Dave’s Balloon Bike, Teil Zwei*…

Remember Dave’s lovely retro machine from a couple of weeks ago… well, he’s been busy with the spanners again and taken his evolution one step further with the addition of a Schlumpf Mountain Drive…. a clever piece of Swiss Engineering that isn’t a wristwatch or pocketknife… I’d not seen one of these until now, basically it’s a crank with an epicyclic gear system built in which effectively doubles the range of gears already fitted to the rear of your bike, whether hub gear like Dave’s or derailleur setup. The gear change is rather clever – a tap on the end of the crank axle is all that’s needed to shift gear range, and the whole thing is remarkably neat and tidy. I can’t help wondering on the practicality of this set-up on a fixed gear touring bike…. I may just have a chance to try that with my winter project (more on that soon).

Dave’s email says it all really so…

“The Mountain Drive appeals to my slightly twisted ‘do it differently’ mentality and should make a great conversation point when chatting with those interested passers by that love to ask about my German oddity. I have been assessing the end result with my original design brief and expectations in mind, this was never meant to be a super efficient whippet project more the ultimate city comfort bike with the capacity to climb big hills and keep the oily bits off my suit. I also wanted to retain the Retro look, did you know The Coventry Cycle Company introduced an almost identical two speed epicyclic crank in 1892 and the principle was later adopted by others like Sunbeam (see attached photos).

Back to the 21st century and following yesterdays testing I am declaring the project a success, however there are a couple of gripes.

PROS:
1) Excellent range of ratios
2) Everything internal (No Oily Bits)
3) Very low maintenance
4) Doesn’t detract from the Retro theme
5) No perceptible loss in efficiency (Schlumpf claim the unit is 95 – 97% efficient)

CONS:
1) Engagement is tricky, although this should improve with practice
2) The 14 ratios are not strictly speaking sequential, when you reach 7th in Mountain Drive you must then return to first gear on the hub and disengage the Mountain Drive to get the next ratio up, you are now effectively in 8th gear and the six higher gears are available on the hub twist shift again.

In practice this is all a bit of a tap dance that I’m still learning. The engagement and disengagement is best done with the crank in the horizontal position and the pedal facing forwards, I am currently finding it easier to momentarily stop pedalling as my brain tries to get the heel tap and wrist twist thing coordinated. This is not such a problem when going from Mountain Drive to direct drive as a few seconds of coasting can typically be accommodated when moving up the gears. The problem comes when you are in the lowest direct drive gear and you want to drop to the lower Mountain Drive mode, this usually happens as you start to climb and the loss of momentum is not welcome.

SUMMARY:

Overall I am very happy with how things have turned out, for £300.00 I have greatly extended the usability while keeping things “Old School”. The gear shifting issue is not a big deal, most cruising can be tackled either in Mountain Drive using 5th, 6th & 7th gear or in direct drive using 1st, 2nd, & 3rd gears. am confident my technique will improve with a little practice, still I say that to all the girls….. “

Here’s a ‘taster’ pic of the crank itself, the rest of the photos can be found over on Dave’s album which is just a click away here.

and here is the original Sunbeam crank drawing for you vintage enthusiasts.

I suppose the cynics out there will say it would have been better to fit a Rohloff hub in the first place but that would have required big capital commitment up front and I think it’s more interesting this way as the bike has evolved rather than being ridden right off the drawing board. Besides, it’s fun playing around with interesting kit. This might not be a bike I’d rush out and buy (I would in fixed gear form though) but as a change from the usual carbon and titanium race machinery I think it’s brilliant.

*part two… it seemed appropriate for a German bike.