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 Calculations with & without MOUNTAIN DRIVE OPTION

   

inches

Brompton Standard Wheel Size

Data
Entry
Area

Rear Sprocket

teeth

teeth

Front Chain Ring

Resulting Sprocket Ratio

inches

Note

Resulting Direct Drive Wheel Size

Note

REAR HUB GEAR SELECTION

Resulting Wheel Size

Resulting % of Direct drive

With Mountain Drive Engaged …

1st gear

inches

inches

inches

inches

inches

inches

inches

inches

inches

inches

%            
2nd gear

%            

Note
3rd gear

%            

4th gear

%            

5th gear

%            

Without Mountain Drive Engaged ….

1st gear 66.13%
2nd gear

79.03%

Note
3rd gear

100%

4th gear

125.81%

5th gear

149.39%