700 X 44 | 236 |

700 X 38 | 231 |

700 X 35 | 230 |

700 X 32 | 227 |

700 X 28 | 225 |

700 X 25 | 223 |

700 X 23 | 222 |

700 X 20 | 221 |

27 X 1 3/8 | 232 |

27 X 1 1/4 | 230 |

27 X 1 1/8 | 228 |

27 X 1 | 226 |

26 X 2.125 | 225 |

26 X 1.9 | 220 |

26 X 1.5 | 212 |

26 X 1.25 | 206 |

26 X 1.0 (559 mm) | 205 |

26 x 1 (650C) | 206 |

Wide Tubular | 224 |

Narrow Tubular | 223 |

26 X 1 3/8 | 222 |

24 | 205 |

24 x 1 | 188 |

20 X 1.75 (406) | 158 |

20 X 1 1/4 (451) | 173 |

17 x 1 1/4 | 142 |

16 x 1 3/8 | 137 |

If calibrating these Avocet computers using a rollout test:

- For miles: use circumference in inches x 2.7273 (30/11)
- For kilometers: circumference in millimeters x 0.108.

The numbers are from an original Avocet 20 manual. The two results are slightly different. Use the appropriate result for greatest accuracy.

Why are the results different? Warning: math ahead!

Avocet explains that 2.7273 is 30 / 11 (actually the repeating decimal, 2.727272727...)

30/11 is 4 times the ratio of miles per hour to feet per second, 15/22.

These Avocet computers are unusual, then, in being calibrated directly to miles rather than to miles by reference to kilometers.

But for kilometers, the same computers ask for the circumference in millimeters x 0.108.

Now let's see how the mile and kilometer calibrations compare:

25.4 is the number of millimeters in an inch.

25.4 * 0.108 is 2.7432 -- slightly but significantly different from 2.7272...., 30/11.

2.7432 * 11/30 is exactly 1.00584

There are exactly 1.609344 kilometers in a mile, and 1.609344 / 1.600000 is also exactly 1.00584.

http://www.sheldonbrown.com/cyclecomp_b.html

Last Updated: by Harriet Fell