Install hitch for bike trailer on 12 mm axle

[pajtaz]

Hello,

I have a Q128C rear hub motor that has 12 mm axle. I have a bicycle trailer hitch (see attached picture) that is made for standard 10 mm axle. Specifically, the hitch comes with cogs that are used to prevent the hitch from moving when installed on the axle. See pictures I attached below. First picture is how the hitch looks installed, second picture shows the hitch with corresponding cogs that are used to prevent the hitch from moving, and third picture shows how the hitch is installed with the cog.

Diameter of the cogs is 10 mm. Therefore I cannot put the cogs on the axle in order to prevent the hitch from moving. My question to you is how can I then install this hitch on the axle?

1. Is it ok to install the hitch without the cog? There will be a nut and washer against the hitch but will this be sufficient to prevent hitch from moving when I am towing?
2. If it is not sufficient to install without cog, are there these types of cogs made for 12 mm axles?
3. Are there other types of hitch plates that can install into 12 mm axle without moving? I can just remove the ball and install it on another plate. The ball is held in place with a nut and a washer.

I have and do not want to use an alternative plate that attaches to the frame. That cannot fit because of all the wiring and motor cable being there and I do not want to put that much stress on the frame.

I appreciate any advice. Thank you in advance.

 

[HK12K]

If you have the axle length you may be able to sandwich the receiver between a pair of nordlock washers. I'd expect that to keep it put, but keep an eye on it. Unless someone has a better idea, which they may.

 

[pajtaz]

Reading about people's experiences with mounting hitches without locking them, it is not a good idea. It will probably not hold.

My best solution is solution number 3 from my first post. There must be hitch mounting plates that have the hole drilled out just like the axle of typical rear hub motor, 12 mm on top and bottom, and 10 mm flat on the side, just like the lock washer that comes with hub motors. If I can find a plate like this then it will naturally lock in correct position. Problem is to find a manufacturer/seller of these kinds of plates. Does anybody know of any?

Final option is to drill out the correct size hole in the existing plate or locking cogs. I don't want to do that but I might have to.

 

[HK12K]

If sandwiching the plate with nordlocks isn't something you'll consider you can try to file the existing sprocket until it accepts the axle, which may be easier said than done depending on hardness, or bring it to a metalworker and ask them to modify it to accommodate you. Finding an off the shelf part for this is unlikely, though I would be happy to be proven wrong.

 

[docw009]

The Q128 will have the power cable coming out of the axle on that side, and half of the metal is ground away, to let the wire exit, so there's not a lot of threaded metal rod on that side to hold additional nuts/plates. Even if the axle was long enough for extra nuts, I think mounting a plate that supports a trailer and that also can twist the axle is a losing proposition.

THe plate needs to rest against the frame like in the picture. One could use a file and cut the rectangular 12 x10 mm slot, but it's an exacting job. Then add a bracing arm to the plate that connects to the frame. Then the hitch mount can serve double duty as a torque arm as well as a hitch,

 

[dogman dan]

Best bet might be to fabricate some kind of plate to bolt the hitch to.

Possibly it would clamp to both of the stays, then the hitch bolts to the plate.

Or it could be a torque plate, which also includes a tab protruding to the rear, which the hitch can bolt to.

 

[pajtaz]

Thanks for all the advice. I'm thinking of filing the "cog" that is used to lock the hitch plate on the axle with a 10 mm round file to only enlarge top and bottom so that it fits on the 12 mm axle. I have to make sure I file correctly so that once the cog is installed in the hitch plate, the hitch is in the correct orientation (the locking part must be at the bottom). The hitch plate itself already has a hole large enough to fit on the axle.

I am not in favor of using additional plates or plates that connect to the frame. I was really hoping someone knew about "standard" hitch plates for 12 mm hub motor axles. I figure by now these would exist.

 

[dogman dan]

Let us know which fails first, the filed down hitch, the axle, or the frame. It will be interesting to see.

The hitch looks like it would be a weak torque arm, ( similar to tabbed torque washers) if the round hole was filed into a flat D shape. Might work better than we think. Or not.. as I said, it will be interesting to see if it works, in a season.

 

[pajtaz]

There is no reason for any of those parts to fail. Hitch will not be filed down, only the cog.

What will fail is the cog. It already broke on another bicycle without being modified. Cog broke in two pieces. I suspect the cog was made out of some not particularly strong material, couldn't tell what it was.

 

[HK12K]

500-1000w is enough to mangle regular bicycle dropouts that weren't designed for it and QS isn't exactly known for it's axle strength, so really if any kind of movement were to present itself it could become a problem quite quickly and potentially catastrophically. Since the discussion was mostly about a hitch and not the bike at large I was operating under the assumption that axle retention had already been considered and a torque arm/plate of some kind was already at play. (Preferably on both sides) Essentially what I'm suggesting is that if you're relying on the d shaped washers that came with the kit to prevent the axle from spinning there is a good chance that those washers will eventually deform and stop serving their purpose, or the increased movement that they may eventually allow could put unforeseen stresses on the axle which it may not be able to withstand. Nothing good will come of that.

Since you've seen others reference the cog breaking I would not bother attempting to modify it. If it'll break under normal usage filing away a bunch of material isn't going to do it any favors, if it can even be filed at all. A failure here is not something I would want to recommend inviting, especially considering what's at risk both on and behind the bike.

Your best bet imo is to have somebody build you a torque plate that will retain the axle, connect to the bike so it absolutely cannot spin (preferably using an unused hole on the frame to accomplish that) and then have them attach the hitch ball assembly to that plate. Those who suggest that you are playing with fire if you're not properly securing the axle are not wrong.

 

[pajtaz]

Great point. Ideally I would do exactly what you suggested - torque plate to which I can install the ball. I don't even need the hitch plate itself as long as the torque plate has the same angle plate to which I can attach the ball.

I already have an alternative plate with the ball but I just don't want to install it unless it is the last resort. First, it also has a 10 mm hole which will have to be enlarged to fit 12 mm Q128c axle. Second, it will be difficult to fit it on the frame because of the motor cable and the hidden wire brake sensor which run along the frame. Third, it will put additional stress on the frame. The plate I have is attached.

 

[dogman dan]

Nope, you are dead wrong. That is exactly the one you need. Its the torque arm you must have to run the motor.

Align it with your dropouts, ( horizontal or vertical) and mark it. Then file the hole into a D shape that perfectly fits the flat sides of your motor axle. Make it nice and tight on the flat, it can have extra room on the round sides.

Now you are good to go, got a great torque arm and the hitch.

Run your cables down the arm till its past the hitch, with some zip ties. If its a serious problem, lengthen the arm and move the U bolt down the stay till its ok. You can bolt on a bar to lengthen it.

I should have been more clear,,, I meant the motor was going to break the filed down cog. Motors need a good torque arm, and you got the part to make a superb one.

 

[HK12K]

What Dan said. Assuming the metal isn't made of cheese that will make both an excellent torque arm and hitch mount. Just file carefully and keep checking for fitment.

As for wires, I slid a strip of dense closed cell foam padding between the hitch plate and wires on mine to prevent chaffing. Secured with velcro straps. For yours a stretched inner tube wrapped around the stay could help to prevent damage to the finish and a piece of strategically placed foam or even a couple inches of loom for wire protection, but hard to say without seeing it.