Larger pulleys.....
10-12-20, 06:37 PM
#51
Full Member
I suspect if the der is aligned, adjusted and well-maintained, they all work pretty well.
10-12-20, 09:38 PM
#52
Junior Member
In the attached article they found a savings of about 2 watts. Meaningful for a racer perhaps.
Oops. I can't attach an article it seems. Look up friction facts bigger pulleys really are more efficient.
Oops. I can't attach an article it seems. Look up friction facts bigger pulleys really are more efficient.
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10-13-20, 03:11 AM
#53
Junior Member
Below are two of my setups. 1st image: Alfine 8 with a 16t sprocket in a 305mm wheel. 2nd image: Rohloff in a 406mm wheel.
Last edited by comfort rider; 10-13-20 at 04:43 AM.
10-13-20, 04:52 AM
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Interesting... While it (i.e. the infrared video) shows the temperature, and you mention a correlation with link angularity, it does not follow that this is a causal correlation. it is highly likely that the chainring, having the highest thermal mass and heat transfer, is quickly dissipating any heat that is generated (and thereby staying close to the ambient temperature). In second place in these properties would be the sprocket (smaller, steel), and bringing up the rear are the jockey wheels (smallest, plastic).
Bunkie
I'm not an engineer but I have stayed in a Holiday Inn
I would say the chief reason larger pulleys are touted as "better" is that they reduce the angle/bend of the chain when it goes around the pulleys, thereby reducing friction. I'm sure they have some kind of fancy bearing in them that further reduces friction but I don't know that to be a fact.
I'm not an engineer but I have stayed in a Holiday Inn
I would say the chief reason larger pulleys are touted as "better" is that they reduce the angle/bend of the chain when it goes around the pulleys, thereby reducing friction. I'm sure they have some kind of fancy bearing in them that further reduces friction but I don't know that to be a fact.Right from the horse's mouth:
"Technically, it would. But when you think of how a drivetrain operates — a chain winding its way over chainrings and then around a cassette, and finally, through the serpentine pulley system of a rear derailleur — the more significant cause of friction is actually the angle the chain reaches as it wraps through the rear derailleur.So by opening up those angles and making them less sharp, the chain can articulate less than it would when it passes around smaller pulley wheels. Voila! Less friction."
“The biggest advantage is friction reduction, or increasing the efficiency of the drivetrain,” says Smith. “There’s a couple of ways the OSPW reduces friction. In other words, it’s part of a system. The biggest factor is the larger pulley wheels. The less amount a chain has to articulate as it engages and disengages the pulley wheels, the less friction is produced. The next thing is on the larger pulley wheels, the bearings spin slower so you don’t have as much drag there.”
https://www.velonews.com/gear/tour-d...ys-should-you/
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10-13-20, 05:21 AM
#56
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If you read my post carefully, I never disagreed with the contention that larger idlers reduce losses. I only contend that the infrared imaging is inconclusive as to the relative magnitude of losses along the chain's tour of the drivetrain.
10-13-20, 06:03 AM
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I have a couple Altus RD's that use the large pulleys. I suspect that the design allows the quick snappy shifts you get with a short cage (vs long cage) RD, but you get the extra chain wrap of a long cage RD. Brilliant idea, and I think it will catch on gradually, as more people run 32 and 34 tooth cassettes on their road bikes.
The Altus RD's are pretty heavy though, so I hope we start seeing the large pulleys on some higher end, lighter RD's.
The Altus RD's are pretty heavy though, so I hope we start seeing the large pulleys on some higher end, lighter RD's.
10-13-20, 08:00 AM
#58
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Wouldn't larger cogs cause the same effect?
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10-13-20, 10:39 AM
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Is there a market for larger jockey wheels? Perhaps an upgrade kit that included the cages to accommodate the larger wheel.
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10-13-20, 10:57 AM
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Interesting discussion. It tells me that there is a miniscule amount of less friction with the larger derailleur pulleys because they will rotate slower than smaller ones. It doesn't matter to me. It might matter to Mark Cavendish when he needs that tiny little advantage across the finish line 
10-13-20, 11:33 AM
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10-13-20, 12:34 PM
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Yes they would, if that was the only thing changed. But we should consider that in reality the cage will rotate with each shift. Additional variables are present as well: variations in cage shapes and in how much the chain lengths are changed to accommodate the added pulley diameter. I think it would be hard to go from a general and isolated statement to an accurate real-world prediction. One would need to do some math to make a strong prediction.
