I ride a triple crankset with 30/42/52 teeth and a sprocket from 13 to 25 teeth. Now I want to switch to a double. Will I be able to match the gear range of my old triple crankset with 39/52 at the front and sprockets from 12 to 27?
Franz Spacek, Vienna
Unfortunately not. With one turn of the crank in the easiest gear of your triple drive, you cover 2.52 metres. In the 39 to 27 ratio, however, it is 3.03 metres, the gear is heavier. If you want to ride a 39 chainring, you have to fit a 32 sprocket as the largest sprocket at the rear to cover almost the same distance per pedal stroke as before. For sprockets of this size, however, you need a mountain bike rear derailleur. Shimano's MTB rear derailleurs and road bike brake levers work together. Campagnolo offers a maximum of one 29er sprocket. Tip for Campa riders: Fit a compact crank with a smaller bolt circle from manufacturers such as FSA, Specialités TA or Ritchey (see TOUR 10/03, p. 46). Or a triple MTB crank where you omit the third chainring.
You can determine the distance travelled per crank revolution in order to select the most suitable gear ratios.
Formula: Front chainring divided by rear sprocket, multiplied by the wheel circumference (approx. 2.10 metres).
Example: 53:11 x 2.10 = 10.12 metres per crank revolution
