Phil_gretz

Here's the calculator:

https://www.sheldonbrown.com/gear-calc.html

And here is the numerical table that results in "gear inches" for a 3 x 7 system like the OP describes. Gear inches mean the relative difficulty of pedaling, or the distance that your bike travels for one rotation of the cranks:




Note that in the center column, you'll find the relative difficulty of pedaling when solely in the middle chainring. Also notice how the numbers in the columns overlap one another in a pattern. That's the pattern that your gearing represents over the entire range of your front chainrings and rear cogs. Now to relative speed:




The numbers above are miles per hour assuming that you pedal at a constant 80 rpms. As one poster said above, you should find the rpm rate that you find challenging but sustainable. Bike riding doesn't require you to be straining all of the time, but should be (normally) at a sustainable pace that balances the load on your heart/lungs with the strain on your muscles. 80 rpms would be a good starting cadence. 90 would be better, and you might reach that comfortably in a year or two. This is meant for average folks who ride, not for the very muscled or for the very wiry. Simply average.
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