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PostPosted: Wed Jun 19, 2013 5:17 pm 
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Location: Atlanta, GA, US
Including a nice shout-out to forum member djconnel:

http://www.cyclingnews.com/features/fri ... -efficient

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PostPosted: Wed Jun 19, 2013 5:25 pm 
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Location: San Francisco, CA
That's cool. Issue is I did my calibration based on old Spicer data, which I tried to fit. The FrictionFacts data are so much better. I should recalibrate my model to those. I'd actually slightly overestimated the benefit. The major benefit in the test isn't 15-teeth versus 11-teeth, but rather how bad the Dura-Ace pulleys are relative to everything else. Once you get down to quality 11-tooth pulleys, the further advantage of going up to 15 is relatively small. But on this forum we're all about small differences, and I admit to being seriously tempted. I had liked the Dark Albert version, but it turns out Berner's design has more advantage than simply larger pulleys, so Berner seems a solid solution. And there's no denying the bling factor.

It will be interesting to see if Berner gets backup up on orders from the quantitative validation.

Basic model was factors which affect loss:
1. chain tension on the upward, tensioned path
2. chain tension on the downward, low-tension path (efficient derailleurs minimize this)
3. chain speed
4. chain bending angle
5. pulley rotation rate
6. pulley bearing friction
7. chain bending friction

Large pulleys reduce 5 and 4.
Large chainrings & cogs (same ratio) increase 3 but reduce 1 and 4.

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