are 12-21 clusters are stupid?

I was reading (I think) Frank Berto's "The Dancing Chain" book last
weekend, and it mentioned some efficiency research that Berto did with
3-speed hubs, 7-speed hubs, and regular derailleur bikes. If I
remember correctly, drivetrain energy loss was about 3-5% for
derailleurs, and 5-7% for internally geared hubs.

More interesting than this was a statement that the highest losses on
derailleur bikes came from 13-tooth cogs. The results implied that
using a 13-tooth cog was tanamount to using a Sturmey Archer 3-speed
hub. And Berto asserted that this is why 14-28 rear clusters are so
popular on road bikes of the 1970's and 1980's.

Has anything changed ?

Are 13-tooth (and 12-tooth (and 11-tooth)) cogs only 90-92% efficient?

- Don Gillies
San Diego, CA

Donald Gillies wrote:
I was reading (I think) Frank Berto's "The Dancing Chain" book last
weekend, and it mentioned some efficiency research that Berto did with
3-speed hubs, 7-speed hubs, and regular derailleur bikes. If I
remember correctly, drivetrain energy loss was about 3-5% for
derailleurs, and 5-7% for internally geared hubs.

More interesting than this was a statement that the highest losses on
derailleur bikes came from 13-tooth cogs. The results implied that
using a 13-tooth cog was tanamount to using a Sturmey Archer 3-speed
hub. And Berto asserted that this is why 14-28 rear clusters are so
popular on road bikes of the 1970's and 1980's.

Has anything changed ?

Are 13-tooth (and 12-tooth (and 11-tooth)) cogs only 90-92% efficient?

- Don Gillies
San Diego, CA

There's an inherent relationship between cog size and mechanical drag,
since the chain links have to rotate further on their pins the smaller
the cog gets.

In actual usage, however, if you are in the 53-11 and pedaling at a
decent cadence, the speed would be high enough so that the mechanical
drag would be trivial compared to aerodynamic drag.

Good answer... but as i said before... if are not strong enough doesnt
matter it will be less eficient hehehe... common sense right? :P

cya



There's an inherent relationship between cog size and mechanical drag,
since the chain links have to rotate further on their pins the smaller
the cog gets.

In actual usage, however, if you are in the 53-11 and pedaling at a
decent cadence, the speed would be high enough so that the mechanical
drag would be trivial compared to aerodynamic drag.