What causes a rim to crack or split on a rear hub motor?

[e-beach]

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Why do you say this? A properly built wheel that is not damaged should only need minor truing a few times over the life of the wheel. If it needs more that is a sign it was not correctly built in the first place.

Depends on how and how much you ride your e-bike divided by original rim condition and bike/rider weight. Converted e-bikes are much heavier then the manufactures original intent, sometimes by a factor or more then 5. They go faster and are harder to stop due to inertia.
If the OP is delivering every day, then his bike is getting an everyday pounding. Will a good rim hold up for the weekend Lycra warrior? Yep, but for e-bike safety, consent maintenance is required.

 

[Voltron]

Ha... that was a funny coincidence. Out of the blue, one of the customers that cracked a rim 4 or 5 months ago that I laced a Bionx branded rim I had sitting around onto rolled by to say hi. Medium satisfying that even though they didn't come back to get it checked like I told them too... still nice and round...mmmmm.



Her main complaint? Having to get her husband to readjust her brakes every week with all the miles she puts on.

 

[amberwolf]

"Constant" rim / wheel maintenance is not necessary if the wheel is built well with the right spokes and a good rim, unless the wheels are really abused.

I use my wheels pretty harshly (for city riding), almost every day, given the weight of the SB Cruiser (and CrazyBike2, and others, and trailers), and the weight of cargo they have to carry or pull; some of the stuff I cant' always avoid on the roads is not fun to ride thru. But I don't have to keep tweaking them all the time--once I've got them trued and tensioned, they stay that way unless I hit a big sharp edged pothole, or similar. That happens every so often, and can trash the rim and has even broken hubmotor axles (but it doesn't usually break spokes).

I've used (and sometimes had problems with) OEM wheels off of various bikes, without doing any tensioning or truing on them, on various versions of various trikes/bikes/trailers. The cheaper the bike they came from, the more problems I had with them. The better the bike they were from, the less (or no) problems I had with them, even though they weren't built/intended for the uses I put them to. Even the cheap-bike wheels, once tensioned up and trued, mostly work out fine. Some of them don't, usually because of problems at the rim nipple holes.

Converted e-bikes are much heavier then the manufactures original intent, sometimes by a factor or more then 5.

THough this isn't usually that much of a total weight change---the rider usually weighs more than the bike to start with, and some riders weigh several times the bike weight. If you start with a 200lb rider, and a 30lb pedal bike, then add 30-50lbs of electric stuff to the bike, it's not a huge change--from 230lbs to 260-280lbs.

If you start with a really light bike and add a really big battery and motor, the difference in bike weight might be high, but once you add on the rider weight it's still not usually that much difference.

There are exceptions...but I doubt most of them are all that much of a change.

HIgher total weight making higher inertaion to have to stop, so more breaking wear--that's probably true for all of them.

Higher speeds making higher inertia to ahve to stop, so more braking wear--for some that's true. Possibly even many.

 

[MadRhino]

Mountain trails are hard on wheels, even with a smooth rider. We can’t avoid hitting everytime, and some trail sections that would require slowing down are sometimes rushed through. Maintenance is a must, for if you start a trip with wheels less than perfect, you often have to pay double trouble after the ride. Perfect doesn’t mean as new, we are riding disc brakes and our rims are not replaced for dings and dents. I re-shape mine with a small plastic hammer and a heavy rubber mallet. That is why I like using rims that are welded, thick, wide, and not too hard alu grade. They can survive very long, end up being replaced for aesthetics reasons. Carbon rims might change that, because they are the kind to take a beating without any damage, or fail to garbage. Very hard alu grade racing rims are like that too, but at least their cost is relatively cheap as compared to a good carbon rim. My street bike is not hard on rims, even if the streets here are often like mine fields. When I damage a street rim, it is because I did ride it in the mountain, or abused it in parks, curbs and stairs. 3 inch tires are a good rim cushion, but I like riding them low PSI, and fast.

 

[ClintBX]

......
Why do you say this? A properly built wheel that is not damaged should only need minor truing a few times over the life of the wheel. If it needs more that is a sign it was not correctly built in the first place.

Depends on how and how much you ride your e-bike divided by original rim condition and bike/rider weight. Converted e-bikes are much heavier then the manufactures original intent, sometimes by a factor or more then 5. They go faster and are harder to stop due to inertia.
If the OP is delivering every day, then his bike is getting an everyday pounding. Will a good rim hold up for the weekend Lycra warrior? Yep, but for e-bike safety, consent maintenance is required.

As far as keeping a true rim goes, I've been lucky. As long as it's a rim that comes already attached to the hub motor and all, I don't encounter any issues. At least none that are obvious.

It's only when I try to add a rim myself that I run into problems. Though, I haven't done it enough and it doesn't help that the one I have done is a single wall rim from a regular bike wheel and I had to lace it in a conical pattern because the spokes were too short.

 

[-dg]

As far as keeping a true rim goes, I've been lucky. As long as it's a rim that comes already attached to the hub motor and all, I don't encounter any issues. At least none that are obvious.

It's only when I try to add a rim myself that I run into problems. Though, I haven't done it enough ...

Keep practicing and read or re-read Sheldon Browns wheel building page: http://www.sheldonbrown.com/wheelbuild.html. The bit about pre-stressing is key. Patience helps when truing.

I've been building my own wheels for a long time but I finally stepped up and bought the Park spoke tension guage and started using a dial indicator on the truing stand. You can build good wheels without these, but they really help. The wheel I just finished has +/-0.002" lateral runout and spoke tension is within 10% on all spokes. You can get to +/- 0.01" runout without a dial indicator but it takes longer. 0.01 is more than good enough, bike tires are not perfectly straight and round anyway, but there is something about chasing perfection.