Wednesday, July 11, 2012

Build a simple short wheel base recumbent bike

Here is a very simple 20 inch wheel short wheelbase recumbent bike that you can build in a few hours using nothing more than a kid's bike and a few lengths of round tubing. This project makes a good starter recumbent and is a good experimenter’s platform for those who want to try out various seating positions and angles.

The completed bike doesn't weigh much more than the bike used as parts, and can be stored in the same space as a regular bicycle. Of course, this simple project lacks many of the more advanced features offered in our DIY plans, but you could always add your own modifications to expand on this project.

You can build a 20 inched wheel short wheelbase recumbent out of just about any kid's bike or BMX bike. You will need to start with a working cycle or at least one that has functioning wheels, cranks, and a transmission system.  The rear wheel should have a multi-speed freewheel so that you can have multiple gears, but you could also build the SWB around a coaster hub and just make your bike single speed. If you want to climb a hill or reach any decent top speed, then you will need a rear wheel that has at least a 5 speed freehub.

Besides a working 20 inch bike, you will also need a few feet of round tubing. You can cut up another bike frame for the tubing, or just use some thin walled electrical conduit (EMT) for this project. Basically any square or round tubing with an approximate 1.25 inch diameter and a wall thickness similar to bicycle frame tubing will work.

The other part shown in the photo is the bottom bracket and crankset that will be placed ahead of the front wheel. You can cut the bottom bracket from another frame since the original bottom bracket will be unused and left on the frame. For more information on bottom bracket sizes and assembly, see the tutorials on our main page.

This simple recumbent bike is made to fit the rider, so it has no adjustable seat or bottom bracket. For this reason, we will make the seat first so that you can later use your body as a measuring system in order to determine the optimal placement of the cranks for your leg length.

Chop off the top of the seat tube as shown in the photo and then find another 12 inch long tube that can be welded over the top of the cut-off seat tube. This tube will become your seat back tube, and it will support the back of the seat as well as set the recumbent angle of your seat.

Part 2 in tomorrow's blog.