Are Middrives Really Prone To Chain Derailment?

D

doubledipsoon

100 W
Joined
Feb 22, 2013
Messages
151
OK, I'm almost finished with my DIY Middrive ebike, and I'm beginning to hear about "front chainring to rear cassette" anomalies leading to inadvertent chain derailments. My front chainring is lined up perfectly with the middle spline (sprocket) of a 7 speed (sprocket)cassette- I've heard that because of the high gears not being perfectly centered to the "chainline", chains don't always "accept" a running chain, and pop off. So what's the real story, my middrive enthusiasts? And if it has been a problem with your middrive setup, what was your solution? Try to keep it simple.
 
BBS02, original Bafang 48T chainring. Had problems with chainline, so couldn't use lowest two gears. Swapped to custom 42T chainring, all gears usuable, but had made the mistake of removing the front derailleur cage with the swop. Occasional chain deraillment on rough terrain. Front derailleur cage back on, absolutely no problem whatsoever now.

Lessons learned along the way :D
 
Haven't had a drop in awhile but like previous person, I have front derailleur that keeps it in check. You need something like this if you ride rough terrain.

There are a lot of other cases for dropped chains though. Sometimes you can't get the chain line right because of the frame design or where motor mounted.

In a previous build that was higher powered, it would flex the frame and cause the chain to pop off. Or the higher power would bend the brackets and would mess up chain alignment.

There are others but those are what I ran into.
 
I have had a BBSHD for a year now, and today I had my first chain drop off of the front sprocket. I was going through a bumpy section, and the chain was bouncing a lot. I have heard from the off-road guys (who ride bumpy sections all the time) that it helps if you have a "chain guide" located just in front of the place where the top of the chain feeds into the front chainring.

(it's the green thing)

p5pb12570292.jpg
 
Thanks for all the replies so far.....OK, I've been brainstorming about this- sounds like a "narrow wide chainring" + a "clutched derailleur" may be the latest chain grabbing technology around, and a one way ticket to keeping your chains on. But, I like to exhaust cheaper and more creative ways of solving problems, before blowing another $200 on what may be "overkill" with more "complicated" technology, if you know what I mean. - SpinningMagnets, I like that little "green thing"- sounds like a cheap and more low tech but just as efficient way of keeping the front chainring in its sweet spot (in the "chainline"). Where can I get one of those? I know there's a million kinds of chain guides out there, but I love that color! Thanks again for all the info.
 
I've used this one very successfully, might be easier to fit around a BBS

https://www.bike24.com/1.php?content=8;product=146800;menu=1000,2,228;backlink=108%7C3%7C240%2C245%7C%7C%7C%7C%7C%7C%7C%7C%7C
 
doubledipsoon said:
OK, I've been brainstorming about this- sounds like a "narrow wide chainring" + a "clutched derailleur" may be the latest chain grabbing technology around, and a one way ticket to keeping your chains on.
Click to expand...

A chain guide, or just a normal front derailleur locked in position and pushed down to overlap the chainring, does the same job more effectively at a tiny fraction of the price. Not that funky chainrings and funky derailleurs don't help, but their primary purpose is for you to spend lots of money on them. I suggest you start with the thing that's least costly and most effective, and add gimmicks only as necessary to tickle your fancy.

My latest bike drivetrain (a couple of months in service now) uses a $20 chainring, a road bike front derailleur set up as a guide, and a high quality but well-used '90s MTB rear derailleur to shift across the 11-34 7-speed freewheel. It works as well as any new equipment I've tried, doesn't drop the chain, and requires no adjustment so far.
 
you mentioned 7spd so that rules out narrow wide and clutched derailleurs. narrow wide chainrings are optimized for 10 or 11spd chains. 7/8spd chains will still get thrown out

clutched derailleurs for shimano are for 10 or 11spd only. you can't use them w/ 9spd and below because the cable pulls are different. but i'm sure there are hacks to make them work but i haven't tried yet...
 
Overclocker, OK, my previous possible option to use a "narrow wide + a clutched derailleur" won't interfere with my now present plan- ditching that whole idea for a simple chain guide...period. It sounds to me that since my chainline in the granny gear (lowest gear)is only being violated by 3/8", and I'm only running a 600w 24v motor, I shouldn't have any of the chain throws that 1000w BBSHD users are complaining about. This is just a guess, but less torque should produce less chain throws, right? Besides I mainly do asphalt roads and an occasional dirt road. My main goal is to make it up the hills around here without chains flying in my face. OK, the proto run is scheduled for about a month from now. I'll let you all know how it goes. And thanks...
 
