My son is purchasing a new gravel bike.
He is considering two bikes. One is more a cyclocross speedster, the other more a long haul tourer. Both are equipped with disc brakes, one hydraulic, the other mechanical. One is outfitted with a Shimano Deore triple crankset (48-36-26), derailleurs, and a 9-speed cassette (11-32). The other with an FSA compact crankset (50-34) and SCRAM Rival levers, derailleurs, and a 11-speed cassette (11-32). Both very nicely equipped.
He came to the house the other day questioning which setup would give him the best gearing. I initially thought the triple would give him lower gearing for touring but didn’t realize the SCRAM Rival setup has an 11-speed cassette. Clearly the smaller chainring on the Deore setup would give him a lower gear but the larger Rival chainring would give him a larger, faster one.
But which setup is best for him?
I found a gear calculator on line that takes into account chainring and cassette sizes, rim diameter and tire profiles. I’m not going to bore you with all the numbers.
Well, maybe I will 😂
The origin of this relative measure is not obvious. It dates back to the penny-farthing bicycle. You know, those bikes with large front wheels.
When the high wheeler or penny-farthing was the “ordinary” bicycle form, the comparative diameter in inches of the driven wheel was an indication of relative speed and effort. A 60-inch wheel propelled a bicycle faster than a 50-inch wheel when both were cranked at the same cadence. The technology of the high wheeler imposed a natural limit—a 60-inch wheel was about the maximum size that could be straddled by ordinary sized legs. When “safeties” replaced “ordinaries,” chains and sprockets allowed small wheels to be turned faster than the pedal cranks. As result, a 28-inch wheel could be made to move a bicycle at the same speed as a 60-inch wheel. Such a bicycle was then said to be geared at 60 gear inches and pedalled similar to an ordinary with a 60-inch wheel. Thus on a bicycle geared at 72 gear inches one revolution of the pedals advances the bicycle the distance that a 72-inch wheel would in one revolution.
Here’s what the calculations look like for my road bikes with compact chainrings and a 11-28 cog cassette. One revolution of the pedals in my highest gear advances the bike the distance that a 121.5 inches would in one revolution.
Not only does the calculator provide gear inches, the measure I’m most accustomed to, but equivalent speed and cadence calculations as well.
Have you ever wondered how fast you would travel hammering in your highest gear at 90 RPM? If I could spin in my large chainring (50 teeth) and smallest cog (11 teeth), I would be travelling at 52.3 kph. The only time I see speeds like this is on a long descent. Pro riders see these numbers on the flats.
If you don’t know much about your gearing, I suggest you spend some time with this gear calculator. You may discover you would be better off with a different setup – compact chainrings, a triple setup, or a different cassette.
Have a look and let me know if it helps.