Near-Catastrophic Rim Failure

[Dave]

Hey:

I've been putting my ebike with the rear wheel kit to good use this year, when the weather allows anyway -- very wet & cold spring. So far I've put about 150 miles on the motor, and it's been working great, at least up until last week.

Saturday morning I pulled it out to run a couple of errands, and noticed the rear end felt a little squirrelly. Thought the tire might be a little low, so went back home to check it out. While attaching the pump to the valve, noticed a problem with the rim:


It ain't supposed to look like that. The wheel was way out of true, pushing hard against the brakes on every revolution. Closer inspection showed that other spoke holes showed significant cracks, and would probably start looking like this one before too long. I remember hitting a piece of wood in the road one morning last week, but it didn't seem to affect it too badly at the time. The bike was parked for two or three days after that, but my 14 year old son may have taken it out while I was at work; he doesn't remember hitting anything with it, but that doesn't mean it didn't happen either.

This was the rim supplied by Golden with the rear wheel kit -- a cheesy single-wall alloy unit. I knew from the get-go that it probably wouldn't last too long, but I was hoping for a little more time than this. I've got a couple of spare 36-hole wheels sitting around, so it looks like I'll be doing a rim swap in my spare time this week. Will probably have to drill out the spoke holes for the heavier ones that came with the hub motor.

Anybody interested can check my blog for more info on my ebike and what went into getting it on the road. Link.

[philf]

I relaced two out of the three wheels I've installed so far right out of the box.  I put Mavic double-wall rims on, with spoke eyelets and machined sidewalls.  MUCH nicer.

My sister has the one that we didn't relace, though I spent a fair bit of time truing it (it was the best of the three).  I'm wondering if your spokes weren't too tight, but I can certainly attest to the fact that the spokes do exit the original GM rim at a strange angle that's just not good to begin with.

Glad you caught it before something worse happened while riding!

[ahend]

I just swapped my stock rim out. Guess I dodged a bullet! As with many other owners, my rim was thrashed straight form the box and required extensive truing. Even then there was still a flat spot that could not be worked out. When unlacing the Golden Motor wheel, I ran into a couple rough looking nipples, one was cracked and required replacement. I had a shop true up the new wheel after I laced it up. They had to make two new spokes to replace some that were damaged. The Golden Motor nipples fit down into my new rim with out modification, I was surprised. You may find one of your wheels will take them. 

As for my old Golden Motor rim, I stomped it flat (purely for recycling purposes you understand). When I did, the rim seam simply opened up. The alloy was not fused in any way. I do not know exactly how a bike rim is produced, but I would have thought that the ends would be welded in some way. To be fair, there are two heavy round wire hoops encased in the aluminum extrusion and they seem to be the only thing holding it all together.

[Dave]

I relaced two out of the three wheels I've installed so far right out of the box.  I put Mavic double-wall rims on, with spoke eyelets and machined sidewalls.  MUCH nicer.

My sister has the one that we didn't relace, though I spent a fair bit of time truing it (it was the best of the three).  I'm wondering if your spokes weren't too tight, but I can certainly attest to the fact that the spokes do exit the original GM rim at a strange angle that's just not good to begin with.

Glad you caught it before something worse happened while riding!

I hadn't thought about the spokes being overly tight; when I first got the kit it went to a bike shop to have it trued/dished. They weren't able to do much to affect the dish of the wheel because the spokes were a bit too short... I too am glad it didn't blow out completely while riding it. That would've been a long walk home, especially if the wheel wouldn't turn!

Wondering about your Mavic rims with the eyelets; were they large enough for the heavier spokes/nipples that came with the Golden hubs, or did you put lighter gauge spokes on it?

Thanks!

[philf]

The Mavic rims worked just as they were, with the existing spokes.  The eyelets tend to want to keep the spoke nipples straighter than the spoke wants to bend in order to match the GM supplied pattern, but this minor deflection doesn't cause any issues.

The other thing to remember to get is a decent rim liner.  I think electrical tape would be more effective than the jaggy piece of brittle plastic supplied with the original wheel.

This is the model of Mavic Rim I am using - I paid $39 (Canadian) for them.



