what would happen if…

You fitted two drive side cranks to a (square taper) bottom bracket and ran a flip flop fixed hub at the back, then fitted two sets of running gear, one giving say an 85″ gear and the other say a 60″ gear ???

This is what I pondered when I woke up!

I tried this, the left hand pedal will just keep blowing off and ruin the threads. Which was obvious really.

Assuming you could make the chain tension even, I guess one chain would snap or derail – no idea which though 😆 . Actually someone did build a dual drive Kona A and posted over on mtbr.com . . . I’ll have a look.

There you go . . .

Why does the pedal come undone???

Why does the pedal come undone???

Drive-side has anti-clockwise thread to prevent the pedal loosening, swap it to NDS and pedalling unwinds the pedal from the crank.

Doh yea course, same as the screw on sprocket I spose.

So if you used a BMX lhd crank, what would the result be? Would the wheel turn? And if so at what gear inch???

You will need tandem-specific cranks. On a tandem, only the rear drive side crank is of the “normal” variety. So all you need is a front LHS and a rear RHS for correct spider and threading.

You can also do the reverse with the spare set and run the drive down the LHS.

It would lock solid.

However, if you want something odd that works, how about a retro-direct system?

http://myspace.voo.be/pcoupard/retrodirect_drive/

I’ve been noodling this, and it is interesting. What if you had free wheels instead of fixed gears? And resolved problem of left-side freewheel going “wrong” direction (ie if you could get it to freewheel properly on that side). What would happen then?

Would you get a “low” gear, up the point that the lower gear would freewheel and the taller gear would kick in?

It would only work if both side had the same ratio gear. Otherwise one side would need to turn faster than the other so you wont even be able to turn the pedals. Unless the chain on one side snapped.

Would you get a “low” gear, up the point that the lower gear would freewheel and the taller gear would kick in?

No, because a freewheel doesn’t know how fast your bike is going. You’d have the high gear, and the low gear freewheel would be clicking continuously.

I know its a hypothetical thread, but you don’t have to have a tandem specific LH crank, you can get away with a Heath-Robinson set-up.

On our tandem I’m running a Raceface Evolve crank at the front, fitted the wrong way round, and a normal square taper drive crank on the stokers LHS. We run SPD’s on the Ventana, so I had to strip the pedals and swap the axles round so the pedals stay in the correct orientation. A dab of threadlock on the cone & locknut.
Then a healthy dab of threadlock on the pedal threads and nice & tight onto the crank. I put a line of tippex across the crank & pedal axle so I can see if the thread starts to back-off, but after 18 months none have moved at all.

Continue brain-storming!

Rob

What benefit would a rider get from having a drivetrain on both sides?