Cranks, gears and wheels/tires are a system. Any gear calculator that does not ask you to input all three of these parameters is not going to be able to tell you exactly what your feet are going to be feeling in a given gear. Chainwheels and cassettes are still sold with ~160mm - ~175mm cranks in mind. Going higher or lower shifts your torque curve correspondingly. As I understand it, 130mm is the shortest practical crank. Even at 140mm the average rider is struggling to turn gears that are no issue for a longer crank. So gear down, duh... ok so lets do that. The average gearing is set up so you have big jumps at the low end that get smaller and smaller as you go to higher gears. This works well with the human torque curve. You will be miserable with a gear system that forces you to remain in the lowest gears of the range where all the increments are 15% and more. There is evidence that, for recumbents, shorter cranks can be useful. You will lose torque and possibly, speed, but recumbents are more aerodynamic so there is a trade-off. With DF bikes there is no such trade-off. You lose torque, speed and you still have the frontal area of a DF so unless you constantly spin like a madman you go nowhere fast. It might be instructive that despite all the excitement in America over short cranks, Europeans mostly don't touch them. Not even recumbent riders. Even in velomobiles where space for feet is often lacking the standard crank remains 175mm. Just throwing a whole bunch of stuff out there. There is a point in there too but I've forgotten what it is. FWIW.