Now I have something "new" to me... and a new project

Larry Fine said:
That's a lot of trailer! How does it pull? Mine all but disappears at speed.
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I no longer have that trailer. One that I sometimes wish I did still have though. But if I did still have it I wouldn't be pulling it with my AK. On the ST it was only noticed when stopping or starting up and otherwise invisible at speed. Pulled very nicely behind that bike.

I am hoping the Uni-Go I have now will be the perfect trailer for my AK to pull. The trailer is half the weight loaded compared with that Mini Mate camper. The AK is 230 lbs lighter than the ST1100. A matter of scale.
 
Now that I've decided to bolt the stainless steel hitch frame to the cast aluminum bike frame I went about looking up what bolts to use.
I wish I had looked into that bit first and then I might have chosen to use a different steel for the hitch frame. Actually I wish I had remembered to check metal compatibility first.

I chose stainless steel for corrosion resistance. I did not choose aluminum since it is so much weaker than steel. Now I'm finding out that I really should not use stainless bolts and nuts or the aluminum bike frame will degrade (galvanic corrosion) if moisture gets to the joint... which will happen to some degree even if I don't ride. Stainless steel touching aluminum will also cause the aluminum to degrade/corrode. Not good since that is what the bike frame is made of. I am also learning that there are ways to insulate the 2 dissimilar metals from each other, usually paint or rubber or plastic or tape. But then the question is how much rubbing between them will render any insulation useless? I am looking for a metal to use for bolts/spacers/nuts/washers that is somewhere in between aluminum and 304 stainless on the galvanic metals chart that will work better in the joint. Perhaps brass?
 
Make those angled spacers/washers 1st so you‘ll maximise contact surface area and have no twisting of tubes when bolts are tightened.

Then insert plastic washers between touching parts to insulate.

Can also coat all steel parts with tough insulation layer. https://www.cerakote.com/

Unfortunately, aluminium will always be sacrificial in pretty much all combinations.
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edit: nope, not brass. Aluminum is good with Zinc so maybe zinc coated bolts and nuts and washers and spacers. But the stainless would need to be insulated from even zinc. So maybe zinc coated bolts and spacers and plastic washers with electrical tape wrapped around the stainless and on the aluminum frame where they contact. (I'm cheap). At least the aluminum frame is painted so that should help.
 
Pulled the storage box out again to take and mark measurements on the square tubes for where welds and bends should be.
In these pics I show the 1/4" x 1" x 10" bars that I intend to weld onto the ends of the square tubes.

One picture shows them in place where they will be on the bike. Since I moved the forward mounting point about 4 inches toward the front that caused the square tubes to interfere with the storage box fitting in place. They ended up intruding about 1/2" on each side too far. Adding the flat bar as brackets on the ends straight inline with the square tubes provides plenty of space for the brackets and bolts on each side. There is no issue where the square tubes are against the lower bike frame. I also found, as I suspected would happen, that adding the flat bar brackets as shown causes the square tube to lay flush against the lower frame so no spacer or shim will be needed there. The flat bar brackets can be very slightly bent or twisted to create a flush fit at the upper frame as well.

While I had the hitch frames in place on the bike I measured and marked where the bends are needed and where the end of the hitch frame will be. Since I am now looking into the V-cut then bend and weld type of bends I can nail down how long each section is between each bend. In the other picture it can be seen that both sides will be the same. It also shows that since adding the flat brackets on the front ends there is a lot of excess square tube left over when I cut it off. Also, while I had the square tubes on the bike I measured how wide I will need for the mounting plate that will be welded between the two hitch frame tubes. This is the plate that the Uni-Go receiver will mount directly to. This plate will be 1/4" x 4" x 12 inches wide. The Uni-Go receiver is just under 4" tall (maybe 3-7/8").
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I don't know... but that angle messes with me... a hard stop and it may unload your suspension enough to break the rear tire loose... have you looked at the hitches some sport bikes have used like the hyabusa? an extended axle used for the connection point then another hard point on the swing arm assuming there are 2 points on each side that moves w/swing arm. If not, I guess you have no choice.
 
