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Chain Alignment

Screen shot of chain alignment window fully expanded to reveal data entry area Click cassette cog to learn more about the gearing diagram Click chainring cog to learn more about the gearing diagrams

The bicycle gear calculator provides this form which is intended to be used in conjunction with the Gear Usage Table, and Assessment, for fine tuning your gear usage. The Suggest button on the gear usage table now contains some cunning code that automatically weeds out duplicate or near duplicate gears, starting with the biggest chain angles, so it will produce different suggestions according to your chain alignment. If one of these suggestions corresponds to the way the gears actually get used in practice, then spacers or a custom bottom bracket might be considered in order to straighten the chain line and produce a marginal increase efficiency'

If you grab the bottom right corner of the form and open it out a bit you will find that the form also contains a table of offset distances and approximate chain angles for each gear. Click on the table when the gear diagram is visible in the parent form, and GearCalc Pro will show you visually which gear is referred to. This form is unitless. The only important thing is that all entries should be in the same units. If you measure the pitch of your chain in inches, then all the other measurements within this form must also be in inches. There is no need for a metric/imperial toggle here because the method of calculation is the same for both.

The following data is required to calculate the chain angles:

  1. Distance between cog centres: Measure the distance from the centre of the bottom bracket spindle, to the centre of the rear wheel spindle.
  2. Chain Pitch: Measure the distance between two adjacent chain rollers.
  3. Chain roller diameter: Measure the outside diameter of a single chain roller.
  4. Front spacing: Measure the gap between the centres of two adjacent chainring cogs.
  5. Rear Spacing: Measure the gap between the centres of two adjacent freewheel cogs.

Diagram of how to make the measurements

These boxes are provided purely for the satisfaction of the curious. As you can discover for your self these numbers can vary quite significantly without effecting the functionality of the assessment, or suggest buttons in the gear usage table. So measurements don't need to be particularly accurate, and for most people the factory settings will do just fine. If you click the mouse on the lower right corner, and drag it towards the top left corner you can re-size the window so only the diagram is visible, and forget about the rest. Delete the file 'default.cha' to restore factory settings.

Gear Calculator For Single Speed Fixed Wheel Bicycles
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Designed by Nigel Jones