USER INSTRUCTIONS: The BLUE entry points   Blue  below are where you may enter combinations of different values for the number of teeth on the CHAIN RING and REAR sprockets and the chart will compute the resulting Wheel Sizes for the different Gear Settings. If your browser is MS Internet Explorer then to compute the result after entering new data you may press Enter or click on any other part of the form. With other browsers use only the second method. On changing the option in the combo box the result is computed automatically.

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Mouse or Keyboard TAB key: You may reach the DATA ENTRY points by pressing the TAB KEY on your Keyboard which cycle you through the various data entry points or by MOUSE CLICKING the entry point allowing you to enter different spocket teeth values for comparison combinations.
HELP Messages & Notes: On the right side of the chart, you will see the words HELP and NOTE. MOUSE CLICK on these words for the Help or Note message associated with that area.

BROMPTON STURMEY 5 SPEED GEAR CALCULATIONS with FRONT DERAILLEUR OPTION

   

inches

Brompton Standard Wheel Size

Data
Entry
Area

Rear Sprocket

teeth

teeth

teeth

SMALL Chain Ring

LARGE Chain Ring

Small Chain Resulting Sprocket Ratio

inches

inches
Note

Large Chain Resulting Sprocket Ratio

Resulting Small Chain Direct Drive Wheel Size

Note

Resulting Large Chain Direct Drive Wheel Size

REAR HUB GEAR SELECTION

Resulting Wheel Size

Resulting % of Direct drive

With   SMALL Chain Ring Engaged …

1st gear

inches

inches

inches

inches

inches

inches

inches

inches

inches

inches

66.13%
2nd gear

79.03%

Note
3rd gear

100%

4th gear

125.81%

5th gear

149.39%

With   LARGE Chain Ring Engaged …

1st gear 66.13%
2nd gear

79.03%

Note
3rd gear

100%

4th gear

125.81%

5th gear

149.39%