Thursday, May 1, 2008

my experience with 'bent bikes

D: and what is this a pic of? It is a recumbent bicycle profile from the front.
And therein lies the key appeal, performance-wise, for a 'bent bike.

The faster you go, the more air resistance matters relative to other factors.
Air drag increases as the square of speed.
This has 2 implications:
1) at lazy commute speeds, a 'bent doesn't matter
2) anyone performance-oriented at speeds around 30kph or so should care.
D: a primer on 'bents.


Recumbents hold all human powered speed records. Period! The world’s cycling organizations, or even national cycling organizations such as the USCF recognize none of these records. These organizations have decided that the diamond frame bike (traditional road bike) is the only device they will admit to the record books"
This translates into measurably faster speeds. Many cyclists who ride both types of bike (diamond frame as well as recumbents) report 3 to 8 mph faster average speeds on the recumbent bikes."

(Recumbents hold the world speed record for a bicycle and were banned from international racing in 1934.)
D: a more scientific analysis.
For the standard bike in the upright position, we have this:
"At 250 Watts, the upright bike goes 29 Km/Hr or 8.0556 m/s. To go 40 Km/Hr or 11.111 m/s, the upright bike needs 622 Watts.

For the recumbent bike with the full foam fairing, we have this:
At 250 Watts, the bike goes 51 Km/Hr or 14.167 m/s. To go 40 Km/Hr or 11.111 m/s, the bike needs 135 Watts.

For the recumbent bike with the full hard shell fairing, we have this:
At 250 Watts, the bike goes 69 Km/Hr or 19.167 m/s. To go 40 Km/Hr or 11.111 m/s, the bike needs 75 Watts."

D: with such a potential for speed, many dabble with even lower CD (drag) with fairings - shells.

(Insert bitter ranting about cruddy blog interface here.)
Ahem. See the start of the page. I have a pic of a Rotator Tiger short wheelbase recumbent with 20" wheels, and no suspension.
I rented it from
D: they were oddly difficult to contact.
If you instead wish to purchase 'bents in town, there is Rebel Cycles.
I sent them a query and never heard back from them either. Nice business model...

Anyway, my impressions of a Rotator:
1) felt like I was being karate chopped on the backside on sidewalks and bumps.
Those high pressure small 20" tires with no suspension are no fun.
2) it was very hard to start from a stop. On an incline, forget it!
3) you don't steer by leaning, only by turning the handlebars. You learn to not oversteer in a hurry.
4) you feel very invisible in traffic. You cannot see past cars. You are grill height on a sedan, bumper height on a SUV.
5) you are at doggy-bite level. Leaning back you also feel vulnerable.

As fun (and scary) as it was, I remain convinced that recumbents are simply not practical in typical commuting situations.
There are a few improvements on this basic model.
For example, here is the full suspension award-winning alternative.,nl/

And here is a highracer with dual 26" wheels.

Here is a mountain bike tire and dual suspension, available in kit form.
D: THIS is the only 'bent I consider practical for commuting.
It can handle potholes and bumps. The rider is quite high.
It might be able to mount on the front of bus for transport during rain.

Since I will be exploring variations later, I'll mention the mid-steering DIY, the Python.
D: you'll notice it is a more fully mid-steering arrangement than the Cruzbike, which still technically remains a front steering arrangement, although your legs remain aligned with the front wheel.
I assume that prevents sharp turns though.
Without a midsteering arrangement, a front steering short wheelbase bike has 'heel clip' issues.
That is the term for when your foot on the pedal hits the front wheel when you turn too sharply.
This concern limits the size of the front tire unless you switch to a highracer layout.

Specialized racetrack designs just don't worry about turning much.
This is a treasure-trove for how-to.

In future posts, I will instead discuss my various design ideas.
The themes will be
1) adjustable seat height
2) able to change between short and long wheelbase in process
3) a midsteer/front steer dual arrangement, able to change over in a few minutes
4) partial fairings that attach to the front and rear frame on a mid-steering bike
5) an attempt to create a new practical partial fairing for commuters
6) a mid-steering approach that mounts the pedals through the front wheel axle area. Essentially, a hub gear powered modern version of the ancient "Penny and Farthing".
7) various power assist concepts including electric, solar and compressed air. This serves 2 purposes:
i) a front wheel drive has problems getting purchase uphill on gravel.
ii) an assist to accelerate from a stop, particularly on an incline addresses a major 'bent issue
8) optimizing the benefits of a fairing without too many weight/crosswind issues.

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