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Old 11-12-08, 01:19 AM   #26
recumelectric
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Quote:
Originally Posted by Zeuser View Post
It only takes 2 minutes to go from one form to another including minor adjustments to ensure the disc brakes aren't rubbing.

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I have read (from the Bionx dealers) that Bionx is incompatible with disc brakes. How do you make this work?
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Old 11-12-08, 05:45 PM   #27
SmokeyD
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Bionix makes weak wheels.

Be careful young sir. I repaired Bionix bikes in B.C. which were ridden daily for two years. Because the rear wheel with the motor weighs 15 pounds, then you add the battery box, then the normal weight of the rider.... you get my drift. The spokes should have been thicker to compensate for weight. After two years of just on-road riding, the spokes were all failing at the threaded end. Your bike looks like it's going to be ridden off road on top of that. Have your wheels trued up regularly and make sure someone checks the threaded ends for stripping.
Other mechanics who told me about e-bike problems in B.C., said that motors on the front wheel caused the forks to break because of the extra stress on the forks. The forks on those bikes with front wheel motors should also be tougher. For that matter, I believe your frame is not protected by the normal warranty one you start modifying your bike by making it electric.
E-bikes made in China have tougher frames, 3 1/2 mm spokes on the wheel that contains the motor and 3.2 mm spokes on the front wheel. They don't get into fancy computer circuitry so there's no electrics to go bad if they get wet. Speaking of wet, the Bionix I repaired had an electrical connector joining two parts of the wiring harness right under the left chain stay. The thing was constantly unplugging right from the start, according to the owner. It had to be kept taped up to keep the connection dry also. What a dumb place to put a connection plug!
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Old 11-13-08, 01:34 AM   #28
unime
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Originally Posted by SmokeyD View Post
The spokes should have been thicker to compensate for weight. After two years of just on-road riding, the spokes were all failing at the threaded end.
"At normal loading, no spoke should ever break..." - Jobst Brandt, author of The Bicycle Wheel.

The loading of hub motor wheels is not that much greater than an ordinary bicycle, so normal 2mm spokes should be a workable solution. Never having seen a Bionx wheel, I can only speculate about the cause of the failures, but too little tension and lack of "stress relieving" at the nipple are prime suspects (particularly the latter since the large hub creates a steeper angle where the spoke enters the rim).

There is something wrong with wheels that use 3mm+ spokes. I have seen pictures of Chinese hub motor wheels with visibly curved spokes - a condition that just screams early failure. Maybe they just don't care to build good wheels and realize that ridiculously oversized spokes might last long enough to avoid warranty issues, even though they know the spokes will eventually break. In any case, it is the wrong solution.
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Old 11-17-08, 08:03 AM   #29
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"At normal loading, no spoke should ever break..." - Jobst Brandt

The loading of hub motor wheels is not that much greater than an ordinary bicycle, so normal 2mm spokes should be a workable solution. Never having seen a Bionx wheel, I can only speculate........"

If you have never seen a Bionix wheel why bother offering advice?
You quote Brandt - but the continuous load of a 15 pound motor is not "normal loading"
There are reasons that spokes come in different thicknesses. A modern road race bike can weigh just 15 pounds in total. Are you suggesting that it should use the same spokes as a Bionix?
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Old 11-17-08, 11:29 AM   #30
unime
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Quote:
Originally Posted by SmokeyD View Post
If you have never seen a Bionix wheel why bother offering advice?
Because I have enough engineering sense to be certain that 3.5mm spokes are the wrong solution to spoke breakage on those wheels.

Quote:
You quote Brandt - but the continuous load of a 15 pound motor is not "normal loading"
Perhaps, but it is certainly less than the abuse a downhill mountain bike using large disc bakes undergoes. Or tandem wheel (or unicycle), for that matter.

Downhillers often go with straight 14 gauge (2mm) spokes, but their reason for using heavy spokes is stiffness, not durability. Double butted (2/1.8/2mm) would make for a more durable wheel. Please understand that the torque exerted by the motor on an electric assist bike is small compared to disc brake torque.

Tandem wheels have to cope with twice the load of an ordinary wheel - not a measly 15-20 pounds extra, but 80 or more - and the typically do this using standard spokes (though 50% mor of them).

Then there's my mountain unicycle which takes my 200 pounds of weight multiplied by the acceleration encountered when doing drops: a minimum of 400 pounds of force, probably much higher. Its 36-spoke 14-gauge (for stiffness) wheel is holding up quote well, thank you.

Quote:
There are reasons that spokes come in different thicknesses.
"The idea that spokes are not strong enough is based on failures of
spokes that were not stress relieved after building the wheel. For
wheel builders who cannot understand the concept and refuse to take it
on faith, thick spokes are the only answer..." - Jobst Brandt

The bottom line is that 1.8mm spokes are more than strong enough for a hub motor wheel. The fact that larger spokes are failing suggests a design error or inadequate build quality. The suggestion that 3.5mm spokes are the correct solution to a problem of this nature shows a misunderstanding of the causes of wheel failure.

Quote:
A modern road race bike can weigh just 15 pounds in total. Are you suggesting that it should use the same spokes as a Bionix?
This choice of example demonstrates a misunderstand of bike wheels. Most modern racing wheelsets feature low spoke count, meaning each spoke on a racing wheel is under significantly higher tension than the spokes on a standard (32 or 36 spoke) wheel. If spokes failed because in proportion to strain/tensile strength, the racing wheels should fail long before a hub motor wheel. The fact that racing wheels are reasonably durable when (some) hub motor spokes are failing early points out the flaw in that assumption.
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Old 11-17-08, 02:29 PM   #31
Kermit 43
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The reason for the connection on the rear chain stay is so you can actually change a flat tire without disassembling the whole setup. That's a very smart place to put a connection. The connection would have to be submerged to short out the power conntection ( and if you get your bike this deep most likely your hub will get water into it causing a much more catastrophic failure.) The controlling cable has an o-ring gasket that keeps it water tight.

You mentioned you have seen the spokes strip out at the threads. Usually the spoke head or the nipple will fail a lot earlier than this happens. I would attribute this to a wheel that hasn't been built properly and may have been stripped from the machine that built it.

And to address an earlier post, My Bionx wheel has a rotor adapter on it and I run an 8" Hayes disc on the back with no problems what-so-ever.
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