Rick Paulos writes:
>>They initially feel like something is slipping. But you get used to the different pedaling very
I picked up an old Lotus Leger tri bike that had the Biopace rings on them and have a similar impression. Pedaling felt kinda soft at first, but soon it was unnoticeable. I kinda liked it, thought maybe acceleration was improved a bit, especially in higher gears. But it is flat as a floor where I live and ride, and hilly terrain and mashing up hills might be less optimal with them.
>>I've ridden perhaps 250k-300k miles and protecting my knees is
I never noticed any knee pain, but I do nowhere near that much mileage and the bike was a good fit. Those ovoid rings still appear on eBay regularly and usually fetch a good price.
-- jim / so. fla.
From: Rick Paulos <rick-paulos@...>
Sent: Thursday, July 11, 2013 3:56 PM
Subject: Re: [Geared_hub_bikes] Non-round chainrings come around again
I still have the scientific paper on the Biopace
rings somewhere. I recall the whole idea for
Biopace was to reduce knee stress at the
peak. The shape of the rings is such that you
get a lower effective ratio during the down
stroke. The paper had charts & graphs showing
that. I've owned a few bikes with Biopace (or
Sugino clones) rings. I notice them for the
first mile or so then not any more. They
initially feel like something is slipping. But
you get used to the different pedaling very
quickly. It's when you switch between bikes regularly that you notice.
Seems to me, the opposite would hold true
too. By putting the lobe at the downstroke, you
would be increasing stress on the knees (and probably your heart too).
Scott Dickson rode the PowerCam to countless wins
including 4 Paris-Brest-Paris wins. I rode his
bike one time to try it out. Yowza. I was in a
56x11 at 20mph an it felt okay? I was baffled
but Scott said that was the normal feel. No way
you can even get the rpms up on that system. The
Powercam used round rings that were not attached
directly to the crank arms. It used a odd shaped
cam & follower at the bottom bracket. The net
effect was similar to non-round rings only it
could be more extreme depending on the cam shape.
But if your goal is short term gains and you get
cash for it, why not. But not for me. I want to
be able to ride for the rest of my life. I've
ridden perhaps 250k-300k miles and protecting my
knees is very important. Proper seat height and
high rpms does the most for keeping the knees happy.
"Everything old is new again" unk.
At 07:13 AM 7/11/2013, you wrote:
>The current Tour of France leader, Chris Froome,
>is once again (or still) using an Osymetric
>non-round chainring. The shape is described as
>'twin cam' and you can clearly see it 'bouncing' as he pedals.
>The basic idea has been around since a few days
>after bikes got chains in the mid-1880s, and
>seems to have a fresh iteration every 10-15
>years. IIRC Bobby Julich used a non-round
>chainring to win his Olympic medal in 2004.
>The Osymetric may have a unique,
>computer-derived shape, but it's a classic "more
>leverage during the power stroke" non-round
>chainring, like the majority of non-round
>chainrings over the decades (and opposite of the infamous Shimano Biopace).
>As the Osymetric chainring rolls though a
>revolution, the rear derailleur cage has no
>perceptible movement. I suppose one could use a
>Osymetric chainring with an IGH without a chain tension device.
>The other big name in non-round chainrings these days is Rotor.