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Re: [Geared_hub_bikes] Non-round chainrings come around again

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  • stephen lewis
    Hi Rick I ve been trying to replace a 36T Biopace chainring. You might well have problems getting replacements (although I m in Singapore). I m left to hope
    Message 1 of 4 , Jul 13, 2013
    • 0 Attachment
      Hi Rick
      I've been trying to replace a 36T Biopace chainring. You might well have problems getting replacements (although I'm in Singapore).
      I'm left to hope what I want comes up on ebay and resolve myself to chain slips in the interim.
      Regards
      Stephen

      From: jim <jimbofla1138@...>
      To: "Geared_hub_bikes@yahoogroups.com" <Geared_hub_bikes@yahoogroups.com>
      Sent: Friday, 12 July 2013, 9:19
      Subject: Re: [Geared_hub_bikes] Non-round chainrings come around again
       
      Rick Paulos writes:
       
      >>They initially feel like something is slipping. But you get used to the different pedaling very
      quickly.
       
       
      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 very important. 
       
      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@...>
      To: Geared_hub_bikes@yahoogroups.com
      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. rick "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 > ><<http://www.osymetricusa.com/>http://www.osymetricusa.com/> > >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. > ><<http://www.rotorbikeusa.com/>http://www.rotorbikeusa.com/> > >pj > >
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