Dual BBS02B 2nd person controlled mobility quad: Chain and rear sprocket advice

JB in TH

10 µW
Jun 16, 2019

Two newbie questions for my first post and hoping someone has some experience.

First question:
Does anyone know where to buy either a threaded freewheel to BCD chainring adapter or a disc hub to BCD chainring adapter? I saw some custom machined ones discussed online but nothing recent that leads to a supplier. The bikes have v brakes but the hubs also have 6 holes to take a disc brake rotor on either side. Being able to use a front chainring on a threaded rear cog would be best, bolting a front chainring to the rear hub via disc brake mount would be second best, and third option is in my next question.

Second question:
Assuming no joy with question 1, I have found aluminum adapters for threaded hubs to disc brakes and also sprockets with 6 holes for installation in place of disc brakes. Could not find steel adapters. Question is on chain width compatibility with these various single speed large tooth count sprockets as they are 415 and 420 chain compatible. I could not find them for 410 chain.  Lunacycle sell a 410 single speed chain that is compatible with a Bafang front chainring so I know that the front chainring is at least OK up to a 410 chain width. With 410 having ¼” width, 415 having 3/16” width and 420 having ¼” width (all same pitch and roller diameter), will a 415 or 420 chain work with a Bafang chainring or will the extra chain width cause any issues?

I did try many searches and found roundabout answers but nothing definitive to give me confidence in being sure that what I choose will work.

Thank you very much for your patience and if you want to read more about my plan then please continue reading my long introduction:

Please allow me to introduce myself: I am a British expat working in Thailand and I have been a lurker on endless sphere for a decade. I have converted two mountain bikes with rear geared hub kits in the past (so still a beginner). My eldest son has some mobility and cognitive challenges that means he cannot walk over rough ground and cannot control a bike on his own. I could manually push him on off road wheel chairs when he was smaller but he is reaching adulthood and so I am the one who needs assistance to help him get into the outdoors. I was inspired by a youtube user “JerryRigEverything” who bolted two rear hub drive bikes together to create a fantastic off road mobility bike for his partner. My take on this will be basically the same except I will use two BBS02B and I will have full control of the bike. I will be walking from behind, steering with a third headset cut off a spare bike. Two separate mid-drive motors, two batteries, two LCDs and two thumb throttles. I will have a “flip over” bracket that combines throttle levers to deliver same amps to each motor and I can use them separately if need be. I will program the controllers to deliver slow start up amps so as not to risk the front lifting when throttling for climbs. Batteries will be mounted on the front of each of the bike headsets so as not to pull the steering and keep more weight forward. I will make the width between the bikes enough to mitigate any roll over risks, the spanning frame/seat will have a roll over bar and seat will have a four point harness. I plan for braided wire and pulley wheels to link the rear steering to the front forks.  I have two round tubular steel framed 20” fat bikes with single speed, horizontal dropouts, and V brakes and I have removed the rear threaded sprocket ready to choose new rear sprockets. I chose 20” rims because I wanted a short enough bike length with front wheels removed to fit in the back of a big car when the spanning seat frame in the middle is removed.

I have two Lunacycle BBS02 30T front chainrings on the way. I plan to install single speed cogs on the rear wheels in 50T to 60T range. Tooth count choice being two fold – best motor RPM for walking speed (I will steer from behind while walking), and to keep the motor temp low for extending climbs. Range is not an issue as the walks will be relatively short limited by how far I can walk on a one day hike and the batteries are both 48v/17Ah. I am running two motors for redundancy and to allow easier disassembly for transporting. Redundancy is a big deal for me – I can handle punctures/chain issues easy, but a complex drivetrain failure will be more will be a problem because the quad with my son will be too heavy for me to push home – hence two completely separate systems. Also two motors allows plenty of torque and traction to climb stairs for beach access. I used ebikes.ca motor simulator to check various total weight/slope gradient scenarios both for separate and combined motors. It should do jogging speed at full throttle with 52T – 60T rear cog range but I will not waste my own energy jogging – I only need 5km/h walking speed on the flat.

Thank you again,


JB in TH said:
Does anyone know where to buy either a threaded freewheel to BCD chainring adapter or a disc hub to BCD chainring adapter?

BCD is just Bolt Circle Diameter, so you have to specify the actual BCD you're after.
Thanks for reading and the clarification. Preferably 104BCD and 130BCD. Both have up to 58T chainrings on lots of sites.