Brompton SA sprocket set 13T for any 3 spline Sturmey Archer

Brompton / Sturmey Archer rear sprocket set 13T

Brompton / Sturmey Archer rear sprocket set - 13 teeth - for all 3 spline Sturmey Archer Brompton hub rear wheels

As used on standard C Line Utility 3 speed BSR (Brompton Standard Ratio) Sturmey Archer equipped hub gear Brompton folding bikes

This is the 3/32" sprocket - introduced in 2012 (compatible with all 3 spline Sturmey Archer hubs used on Bromptons) - the 1/8" sprocket has now been discontinued (in 2017)

If you currently have the wide 1/8 inch sprocket, you can change to this sprocket set - you will also need to change the chain (recommended anyway when changing sprockets)  - the front chainring can handle both 3/32 inch and 1/8 inch, so you will only need to change that if it is worn

How to remove the existing sprocket

How to install the new sprocket

How do I know if my hub needs a 3 spline sprocket?

The 3 spline / ISO (International Standards Organisation) hub is identified by the three groves onto which the sprocket(s) slide.

3 spline Sturmey Archer hubs include (but we are sure aren't limited to - so we would appreciate suggestions) Brompton/Sturmey Archer BSR (Brompton Standard ratio) hub, Sturmey Archer AW hub, Sturmey Archer SRF-3 hub, Sturmey Archer SRF-5 hub.

Below is a picture of showing the 3 grooves (or indentations running from outside to inside of the driver) for the splines on the sprocket used on a Brompton / Sturmey Archer BSR hub

From this straight on view it is easy to confuse the 3 spline grooves with the 4 grooves used for removing the hub internals cover

The below picture shows one of the ISO spline grooves on the hub driver 

If you have removed your existing sprocket, you see that there are 3 splines on the sprocket and 3 corresponding grooves on the hub driver.

Not sure if this is the right one? Our pictures show both the old, and the new version - both fit - they just require a different chain

The SA-13 sprocket kits consists of:

• Plastic chain guard
• Circlip - to hold the sprocket in place
• Spacer
• 13T sprocket with ISO fitting (3 splines) - silver in colour 3/32" (The sprocket width is the same as the older sprocket - at the bottom it is thicker)

Tools required: To remove the sprocket from the wheel you will need a flat head screwdiver (to prise the circlip apart), some brute force (to remove the existing sprocket) and some hand cleaner (as you are going to get dirty hands unless you wear gloves)

This video from Brompton shows how to remove / re-install the rear sprockets 

Chains for this sprocket set are dependent upon the number of teeth on the front chainring:
44T = 96 link chain - QCHAIN096DR
50T = 98 link chain - QCHAIN098DR
54T = 100 link chain - QCHAIN100DR 

Brompton Q part code: QRSPRSTACK-SA3-13
Brompton part number: 9024179 

Brompton 13T sprocket stack installation sequence

The older steel Sturmey Archer hubs use the supplier no longer supplied with this part, the newer alloy hubs do not

The installation sequence is the same for the 13T and 14T sprockets

1/ Install the plastic chain guard disk

Simply slide onto the hub and push snug to the spokes

2/ Install the 13T sprocket

This simply slides onto the hub driver - lining up the three notches on the sprocket with the three grooves on the hub

The sprocket has a wider part in the centre on one side - this should be facing towards the wheel, it ensures the correct spacing away from the chain guard

3/ Install the circlip

Next up is the circlip - sometimes know as other names such as c-ring

The circlip fits into a groove on the driver, and holds the sprocket stack in place

It's fitted by prising the open part with a screwdriver then manoeuvring onto the driver - it can be the cause of some cursing

When the circlip has been installed, it will have a small gap as shown in the above picture

The tension of the circlip and the fact it is seated in the groove will keep the sprocket set in place

A simple but effective solution

Now you can re-fit the wheel and go for a test ride :-)