Rear dropout fix

[ChapinB]

Need some guidance for preventing further dropout damage.
Backround-
This entire build has been built on compromises. Started out as a free build, built with parts I had, walmart bikes, spares, ect just to have a some fun. However as it got built, put some miles on it, I really like it and some things needed better parts than I had originally used. Disk brakes, tires, ect. Now the rear dropouts are starting to slowly spread. The motor axle isnt rocking back and forth in its slot. Bike has stamped rear dropouts with a long slot, like below, with the spreading happening along the red line. Currently spread maybe 1/4". Photo is not my bike.


26" 1500w hub motor 9c clone, on 18s/24ah lipo. Current draw tops out at 70amp (5kw), but has a super soft start. No regen. 3x cheap gen 1 style torque arms that clearly arnt holding it well enough.

So to remedy the situation Iv got a few paths, but need some guidance on what might be best or what might just be downright dangerous.
1. Bend the dropout back, add a proper torque arm and call it good.
2. Bend dropout back and weld 1 or 2 additional sets of dropouts from other bikes to mimic a torque arm.
3. Cut and reweld new dropouts with a torque arm and/or additional dropouts. New dropouts will be sufficiently reinforced with a steel rod inside.
4. Replace the whole rear triangle and add extra dropouts/arm. Possibility of adding rear suspension by doing this at the cost of making the long boi even longer and heavier than it is.




Please excuse the zip ties on the torque arm - they were there for only a short period till I got better clamps.

 

[E-HP]

If welding is an option, then replacing them with clamping dropouts would negate the need for torque arms.

 

[ChapinB]

If welding is an option, then replacing them with clamping dropouts would negate the need for torque arms.

Whats a clamping drop out? The typical style seen on walmart and cheap hub motors? Thats whats on it now if so.

But it did just dawn on me that that nut may be a culprit, or part of it. The axle nuts are torqued fairly hard, without a washer between the nut and drop out. Could that action be opening the dropouts over time? The wheel has been in and out a number of times over the build.

 

[Risky Rob]

On other threads, I see people recommending tightening the nut to 55 ft/lbs.

Hub motor axle bolt tightening torque - How much is enough?

Folks: I've got an ongoing problem with loosening axle nuts. I'm using a medium-power Nine Continents M3006RC as sold (but now discontinued) by Grin: http://www.ebikes.ca/shop/discontinued/m3006rc.html and on both left and right dropouts, Doctorbass's hardened steel torque arms...

endless-sphere.com

 

[E-HP]

Whats a clamping drop out? The typical style seen on walmart and cheap hub motors? Thats whats on it now if so.

But it did just dawn on me that that nut may be a culprit, or part of it. The axle nuts are torqued fairly hard, without a washer between the nut and drop out. Could that action be opening the dropouts over time? The wheel has been in and out a number of times over the build.

There’s a few threads here on fabricating clamping dropouts. The torque arm picture thread has a few examples of replacing them with clamping dropouts with beefier clamping dropouts. In a few cases, it also eliminates the need for axle nuts.
torque arm picture threadtorque arm picture thread | Endless Sphere DIY EV Forum

 

[A-DamW]

Whats a clamping drop out?

Here are some pics from ES to give you an idea:

 

[ChapinB]

Appreciate it guys! Definitely have some ideas to look into now!

And Im probably overtightening the axle nut, if I had to guess. But no damage to the thread in any case.

 

[amberwolf]

Now the rear dropouts are starting to slowly spread. The motor axle isnt rocking back and forth in its slot. Bike has stamped rear dropouts with a long slot, like below, with the spreading happening along the red line. Currently spread maybe 1/4".

Having significant failure experience with various hubmotors of even much lower power than yours in that kind of dropout on Crazybike2 before I rebuilt them, I can say with some confidence that the problem is the axle prying them open--even if it isn't rocking back and forth in any apparent way, the forces it's flats are applying to them are opening them up. It can happen even without regen, and even with soft start, if there is enough torque overall.

A perfectly fitting torque arm that is correctly fixed to the bike frame, that *does not* allow *any* movement of the axle, will prevent this.

A poorly fitting arm won't help


Even the best fitting arm that isn't completely fixed to the frame won't help


Additional paralleled dropouts will slow the process, but won't stop it. (tried that, the metal is just too soft; it's not meant to resist torque because a bicycle wheel axle does not apply any).

Replacing the dropout with a clamping type, or attaching clamping pieces to it, will prevent the dropout from spreading...but the clamps need to be fixed to the frame tubing properly, not just the dropout plate, because the metal really is pretty soft on those types of dropout plates (you can bend them *by hand*! (at most, a pair of pliers, even with my arthritic joints).


This was my solution for Crazybike2, using some thick hard dropouts off a BMX frame:

2WD Semi-Recumbent Recycled-Parts Cargo eBike: "CrazyBike2"

How to turn a front 9C hub into a rear: First, this old hub (originally from DayGlo Avenger, when I tried JBWeld to hold sprockets to it for my first motorization attempts. :lol:) And cut the threaded end off including it's spoke flange: Then because the bearing hole is not big enough for...

endless-sphere.com

I made better-working ones on the SB Cruiser trike; they're in teh torque arm picture thread.

 

[ChapinB]

I like the idea combining a beefed up drop out/track into the clamping surface. That might not be too bad given how mine sits.

 

[delta bedbug]

You do need to use washers to keep this from happening, Big fender washers.

 

[ChapinB]

An update in case anyone else finds themselves in a similar situation. I have since ran ~100 mi without it spreading any more.
Had the rear wheel off, fixing an alignment issue. Bent the dropouts back to stock, - probably weakening them in the process. Torquing the wheel nuts, I noticed the drop outs opened back up, and a significant amount at that. The torque washer things in every kit were spreading the drop outs.

Heated up the dropout, knocked it back tight and secured a grin TA on each side. ~100 more miles on the odo and the dropouts are still snug as can be.

Lession learned - Secure that TA before before torquing the wheel nuts to keep the load off the dropouts.

 

[n00b]

Here are some pics from ES to give you an idea:

Aw! I was just talking to the bed frame guy!
That's very interesting! Still wanna know what that bottom piece is.
I might be a dumbass, but I consider that unrecognized genius right there!
That last pic looks like something I could/would do.