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Old 02-01-12, 09:15 PM   #1
bicyclridr4life
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Bio-Pace Question

Do 48/38/28 Bio-Pace chain rings have the same effective diameter as 48/38/28 round rings?

Thanks
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Old 02-01-12, 09:20 PM   #2
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Yes they do
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Old 02-01-12, 09:28 PM   #3
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Thank you, I thought they did but was not sure.
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Old 02-01-12, 09:28 PM   #4
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circumference is the same, but the radius is varied.. D is 2xR..
in different parts of the rotation, that is their whole idea.
so on average it is the same..
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Old 02-01-12, 10:10 PM   #5
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circumference is the same, but the radius is varied.. D is 2xR..
in different parts of the rotation, that is their whole idea.
so on average it is the same..
...meaning you need to check the FD clearance at the spots where R is greatest, and you can (should?) likely lower your FD if switching from oval to round rings. Nobody goes the other way, right?
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Old 02-01-12, 10:48 PM   #6
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...meaning you need to check the FD clearance at the spots where R is greatest, and you can (should?) likely lower your FD if switching from oval to round rings. Nobody goes the other way, right?
Actually ... I installed the Bio-Pace crank I took off another bike (only because I could not get the ring sizes I wanted) and put the Bio-Pace on another bike that had a cheap HEAVY as HECK non-replaceable ring Shimano crank, have to raise the FD about 3/16 inch it looks like.

I actually like the Bio-Pace
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Old 02-02-12, 07:20 AM   #7
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Actually ... I installed the Bio-Pace crank I took off another bike (only because I could not get the ring sizes I wanted) and put the Bio-Pace on another bike that had a cheap HEAVY as HECK non-replaceable ring Shimano crank, have to raise the FD about 3/16 inch it looks like.

I actually like the Bio-Pace
I had a 1987 Centurion Ironman with a 105 biopace crankset. I liked it too. Though, the first time I went to fine-tune the FD, I had a "WTF!" moment when I realized the chainrings weren't round! I had never heard of such a thing and thought I had bought a junk bike. Can't say I noticed any vast improvement in pedaling efficiency, but at the very least they are a nice conversational piece.
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Old 02-02-12, 09:19 AM   #8
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Similar deal for me. When my brother gave me an 80's MTB (it was a size too small for him) that had good-condition BioPace rings, I couldn't resist the urge to transplant them onto my main bike. I can't perceive an improvement in efficiency or knee strain, but I like them anyway.
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Old 02-02-12, 03:13 PM   #9
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... but at the very least they are a nice conversational piece.
Especially when the ... shall we say ... "uninformed" call out "HEY! MISTER!! YOUR CRANK RINGS AREN'T ROUND! I'VE NEVER SEEN A CRANK BENT SO BAD!!! "
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Old 02-02-12, 06:05 PM   #10
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you can (should?) likely lower your FD if switching from oval to round rings. Nobody goes the other way, right?
Only the enlightened ones

Yes, as fietsbob says the average radius is the same but of course it's not the same everywhere.
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Old 02-02-12, 06:14 PM   #11
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Do 48/38/28 Bio-Pace chain rings have the same effective diameter as 48/38/28 round rings?

Thanks
I don't think they do. They are lower when the cranks are horizontal but higher when the cranks are vertical. The pedaling effort is lower except if you use clips or clipless pedals to keep pushing on the cranks when they are vertical, when it is higher.
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Old 02-03-12, 04:02 AM   #12
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That's true, but a 48t ring will still pull through 24" of chain in one rotation, whether it's round, oval or square. You get a slightly higher gear at some points and a lower gear at others, but the average gear ratio is the same as a round one.
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