Originally Posted by
atitagain
The point is that if you figure out the gear inches of each gear combination or ratio then you can determine the sequential shift pattern and learn to use all those gears on your bike more efficiently . If it does not matter to you I don't care . Peace .
Sequential shifting is OK up to a point, but it can get messy if you have a triple crankset.
Doing up a gear-inch chart will probably show you that there are repeated or very close-together results.
Hence the simplification for triples --
Small chainring for steep climbing, and use half the cogs from biggest down;
Middle chainring for most riding, using the full range of cogs on the rear*; and
Big chainring for fast speed using half the cogs from the middle down to the smallest.
* On triples, the chainline should be set up for the middle ring and the middle cog on the middle. It also is the chainring likely to get the most wear, and therefore is the one that likely needs to be changed out more often than the other two.
On doubles, a similar explanation could be used -- small ring for general use and climbing; big chainring for speed. Either chainring on a double should be able to run through all the rear cogs. There might be repeated ratios when you work out the gear-inch chart.
The "purest" form is single chainring to a cogset on the rear. All the gear-inch ratios will be unique.
In practice, the repeated ratios on triples and doubles don't really cause much of an issue, and especially if you are skilled at shifting the front and rear gears at the same time.