I thought I should write a bit about Brompton rear pivots, as a few people have asked. Brompton rear pivots are all the same, going back 30+ years. Now I’m going to immediately contradict myself – there are two types 🙂
What I mean is this: The mainframe is the same, it’s got a tube that has two bushings pressed into it, as in the picture above. But there are two ways that the rear triangle can attach to the mainframe:
- Old: This uses a threaded centre tube, with two bolts that thread into it from either side. The bolts are a bit weird, they’re 1/4″ UNF with an 84-degree chamfer – probably what Andrew Ritchie had spare in his shed long ago – but they’re available off-the-shelf without too much trouble (which is why mine are black). It’s a bit fiddly to remove sometimes (see hints here) but not too bad.
- New: Also called Advance, this is the arrangement on P, T and G rear triangles at the moment, but will probably become the new standard on everything. It uses an unthreaded tube, and a special long bolt that threads into the frame on the other side. It’s easier to remove, but I don’t like it for a few reasons* so I’ll be sticking with the “old” system for the moment.
* That special long bolt is custom-made and only available from Brompton. I don’t like the idea of threads in a frame part like that, because if they strip or the bolt snaps in the frame, the frame is a write-off. And it’s more complicated to make, because the two sides of the rear triangle aren’t symmetrical.
So what does this mean for fitting Kinetics rear triangles? It’s still pretty simple – if you have an older Brompton, or a current A or C Line, one of my triangles will be a direct replacement with the same bolts and fittings. If you have a P or T, then you’ll need to buy the older rear pivot kit to fit it. For the moment, rear pivot kits are easily available – if that ever changes, I can easily make them.