Originally Posted by khuon
Code:
Semi-Log Graph
2 3 4 5 6 7 8 9 1 1 2 3
----------------------------------------------------------------------------------
I 1 2 3 4 5 6 7 8 9
M 1 2 3 4 5 6 7 8 9
O 1 2 3 4 5 6 7 8 9
Sheldon Brown's Gain Ratio Chart
| 12 13 14 15 17 19 21 23 26
----+------------------------------------------------------
52 | 8.54 7.88 7.32 6.83 6.03 5.39 4.88 4.46 3.94
42 | 6.90 6.37 5.91 5.52 4.87 4.36 3.94 3.60 3.18
30 | 4.93 4.55 4.22 3.94 3.48 3.11 2.82 2.57 2.27
The semi-log chart is probably what you're looking for. This chart shows gear position as overlayed onto a development table. Across the top are gear-inches. The letters on the side denote (I)nner, (M)iddle and (O)utter chainrings and the numbers in each row indicate cog position with 1=26T and 9=12T.
The gear-inch chart is OK to compare gear ratios on a single bicycle, but aside from the fact that it is not dimensionless and, worse yet, is measured in inches, the gain ratio is the only fair way to compare gear-ratios among different bicycles. And I can't for the life of me figure out why the plot is semi-logarithmic. It only covers a factor of about 4 along the x-axis and the forward movement of the bicycle in relation to the rotations of the crank, i.e., the gear-inches, couldn't be more linear. Am I missing something here?