How to Use a Measuring Wheel to Calibrate a Bicycle Computer

A bicycle computer, also known as a cyclometer, tracks your speed, distance and other cycling statistics during your ride. The cyclometer takes readings from a sensor mounted on your bike's fork and from a magnet on your front wheel. When you install your cyclometer, the accompanying instruction sheet will have a chart of numbers to enter depending on your wheel size. The number you enter tells the computer how to calculate your speed and distance each time the magnet passes by the sensor. Most charts are accurate, within a five percent range, but to track your rides more precisely, calibrate your cyclometer with a measuring wheel.

Things You'll Need

  • Masking tape
  • Measuring Wheel
  • Pencil
  • Paper
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Instructions

    • 1

      Find an area where you can do your measurement. Ideally, the area should be flat, with no obstacles. A running track, bike path or low-traffic neighborhood street are your best options.

    • 2

      Stick a strip of masking tape on the ground to indicate your starting point.

    • 3

      Set the measuring wheel to zero and walk at least a half mile. Walk the entire half mile in the same lane if you are doing the test at a running track. If the route is not circular, such as at a running track, place another strip of tape on the ground at your end point.

    • 4

      Take your bike to the starting point and set your cyclometer to zero. Ride to the endpoint while maintaining as straight a line as possible. If you are doing this test on a track, stay in the same lane that you walked with the measuring wheel.

    • 5

      Check your cyclometer when you get to the endpoint. If the reading is not 0.5 miles, do a simple calculation: divide the distance measured by the cyclometer reading. This will give you the conversion factor. Hang on to that number.

    • 6

      Look on your cyclometer instruction sheet for the number you entered for your wheel size, which is also known as the wheel size setting. Multiply your wheel size setting against the conversion factor to get the new wheel size setting. For example, if the cyclometer reads 0.6 miles and the instruction sheet says to enter 2120 for the wheel size, the conversion factor for a half-mile test is 0.83 (0.5 divided by 0.6 equals 0.83). So, you would reprogram your cyclometer wheel size with 1767 (because 2120 times 0.83 equals 1766.66).

    • 7

      Remove your tape from the ground.