Brompton factory build:     Brompton-compatible data only: 
Options:
Chainring:  Factory sizes are 54/50/44 teeth (+8%/standard/-12%)
Tyre:  Manufactured by Schwalbe
Hub:  Same ratios as most SA 3-speeds
Schlumpf: 
Units:     

Gear InchesHub Ratios
75%100%133%
 Rear sprocket:  42.256.274.9
   
Range: 178%