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Gears providing the same length(7 posts)

Gears providing the same lengthMatteo
Sep 24, 2002 10:21 AM
53/19 and 39/14 deliver the same length.

Do you think it's really the same thing pushing one or the other?

simple gear ratio...C-40
Sep 24, 2002 11:00 AM
These are gear ratios, not lengths. Both ratios are virtually identical. The only minor difference is the amount of chain in contact with the cogs and chainrings.

There should be no perceptable difference in performance.
Are you thinking of "gear inches?"retro
Sep 24, 2002 2:20 PM
One method of measuring gearing is in "gear inches," the number of teeth in the chainring divided by the number in the cog multiplied by the diameter of the driven wheel (by convention, mountain bikes use 26 inches and both 27-inch and 700C use 27 inches). Figuring that way, 53/19 would be 75.31 inches and 39/14 would be 75.21. I'm sure I'D never feel it.
Sep 24, 2002 2:56 PM
Maybe I'm nuts but wouldn't the difference in chain tension and chain line have at least a small input in perceived effort.
Princess and the peaKerry
Sep 24, 2002 4:58 PM
You can propose all sorts of theoretical reasons why one gear would be more efficient (most engineers would lean toward the larger ring/cog) but it's doubtful you could feel the difference.
avaialble gears, chainlineoff roadie
Sep 25, 2002 5:37 AM
Assuming you could choose either, it would make sense to pick the one that set you up for a quick shift to whatever gears you needed to use next.
Barring that consideration, pick the one with the straighter chainline.

If you had two riders using such close gear ratios, missed shifts and crossed chains would probably have a bigger impact on overall effciency than chain tension / sprocket size.
If you rode either for 1000 miles nonstop...aeon
Sep 26, 2002 10:45 PM
You would end up with more wear using the 39. Don't ask me how much though.

If you use the 39 you limit yourself in terms of available gears and efficiency. You can only get 1 or 2 gears harder than that before you have to go to big ring, and the whole shifting mess will be slower. Using the 53, you place the chain in about the middle of the range, depending on the cassette, which is a nice place to be.