Originally Posted by
arfer1
Thanks noglider. If I understand the formula you used, you take the number of teeth on the smallest crank, and divide that by the number of teeth on the largest ring on the freewheel, and multiply that by the size of the wheel to get gear inches. Is that correct?
Yes that's how you calculate your lowest gear. Any gear is calculated as F/R*D where
F = number of teeth in front
R = number of teeth in rear
D = wheel diameter in inches
This gives you the effective wheel diameter, if you were riding an old fashioned high wheeler bike. Back in those days, to go faster, you bought a bike with a bigger wheel if your legs could handle it.
Some perspective: 25 or 30 inches is about the lowest useful gear that adults use. 72" is a moderate gear for general purpose if your terrain is flat. 100" is for hammering really hard or going downhill fast. Very few people can pedal at 90 rpm in a 100" gear for long, so you rarely want a gear higher than 100" or 110" as a top gear.
Now make a chart of all your gears. See the pattern of shifting, going from one gear to the next.