How to measure gear inches on a bicycle

[@tomjones6296]

You don't need to do all that measuring. All you have to know is pi (3.14159) times the diameter of the wheel gives you the wheel circumference. Then you just take the gear ratios to determine how far you travel with one rotation of the crank. For instance a front sprocket of 48 teeth and a rear of 14 gives 48/14 or 3.43. So with one rotation of the crank, the wheel turn 3.43 times at a circumference of (26 x 3.14 = 81.64 inches x 3.43) then assume a cadence of 90 per min you finally get (81.64x 3.43x90= 25,202 inches min). Divide by 12 to get feet per min.(25202/12=2100 ft per min) then divide by 60 to get ft sec. 2100/60= 35 ft sec. the ration between ft/sec and mph is 88ft sec = 60 mph so 35x60/88=23.86 mph. Done.

[@cougarmanufacturing6582]

I'm fully aware of this. This is actually an assignment I give my college and advanced high school students to do. They compare actual rollout dimensions to calculated ones. This assignment gave them something hands on to do when everyone went on Covid lockdown.

[@namdarbolour9890]

Agree with original commenter. All you're really doing with this exercise is confirming empirically that the formula for the circumference of a circle is correct!