meb

I just picked up a 53T Biopace chainring I'd like to try out.
Is there any reason this should this be oriented on a bent crankset different from an upright crankset?

Bryan Ball

I guess I can't see why you'd have to. I'm not much into the Biopace concept as a whole though.

bikebob

Try contacting Gardner Martin at Easy Racers. On the plans from Mr. Martin for building a clone (since lost) there was a different orientation recommended.

ljbike

The gears aren't profiled, so there shouldn't be a problem. I'm assuming you only have the one gear. For a biopace set there was a specific orientation.

meb

As nobody else saw differently, I installed the ring about 4 weeks ago with the same chainring-pedal orientation as an upright. After your post, I diagrammed it and see any chainring orientation difference for a bent relative the upright should be relative the difference in cyclist leg angle change between the two bike types minus any change in the chain attack angle as it enters the top of the chainring for the two bike styles. Both those figures will change for each specific bent, and the Biopace design would have been for standing riders, seated riders or a compromise position.

On the Martin plans, were your talking about the Gold Rush streamliner or another model? Do you known if the Gold Rush in the Smithsonian has Biopace rings?
Do you recall if it was a small angle change on the plans you saw?

Anybody know if the proper upright Biopace orientation was designed for a seated rider or a standing rider or a compromise of the two?

Upon analysis, it looks as if my installed chainring (on cranks by its lonesome) is off about 20-40 degrees depending on which upright rider position the chainrings were designed for-my Biopace max effect points lagging since my seat angle differs more than my chainline angle from the upright bike angles.

bikebob

When Gardener Martin started out, in order to help fund his then fledgling enterprise, he offered plans to build your own "tour easy" from two old bike frames and a couple of additional tubes. It was more or less patterned on the Gold Rush frame, I would assume, without the giant chainring required to get one to world record pace. So, no, I don't believe the Gold Rush was biotech equipped. Along with the drawings came a manual with building tips, getting started and possible sources for things like handlebars tubing et. This is where, if I remember correctly, is where the subject of biopace came up.
Intuitively it would seem that the spot that the biopace rings are trying to get you thru the fastest would change depending on your relationship to the cranks?
You could also try Sheldon Brown's website for info. He seems to like 'em.
Bob