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Brompton 4-speed to 12-speed upgrade

9 January 2026 by
Brompton 4-speed to 12-speed upgrade
Brilliant Bikes

Changing a Brompton 4-speed to 12-speed

Needs updating for new wheels and brake levers!

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

While there is no official Bompton 12-speed upgrade kit - this guide will show all the parts required make the upgrade from 4 to 12 gears

Note: As it says in the title - this guide is for converting a Brompton 4-speed to 12-speed. To convert a 2 speed / 6 speed you would also need a rear frame and derailleur system and would have no choice but to change the chain and sprockets

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

At the beginning of 2024 Brompton launched the following 12-speed (also known at the time as Explore) bikes:

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

At the beginning of 2025 Brompton launched the 12-speed C Line - and the Urban and Explore names seemed to vanish (we guess it would be confusing to have 2-speed Urban, 4-speed Urban, 6-speed Explore and 12-speed Explore)

As at the end of 2025 the Brompton 2-speed and 6-speed models have also been discontinued

So then came the question ...

Can my 4-speed (aka Urban) be upgraded to a 12-speed (Explore) model?

(At the time we originally created this guide there was no 4-speed C Line)- but there is now!

Assuming the answer to the upgrade question 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 (also called explore) which combined a 3-speed Sturmey Archer hub with a Brompton proprietary 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 new 4-speed derailleur system (3 x 4 = 12)

Brompton 12-speed hub

Above is a picture of the new Brompton Ultralight 3 speed hub showing the Brompton logo and the Shimano style driver which can accept 4 sprockets

 What difference will it make to the gearing? 

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 - and see how fast you will be going in each gear at a 70 rpm cadence


Replacement and new parts needed for 12 speed upgrade

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

* Note: The Ultralight wheel is not similar to the BWR 3/6 speed wheel - you can't upgrade your P Line from 4-speed to 12-speed using a BWR wheel

Visit Brompton gear calculator

Brompton gear calculator

 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

We made this YouTube video (see below) showing the 4-speed to 12-speed upgrade process: