Bottom bracket the weak point on mid-drives?

[squashua]

Hi. New to the forum and new to electric bikes aside from lurking.

So, an avid cyclist with many bikes, I have a hip flexor pull and am moving to an electric Yuba Mundo while I recuperate.

I thought I had settled on a 500w Ezee front hub as the drive as I would like to retain the carrying capacity of the rear hub (400lbs, needed with two kids, groceries, etc.) vs. most rear hubs which are rated at 200lbs.

However, these mid-drive units have peaked my interest and I have read they are efficient in terms of energy. Also, from what I have gathered, they would allow me just to use the throttle to power the bicycle with nearly no pedaling required (desirable right now).

That said, and as a cyclist, I can't help but notice they seem to have a potential weak spot: an integrated bottom bracket. This can be a mechanical failure trouble spot in bicycles and, in a mid-drive, it appears if the bottom bracket fails, the entire motor would need to be replaced.

Is this correct?

This would seems an obvious advantage to a front hub as all of the mechanics of the drivetrain are left intact and replaceable, regardless of what happens with the electric system. Hub fails? Put on your original front wheel and ride on. Mid drive fails, you are stuck.

Please tell me why a mid-drive (and I'm looking at the Bafang 8Fun 750W in particular) would be superior to a front drive Ezee?

I do very much appreciate the input of those more knowledgeable/experienced on the subject.

Thank you.

 

[dusan]

Hello, that is exactly reason why I didn't choose Bafang or in general integrated BB.
There are few other end user options like GNG and Cyclone.
Regarding crankset
http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=47618
But you really don't need to care about bottom bracket if not pedaling in these cases.
Forget about motors below 750W.
And in my opinion, if you have well geared mid drive, let's say 2x9 gears, I don't see reason why to handle another kilograms for hub.
This is friend of mine Cyclone, he can't pedaling, has problem with joints. He usually does 70-90km with 30Ah. He (120kg) + bike weight = 150kg. After over year experience with his 750W Cyclone, he is happy but think to change controller for 1280W. His average consumption is 3,23km/Ah

http://teslabike.sk/rocni-zkusenost-s-cyclone/

 

[astmacca]

I have put im 1200km in 2 months on a BBS02 with no problems. At some point i will have to pull it apart and service it,
and the bottom bracket section will i'm sure be a significant part of that.

I'm not anticipating too many problems however and the unit seems pretty robust.

it appears if the bottom bracket fails, the entire motor would need to be replaced.

No. Bearings replaced sure, they wear out. Shaft, freewheel and large reduction gear maybe, and that assembly is available as a spare part.

Probably able to head this off by doing the normal thing and disassembling and lubricating periodically.

Primary reduction gear with built in sprag clutch is available as a spare part as well.

There is a thread here on fixing the BBS02 that covers a few non-controller issues like bearings.

On balance i wouldn't see the BB as a particular problem with these drives.

 

[Ypedal]

I've used and sold eZee kits for a long time now, they are solid and dependable.. Have had the chance to ride both the bafang BBS and eZee side by side, and got feedback from many first time e-bikers, almost everyone prefers the eZee powered bike.

That being said, with a cargo hauler, kids and groceries on board, the chain drive might be better if you can get it to run reliably... due to the option of running granny gear when fully loaded. but if you are an avid cyclist and can already handle this bike/kids/food machine, even a front wheel drive eZee will be a huge help.

I also like the front hub for redundancy ..if the chain fails at any point, you got means to motor on home ! lol.. been there, done that.

 

[dusan]

I also like the front hub for redundancy ..if the chain fails at any point, you got means to motor on home ! lol.. been there, done that.

And if front hub fails then astalavista my head.
BTW, chain is used in motorcycle, cars...

 

[Ypedal]

and i've had broken chains on all of the above.. ATV, MX, Bicycle.. etc... more than once on each.

 

[squashua]

Thank you for all of the responses. Much appreciated.

So, the Bafang does not have a sealed bottom bracket? Yes, than I guess it will need regular maintenance but that is good it's rebuildable.

If 500 watts not enough to haul a loaded cargo bike on flat ground with no pedaling? Anyone know?

 

[dusan]

I'm not sure about Bafang. It looks like one-shot kit.
In case of Cyclone or GNG, you actually don't need to care about power, it's always same motor with different controller. Cyclone internal gearbox can properly handle around up to 1kW. That's why they overheating. Most common version is wounded for 24V.

 

[maxwell92036]

Thank you for all of the responses. Much appreciated.

So, the Bafang does not have a sealed bottom bracket? Yes, than I guess it will need regular maintenance but that is good it's rebuildable.

If 500 watts not enough to haul a loaded cargo bike on flat ground with no pedaling? Anyone know?

When people say 500 watts is not enough they mean to say it is not enough for them!

You can buy replacement clutches, controllers and bottom bracket assemblies for the Bafang mid drives. If a chain breaks simply have a chain tool and and extra link. I have broken chains many times on my non assisted bikes and those items should just be part of your repair kit much like having an extra tube, pump, tire levers and a patch kit.

I have 3 bafang mid drive bikes, two 500 watt models and a 750 watt model. All are plenty powerful for most people.

 

[dusan]

Well, even 250W could be enough with proper chainring and sprocket. But speed is adequate. You probably don't need power for speed but for comfort. With external controller and robust motor you still can choose.