Fucking Biopace
Mar. 7th, 2018 08:28 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
scrottieSheldon Brown wrote about Biopace, and as usual, he's fucking right:
http://sheldonbrown.com/biopace.html
An important detail there is that, before Biopace, people repeatedly re-invented an oval chainring with maximum resistance in middle of the push. He explains, and that's required reading, but, superficially, it seemed like a good idea to make the pedal stroke harder where you have the best leverage. The problem with that is that there is a big lump in middle of the peddle stroke... and unless you're on that lump, there is no resistance and you're just spinning around to hit the lump again. Then you get bouncing in the saddle as people spin around fast, hit the lump so hard that they bounce up, very quickly hit zero resistance again, and repeat... which is precisely what I was doing on this tiny round chainring. Biopace smooths the lump out so you engage the resistance sooner, disengage it later, and the peak is shaved off.
But everyone either assumed that Biopace was the old oval chainring Sheldon Brown picture that made the lump worse or else missed that bit of history and assumed that making the lump worse is what you want to do. Regardless, virtually everyone thinks Biopace is wrong, though for conflicting reasons.
So now every non-round chainring has to try to distinguish itself from Biopace:
http://www.jensonusa.com/Absolute-Black-10464-Oval-Chainring
"Narrow Wide Oval Single Chainring works to maximise your power output where the most force is applied and minimise resistance where it isn't." ... "32T is equivalent to 30T at dead spot and 34T at the power zone"...
So trying to be the opposite of the thing that's the opposite of the thing that's bad that people think is the same thing as the thing that's bad, it is bad... they're making the lump worse.
http://rotorbike.com/wp-content/uploads/2016/07/Q_Rings_german_tab.png
http://forums.roadbikereview.com/attachments/retro-classic/302408d1418612031-rotating-biopace-ovaltech-rings-different-offset-i-did-1-powerstroke.jpg
There's no need to have a lower effective gear through the dead spot because you're not pushing anything. You're only moving chain. Your pedal rotation accelerations on each downpush (unless there is too much resistance and you bounce instead) and then slows. Even slowing a tiny bit on a round ring, you effectively encounter no resistance. Instead, being a higher gear there and moving more chain through would help keep power engaged.
As Sheldon points out, if you want a higher gear on the downstroke, shift into a higher gear.
A range of competitors have introduced things attempting to do the same basic thing as Biopace:
https://imgs.inkfrog.com/pix/coronadelmar/Shimano_Deore-XT_Biopace_Chainring_Information_01.JPG
... but apparently saying "oh no we're the opposite of that" is better marketing than "yes, they were right and ya'll are just ignorant".
Spinning like mad on a tiny round chainring is horrible. Spinning on a round chainring is already bad to start with.
So I have a cankset with 104 BCD and I'm trying to figure out how much https://www.ticycles.com/store/104mm-to-130mm-bcd-adapter would throw the clocking off (when effective gearing changes relative the pedal stroke) or else new bottom bracket again so that I'm actually on an old standard BCD.
http://sheldonbrown.com/biopace.html
An important detail there is that, before Biopace, people repeatedly re-invented an oval chainring with maximum resistance in middle of the push. He explains, and that's required reading, but, superficially, it seemed like a good idea to make the pedal stroke harder where you have the best leverage. The problem with that is that there is a big lump in middle of the peddle stroke... and unless you're on that lump, there is no resistance and you're just spinning around to hit the lump again. Then you get bouncing in the saddle as people spin around fast, hit the lump so hard that they bounce up, very quickly hit zero resistance again, and repeat... which is precisely what I was doing on this tiny round chainring. Biopace smooths the lump out so you engage the resistance sooner, disengage it later, and the peak is shaved off.
But everyone either assumed that Biopace was the old oval chainring Sheldon Brown picture that made the lump worse or else missed that bit of history and assumed that making the lump worse is what you want to do. Regardless, virtually everyone thinks Biopace is wrong, though for conflicting reasons.
So now every non-round chainring has to try to distinguish itself from Biopace:
http://www.jensonusa.com/Absolute-Black-10464-Oval-Chainring
"Narrow Wide Oval Single Chainring works to maximise your power output where the most force is applied and minimise resistance where it isn't." ... "32T is equivalent to 30T at dead spot and 34T at the power zone"...
So trying to be the opposite of the thing that's the opposite of the thing that's bad that people think is the same thing as the thing that's bad, it is bad... they're making the lump worse.
http://rotorbike.com/wp-content/uploads/2016/07/Q_Rings_german_tab.png
http://forums.roadbikereview.com/attachments/retro-classic/302408d1418612031-rotating-biopace-ovaltech-rings-different-offset-i-did-1-powerstroke.jpg
There's no need to have a lower effective gear through the dead spot because you're not pushing anything. You're only moving chain. Your pedal rotation accelerations on each downpush (unless there is too much resistance and you bounce instead) and then slows. Even slowing a tiny bit on a round ring, you effectively encounter no resistance. Instead, being a higher gear there and moving more chain through would help keep power engaged.
As Sheldon points out, if you want a higher gear on the downstroke, shift into a higher gear.
A range of competitors have introduced things attempting to do the same basic thing as Biopace:
https://imgs.inkfrog.com/pix/coronadelmar/Shimano_Deore-XT_Biopace_Chainring_Information_01.JPG
... but apparently saying "oh no we're the opposite of that" is better marketing than "yes, they were right and ya'll are just ignorant".
Spinning like mad on a tiny round chainring is horrible. Spinning on a round chainring is already bad to start with.
So I have a cankset with 104 BCD and I'm trying to figure out how much https://www.ticycles.com/store/104mm-to-130mm-bcd-adapter would throw the clocking off (when effective gearing changes relative the pedal stroke) or else new bottom bracket again so that I'm actually on an old standard BCD.
no subject
Date: 2018-03-08 04:49 pm (UTC)