Wednesday, September 10, 2008

use an oval chainring to smooth out cruzbike/mid-steer handling!


Biopace is a patented non-round chainwheel design made and licensed by Shimano. To a casual glance they resemble elliptical chainwheels, but on closer examination they turn out to be the exact opposite of the classical elliptical design. The product of extensive research and computer-aided design, Biopace chainwheels have the small radius engaged when the cranks are horizontal, the large when they are vertical. This is because the Biopace design is based on a dynamic analysis of the motion and momentum of moving cranks and legs, unlike the static, geometric analysis that produced classical ellipticals.

The theory is that during the power stroke, when the cranks are more or less horizontal, you are using the power of your legs to accelerate your feet, which get going quite fast in the lower gear provided for that part of the stroke. The momentum of your feet then carries the pedals through the "dead spot" when the cranks are near vertical. Since the rider doesn't push as hard during the power phase of the stroke, and motion is slower when the leg is changing direction, the Biopace design is gentler on the knees than even round chainwheels."

D: I hope this will address an issue with my Cruzbike.
I am only used to normal bikes. I once rode a SWB recumbent.
I am totally unfamiliar with anything that feels like a mid-steering bike.

So I push too hard on the pedals, and this pulls around the steering.
With practice, I can keep my pedals smoother, or countertug on the handlebars.

But there must be an easier way!

I think there is.

An asymmetrical chain-ring should manage to smooth out this 'power crank' I do, thereby minimizing the steering demands on me.
I am not yet precisely sure what sort I should be looking for, though.

Aside: see KneeSavers for a nifty add-on to
1) prevent knee pain on a normal bike
2) minimize 'heel clip' on a SWB 'bent.

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