But simply moving the sprocket teeth closer to the pulley teeth, yes that would reduce free length and make it easier for the "next sprocket" to pick up the chain and complete a shift. It reduces the amount of overshift needed, in case any was needed.
But simply moving the sprocket teeth closer to the pulley teeth, yes that would reduce free length and make it easier for the "next sprocket" to pick up the chain and complete a shift. It reduces the amount of overshift needed, in case any was needed.
10-13-20, 05:37 PM
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Turns out the night at the Holiday Inn worked for me
Right from the horse's mouth:
"Technically, it would. But when you think of how a drivetrain operates — a chain winding its way over chainrings and then around a cassette, and finally, through the serpentine pulley system of a rear derailleur — the more significant cause of friction is actually the angle the chain reaches as it wraps through the rear derailleur.So by opening up those angles and making them less sharp, the chain can articulate less than it would when it passes around smaller pulley wheels. Voila! Less friction."
“The biggest advantage is friction reduction, or increasing the efficiency of the drivetrain,” says Smith. “There’s a couple of ways the OSPW reduces friction. In other words, it’s part of a system. The biggest factor is the larger pulley wheels. The less amount a chain has to articulate as it engages and disengages the pulley wheels, the less friction is produced. The next thing is on the larger pulley wheels, the bearings spin slower so you don’t have as much drag there.”
https://www.velonews.com/gear/tour-d...ys-should-you/
Right from the horse's mouth:
"Technically, it would. But when you think of how a drivetrain operates — a chain winding its way over chainrings and then around a cassette, and finally, through the serpentine pulley system of a rear derailleur — the more significant cause of friction is actually the angle the chain reaches as it wraps through the rear derailleur.So by opening up those angles and making them less sharp, the chain can articulate less than it would when it passes around smaller pulley wheels. Voila! Less friction."
“The biggest advantage is friction reduction, or increasing the efficiency of the drivetrain,” says Smith. “There’s a couple of ways the OSPW reduces friction. In other words, it’s part of a system. The biggest factor is the larger pulley wheels. The less amount a chain has to articulate as it engages and disengages the pulley wheels, the less friction is produced. The next thing is on the larger pulley wheels, the bearings spin slower so you don’t have as much drag there.”
https://www.velonews.com/gear/tour-d...ys-should-you/
10-14-20, 05:22 AM
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Ceramic Speed, for example, will sell you that 2 watts at the RD for $600. You can add some more watts with their BB bearings for $600 more. Custom hubs have already been around for a while. Carbon chain rings are coming out, short term, short range.
The weight arms race is sort of over, given the ease with which 15.1 is reached. The UCI could change this tomorrow.
The next areas are aero, friction mitigation and where on the bike to put the 15.1 pounds, be it in rotational mass, or not.
Last edited by RobbieTunes; 10-14-20 at 08:57 AM.
10-14-20, 11:38 AM
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Looking at the pro peloton lack of these gizmos, I'd say the $600 is well spent.
10-14-20, 11:41 AM
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Sez the guy with full super record.
10-14-20, 01:05 PM
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My Hero... i.e. I blame you.
I'm picking up my SR 11 this week sometime... on the trickle-down side of a SR 12 purchase.
The calipers are SR 12 because he has direct-mount calipers already.
I don't even know what bike to put it on. Probably will end in a vowel.
I'm picking up my SR 11 this week sometime... on the trickle-down side of a SR 12 purchase.
The calipers are SR 12 because he has direct-mount calipers already.
I don't even know what bike to put it on. Probably will end in a vowel.
10-14-20, 03:18 PM
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Mine is on a bike ending in a vowel and it was acquired as a trickle-down EPS purchase in 2012.
10-14-20, 03:30 PM
#72
Strong Walker
If you ever held a new or freshly lubed chain in your hands and bent it - the difference between bending one link 30 degrees, and being it only 22 - that's the advantage you get (minus the weight disadvantage from using two more chain bits, and a larger pulley, and a bigger cage of course) from using larger pulleys.
10-14-20, 04:35 PM
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So it will be Scirocco 35mm, most likely, from another build. Or some 11-sp non-Campy (Roval CL60) since the spacing is the same...
I'd like 3T's, to stay Italian, but Gail gets those on her reDo-mane. Pretty sure the name will end in "i." (Super Mario's "comfort" bike)
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10-14-20, 05:13 PM
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Cinelli XCR with Super Record 001 by iabisdb, on Flickr
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