Author: admin

A reasonably common question I get asked about my Brompton frame parts is what standards are they built for (and why)?

All my forks are 100 x 9mm QR, rear triangles are 135mm x 10mm, and disc mounts are IS (International Standard), intended for 160mm rotors.

Some people do ask about through axles, flat mount, and other standards – so why do I stick with these older standards? There’s a bunch of reasons:

• Compatibility: a few hub gears can be made to work with through axles, but everything works with 135x10mm, and it can also work with derailleurs and pretty much anything else. At the front, 100x9mm works with disc hubs, dynamo hubs, and it works nicely with the fork hook. For disc mounts, IS allows a wide choice of brakes.
• Ease of manufacturing: Not a trivial concern when I make several hundred of these every year! Flat plate dropouts and disc mounts are much quicker to manufacture than through axle or different disc mounts.
• Cost: A connected reason (because time is money) but different standards would either need more expensive parts, or would need custom parts made via more expensive processes (CNC machined vs laser cut).
• Being ornery: New standards come and go, sometimes the new standards actually make something better, sometimes they’re just a marketing thing, sometimes they’re a good idea but not for little folding bikes. Bromptons don’t need the stiffness of through axles or the aerodynamics of flat mount brakes.

Brompton’s naming conventions are a bit confusing, and have changed several times, so I thought I’d put together a simple table to show you what upgrades are possible on the different models: