Front & rear chain ring sizing for BBS01 Install

Richard@Paris

New Member
I have a Focus Urban with an Alfine 8 speed IGH, and it is fitted with a Gates Belt drive. When i install my BBS01, I need to change over the rear sprocket for a standard chain drive.. I know the front chain ring on the BBS01 is a 46T, but i am thinking to replace this with a RaceFace narrow wide chain ring..
I use this bike mainly for my daily commute which is 22 klms approx each way, and not especially hilly although there are some inclines of up to 1 klm which is tiring..therefore I would like to know what is your recommendation concerning the sizing of the front and rear chain rings to optimize the performance and ensure the longevity of the motor?
thanks in advance for any help provided..
 

Richard@Paris

New Member
@Richard@Paris have you contacted e-RAD/Lectric Cycles? They have done conversions with your type of motor using a Gates Belt drive. Why dump a really quiet smooth transmission if you can have both the mid drive and belt drive.
Hello and thanks for your reply. I had originally set out to retain the belt drive and had purchased the adapter for the front sprocket, but when i installed the mid-drive unit, the chain line was out by approx 7mm, and as I had no spacers to remove between the drive side of the motor and the bottom bracket, I had then to address how to get the front sprocket closer but i found it would touch part of the mid-drive casing.. i thought of ordering a bigger front sprocket which would hopefully provide more clearance but then I would also need a new carbon belt, so the whole idea was getting somewhat expensive without any guarantees.

Since then, I have found out that the mid-drive recently supplied to me is in fact a BBS02 750w and not the ordered BBS01 so an exchange is now taking place. When the BBS01 arrives in a few days I will try again to see if the mid-drive unit is perhaps a little smaller and thus removing the 7mm chain line issue..

I would like to retain the belt drive as i really love it.. I will contact e-RAD/Lectric Cycles and see what they can propose.

Thanks again..
 

Dewey

Well-Known Member
I recently installed a 2013 BBS01 kit on a 1995 hybrid. My commute is 4 miles up and down some 6% hills. I found the Bafang 46t front chain ring too big for the bike's 7-speed 11-28t rear cassette plus the motor seemed to really bog down when climbing hills. I replaced the gears with a 42t lekkie narrow wide front chain ring, and a 7-speed 12-32t rear cassette because I read on another forum someone had suggested no more than 10 tooth difference made the difference for moderate hill climbing. I bought a programming cable and changed the BBS01 controller PAS settings to raise 'keep current' from 20%-75% and set a speed limit, this improved the motor performance because the default BBS01 controller 20% 'keep current' setting was strangling the motor when I needed the most power. Now I can maintain a 60-70rpm cadence, and 14mph in 3rd gear climbing hills, if you like to pedal faster or have steeper hills you might find more comfortable a gear combination less then 10 tooth difference. I can't speak for longevity because I just did the conversion, but to prevent crunching the chain/sprocket when changing gear under load you should consider either tapping the ebrake lever or stop pedaling briefly to cut the motor before changing gear, or install a gear sensor (get the right version for IGH or derailleur) or mount a 'big green button' above the left grip to use like a clutch to cut power and change gear while pedalling.
 
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Richard@Paris

New Member
Hello Dewey, I appreciate you taking the time to reply.. I have found your info very useful.. I have done some further investigation, and found that "the Alfine eight-speed IGH gear range is more than enough for regular town and country use. With a 20-tooth sprocket on hub, this approximately imitates the gears on a 12-38-tooth cassette". I have a 20 tooth rear sprocket so I will add a 42 tooth front chain ring and see how that goes.. I have the IGH Gear sensor but yet to install it.. Once i have tested this, I will then update the Controller PAS setting as you have done and see how this improves the overall output..

Thanks again for your assistance..
 

Dewey

Well-Known Member
I have the IGH Gear sensor but yet to install it.
You may need a new gear cable if the end is frayed, the gear sensor requires a tight fit through a very cheap piece of plastic and I accidentally destroyed the one I bought with the kit when I attempted to pull through a fraying gear cable. I also made the mistake of attempting to cut the derailleur cable housing with wire cutters - don't do this it ruins the housing, use a cable cutter. After that I gave up and installed a big green button :)

With the Alfine IGH can you change gear when stationary? Riding a derailleur bike with the BBS motor requires a conscious effort to change down gears before coming to a halt, which is good practice anyway but also necessary so as not to strain the motor when pedalling away from a stop. I briefly considered having my local bike shop build a new rear wheel with one of the updated Sturmey Archer RX 5-speed IGH hubs which permit shifting gear when stationary, but I'm happy for now with my set up.
 
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