Evolution of a Recumbent

I've been working on this project for some months now. I'm posting the story of the evolution of the design and construction of this bike for no particular reason other than to demonstrate how what seems like a sound idea at concept stage, can become something completely different over the period of detailed design and construction. If there's a lesson in this anywhere, please let me know what it is :^).

The original idea was to make a lowracer recumbent that didn't have the chainline problems and skittish handling that seems to plague these types of bicycle. I also wanted to eventually add a fairing, and I also designed this to be something of a departure from what is normally prescribed for these bikes.

By the way, if you're unfamiliar with the concept of the lowracer, Bentrider Online has a comprehensive guide. I recommend it to you.

Anyway, here is the original concept sketch straight from my notebook. (as usual, click on the picture to enlarge)

As so often happens in these things, once I started modelling the bike in detail certain compromises had to be made to make the original sketch into something workable, if not necessarily rideable. The proportions lost something in the translation, and I guess even at this stage I knew the design was in trouble.

I went with a 20" front and a 27" rear wheel (or whatever the proper diameter in mm is). I had by this time picked up a Giant hybrid frame at a garage sale and intended to use the rear triangle from this, and the front end of a bmx for the fork.

Here's a render of the first stab at a model -

Second stab -

Up until now I had been working on about a 10cm seat height from the ground, with the back at about 30 degrees. This gave me a wheelbase well over 2m. It also meant it would be rather difficult to see over the handlebars. By this stage it wasn't looking much like the original sketch anyway, so I did some major revisions in the interest of making it a bit more street worthy.

I raised the seat to about 20cm, increased the back angle to about 40 degrees, re-laid the main tube out to represent how the local muffler shop could bend it up, and accurately modelled the fork that I had eventually acquired. With a little further removal of some metal and other tweaks I ended up with this -

and did a bit of experimentation with a fairing - 

I was pretty happy with this, and was ready to build it - so ready that I had the main tube bent up, and built a jig.

I say 'was' happy with this. Was, that is, until I entered an email discussion with one Mark Stonich from Minnesota who has built many fine looking recumbents. It started as a discussion on how to poke a hole through a tube, and, to make a long story short, ended up with me rethinking why I was even making this kind of bike. I have to say though, that I guess I've been slightly uncomfortable from the beginning with the layout, mainly because I decided I wanted to use it to commute. Let's just say that it didn't take too much prompting to do some serious hack work on the model and come up with something that will probably be far more rideable, and to be honest, I am much more happy with.

I worked it so that I could reuse the main tube and other bits I already have, and my next job is to rework the jig to suit the new layout, but that's a mere technicality. For now, here's a render of the current incarnation - 

I still may tweak the fork angle and rake a bit, and am currently debating whether to use a cut down and reraked road fork, but for now that's it. (Damn, it looks so ordinary. Maybe I'll start working on the semi-prone soon....)

Stay tuned for further updates.

For some pictures and information of the dragster that was my first project, click Here