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Old 09-04-05, 07:01 PM   #1
phantomcow2
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Shimano biopace, what odd things

I was at the metal scrap yard a few days ago and found a Shimano Biopace ring, the ovalized chain ring. I dont understand what advantage it has, it looks very odd.
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Old 09-04-05, 07:07 PM   #2
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http://www.sheldonbrown.com/biopace.html
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Old 09-04-05, 07:22 PM   #3
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Basically, the advantage is like switching gears every 1/4 rotation to give you better leverage. Most of your energy in each stroke is (obviously) in the down stroke.
By having a high gear in the downstroke and a low gear on the "swing" through the deadspot, you'll increase efficiancy through flat terrain.

On hilly terain, the point of the deadspot changes, thus rendering advantages of the eliptical sprocket pretty much useless if not a disadvantage.


EDIT: Upon read the Sheldon Brown page, I am mistaken. The Shimano ones are opposite to what I just described. They have a low gear for the downstroke and use the legs momentum to "power" through the dead spot.
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Old 09-04-05, 08:09 PM   #4
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I wonder if we will ever see them again, seems like it would be a good idea for the granny ring, since that is where you could really benefit from it. I suspect that they have been tarred with the "Obsolete" tag, but one can only wonder.

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Old 09-04-05, 09:29 PM   #5
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Quote:
Originally Posted by Mentor58
I wonder if we will ever see them again, seems like it would be a good idea for the granny ring, since that is where you could really benefit from it. I suspect that they have been tarred with the "Obsolete" tag, but one can only wonder.

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Who remembers a Spec. Sirrus he had with BioPace rings
You want to see it again - how about tomorrow at about 7:30 Am in my drive way - I ride mine all the time.
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Old 09-04-05, 09:32 PM   #6
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Seems like I saw a bike in the Tour de France with an eliptical chainwheel.

Was I mistaken?
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Old 09-04-05, 09:38 PM   #7
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Quote:
Originally Posted by georgiaboy
Seems like I saw a bike in the Tour de France with an eliptical chainwheel.

Was I mistaken?
It's a different concept from Bio-Pace.


Quote:
Originally Posted by http://www.cyclingnews.com/road/2005/tour05/tech/?id=/tech/2005/probikes/julich_csc_carbon
As we mentioned back in March, the O.Symetric Harmonic design isn't a resurrection of Shimano's Biopace rings of the 1980s. An elliptical chainring changes the effective gear ratio as you pedal. Biopace reduced the gear ratio as crank passed through the horizontal; the O.Symetric Harmonic increases it. The idea is that the sector of the pedal stroke where the crank is horizontal or nearly so is where you can push hardest, so it makes sense to increase the gear at that point, then drop it to get your foot through top and bottom dead center quickly.

This is an idea that's come and gone many times in the last 100 years or so, but it clearly seems to work for Bobby Julich. It causes teeth-grinding among the team's mechanics, though, because it's tricky to get the front derailleur to work properly when the chainring is in effect moving up and down under the derailleur. In fact, Shimano used to claim that one of the reasons it abandoned Biopace was that indexed shifting of the front derailleur on triple chainrings couldn't be made to work well with elliptical rings.
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Old 09-04-05, 09:51 PM   #8
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I had the old Shimano bio-pace on my Miyata 1000 touring bike. I never really noticed any difference except on the granny ring, so I ended up changing it for a round one.
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Old 09-04-05, 11:10 PM   #9
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I would rotate my Biopace rings by 144 degrees so that it had the opposite effect. I would give me bigger gearing on the downstroke (slows down the rotation, give more resistance) and give me smaller gearing on the dead spots at the top & bottom. This then evened out the spinning-rhythm more, kinda like that O'symetric showed above.

