Ohhhh the three speed. I forgot what putting some miles on a 3 speed is like. Well it's been a 2 speed for the most part. I've noticed I don't use 3rd a lot. Most of the time I use 2nd (40x16), after all it's the gear I've been using lately when I ride fixed. So me being me I decided to investigate.
I chose 40x16 because I usually ride between a 17Mph and 20Mph pace. At 85RPM I'm around 17Mph, and at 100Rpm I'm around 20Mph . . . I call it close enough.
The hub I'm using is a Sturmey Archer AW. They call it a wide range.
1st gear at 100Rpm = 2nd gear at 75Rpm.
2nd gear at 100rpm =3rd at 75 Rpm.
Thats a 25 Rpm drop or rise.
If you like to ride with a cadence between 75Rpm to 100Rpm this hub work perfect for you. however in my case if I'm riding comfortably at around 18.7 Mph/95Rpm in 2nd gear, then catch a tail-wind or whatever, this forces me out of my comfort zone. So I shift up . . . To What? . . To maintain 95 Rpm I have to increase my speed almost 6Mph, or drop cadence to a 70 to 75Rpm grind?
I was talking to some people about it the other day and they said they couldn't do with just 3 gears and I joking replied, you actually have 6. 1st gear standing out of the saddle, then 1st, then 2nd standing out of the saddle, then 2nd, . . . and so on. However it's not to far from the truth, and gives us something to consider. It's a fact, with just 3 gears you will stand, but how many times do you stand and pedal out of the saddle in 3rd gear? . . . almost none. A lot in 1st, and 2nd going up hills; but not 3rd so much, if at all.
So I'm going to try using a gear in the back that has 2 more teeth. I'm going from a 16 tooth cog to 18 teeth.
and this is what the chart will look like. Now in order to maintain 19.7Mph in 3rd gear instead of maintaining a cadence of 75Rpm and can pedal at a comfortable 85Rpm. Hopefully I find myself using 3rd gear some more. We will see.
In conclusion if you want to change from a single speed to a 3 speed wide range hub, add 1 to 2 teeth in the back.