 I couldn't find anyone in the US who made a trailer hitch for my 1994 R100GS. So, I designed and built one myself.
Mechanical Design
The design is quite simple. There are two horizonal and two vertical supports. The main horizontal supports are 1/8" x 1" mild steel. They tie into the footpeg mounts. I replaced the footpeg bolts with slightly longer versions. 
I welded the two horizontal members to a piece of angle iron that serves as the platform to which the 1 7/8" hitch ball mounts. I later added some 1/4 rods criss-crossed ahead of the platform to increase stiffness (not pictured).The vertical supports tie into existing holes in the subframe at the top, and into the horizontal supports at the bottom. There are also 1/8" x 1". I ground some small notches into the right vertical support to hold zip-ties in place for securing the trailer wiring.
 I used metric hardware throughout, so that the existing BMW tool kit could be used if there was any need to make adjustments during a trip.
I am still able to remove the rear wheel without removing the trailer hitch.
 Electrical Design
 For the electrics, I used a Hopkins 48935 converter to convert the 5-wire (ground, left, right, tail, and brake) setup on the BMW to the 4-wire (left/brake, right/brake, tail, and ground) arrangement used on the trailer. I tied into the subframe wiring harness using Posi-tap connectors from Posi-Lock. These connectors are a pleasure to use. The Hopkins converter comes with a 48" extension, which I sheathed in some split tubing and routed back on the subframe, then down the right vertical support. It terminates at a Hopkins 48595 mounting bracket hidden under the ball mounting platform. I'm pretty proud of the clean overall exterior look. 
The trailer uses LED lighting and I replaced the bike's stock incandescent tail light with an LED unit model 1157-R19W6 from SuperbrightLEDs. I believe that using LEDs in both applications will keep the net electric current draw well within the motorcycle's capacity.
Trailer
 I believe it has recently been discontinued but similar models may be available from other suppliers. The trailer is essentially a car-top carrier on a small trailer frame. I made no effort to allow more rotational movement beyond what is available from the standard trailer ball and tongue. I've read a number of reports that the 360-degree systems may cause more problems than they fix. A trailer ball on a hinge is available too, but reports on those are mixed at best.
 A number of reviews of this trailer suggest lengthening the tongue for added stability in motorcycle applications. I may still do that.
Overall impressions
So far, I'm happy with the design, looks, and performance of hitch. It adds about eight pounds to the motorcycle. I've only done short rides on it so far with 50 lbs of payload. I plan to keep it under 100 pounds in normal usage behind the motorcycle. I have been gradually trying out faster and faster speeds. So far, there have been no handling problems. I need to do some more steep turns to see how it handles as I hit the limit of the rotation allowed by the ball and tongue.
The only thing disconcerting so far is seeing this big object so close in the mirrors.
I will update this as I get more experienced in towing. |