Before I get into the details on this project, I want to give some background and outline my goals for it.

I've been riding for nearly thirty five years. I started riding 'bents about seven years ago. There was a noticeable reduction in speed, which I assumed was the price to pay for comfort.

A couple of years ago I did a very long ride, and found that my average speed was about 8mph. This was completely unacceptable, so I started to learn how to improve my speed.

I ended up buying half a dozen bikes, and learned a lot about going faster. After a couple years, my speeds had nearly doubled. I average about 15mph on my two fastest bikes, but my diamond frame is STILL faster.

So, the goal of this project is to finally get that one last 'push', and craft a bike that's faster than my diamond frame.

I know that 'bent riders and DF riders tend to run in seperate circles, but I honestly have no allegiance to either camp. That's the reason I'm not posting in a recumbent specific forum. I believe the methodology and technology to build a bike is applicable to both, and cross-pollination of ideas pushes the state of the art ahead.


Based on my admittedly limited knowledge, the fast speed of my diamond frame is due to decades of refinement. Basically the design isn't the most aero device in the world, but that lack of aerodynamics is offset by the fact that the bike is ridiculously light and strong, and light and strong improves the efficiency of the drivetrain.

IMHO, this is why aero improvements on DF bikes make such a noticeable difference; the design is so mechanically efficient that big gains are found when you can improve the aerodynamics.


After studying the problem for a few years, I think recumbents have nearly the opposite problem. The reclined position affords a level of aerodynamics that's quite good, but the mechanical efficiency isn't as good as a DF. I hope that isn't an inflammatory statement; I love my 'bents, but the triangulation of the diamond frame bikes affords a level of mechanical efficiency that's VERY tough to beat.

This is noticeable in two aspects in particular. The first is frame flex. On a 'bent, there's a noticeable power loss as the power applied to the crank twists the frame. I believe this is one of the reasons Bacchetta uses stick frames; a straight pipe is stiffer than one with a bend in it.

The second think that sucks efficiency in a 'bent is that looooooong chain line. The chain weight isn't insignificant; in fact 3-4% of the entire bicycle weight is bike chain! Could you imagine if the driveshaft in your car weight 450lbs? That would hardly be efficient.

Honestly, I think this efficiency is really difficult to appreciate until you sit down with a CAD program and try to design something which is superior. It's very very tough to do. In a bicycle, it's amazing how all the variables are connected. For instance, one easy way to improve the aerodynamics is to simply lower the seat closer to the ground, but as soon as you do that you have to increase the wheelbase. And increasing the wheelbase increases the weight, which slows you down.

It's a heck of a juggling act - and it makes me give mad respect to all the bike designers at places like Rans, Cervelo, Bacchetta, Velokraft, etc.

That's the reason I am starting this thread. I believe that the only way to make a measurable leap past the existing designs is to break out the CAD program, tweak a few variables, and see if I can shave a few seconds off my laps times.