BioPace/Ovaltech problem - need your help

raleighmontage

Devout Dirtbag
Hi,

As some of you may know, My 1991 21spd Raleigh montage was fitted with Ovaltech.

Stupid I know, but i took the chainrings off and cant remember where they're supposed to line up... as they're bent, you see.
Anyone know?

Thanks
Max
 
There should be a small tab on each ring which lines up with the crank arm. If not, line the largest diametre point to about the 2 o'clock position with the crank arm at the 6 o'clock position.

SP
 
Although if you want them to work properly then rotate them through 90 degrees so that the narrowest point is inline with the crank arm. This means that you have maximum effective c-ring size when you are in the power-stroke of the pedal revolution.

Shimano et al got it wrong, but bearded british (is there another type) engineer Chris Bell, got it right!

http://www.highpath.net/cycles/ovals/01.html
 
pete_mcc":346ajrwr said:
Although if you want them to work properly then rotate them through 90 degrees so that the narrowest point is inline with the crank arm. This means that you have maximum effective c-ring size when you are in the power-stroke of the pedal revolution.

Shimano et al got it wrong, but bearded british (is there another type) engineer Chris Bell, got it right!

http://www.highpath.net/cycles/ovals/01.html

Ah, I remember a few mates doing the same thing BITD but could not remember the tweek. Going to try it out on my stuff tonight. Cheers Pete!
 
pete_mcc":1fs1d7wl said:
Although if you want them to work properly then rotate them through 90 degrees so that the narrowest point is inline with the crank arm. This means that you have maximum effective c-ring size when you are in the power-stroke of the pedal revolution.

Shimano et al got it wrong, but bearded british (is there another type) engineer Chris Bell, got it right!

http://www.highpath.net/cycles/ovals/01.html

How do you rotate a 5 arm chainring through 90 degree's ?


BioPace is designed around a differetn concept
Biopace

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.


http://www.sheldonbrown.com/biopace.html
 
It doesn't line up perfectly with the narrowest part at the crank arm, but I'll give it a go. It seems like it should work better that way, so I'll try it when the cranks go back on.

Thanks for your advice :)
 
I tries it BiTD (with BioPaceII anyway) and you'll notice bugger all difference ;)

Just leave as be.


EDIT/ well when I say no difference, I should add that after a few month in the 1 turns forward position I didn't like it as much as the correct poistion (these are not oval rings), I tried 2 turns forward for a while, but just ended back up in the normal position.

Then went back to round rings and really didn't notice any loss.

Maybe now I would if I tried it again.. may be on that SingleSpeed people keep saying I should give a go.
 
Back
Top