I've confused myself, and maybe some of you can help: I was just messing around with this new unit converter (mph to kph, fahrenheit to celsius etc) and decided to figure out some bike stuff. I wanted to see how many crank rotations it takes me to go a mile. Here's how I broke it down:

If I have 48x17 gearing with 700x23 tires, I know that I am traveling 74.3" per rotation.

74.3" is 0.0011726641 miles.

0.0011726641 goes into 1 (mile) 852.759115 times (I rounded to an even 853 for this thing here), so 853 rotations of the cranks will take me 1 mile, right? OK, so let's continue:

If I am traveling at the rate of 20mph, I would multiply 20 (miles) x 853 (rotations) to get 17060 rph (rotations per hour) right? OK... so here's where I get confused.

If I'm traveling at 20mph, my cadence is roughly 90.5 rpm. If I multiply 90.5 x 60 (minutes in an hour) I get 5430.

Where am I messing up? If I figure out my rotations per hour by distance, I get a very different figure than when I figure it by time. I am hoping that someone here can help me figure this out, it will bug me enough that I will try to count my rotations on my next hour ride!