That's the Mavic "X221 UB".  The machined sidewalls are just so much nicer for braking than the GM one which, apart from the seam, didn't have parallel sidewalls to begin with.

[biohazardman]

I put some of the Weinmann DM 30s on mine $45 never even installed the rim that came with the kit as it was to warped to be usefull. These are a heavy and wide double walled rims that did not have to be drilled for the larger spoke nipples.  Only 250 miles or so on them at the moment but I don't see any problems as yet. Also had to tighten the spokes several times as they seemed to stretch quite a bit. Had planned on putting a couple of barely used Mavics similar to philf's post above but was told they needed drilled for the larger nipples and this could not be done. Looks like that was not the case but the DMs are way beefy so happy with the end result albeit a bit more money was spent.  It's a good thing you found that before you crashed and burned.

http://i3.photobucket.com/albums/y51/biohazardman/bike1/hubandwheelsm.jpg

[Dave]

Thanks for the input. The rims I have on hand are plenty heavy, but do not have eyelets. Not sure how necessary/beneficial eyelets are if the alloy around the spoke hole is heavy enough. One of the rims came off an older Giant LaFree electric bike, so I'm pretty confident that it'll hold up. My bike weighs less than the LaFree's.

Is that a front wheel hub in your photo?

[Dave]

You know, I was shopping online for bit today, seeing what was available for replacement rims, and was surprised to find some rims with offset spoke holes, which makes it easier to dish a wheel properly.

 

Golden could sure use something like that on their rear wheel kits to help get them centered in the frame.

Anybody listening?

[philf]

Wow!  I confess, I didn't do much looking around when I bought the Mavic rims.  Just went into the local bike shop and asked what they had with 36 holes that was reasonable.

Does anyone know if it's actually possible to shift the motor on the axle?  I think I read somewhere else on this forum that the bearings are just press-fit, but I'm not sure how the axle is machined - how possible it is to shift the motor left or right.

Those offset rims are definitely intriguing.  Even as all three of the bikes I've done are, I replaced the freewheels with Shimano ones (much smoother and quieter), but even at that, there's one of the bikes whose derailleur pulley cage will run into the motor housing if you pull up onto the low gear.  Having more room would be an asset, even with the 5 speed cluster.

[Dave]

Wow!  I confess, I didn't do much looking around when I bought the Mavic rims.  Just went into the local bike shop and asked what they had with 36 holes that was reasonable.

Does anyone know if it's actually possible to shift the motor on the axle?  I think I read somewhere else on this forum that the bearings are just press-fit, but I'm not sure how the axle is machined - how possible it is to shift the motor left or right.

Those offset rims are definitely intriguing.  Even as all three of the bikes I've done are, I replaced the freewheels with Shimano ones (much smoother and quieter), but even at that, there's one of the bikes whose derailleur pulley cage will run into the motor housing if you pull up onto the low gear.  Having more room would be an asset, even with the 5 speed cluster.

The axles are press fit, and shifting them would be a real task. But shifting the motor left to right is fairly easy by cutting spacers of different widths. As long as the left spacer width + motor width + right spacer width is equal to your dropout width, you can cut them any size you like. The biggest constraint though is where the rim ends up between the chainstays. You've only got so much you can do to adjust the placement of the rim by tweaking the spokes; that's why I was so fired up about the offset rims.

Another thing that I've been considering with mine is eliminating the multi-speed freewheel on the bike and going with a single speed instead. I'm finding that I do most of my gear changing on the chainrings anyway, keeping the chain on the smallest rear sprocket. The main drawback with a single speed is that the smallest sprocket you can possibly get is 15-tooth; with the motor assist I'm finding that I need a higher gear ratio than what I currently have with a 14-tooth rear sprocket, so I'd have to get an even larger chainring.

Someone else on this forum (from Australia I think) was using a three-speed freewheel with his motor, which is narrower (less wheel dish) and might give a little more flexibility in gear ratios, but I haven't been able to find one in the US.

[Dave]

Just a progress report: Last week I was able to get a new rim laced up to the hub, had it trued up at a bike shop, and it's on the bike once again.

