, possibly with some consideration of the center of mass of the rig. For rigs with a brake on the sidecar, this would move the hitch point towards the sidecar wheel proportionate to the amount of braking force coming from the sidecar wheel, vs the total braking. If I had to compromise one thing versus another, I'd compromise the pulling. I'd prefer to have to back off on acceleration vs. not have the ability to brake in a controlled manner.

Another consideration, placing the hitch nearer the center of the combined rig doesn't increase your overall width. Placing it on the motorcycle axis almost certainly does, at least for any conventional, two wheeled trailer.

 

[Unkle Krusty]

Wot JV is saying.
The Ural is a locked diff. So it will not go around corners with a lot of traction. Which is pavement. Even a limited slip has cornering problems, especially from the front wheels. Many 4 X 4 vehicles go straight into the ditch on tide corners.
Braking is the opposite of what I talked about above. With no brakes on the side car, braking causes the rig to turn left, while throttle causes it to go right. No horsepower, and not much weight, minimizes this.

UK

 

[hogcowboy]

So are you saying a Ural should not tow anything? I know I wouldn't as I thought
they are for rough going terrain where both the cycle rear wheel and the hack's
wheel will help get you deep in trouble.??? Oh, I mean help you.

 

[Pa Pa's Hack]

As you might figure for every 10 or so towing video's on You tube, there " may be" one video for the sidecar/hack. However of the few hack video's towing a trailer better than half of them ( at least of the number I've seen ), have a trailer hitch located in between the Tug and Hack. Some of the video's that have the trailer hitch on the bike, Leave me with a reasonable suspicion that the trailer hitch may have been installed on the bike before the hack was added?
I've watched a few video's of military type hack rigs pulling ammo carts and such. Like Uncle Krusty pointed out most of these were Ural's with two wheel drive. They have the hitch installed amid ship. I seen one video of a war time BMW R100? with the hitch amid ship as well. Was this a two wheel drive as well?
There are a few videos of Gold wings with a trailer hitch amid ship. I'm not aware of any two wheel drive options for the Gold wings?
The braking effect would seem better with amid ship location seeing as my rig has a brake on the hack. The centering of the trailer not increasing the width of the unit would also seem advantageous even if only by a little. Centering of the trailer would possibly obscure one of the lower Tug lights? Since my hack is on the right side of the Tug. It is possible the left portion of the trailer could obscure the right hand light of the Tug. The trailer should be properly lighted. So with the trailer centered a fallowing vehicle should have a clear view of the left hand Tug lights, Trailer lights and Sidecar lights. As opposed to the trailer hitch being mounted squarely behind the Tug it is possible the trailer and sidecar lights would only be visible.
I feel that I'm reaching here? Never the less I feel each point is valid. I do believe I will try the midship location if for any reason I'm not satisfied I can always install a hitch behind the Tug. Of course this logic would apply in the reverse as well.
Thanks Pa Pa's Hack

 

[johnnyvee]

The Ural is a locked diff.

I would say that if there is no possible "difference", in shaft speeds, then it's not a differential, it's just an angle drive.

The Ural's driveshaft ends with the angle drive for the bike's rear wheel and the cross shaft driving the hack wheel is locked to this rear wheel at 1:1 when engaged or it's left unlocked and the hack wheel is not driven. If the cross shaft is engaged, and the bike is driven on a "no slip" surface, one can damage the cross drive or engagement mechanism. Anyway, semantics, ... we are both saying the same thing.

So one could tow with a Ural, same as with any three wheeler, on pavement this would be with the single driving wheel, but towing a trailer through mud and snow, it could be with 2 wheel drive.

The "best" location, for the braking scenario, depends on the braking force distribution relative to the location of the center of mass of the rig, which depends on the load. A lot of analysis could give you a better guess, but my gut says something like offset 30% of the distance from behind the tug wheel towards the hack wheel.

If you were driving the fully loaded hack with no trailer on a slippery surface and locked up the brakes, would the rig spin to the left or to the right? Ideally the trailer center of mass location, projected parallel to the direction of travel past the center of mass of the rig, would act to counter that rotation.

But I bet most folks choose hitch location so the overall rig looks right. As with any towing, it's always smart to slow down.

Sure sounds like a lot of fun!

 

[Unkle Krusty]

JV, answered the Ural on the pavement question. 1 to 1 is a locked diff, no good for street use.
Big rigs with dual rear axles, torture the tires going around a corner. That is what has to happen with a locked diff. Easier to do when the surface is flexible, like dirt. A side car and a trailer, will put a lot of strain on the engine and the brakes. A gearing change would be required with minimum giddy up.
Yami has three good discs and plenty of power. There is a really neat aerodynamic trailer for sale in Victoria BC. $2,000. BC Ferries lets me go as a bike with the side car. A long trailer would take up more space, and cost me more I am sure. But trailers are probably a better way to go. The car can really bugger up the bikes handling. The steering is heavy, for heavier bikes. But you need the big bike for highway speeds.

UK