This is THE original Wobblebike. We coined the name in 2000.
I appeared on stage with this bike at the opening event of last years Tour de France - which was televised worldwide.
Step 1: Getting Started
The best frame to begin with is a ladies MTB frame. A smaller frame than you would normally ride is best. if you are under 5'6", a 24" wheeled bike is best. The construction photos show how we did a 20" wheeled one. You will need another scrap bike for parts.
Once you have stripped the frame of parts, Cut the down tube nea to the bottom bracket, and the 'top tube' nea to the headset.
Step 2: Building the Link Tube
The best bit to construct first is the link tube. This has a headtube at each end, and can be made from the downtube and headtube from the main donor bike, with a second headtube form another bike welded in at the other end. I make the tube about 18-22" long and have one headtube a few degrees shallower angle than the other. If the downtube is about 2" diameter this will do, but if your bike has a slimmer tube, then a double-tube design is needed. In this case, you will need two 'downtube and headtube' bits welded together, or a downtube/headtube and a crossbar/heatube. Difficult to describe, so look at the photos.
Step 3: Rear Part of Frame
Keeping the same sets of forks with each headtube, take the forks that go with the shallowest headtube. Cut off the fork blades and file or grind the crown down to a nice round tube. I'll cut the pink forks in the picture.
This will be welded into the back of your donor bike. Cut a hole in the top tube of your ladies bike about 6-7" forward of the seat tube. I use a hole-saw to cut the hole. The hole can be at 90 degrees to the top tube, this will usually be at a slightly shallower angle than the set tube.
You can cut off any excess tube just beyond this hole.
You then need a handlebar stem and a bit of frame with a seatpost clamp to make the connector for the seatpost. Assemble the bits roughly and check the heights of the bottom bracket and dropouts are similar to the original bike to enable you cut these bits to the right size.
Weld this post connector up, and the steerer tube with the parts in situ as in the last photo in this step.
Step 4: Finishing the Frame
If you are adding gears - and having gears on this bike increases it's uses - you will need a top-pull front mech, and will need to route the rear mech cable down the set stays, so braze on any cablestops that you will need.
Step 5: Build It & Ride
All that is left to do is to rebuild the bike. I recommend a test ride and then stripping it back down to paint.
Note that, unlike some Wobblebike designs, this bike can be stripped right down to be painted properly.
You may want to change the angles around and make improvements. we've made 10 of these and the headtube angles change the steering.
We use these to perform at cycling events and in places such as central London.
They fold conveniently and are suprisingly practical. We have used them to haul huge trailers and have riden them as far as 80 miles in a day.