Recumbent Bike Project

Recumbent Project, Winter 2006-2007

Last fall I decided to see if I could build a recumbent bike. I had wanted one for some time, but couldn't bring myself to fork out the $1000 or so to buy one. I decided this would make a nice little winter project. I started with my old Huffy mountain bike. I purchased a rusty old Huffy mountain bike just like mine for $20 at a second hand thrift store. I stole the front wheel from my daughters old pink kids bike (she is 16 now and won't ride that again!) and I acquired a Bianchi mountain bike frame with brakes and shifters from a trash pile.
I wanted a bike that was quite low and had a crank set that was about even with the seat. This causes some problems with chain placement. It must pass under the seat. I sat on the floor and measured myself for entry into my CAD software. I used Rhinoceros NURBS CAD for the PC. I just did a basic 2D layout to be sure the bike would fit me and to develop the chain layout for the low design.
As you can see, I also wanted under seat steering. This also complicates things and requires a bunch more engineering. Now that the bike is complete, I am glad I went with the under seat steering. It give a "flying" sort of feel to the bike. There is not very much in front of you.

I started out by cutting the rear triangle from one of the mountain bikes. I laid everything out on the garage floor in pencil and tack welded the frame together right on the flat cement floor. I cut and welded the extra tubes and used a 26" set of front forks with a 20" front wheel. The fork rake was relaxed quite a bit to give a stable ride.

After the chains were worked out, I started on the steering. I used a headstock from one of the bikes and welded a gooseneck to it to provide the pivot for the handlebars. I linked the bars to the front fork with a rod with swivels on each end. This cleared the front crankset just perfectly.

Next I built the seat and seat back. The seat is 1/2" plywood with about 3" of dense urethane pad on top, sanded to shape with an angle grinder. I made the seat cover from heavy denier Nylon fabric. The seat back is constructed from 1/2" steel electrical conduit. I bent and welded the tubes.

The tubes were covered with some more Nylon and an open mesh back for cooling and stretch. I inserted grommets in the back and laced the cover on using 1/8" Dacron parachute cord. The seat is very comfortable and is quite strong.

Next was the brakes and controls. I stole the front brakes from the Bianchi, and the rear from the Huffy. I welded the supports in place and the pivots to the front forks. The braze-on's were adjusted and added to the frame and the brakes were done.

I disassembled the bike, made a few minor adjustments to the fork rake angle and prepped and painted the frame. This is the final product ready to ride and all polished up.
Review: The under seat steering is a real treat. It really takes the clutter away from in front of the rider. The seat is very comfortable and you always have a nice place to sit when you stop! The bike rides very nice. Smooth and comfy. it's like riding a bike in your easy chair. The bike also carries a load like a semi truck. I attach a pair of panniers to the rear rack and I can haul lots and lots of groceries and things without adversely affecting the handling of the bike. It, however, is not perfect.
One thing to consider when designing a bent is the steering geometry. To relaxed and you have a hard time turning, too agressive and it is hard to keep in a straight line. I think I have come to a pretty nice compromise, (after 7 changes to the frame.) It takes about 30 second to learn to ride this bike, and about 1 hour to get to the point that you feel really comfortable on it. You always need to remember you are trying to turn an almost 7 foot long bike!
The next couple of things are specific to bents in general:
* The under seat steering is nice to ride, but it stinks to push. It is surprising how much we push our bikes. Downtown, sidewalks, into the garage, etc.
* Bents are inherently difficult to store. They take up a bunch of room in the garage.
* Bents are tough on the hills. You cannot use your body weight to push the pedals, you only have your leg muscles. You refine your climbing technique with practice and that really helps, but it's still more difficult than a standard.
* Finally, it's difficult to see behind you on a bent. You need to initiate a slight turn and at the same time, turn your head to get a brief glimpse behind you. A mirror will be a must in the near future.
Overall, I am glad I did this project. I ended up with a great bike and a lot more knowledge than I had before.

Specs:

Length: 6'6"
Weight: ~ 45 Lbs
Both chains stretched out end to end are almost 13 feet long!
Cost: $62 USD.
Four "donor" bikes were used in it's construction.
Happy riding.