Brompton factory build:     Brompton-compatible data only: 
Options:
Chainring:  Factory sizes are 54/50/44 teeth (+8%/standard/-12%)
Tyre:  All Brompton high-pressure tyres
Hub: 
Schlumpf: 
Units:     

Gear InchesHub Ratios
64%100%157%
 Rear sprocket-Low:  33.051.781.0
 Rear sprocket-High:  40.663.799.7
Range: 302%