Getting a Little Shifty

Ugh, another break that was entirely too long. However, I have not forgotten about this blog, just busy with other things (jobs, life, etc.). I am riding again, although I did take last week off because I over did it the week before and ended up with a very painful cramp in my right calf. (Sounds like another blog entry to me.) Anyways, today I want to shift gears and talk about shifting gears (literally).

Now, unless you have either a single speed bike or an internally geared bike, you have the standard front and rear derailleur configuration. Most people tend to stick with only a handful of gears, often times at the lower end because their bike isn't properly adjusted to their body, but that's another topic. Many people (Americans, especially) like to buy bicycles with lots of gears thinking that "more is better". Well, not necessarily so. Consider this, the typical mountain/hybrid bicycle has a triple chainring up front and an eight or nine speed cassette in the rear, giving a total of 24 or 27 gear combinations. However, not all of those combinations are usable and many are either duplicates or close enough that it makes little or no perceived difference.

Let's take my bike for example. I ride an older Specialized with a triple chainring with a 30/40/50 combination and a seven speed freewheel with a setup of 12/14/16/18/21/24/28. So that should give me 21 speeds, right? Wrong! Out of the 21 speeds, there are three combinations that are duplicates (I'll illustrate that in a minute), four combinations that are unusable due to the resulting chain angle (one of which is also a duplicate mentioned above), and one where the difference is minor.

To better illustrate this, I am using the late Sheldon Brown's on-line gear inch calculator. Since I ride with a 700C x 38 wheel, I factor that into the calculator, along with my 175mm crankarms and get the following gear inch table:

30 33.3 % 40 25.0 % 50 12 68.3 91.1 113.8 16.7 % 14 58.5 78.1 97.6 14.3 % 16 51.2 68.3 85.4 12.5 % 18 45.5 60.7 75.9 16.7 % 21 39.0 52.0 65.0 14.3 % 24 34.2 45.5 56.9 16.7 % 28 29.3 39.0 48.8

The following gear combinations are duplicates: 30x21 and 40x28; 30x18 and 40x24; 30x12 and 40x16. The following combinations are unusable because the resulting chain angle would cause rubbing on the front derailleur and excess lateral flex on the chain: 30x14, 30x12, 50x28, and 50x24. (Note that 30x12 is both a duplicate and an unusable gear.) The gear combinations 30x16 and 40x21 are less than one gear inch apart, so the difference is imperceptible.

A gear inch, for those who don't know, is defined as the number of inches traveled for each revolution of the pedals, and dates back to the old penny-farthings. Most people don't concern themselves with gear inches any more, but it can be useful for devising a shift pattern.

Again, taking my bike as an example, I use twist shifters rather than trigger shifters, but both have numbers that correspond to the respective gear from low to high, so this should translate to other bikes. I printed out the table above, crossed out the unusable gear combinations and highlighted the duplicates. Next, I numbered the chainrings and cogs from low to high to match the numbers on my shifters. Then I opened up a spreadsheet program and created the following shift table:

1-1	1-2	1-3	1-4	1-5
		2-1	2-2	2-3	2-4		2-5		2-6		2-7
						3-3		3-4		3-5		3-6	3-7

Note: The number to the left of the hyphen denotes the left shifter number (or chainring) and the number to the right of the hyphen denotes the right shifter number (or cog).

As you can see, I have three combinations that are (more or less) duplicates, therefore they are listed as being equal on the shift table. I left this as such in case I find myself in the lowest chainring for extended periods of time (like hills or strong headwinds). Otherwise, I start with the combination of 2-1 and start my shift pattern from there. I can now take this shift table, print it out, and tape it to my handlebars as an easy reference (and less memorization).

To use the table, I merely start out with a gear combination (normally 2-1) and shift from left-to-right to upshift, and right-to-left, to downshift. So, a normal upshift pattern would be 2-1, 2-2, 2-3, 2-4, 3-3, 2-5, 3-4, etc. Whenever extra torque is needed (such as strong headwinds, climbing hills, etc.), I'll start with 1-1 through 1-5, then shift to 2-4, 3-3, and so forth. This allows me to shift to each successive gear (according to gear inch) without making a massive jump that could sap my strength and energy in the long run and help maintain my cadence.