Overclocker said:
you mentioned 7spd so that rules out narrow wide and clutched derailleurs. narrow wide chainrings are optimized for 10 or 11spd chains. 7/8spd chains will still get thrown out
Click to expand...

10 speed chains work just fine on 7 speed cassettes and freewheels. They cost too much, but they work.

But narrow-wide chainrings can do nothing to actively retain or return a chain to position; all they can do is prevent it from moving side to side as much as it would otherwise. A front derailleur or other guide can catch a chain that has already jumped off, and feed it back onto the chainring.

I have already encountered clutched derailleurs that I had to switch into the unclutched setting to make them shift reliably. That doesn't seem like an improvement to me.

Anyway, it seems obvious to employ the $10 solution that works, before the $200 solution that might or might not help.
 
Chalo said:
Overclocker said:
you mentioned 7spd so that rules out narrow wide and clutched derailleurs. narrow wide chainrings are optimized for 10 or 11spd chains. 7/8spd chains will still get thrown out
Click to expand...

10 speed chains work just fine on 7 speed cassettes and freewheels. They cost too much, but they work.

But narrow-wide chainrings can do nothing to actively retain or return a chain to position; all they can do is prevent it from moving side to side as much as it would otherwise. A front derailleur or other guide can catch a chain that has already jumped off, and feed it back onto the chainring.

I have already encountered clutched derailleurs that I had to switch into the unclutched setting to make them shift reliably. That doesn't seem like an improvement to me.

Anyway, it seems obvious to employ the $10 solution that works, before the $200 solution that might or might not help.
Click to expand...


yes in fact i have a 1x9 pedal bike that uses 10spd cn-hg54 for better chain retention w/ the NW chainring. but for my mid-drive bikes those chains are too expensive since electric wears chains quickly, so i use cn-hg40, costs P220 or about US$4 at the LBS. cheap 8) so i buy 4 or 5 at a time and rotate them every 2 weeks or so prolong my drivetrain


HCIvSWH.jpg
 
doubledipsoon said:
Overclocker, OK, my previous possible option to use a "narrow wide + a clutched derailleur" won't interfere with my now present plan- ditching that whole idea for a simple chain guide...period. It sounds to me that since my chainline in the granny gear (lowest gear)is only being violated by 3/8", and I'm only running a 600w 24v motor, I shouldn't have any of the chain throws that 1000w BBSHD users are complaining about. This is just a guess, but less torque should produce less chain throws, right? Besides I mainly do asphalt roads and an occasional dirt road. My main goal is to make it up the hills around here without chains flying in my face. OK, the proto run is scheduled for about a month from now. I'll let you all know how it goes. And thanks...
Click to expand...


don't worry too much about it. a simple FD/chainguide solves all your problems especially since you say you have a perfect chainline i.e. lines up w/ center cog
 
Overclocker said:
doubledipsoon said:
Overclocker, OK, my previous possible option to use a "narrow wide + a clutched derailleur" won't interfere with my now present plan- ditching that whole idea for a simple chain guide...period. It sounds to me that since my chainline in the granny gear (lowest gear)is only being violated by 3/8", and I'm only running a 600w 24v motor, I shouldn't have any of the chain throws that 1000w BBSHD users are complaining about. This is just a guess, but less torque should produce less chain throws, right? Besides I mainly do asphalt roads and an occasional dirt road. My main goal is to make it up the hills around here without chains flying in my face. OK, the proto run is scheduled for about a month from now. I'll let you all know how it goes. And thanks...
Click to expand...


don't worry too much about it. a simple FD/chainguide solves all your problems especially since you say you have a perfect chainline i.e. lines up w/ center cog
Click to expand...

Well the chain can still rub against the FD or chain guide (depending on it's type). Just a simple rod 2-3 mm above the chainring should prevent the chain from derailing and it doesn't rub anywhere.
 
Well the chain can still rub against the FD or chain guide (depending on it's type). Just a simple rod 2-3 mm above the chainring should prevent the chain from derailing and it doesn't rub anywhere.
Click to expand...

In my experience when the chain is pulling against the side of the front chain guide then it is doing its job by taking the sideways force from a crossed up chain and directing it straight onto the top of the chain ring. On the BBSHD installs I have done I have moulded a carbon bracket to hold factory downhill chain guides and this bracket is bonded and screwed to 4 of the factory threaded holes behind the gear cover. I would post pics but I took them with too high a resolution and cant upload them.
 
We only have about 400 miles on our tsdz2 750w with stock 42 chainring and 8 speed cassette, but so far not one chain issue and it shifts perfectly through all the gears. Chainline is pretty good.
 
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