It can be useful to calculate bicycle gearing, especially when we’re considering a new drive-train or a new bike, but many cyclists struggle to know where to start.
I see this become an issue most often when the cycling industry comes out with new technology for gearing or drive-trains. Moving from a triple chainring to a double, and more recently, in moving from a double to a single or “1X” (or “1-by”) set-up. Any time this happens, cyclists contemplating this jump have to then consider what they might be losing as the number of gets gets reduced.
Most of the time the purpose of the gearing advancements (moving from three to two or two to one chainring) is meant to maintain the gearing range as much as possible, but usually there is a small to moderate loss of range, on either the high or low end of the range. In these situations a strategic decision needs to be made to determine which end — the high (or downhill) or low (uphill) gearing can be foregone.
A number of years ago the only way to get “big mountain” climbing gears on your road bike was with a triple front chainring, but people (basically anyone that worked on their own bike) realized quickly that the shifting on these systems often stunk. The chain-line was terrible and they often proved to be more headache than they were worth. The compact “2-by” front chain ring became popular and all seemed to improve. A similar thing happened in the mountain bike arena, but much more quickly. We moved from a triple to a double, and then a few years later to a single front chain ring.
Advances in cassettes allowed for roughly the same range in gearing, but there was a compromise (there always is right?). The short-coming of this scenario is that if you mostly maintain the range of the gearing, but you reduce the number of gears, then this creates larger steps in between gears. Going uphill and need just a slightly easier combination? Shift once and you might drop a lot more gear than you wanted. For some riders this was a deal breaker, for others, no big deal.
Regardless, using the simple method in the video will help you quickly calculate bicycle gearing and help you compare what you have with what you think you might change to to determine how to limit what you lose in the transaction.