Graydon
02-12-2008, 10:06 AM
We had this discussion a while back... most of you were clinging to the conventional wisdom that light wheels are faster, despite my attempts to prove using first principles this wasn't necessarily true. Here is something interesting I came across on Velonews (article here: http://www.velonews.com/article/71788).
G.
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[URL="http://www.velonews.com/photo/71789"]http://www.velonews.com/files/images/ActiveSpoke2.Teaser.jpg (http://www.velonews.com/photo/gallery/71788)
A close-up of an Active Spoke mass
Active Spoke Mass Wheels (By Lennard Zinn)
As the wheel’s rotational velocity increases, the weights are thrown to the outside of the wheel, effectively concentrating more mass out at the rim. And as the wheel slows down, the springs retract the weights back toward the center, effectively decreasing the rim mass. Inventor Russell Kalil originally came up with the idea while riding an interval workout on a stationary bicycle with a heavy flywheel.
“I thought it would be great to harness the momentum produced by a wheel with heavy rim weight, but with the advantages of a lightweight rim wheel during a hill climb,” says Kalil. “It’s like a figure skater doing a spin with their arms out; when they pull their arms back in, their spinning rate increases.”
He first utilized long, hollow fishing weights connected to rubber bands on his spokes. Now, the system is quite elegant, incorporating thread-together modular weights with a slot in them so that adjacent segments causes the slots to be offset and lock the weights onto the spoke.
I got a set to try, and the amazing thing is how strong the springs are. Two spring rates are available; there are springs for normal folk and then there are “professional” springs, which are much stiffer. The wheel must be spinning much faster for the same mass to move out to the rim with the stiffer spring, and you can tune the system to your preference not only with stiffer or less stiff springs, but also with different stacks of masses, as they thread together.
http://www.velonews.com/files/images/ActiveSpoke1.Thumbnail2.jpg (http://www.velonews.com/photo/71790)
Eight Active Spokes on a wheel
The angular momentum of each mass about the hub increases 16 fold as the radius to the mass increases from 3 inches to 12 inches. The idea is similar to what Ondrej Sosenka was thinking when he set the world hour record on a 10-pound rear wheel – the wheel’s high angular momentum maintains speed better, except that Active Spokes are not as hard to accelerate once you slow down, since the masses are concentrated near the hub. Active Spokes aid you in going downhill faster and carrying your momentum up the next hill.
Pro rider Dirk Friel has tested them a lot and has set his personal best in the Wednesday Boulder time trial series with them. He correlates his frequent 5-mile test runs north of town with data on wind speed, direction, and barometric pressure from a nearby weather station and says that, once he has corrected for the wind, he is consistently faster on a rolling course with Active Spokes.
G.
[/URL]
[URL="http://www.velonews.com/photo/71789"]http://www.velonews.com/files/images/ActiveSpoke2.Teaser.jpg (http://www.velonews.com/photo/gallery/71788)
A close-up of an Active Spoke mass
Active Spoke Mass Wheels (By Lennard Zinn)
As the wheel’s rotational velocity increases, the weights are thrown to the outside of the wheel, effectively concentrating more mass out at the rim. And as the wheel slows down, the springs retract the weights back toward the center, effectively decreasing the rim mass. Inventor Russell Kalil originally came up with the idea while riding an interval workout on a stationary bicycle with a heavy flywheel.
“I thought it would be great to harness the momentum produced by a wheel with heavy rim weight, but with the advantages of a lightweight rim wheel during a hill climb,” says Kalil. “It’s like a figure skater doing a spin with their arms out; when they pull their arms back in, their spinning rate increases.”
He first utilized long, hollow fishing weights connected to rubber bands on his spokes. Now, the system is quite elegant, incorporating thread-together modular weights with a slot in them so that adjacent segments causes the slots to be offset and lock the weights onto the spoke.
I got a set to try, and the amazing thing is how strong the springs are. Two spring rates are available; there are springs for normal folk and then there are “professional” springs, which are much stiffer. The wheel must be spinning much faster for the same mass to move out to the rim with the stiffer spring, and you can tune the system to your preference not only with stiffer or less stiff springs, but also with different stacks of masses, as they thread together.
http://www.velonews.com/files/images/ActiveSpoke1.Thumbnail2.jpg (http://www.velonews.com/photo/71790)
Eight Active Spokes on a wheel
The angular momentum of each mass about the hub increases 16 fold as the radius to the mass increases from 3 inches to 12 inches. The idea is similar to what Ondrej Sosenka was thinking when he set the world hour record on a 10-pound rear wheel – the wheel’s high angular momentum maintains speed better, except that Active Spokes are not as hard to accelerate once you slow down, since the masses are concentrated near the hub. Active Spokes aid you in going downhill faster and carrying your momentum up the next hill.
Pro rider Dirk Friel has tested them a lot and has set his personal best in the Wednesday Boulder time trial series with them. He correlates his frequent 5-mile test runs north of town with data on wind speed, direction, and barometric pressure from a nearby weather station and says that, once he has corrected for the wind, he is consistently faster on a rolling course with Active Spokes.