I replaced the original rim with one that came off of a dead Giant LaFree's, so it didn't cost me a dime. It's a good heavy rim, and should hold up well. It was interesting to note the difference in weight between the LaFree rim and the original one from Golden; at least twice the weight. The original felt like so much aluminum foil by comparison.

One nice surprise that I got when I picked up the wheel from the bike shop is that the rim is now very nearly centered on the frame. When I first installed the motor on the bike I had cut spacers to make room for a 5-speed sprocket inside 135mm dropouts, but the bike shop mechanic who tried to dish the rim the first time round wasn't able to get it dished so that the rim was centered. I took it to a different bike shop this time, and they were able to pull it off no problem. Not sure if it has to do with the guy who did the work, the new rim allowing a little more room than the old, or what, but I am glad with the result. $20 well spent I'd say.

So, I'm "on the road again..." (sorry if I got that song stuck in your head!)

One mental note I made to myself is to work up some kind of alternate connector for the wiring to the hub. I had wire ties holding the wiring to the frame, which require cutting and replacing any time the rear wheel is removed. Having a connector closer to the axle would eliminate that. Anyone know of a good set of replacements for the main power & Hall sensor leads?

[biohazardman]

Good that you are back on the road.  I have been thinking about the connector also as I had my first flat a couple days back.  Did not relish the thought of yanking the rear wheel with motor off.  But managed to find the nail and only pull a small section of the tube out to repair and put back in.  I have a couple of the molded trailer connectors found here under  http://wiringproducts.com/contents/en-us/d174.html  for the power connection on another motor and they seem to be OK.  A bit of grease or silicon should make them completely waterproof.  But they are a bit large for the hall sensors me thinks lots here and there so I will continue looking for a bit before I come back to them.  Good luck.

[philf]

I went through the same thing you did, working on one of the three bikes.  I had the back wheel off that bike a few times, and every time I took the thing off, I was cutting a bunch of wire ties and using a bunch more to put it back together.  I looked around for a solution to make it possible to put a quick disconnect in the line near the wheel that wouldn't be too bulky, but would also carry the juice to the motor.  There were a few things that grabbed me, but none were really cost justifiable (connectors can be expensive!).

What I wound up doing is putting the 5 wires to the hall sensors through a separate weatherproof LOCKING connector, and using an inexpensive ($4.50 at the local Sayal Electronics) trailer kit for the phase wires.  A little shrinkwrap tubing, and it all goes together tidily.

Here's a picture of the connectors used...



Connected together, they're just over 2 1/4 inches long...  One of the wires in the trailer connector, obviously, isn't used...



I have the DigiKey part numbers for the connectors for the hall sensors around here somewhere, if anyone's interested.  I seem to recall that the pair (male/female) cost me around 10 or 12 bucks Canadian.

[Dave]

What I wound up doing is putting the 5 wires to the hall sensors through a separate weatherproof LOCKING connector, and using an inexpensive ($4.50 at the local Sayal Electronics) trailer kit for the phase wires.  A little shrinkwrap tubing, and it all goes together tidily.

Here's a picture of the connectors used...

Thanks for that, Phil. I had thought of using the trailer wiring also, but after looking at the link above from biohazardman, it appears that there are also three-contact connectors of similar design.



As for the Hall sensor leads, since there isn't likely much current being carried there, I had thought to use some kind of computer connector for that... something like a PS2 or Mac serial plug. But I do like that one that you found that has the locking ring on it. And the weatherproof aspect is appealing. It would be nice to have something not so bulky though. Another thought from the wiringproducts.com link is to use one connector for the three phase leads and the Hall sensor leads. There is this eight-contact connector:



Way overkill for the Hall sensors, but I think it'd get the job done.

I did a little wiring work on my battery/controller/charger leads last week -- the original leads connected to the socket had been flexed a few too many times and were fraying a bit, so I replaced them with two-conductor versions of the trailer-style connectors that I bought at a local farm & home store;



Matching connectors went on the battery pack, the controller and the charger. Much less bulky than the original repurposed power cord style plugs that came with the kit, and works fine. I had been having some trouble with the motor cutting out under load, and that helped considerably on that front, as did going through all the high current spade connectors, making sure they were making good contact. A world of difference after all that.