Some may remember participating in my quest for a 29" rim for my Schlumpf hub. I finally got a 25mm wide touring rim, a Rigida Sputnik, as recommended by a tandem/touring specialist shop here in Paris. According to them, it’s not the lightest ever, but it’s among the strongest. And it comes in 36 holes (harder to find as the whole MTB worlds is into 32H now). And it has a brake pad strip, another elements which is getting rare. And icing on the cake: it has the same ERD as my original KH wheel so the spokes I already had would work.
So I thought that it would do well as a Schlumpf’ed-wheel.
But… as the rim is much narrower than the KH, I would run into a brake problem. I got a pair of Magura brake extenders. Sold for people wanting to put a fat rim on their bikes, those allow to keep the Maguras with such setup. And I thought it could work the other way round: bring the pads closer to the narrower rim.
But no luck, the pads could still not reach the rim!
For a while I rode with a ghetto solution: the pad holders bolted with only the bottom screw and installed sideways. It worked but it was vibrating a lot - thank god I don’t use the brakes intensively.
So I thought about making my own extender. A friend having access to all sorts of machining tools offered to help.
So I sent him this drawing - appreciate my amazing precision tools:
He had told me he had 10mm thick aluminium bars, so I drew it to match what he had. He sent me photos of the operation:
I asked him to make a thread on the pad side to simplify their installation:
The idea is for the adapter to rest on the side of the Magura mounts, to avoid them folding (even temporarily) under the force coming from the pads during braking.
I decided to keep the “bridge” between the top and bottom mount to make the adapter stiffer, and also it wouldn’t move when the brakes are installed/adjusted.
If I was to make another pair of adapters, I would add 2mm (1/12 of an inch) to the offset between the mounts and the new position. I wanted to stay close to the original mounts to avoid bending, but an extra 2mm wouldn’t be a problem, especially if the shoulder was thicker. But it would mean machining from a thicker block which my friend didn’t have easy (and free) access to.
Still, I’m pleased with the result and braking no longer produces vibrations. The adapters are super stiff as they are a perfect fit to the original mounts. I’m not using the brakes agressively so I think they’re the best solution I could find to keep the Magura system.
When I grow up, I’ll probably get a recent hub as they are happy with a crank disc - though I don’t like the idea of a disc brake in high gear, internal brake on the hub would be the best. Having said that, I think Magura brakes are perfectly fine for a Schlumpf setup.
Nice homemade adapter! Really too bad the offset mounts were insufficient…
When I read your temporary solution, it made me wonder if you could have got away with staying like this and use a booster arch to link the 2 unattached parts together like they were selling for MTB/Trial back in the days
Had never seen those! Now they make sense.
The project evolved a lot since, and even if I’m not riding the Schlumpf much, I still worked on giving it better brakes, thanks to @lobbybopster :
