Oval chainrings

General Discussion about electric bicycles.
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jpgey   1 kW

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Oval chainrings

Post by jpgey » Sep 28 2016 2:28pm

Just why ?
oval_chainrings.jpg
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MrDude_1   100 kW

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Re: Oval chainrings

Post by MrDude_1 » Sep 28 2016 3:01pm

The concept is simple enough.. Your legs dont make the same power everywhere in the 360* rotation like a motor does. Instead, you have better areas of up/down-stroke, and are almost coasting power-wise when in-between.
So the oval shape lets the ratio change to match that.

atleast thats the idea. They were popular with road race guys for a short time in the late 90s/early 2000s and then died off quickly. Personally I dont see an advantage for the average joe.. but im just a fat guy that prefers the motor do all the work anyway. :mrgreen:
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jimw1960   10 kW

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Re: Oval chainrings

Post by jimw1960 » Sep 28 2016 3:35pm

My old Raleigh Technium mountain bike had those. It's supposed to give you more power on the downstrokes. I thought it worked well enough. I didn't really notice it while riding.

Punx0r   100 GW

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Re: Oval chainrings

Post by Punx0r » Sep 29 2016 7:09am

It's not just your legs, it's the variation in both speed and both that affects any crank assembly over a revolution. You get maximum torque at 90 and 270 degrees and zero at 0 and 180 degrees. The oval shape gives more mechanical advantage (leverage) where it's more useful.

I think Chalo observed that oval chainrings resurface as new/latest tech idea about once per decade...

Hillhater   100 GW

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Re: Oval chainrings

Post by Hillhater » Sep 30 2016 1:18am

There are still one or two riders using them in the Grand Tours (TDF etc)
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Lurkin   100 kW

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Re: Oval chainrings

Post by Lurkin » Sep 30 2016 3:13am

Marketing the "latest" gimmick required for exxxxtreeeemmmmeee cyclists. :roll:

Which really means there might be a small gain, but to the common joe, unlikely to have much benefit if noticeable.

I test rode a friends bike with one, just wasn't something to write home about really.....

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amberwolf   100 GW

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Re: Oval chainrings

Post by amberwolf » Sep 30 2016 4:45am

The main thing the Shimano ovoid BioPace rings do for me is to help with my knee pain--it hurts less with these than with others, for teh same length of cranks/etc.

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MrDude_1   100 kW

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Re: Oval chainrings

Post by MrDude_1 » Sep 30 2016 9:25am

amberwolf wrote:The main thing the Shimano ovoid BioPace rings do for me is to help with my knee pain--it hurts less with these than with others, for teh same length of cranks/etc.
I could see that.. less stress at the less ideal knee angles.
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Re: Oval chainrings

Post by amberwolf » Oct 03 2016 4:44am

FWIW, I haven't had any on my CrazyBike2 for a long time, or at all on SB Cruiser, which have a different seating position from a normal bike.

After testing here, during my redesign/rebuild of SB Cruiser,
https://endless-sphere.com/forums/viewt ... 0#p1227692

I remember why--they don't do the same thing in this position (though they still help some) because the ovals are angled for pedalling from above them, not behind/above them. So everything is offset by something like 45 degrees...
Image
I'm tempted to figure out a way to rotate the rings around the spider so they do what they were designed for at the seating position I'm actually at on SB Cruiser.

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MadRhino   100 GW

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Re: Oval chainrings

Post by MadRhino » Oct 03 2016 7:23am

They were introduced by Shimano in the eighties. After a decade of growing popularity, most abandoned them to be able to use the new, better front derailers that were not compatible with the Biopace. Still in use today but never pushed further in its development. I used one for a while when they were introduced, liked it and found that the crank feeling was round but it didn't improve my time.
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EVTodd   10 kW

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Re: Oval chainrings

Post by EVTodd » Oct 03 2016 9:05am

My old Blue Max mountain bike has the Shimano oval rings on it. The bike does pedal like a dream. Other than feel I doubt it does much for performance.
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Re: Oval chainrings

Post by keithmac » Oct 03 2016 11:56am

I had a Raleigh Mirage years ago with Biopace-sg chainrings, it worked very well.

Surprised there aren't more bikes still using it to be honest.

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Sunder   100 MW

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Re: Oval chainrings

Post by Sunder » Oct 03 2016 5:11pm

There are two versions: the Shimano biopace which reduced load on the knees, and made LESS power.

And the Osymetric ones which allegedly make more power and still in use by some professional teams: http://www.osymetricusa.com
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