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Changing an Urban (4 speed) Brompton to an Explore (12 speeds)

Originally the Brompton P Line and T line came in one model - the Urban - with 4 speeds (with an additional choice of single speed on the T line to further reduce weight)

A short history of the Urban (4 speed) / Explore (12 speed) Brompton models

At the beginning of 2024 Brompton launched the following Explore (12 Speed) bikes

  • T Line 12 speed
  • P line 12 speed
  • P Line Electric 12 speed
  • C Line Electric 12 speed

So then came the question - can my Urban (4 speed) be upgraded to a 12 speed Explore model - and assuming the answer is yes, what parts are required?

Being clever, smart and intelligent, you assumed right - the answer is yes - one of the things we have loved about Brompton over the years is the availability of spares and the backwards compatibility when new parts are released

In a similar way to the 6 speed which combined a 3 speed hub with a 2 speed derailleur system (3 x 2 = 6), the new 12 speed Explore combines a new Brompton Ultralight 3 speed hub (shown below) with the 4 speed derailleur system (3 x 4 = 12)

Brompton 3 speed ultralight hub

Above is a picture of the new Brompton Ultralight 3 speed hub showing the Brompton logo and the 4 sprocket Shimano style driver

if you want to see the effect of changing your gearing, we recommend the Brompton gear calculator which allows you to compare different hub / derailleur gear setups

http://xldev.co.uk/bgc.html

Replacement and new parts needed for 12 speed upgrade

 For Brompton P Line / T Line the following parts need changing 

* Note (26th Feb 2024): The new Brompton rear wheel (as a standalone item) exceeded expected sales. To protect production of new bikes on the production line, after market sales have been restricted by Brompton

** Note: The Ultralight wheel is not similar to the BWR 3/6 speed wheel - you can't upgrade your P Line using a BWR wheel

 For Brompton Electric C Line (4 speed) / Brompton Electric P Line (4 speed) 

For all models the following parts will need to be added:

 For all Brompton models the following parts will need to be added: 

 For non-Brompton Electric the following part may need to be changed: 

  • Inner tube - depending upon your current rim - the new 12 speed rim uses a presta / racing type valve which has a smaller (6mm compared to 8mm) valve hole than the standard Brompton rim

 The following parts can be re-used (if they are in good condition) 

  • 4 speed sprocket stack
  • Chain

Article created: 5th Feb 2024
Article last updated: 8th Feb 2024