Gear Calculation Tool

Douglas Ruby

Well-Known Member
For years I have used Sheldon Brown's Gear Calculator to calculate gear inches and speed at cadence given rear cluster, front sprocket, and tire/wheel sizes. I used this tool to help set up my 2016 Specialized Turbo, since it was overgeared (IMO) as it came from the factory. However, in email exchanges with a gentleman from Specialized's Swiss development team, I was led to a different tool that can facilitate all of the calculations, and even compare two different setups.

The Turbo comes with 700x45c tires, an 11-32 rear cluster, and 48T front sprocket. I found the gearing too high and changed to 700x35c tires, 11-36 cluster, and 44T sprocket. Over the years I have found that 100 rpm is my maximum sustainable cadence, and that I normally ride between 80-90 rpm. Check out the following URL and see how it shows the difference in gear range and speeds at a maximum cadence of 100 rpm for my Specialized Turbo; both before and after I made gearing and tire changes.

http://ritzelrechner.de/?GR=DERS&KB...44&RZ2=11,13,15,17,19,22,25,28,32,36&UF2=2185

Note that at 100 rpm, with my current gearing, I am going 32.5 mph vs. 36.5 mph in the original setup, yet I now have a 21% lower 1st gear for climbing. Given that the pedal assist cutout is around 42km/h (26.3 mph), this is pretty near ideal for cruising in 8th or 9th and using 10th for downhill.
 
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