durable +2kw derailleur system

One key thing to solve after riding hotrodded GNG:s for a year now is the last reduction-stage.
Things that come to my mind is:
-I really like the option to shift, but 3 speed is enough.
-The bicycle chain can handle enourmos amounts of Power, do we really need bmx-halflink for 2-6 kw?
-Is the short Cage derailleur an advantage?
-how can i build a 25 - 46 tooth rear 3-speed cassette?

This system might give a stable start:
http://www.pinkbike.com/news/sram-7-speed-downhill-drivetrain-first-ride.html

Good find, and good thinking.. but man, $300? ouch.

Many companies do make BMX cassette cogs in various sizes, from 12T to 24T... that seems like a decent spread of gears. I think that BMX chain would be perfect for these higher power mid drives.. perhaps a cassette with 4-5 BMX gears is possible? maybe the gears will need to be ramped, but that can be done with a dremel, no?

I suppose that another option is to use higher tooth counts with regular bicycle chain - like, use the largest front and rear gears you can possibly buy to give you more tooth engagement and reduce slipping. This should add some strength to a higher power setup, but maybe you will find a limit in how much torque the chain links themselves can hold.

Do that, plus use a controller that can have the phase:battery amp ratio tuned downwards to reduce shock loading on gears at 0RPM. In fact, that alone may save many many chains from premature death.

will they sell this to us? 8)

I put 2.5kW (mechanical) through a plain and simple 6 speed derailleur (only using lowest 3 or 4 gears).
I've only done about 5km in testdriving but I had no problems. Only thing I expect is that the chain won't
last very long, I'll be happy if I get 2000km out of a HG-40 chain.

Yep, on road I'm confident it would hold for a fair bit. But offraod, with jumps peak loads and dirt/mud, not a change for normal components...

42T Mirfe sprocket. It's around €45. Does work OK with this derailleur: Deore Shadow RD-M592( shimano part # I-RDM592SGS ). You need a very "steep one" for such a steep cassette

more pics: http://endless-sphere.com/forums/viewtopic.php?f=28&t=45245&start=750#p834472



No chain likes dirt. Still it will work for a while.. I think sprockets larger than 14T are ok for 2000W. Mine lasts a while now with my converted BPM2, which sucks 3500W from the battery. I have a custom 9-speed cassette with 14t-42t.

-how can i build a 25 - 46 tooth rear 3-speed cassette?

Click to expand...

More than 6T difference between the sprockets wont shift well. As said you would need a special derailleur that is very "steep", still even with that one it wont work good. I think 24-30-36-42 might still work OK. Only 3 gears like a 25-32-42 wont work so good.

http://en.garbaruk.com/products/extender
They can make a steel and also other size.

I've been riding the gng for over a year at 4kw. I have replaced at least 5 chains, 4 rear cassettes and a few chain rings that end up bending over time and develope a wobble.

I've read somewhere on the forums that a bicycle drive train can handle up to 2000 watts. As long as the power is applied moderately, your chain and cassette will not last long if you shift under load at 2000 watts.

BMX chains as an alternative was explored by many people in the gng thread. Buried somewhere in the first 1000 posts of that thread. The problem people encountered with the BMX chain, is due to its constructions, does not twist like you need a bike chain to in order to switch gears. They are really designed for single gear applications.

Many GNG owners that run in the 3-4kw range end up replacing the whole derailleur and put in a single speed using bmx chain and sprockets. Which to me kind of defeats the whole purpose of a mid drive. Which is to leverage your gears. Although when you are running at 75-100v, the amount of torque you get and the range of speed you can achieve with a single speed, because of the high volts, does work well.

But like I said, I like my gears. What I did that helped a lot, was remove the 2 smallest gears from my 7 speed cassette. I used spacers behind the largest sprockets to off set the rear cassette a little. Give gave my whole drive train better alignment. I increased my chain ring to the maximum size I could fit, which on my bike is a 44T. That compensated for removing my 2 smallest gears on the rear cassette.

It helped, i stopped eating through chains and rear cassettes. But they still wear ouch much quicker than they would on a non electric bike.

Wishes