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Sorry to beat this topic again, but(6 posts)

Sorry to beat this topic again, butMXL02
Sep 24, 2002 1:00 PM
what is the difference between 30x25 (triple set up) versus the 39x29 (standard set up) in terms of efficiency for climbing.
re: Sorry to beat this topic again, butMike Prince
Sep 24, 2002 1:45 PM
39x29 will be a little harder to pedal. The numbers are:

39x29 = 35.1 gear inches
30x25 = 32.4 gear inches

For comparison, a 30x23 will be almost identical to the 39x29, so picture the feeling of going uphill in basically one easier gear if you use the 30x25. That's the difference between the two combinations you listed.
math challenged...C-40
Sep 24, 2002 6:42 PM
Once again, this is barely even high school level math.

30/25 is a 1.2 gear ratio. A 39/29=1.34.

1.34/1.2= 1.12. The 39/29 requires a 12% greater torque (more difficult) and produces 12% greater speed at a given cadence. The 30/25 will be easier to pedal, but produce less speed at a given cadence.
Length of Fulcrum questionSpunout
Sep 25, 2002 4:11 AM
There was an earlier reference, but I've lost it about the following:

Let us say that 39/29 is the same as some other combination on a 30 ring.

Would not the 39 combination, because the chain travels a wider path around the axis, provide a more efficient energy transfer mode than on the 30?

Ever notice how you pedal smoother in the 53/21 as compared to a similar gear on the 39? The math works out the same, the work done is equal for a given cadence. But there is something different about it.
You may have a point.Spoke Wrench
Sep 25, 2002 5:18 AM
There actually is a difference. The tension on the chain is less due to the leverage differences of the bigger sprockets.

Every six months or so on Tandem & Hobbs a group of responders will argue FOREVER about the advantages of different size timing chain sprockets.
Thanks for responding to us mere mortals. nmMXL02
Sep 25, 2002 6:08 AM