Installation Guide

Installing the Front Hub Motor

The Brompton kits operate with a front hub motor that replaces your ordinary non-electric wheel. 

Remove Brompton wheel

  • Start off by removing the original wheel from your fork. Loosen the axle nuts, defaulte the tire, and if you don't have a spare 16" tire you can remove the original tire and inner tube and move these to the hub motor wheel instead. 

  • Remove the nut and washers from the axle and set them aside.
  • Slide the motor wheel into the fork dropouts, with the wire exiting on the left side. Pay attenion to the axle's anti-rotation key on the non-wire side, this protrusion should point downwards in order for the axle to seat properly all the way up to the top of the dropouts. 


  • Slide the torque arm plate over the axle, seeing that the bent tab on the top locks into the hole in the fork. This tab secures the axle against from the torques that are present when the motor is running. The metal plate should be a snug fit over the axle, so don't be concerned if it feels tight to slide into place and you can tap it on if necessary. 
  • On the left side, follow the torque plate with both the the washer and nut, being sure to firmly tighten the axle nut to 15-20 Nm. 
  • On the right side, you will also be sandwitching the wire hoop for the nylon hook between the torque plate and washer, as depicted.
  • Notice that the wire exits facing upwards in this image, that is a consequence of the axle key orientation in the SAW20 motors. With the NSM motors, the wire will exit pointed downwards, which is preferrable from a water ingress perspective.  


  • Here you can see the hardware installed on an NSM motor. 
  • With the motor wheel installed on the bike, you can now inflate the tire and adjust the front brakes. 


Installing Motor Controller

After much experimentation we found that the most ideal location for the motor controller on the Grin Brompton kit was just above the fender on the front wheel. This keeps the wire cable lengths to a very minimum, it leaves the on/off switch easily accessible, and it stays protected and out of the way once foleded.  To facilitate this mounting location, we manufacture a bent aluminum bracket that secures to the front brake mount and provides mounting holes for the controller flanges. 

  • Remove nut from Brompton front brake assembly, but do not remove the bolt. 
  • Slide the controller bracket on the back of the fork and secure it in place with the nut
  • Be sure to hole the bracket level while tightening the nut so that it does not pivot. In most cases, there will be just enough bolt protrusion to fully engage with the threads on the nut., but if more threads are desired then it is possible to remove the cupped washer from under the bracket. 
  • Use the three M5 button cap screws to screw the controller to the mounting plate through the controller flanges, with the cables facing forwards towards the fork. 
  • In the case of the 15A controller which does not have screw flanges, use a pair of cable ties to hold it in place.   

<image of SAW controller being installed required here. 


Setting Up the Handlebars

The handlebars on the Bromtpon Bike don't provide as much real estate for throttles, lights, and other accessories, but they can still fit the essentials OK. 

  • Remove the hand grips from the bar, modern grips will have a screw and come off easily, while older grips can be difficult to remove without the assistance of compressed air or lubrication. 
  • Slide the thumb throttle on the right side of the bar, followed by the 3-prong plastic spacer which prevents the rotating throttle from binding against the grip. 
  • If desired, trim down the length of the grip so to account for the width that the throttle now occupies on the bar. 
  • Orient the throttle such that it is comfortable to press with your thumb and does not interfere with the motion of your brake lever.
  • If you have a V3 Cycle Analyst, then similarly install the 3 position switch on the left bar. 
  • Slide the grips back into position and ensure that the throttle mechanism springs back properly without any binding. 

Installing the Cycle Analyst or LED Console

The Cycle Analyst includes a special stainless steel mounting bracket that holds it secure and centered on the brompton handlebars. 

  • Remove the M7 handlebar bolt from the stem
  • Replace this with the 30mm long M7 bolt included with your kit. This will provide the extra threads to which the Cycle Analyst will attach
  • Tighten the M7 Bolt to at least 15 Nm so that the handlebars are secure again
  • Insert the Cycle Analyst bracket over the protruding threads, and hold the bracket in place with the included M7 Nyloc Nut. 

If you have the LED console instead, then install that by sliding the extrusion pieces apart and fit it over the handlebar on the left side of the stem, so that it clears the shifter. 

(Optional) Installing the PAS or Torque Sensor

The Pedal Assist sensors are optional upgrades to the Grin Brompton kit to provide pedalec operation.  The split disk PAS sensor is straightforwards to instal:

  • Remove the metal retention ring from the magnet disk and separate the two halves
  • Close the disk back together over the exposed spindle of your left crank. Pay attention to the orientation of the disk, one side says "Working Surface" and this side must face inwards, torwards the sensor. 
  • Use cable ties to secure the PAS pickup sensor to the diagonal bracing tube from the bottom bracket, with a ~5mm spacer block to move it closer to the disk
  • Adjust the PAS sensor pickup to be centered on the magnets with 2-3 mm of lateral clearance. 

If instead you are using the torque sensing bottom bracket, then you will need to remove your cranks, remove your bottom bracket, drill a hole in the bottom bracket shell, install the torque sensing bottom bracket, and reattach the cranks. For that process, please refer to the TDCM torque sensor installation guide as there are some particular alignment details.    

Wire and Cable Routing