2015 Honda Grom: GUS (Grom Utility Sidecar) Project

[Diablo007]

So the Grom GUS project is all but finished (explanation follows).  It was way more involved than the manufacturer's website (https://industrialmoto.com/) led me to believe. The website lead me believe it would be a 'bolt-on' installation.  Installation was much more involved. 

The kit was purchased as an anniversary present from both of us to both of us.  Unfortunately we didn't realize the lead time necessary so it would arrive late.  Industrial Moto was awesome and sent me a swag package to give to my wife while we waited for the kit.

The kit arrived with the box really beat up.  There were large chips out of the powder coating as a result of the poor packing.  What was most puzzling was the large chip out of the powder coating on a smaller part that was wrapped well and protected by the 'car' portion of the kit.

When I started to assemble everything I realized the tabs that bolt from the motorcycle frame to the sidecar were about 1" out of alignment, on two planes; front to back and side to side.  My email to the company was responded to with it's OK to just bend everything to line up.  Really?  To get all 3 holes to line up I had to bent one bracket forward and use the sidecar 'cart' to increase the torque so that I could get the cart away from the motorcycle enough to drop the bolt in.  On top of that, the installation of the rear bracket put the foot peg bracket about 1/8" away from the frame.  Instructions were to just tighten it down.  Yeah not happening, I bought a washer of sufficient thickness to take up most of the space.

OK, 'cart' mounted.  Time for installing suspension and wheel.  The suspension amounted to a swingarm knuckle and a shock.  When all was bolted up the shock was at about a 30 degree angle away from the 'cart' to the knuckle.  On top of that the amount of lateral play because the knuckle was not captured between anything was scary.  I took the rig for a test ride.  Not only was the amount of shaking due to the play scary, the motorcycle went into a hard left after turning at the end of the street and would not stop turning until I stopped the motorcycle.  The instructions stated everything would be setup pretty close to where it should be.  Research showed it was not even close.

After lots of online research and talking to a friend who has setup many sidecar rigs I learned that the sidecar has to have enough toe-in so that it tracks in a straight line, I've set ours for a speed of about 35 mph as that's about the average on our little trips.  The motorcycle should also lean about 3 degrees away from the sidecar.  To get the toe-in correct I had to remove the rear bracket, section out about 2" and weld in an adjuster.  There was not enough adjustment at the front mount to get the proper toe-in.  As for the lean, there is not enough adjustment to correct that, fixing that will take a lot of work.  As such it has not been tackled.

A lot of the shaking was taken care of by machining fender washers on my lathe to capture the knuckle between two planes, taking away the lateral movement.  As the shock included in the kit had rubber bushings, not a rotating eye, for the bolts I machined spacers so that it only moves in one plane, front to back.  All of these modifications made a huge difference.

Sidecars do cause headshake so I added a GPR steering damper.  That was the final modification and made a huge difference.  The damper unfortunately leaked and was returned for warranty service.  Riding without the damper reinforced how much of a difference it makes.  I can't wait to get it back.

Once all the above had been I added a brake light and blinker to the sidecar, and disconnected the right blinker on the Grom (so as not to confuse people).  I spliced a trailer tail light plug into the stock harness in a way that makes it easy to disconnect the sidecar and reconnect the stock lights if necessary.  (Once again to no confuse people when getting the annual safety check required in Hawaii.)

I did contact Industrial Moto regarding all of the above.  They did say they would work with me to modify the rear bracket but never did.  In reality the rear bracket should not be fixed, it should have a Heim joint on both ends so that the toe-in can be adjusted from the rear.  The front should be as close as possible to the motorcycle.  In fact the whole sidecar assembly should.  That is one part of the design that is correct.  The sidecar is about as close as possible to allow an adult foot to use the rear brake.

The sidecar assembly is already showing rust, apparently the powder coating wasn't that good.

The next addition will be a backrest and small rack behind it for the sidecar seat.

Pictures as it is are attached.  I also have pictures of it before bending things to line up, and of the modifications done to it.

All in all we love it, but at $2000 it was overpriced due to all of the issues.  In reality the 'suspension' doesn't do much, it moves about 1/2" when I jump up and down on it, and barely moves when my wife does.

[Diablo007]

Forgot to mention.  Sidecars need weight, otherwise in right turns (in a left hand drive country) the sidecar will come up and the steering characteristics change.  I used a 5 gallon bucket of sand when setting everything up, I could still get the sidecar up in the air.  With my wife (maybe 100 lbs) in it it handles much better, to the point it fights in tight, fast, right hand turns.  That's better than coming up, as then you start drifting to the outside of the turn, or at worst you flip over to the left.  Also the rear slides right in fast, sharp left turns, but that is most likely due to the short wheelbase, or so I've been told.

[m in sc]

wow. good writeup. i remember when these came out everyone was all over them but  yeah, that should have been better. glad you got it sorted out.

[Diablo007]

While out for a ride today in it I realized I forgot some more important information.

The wheel spacers included in the kit were just short pieced of metal tube.  The didn't even fill the space between the axle and seals.  WTH?  They also had the wheel too far out from the suspension knuckle.  In my opinion the spacers should have sealed with the wheel oil seals, and been as close to the knuckle as possible to reduce the amount of torque created at the knuckle as there is no swingarm to evenly distribute the forces on both sides of the wheel so the axle will flex under load and bumps in the road.  I machined two spacers for the wheel, the inside one brings the wheel as close to the knuckle as I could without worrying about the spokes hitting the knuckle due to flex in the axle.  The outboard spacer was machined just thick enough that it cleared the oil seal.  There is some play in the axle.  When I have time I plan to machine a bronze bushing to replace the rubber one in the knuckle, that should remove the play.