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Old 09-05-05, 12:26 AM   #10
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Didn't CSC ride Biopace rings this TdF?
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Old 09-05-05, 12:37 AM   #11
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Quote:
Originally Posted by jur
Didn't CSC ride Biopace rings this TdF?
Read back a few posts. Those were O.Symetric rings. They operate opposite of Bio-Pace.
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Old 09-05-05, 03:42 AM   #12
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More stuff on elliptical chainrings at
http://www.highpath.co.uk/cycles/products/ovals/01.html

These are counter-biopace style.
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Old 09-05-05, 12:01 PM   #13
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I was commuting on an old miyata that I had just bought that turned out to have ovaltech rings. I didn't notice anything different for a week until I was cleaning the chain and I thought my chainrings were bent but then noticed the label, it's possible that there are some small advantages but who knows.
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Old 09-05-05, 04:56 PM   #14
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Some months ago I rode my niece's tri bike (which had biopace rings) for two weeks while on holiday there, but I did not notice any difference.
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Old 09-05-05, 11:58 PM   #15
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One obvious ways to notice the effects of oval chainrings is to ride on rollers. Spin fast in easy gears and you'll notice a slight oscillating whrrr..whrrr...whrrr that corresponds to the variations in power-output at various rotations of the crank. Then install oval chainrings and set them at various rotation angles (5 possible positions). You'll notice that at a certain orientation, the sounds even itself out to be smoother.
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Old 09-06-05, 03:10 PM   #16
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Hahaha.

After a tour with 'way too much weight in the hills with a double chainring, I switched to a Biopace triple. I loved to have that Biopace granny when I toured.

I thought I was the only one that liked them!
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Old 09-06-05, 04:22 PM   #17
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Quote:
Originally Posted by skookum
I had the old Shimano bio-pace on my Miyata 1000 touring bike. I never really noticed any difference except on the granny ring, so I ended up changing it for a round one.
Hey me too! on my Miyata alumicross that I use for touring and some off-roading and winter riding. the middel ring and granny gear are both biopace, while the big ring is not. I have actually found it not that bad. Although, the transition to my road bike is sometimes "fun"
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Old 09-06-05, 05:42 PM   #18
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Quote:
Originally Posted by eubi
I loved to have that Biopace granny when I toured.
Interesting. I had Bio-Pace on an old MTB in the late 80s and if memory serves, the granny was just a standard round ring and not Bio-Pace. Maybe different cranksets came with Bio-Pace granny rings.
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Old 09-06-05, 07:57 PM   #19
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I've got Biopace (on my 2nd set) on the mountain bike and round on the road bike. I honestly cannot tell the difference. NOS Biopace cranks/rings can be had quite easily on eBay. Jones Bikes comes to mind.
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Old 09-07-05, 05:05 PM   #20
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I wish I had a power-meter that would actually display instantaneous force/torque at each spot on the crank-rotation. Then plot it vs. time and calculate average power-output power per pedal stroke. The graph would be like a sine-wave probably. I suspect that with perfect round or oval chainrings, it would make absolutely zero difference in average power-output and the resultant speed you can achieve. Remember that power is a function of force, velocity and time. If during the same amount of time (1 revolution) you push through the downstroke with less force and more velocity or with more force and less velocity, it won't make a difference in the power-output.

I recall one of the exec. at Shimano saying something at one of the '88 trade shows. I was asking him about increased efficiency and power-output and he said that the real reason they created Biopace was to change the velocity of the pedal-rotation so that the movement felt more like walking with rapid up & down strokes and slower transitions across the bottom & top. He said that felt more "natural" for beginning riders...

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Old 09-07-05, 08:03 PM   #21
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Quote:
Originally Posted by eubi
Hahaha.

After a tour with 'way too much weight in the hills with a double chainring, I switched to a Biopace triple. I loved to have that Biopace granny when I toured.

I thought I was the only one that liked them!
Sounds like it was good to have because it was a granny rather than because it was biopace.... i.e. lower gearing to haul touring load up hills..... not that I'm discounting the biopace factor because I wouldn't know biopace from my left elbow.
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