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Front Wheel Drive Moving Bottom Bracket Experiments

 
 

front wheel drive bikeSome random experiments with front wheel drive bikes.

Originally published at Bike-Recumbent.com

 The first iteration is based on Tom Traylor's designs. As with the SWB project I am looking for a bike that I can ultimately try and put in a full fairing. With the short wheelbase bike I ran into a lot of design issues that were addressed by the FWD moving bottom bracket configuration.

The FWD MBB design simplifies the drive train a great deal. It also simplifies seat design and placement as you don't have to route the chain around it. Finally, there is no worry about heel-wheel clearance so you can have much bigger front wheel size and a lower bottom bracket.

I began with the drive assembly; I cut the chain stays down so that the clearance from bottom bracket shell to tire was about 1/2". This will allow me to sit as low as possible behind the front drive wheel. Since this will be a 700x700 bike that will be important, as my inseam is only so long.

I also needed a front wheel for the back of this bike. I had all the parts so I decided to give wheel building a try. With the help of Sheldon Brown's Wheel Building page, I did a pretty good job of it.

weld chain stays     wheelbuilding

Here's the start of the front end. I am going to hold off adding stiffeners until I'm sure the geometry is right. I went for a very conventional 72 degree head angle with a 1.5" offset and a 2.8" trail

front wheel drive bike

I used square tubing for the frame.  I like working with square tuning even though there is a slight weight penalty.  In this case the stock came from a universal gym machine and it had some nice bends in it that I was able to take advantage of.  The rear fork is from a Trek Mountain bike, I squared off the nut and pinned it into the frame with a bolt.  Once I get the seat worked out I'll move the rear wheel forward as much as possible and weld the fork in place.

fwd frame welding rear fork welding

Here's the bike in a early "ride able" state.  I mounted a copy of a Ryan seat that I made years ago for another bike project and gave it a try.  It doesn't work very well, I can only make the slightest turns without my feet coming off the pedals and the front wheel contacts the backs of my thighs on tight turns.  I am going to cut and re-weld the frame to Tom Traylor's suggested geometry of  62 deg. head angle, and a 4-4.5" trail with near 0 offset.

front wheel drive bike

I did some additional research on FWB MBB design and came across some comments concerning side stresses on ones knees. I had some issues with knee pain a few years back that didn't resolve until I switched to a clip less system with full float (SpeedPlay Frogs) so I am particularly sensitive to knee issues. It hadn't occurred to me, but of course a FWD MBB would tend to increase the likelihood of nasty stresses on the knees.

Still, I have always been curious about the Flevo so I figured to make one more experiment before returning to the drawing board. The result is pictured below.

front drive low rider

This bike was ride-able, but only just. I'm sure I could have improved with practice.  However, as was true with my Ryan with it's under seat steering, I don't think I would ever have reached the same level of comfort I have on the Tour Easy.