Originally Posted by
Shahmatt
Use Sheldon's Gear range calculator:
Sheldon Brown's Bicycle Gear Calculator
My input:
Wheel Size: 20x1.75
Crank length: 170mm (does not feature in gear inches calculation)
Gear units: Gear inches
Chainring: 46, 39
Cassette: Custom sprockets
Next line: 27, 30
Internal hub: No planetary (internal) gears
Press "Calculate"
Output shows for the 46T-27T combination your gear inches are 31.8
If you switch your chainrings so that you have a 39T in there your gear inches can drop down to 27.0 (15% drop)
If you switch both your chainrings AND cog set to a 30T (at largest sprocket) then your gear inches are: 24.3 (23.5% drop).
Thank you, Shahmatt, but I think something is off. The gear-inch range listed in the specifications for this bike on the bike-seller's website with the stock 56/46 chainring and stock cassette is 26-95. Plugging 56/46 for Chainrings in the calculator, I had to plug in 11 and 33 in Custom Sprokets to get 26-95 gear inch range, but I know for sure the largest cog isn't 33t. In other words, before trusting the calculator for theoretical chainring sizes, I first tried to confirm that it is calculating correctly for the stock chainrings, but it doesn't seem to be.