+1 on Mellow's comment. I looked at your service manual, the high mount scares even me... Have you considered sacrificing your center stand? Maybe second attachment like the muffler bracket.
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Unfortunately the muffler mount is only on one side. No place on the other side for the same. And even in that photo in the post above the muffler mount is at the top of the rear tire at least. Using the center stand mount means finding a way to get around the horizontal shock and also finding another mount on the way back. If not for the rear shock I'd be using the passenger foot peg mounts like is done on the ST1100. Even so a hitch frame mounted that low (which really isn't "low" in terms of standard hitches for 2 wheeled trailers with a ball coupler type hitch) the Uni-Go receiver has to be located much higher. On Scott's GW the adapter that was needed for the proper height off the ground put the Uni-Go receiver 5 inches higher than the ball coupler would be. I looked on the Uni-Go web site at their hitches and the hitch for the BMW K1200RS/GT has the lower mount for the hitch frame at the top of the rear wheel (not the tire but the wheel rim). I believe where I have it being mounted is the best and only place that I can get to without a lot of fancy bending around lots of parts. Even the swing arm doesn't lend itself very well to mounting. I'd have to raise the receiver up at least 6-8 inches minimum to put the receiver where it needs to be. I can't mount at the axle since that has to be adjustable for the belt final drive. I really did try to find alternate locations to mount the hitch and have had to improvise what I have. Adding a hitch is one detail that this bike was simply not designed for and in many ways is almost prohibitive to do.

As it is the hitch frame exits the bike at a downward slant 4 deg down from horizontal. Then the leg after the first bend is 7 inches angled down about 55-56 deg from that... which ends up being a drop of close to 6 inches. The forward forces in hard braking will be acting on the rear sub frame and translate along that to somewhere between the passenger foot peg mounts and the top engine mount, putting the resulting forward push about the top of the rear tire where it would be regardless where I mount the hitch frame. The hitch frame will become one with the rear sub frame and the rest of the bike frame. I don't anticipate any issues with that any more than anyone else who has pulled this trailer ever had.

I totally agree with all of the above if this were a typical 2 wheeled trailer. But it's not. The mass is about what a passenger sitting on the passenger seat would be... no more than 150 lbs if I can help it. So I don't really expect much different handling than that other than the forces will be acting lower than the passenger seat. I know @Mellow has had experience with this trailer. Did you notice any lifting since the receiver is higher than the typical 2 wheeled trailer?
 
I didn't on the st1300 but I think most of the latteral forces are transmitted to the muffler clamp. If your hitch drops enough that could be enough of a solution.
 
I’m not sure it’s the where the hitch is as much as where the receiver is mounted. Tongue weight is not going to be where a passenger sits. Like Joe said, under braking the trailer will push up on your frame. I’m not talking out of class as I have little knowledge, but I am think aloud. My single wheel.
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I really do appreciate all the comments and consider them all. Many have been posted lately that I wish I had read before I started cutting metal and plastic. Most I have actually considered already but still good to read them again.
 
Now an opinion on gussets...
How big? How thick?
Inside of the welded bend or along the side of the welded bend? If along side, both sides or just one side?

I've been reading about cutting the corner of the gusset at the bend so the gusset weld doesn't overlap the bend weld.

Here is the annotated picture (again) showing where gussets would be needed. I added/corrected the angles of the bends needed to ensure nearly vertical orientation of the Uni-Go receiver without going over vertical depending on how the bike is loaded and accounting for the tongue weight of the trailer.
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Went looking for the 2 additional relays that I need to complete the trailer harness on the bike and found... that I didn't have any more. So I ordered them. Project delay now on that part since the order won't be here until the end of February or just after. Can't really do much on the electrical harness without those. I have all the rest of what I need otherwise.

I was planning to drill the bike frame for mounting bolts and at the same time install the electrical connections. Both side panels and the wheel well and the tail light module all come off as one unit and then can be separated if needed. I won't need to separate the parts but just need to pull the rear body panels off. That will give me access to the frame for drilling and also make it easier to get to the electrical plugs and wires.

I guess I won't be doing any road test of pulling the trailer to the RTE at Scooters Feb 24.
 
rjs987 said:
Went looking for the 2 additional relays that I need to complete the trailer harness on the bike and found... that I didn't have any more. So I ordered them. Project delay now on that part since the order won't be here until the end of February or just after. Can't really do much on the electrical harness without those. I have all the rest of what I need otherwise.
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Not relays you can get at your local auto parts stores?
 
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