It’s a fun challenge recycling old bike parts and converting them into a new bike, and this massive, 7 foot long bike provided some unique challenges. Integrating the tread with the bike frames and turning through a big track on a heavy bike that doesn’t allow for traditional high-speed steering is definitely an adventure.
A MIG welder and a regular hacksaw served as the primary tools for construction, in addition to a common set of wrenches and screwdrivers. This is definitely a great project for diy bike or snowmobile enthusiasts with some junk bikes, scrap material, and free time.
Step 1: Planning the Internal Frame
Start by disassembling the two bikes for the interior assembly down to just the frame with the pedals. Cut down the frames so that they fit inside the track with enough clearance for it to rotate. The frames will be kept parallel with the addition of the third wheel between them in the back. Center the third wheel down the middle of the track by welding the seat and chain stays from an additional bike frame to the inside of the other bike frames, giving another set of dropouts where the wheel could conveniently be attached. When welding to the bike frames, make sure to sand or grind all of the paint off of the surface of the metal. The dropouts on the third wheel also make it easier to remove the tread by just taking off that third wheel first. *Be sure to dimension the assembly so that the track is snug with deflated tires so that once you inflate the wheels, the track will be tight without having any other mechanism to tension it.
Step 2: Coordinating the Drive
Once everything was aligned, remove the two interior pedal arms and cut them down to the point that they will have clearance with the third wheel as they rotate inside the tread. Weld a piece of angle iron joining the two, allowing both frames to be synchronized when pedaling, and make sure that the connection is very durable. It helped to make a jig to keep the crank arms in line to assure that the pedals would rotate on as close to a common axis as possible.
Also make sure that the gear ratios on each frame are the same to that the drive wheels remain synchronized.
At this point, we had something resembling an odd tank tread unicycle…
Step 3: Develop the Frame
Make sure that the connections of the vertical members to the bike frames are durable enough to hold up the rider, but also don't interfere with the chain or other moving components inside the track. I found that it's also convenient to mount the top of the seat tube at the intersection of the rear horizontal bar and the spine.
Step 4: Steering Mechanism and the Front
The track has enough friction and momentum that it would plow through another regular wheel in front, and if the wheel was heavy enough to have enough friction with the ground, it would make the bike even more inefficient. The bike is also so heavy and slow that you don’t experience the usual effects of high speed turning as with a regular bike. There are a lot of options that might work, but I made use of the extra head tubes from the disassembled bikes to go with a lightweight and fun design.
Make a cross with two head tubes so that the handlebars can rotate in the traditional way for steering, but also on a horizontal axis so that the front wheel can swing up and down freely. Pushing the handlebars up/forward in a bench press motion forces the front wheel into the ground, and picks the front of the tread off of the ground entirely so that all the weight is on the front wheel and it can control the bike. The angle iron chopper bike extensions on the fork put the front wheel far enough in front of tread so that they don’t interfere, and extends the bike to its massive length of 7 feet. The addition of the long angle iron, Ghost Rider style handlebars allows you to control the wheel from back at the seat, and gives you enough leverage to easily jack up the bike while you’re sitting on it. This unconventional method takes a lot of practice to get used to shifting your weight differently during a turn and can't make very tight turns, but it still works.
Even if it’s not the most comfortable, effective, or intuitive method of steering, at least you can still push down on the handlebars for the easiest wheelie ever.
Step 5: Finishing Touches
Finally, you can’t have a bike without some LED underglow lighting, making this tank bike perfect for any weather conditions at any time of the night!