Seems like even well built and properly tensioned 36” wheels can rub on Magura rim brake pads under acceleration or idling, especially with the narrower hub used in the Kris Holm and Schlumpf hub 36ers.
I’ve been experimenting with building the ideal Magura brake combination for the 36” unicycle wheel to avoid unwanted brake pad contact with the rim and increase brake control.
I even went as far as precisely measuring the distances that the different Magura brake levers (HS22, HS24 and HS33) will drive the brake pads (see attached word file after all the photos) and I came up with a sweet hybrid set-up that combines the HS22 lever body’s huge 16mm piston and the shorter adjustable HS33 lever blade with the red TPA knob on it. This lever blade is pretty short so it will not stick out too much from a T-7 handlebar and this lever blade will accept a KH spooner.
Really the only semi-custom part here is the lever: I started with a lightly used HS22 lever body then I stripped of its original finish and had professionally powder coated satin black. I reassembled the lever with a slightly modified new pre-2005 HS33 lever blade, filling the extra pivot pin width with ground and polished stainless steel washers (see picture). This lever combination will drive the brake pads a whopping 14.3mm (both sides added together) compared to the anemic 10mm travel that the smaller HS33 lever provides.
I tried this on a 20 mile urban ride on my KH36 this weekend and there was no brake pad rubbing at all and that nifty red TPA knob let me dial in exactly where the brake pads would rest when not being used. This lever worked great! I’m also taking my KH36 with this brake on a century ride with some big hills this weekend with three other Unicycle Bastards on 36ers, so we’ll be using brakes a lot. I’ll report back after the ride.
NOTE ON THE PICTURES: FOR COMPARISON, THE BLUE LEVER IS THE ONE I MODIFIED FOR MY KH36, THE RED LEVER IS A STOCK HS22 AND LEVER BLADE AND THE DAY-GLO LEVER IS A STOCK PRE-2005 HS33 LEVER AND LEVER BLADE
I know that Naturequack in Ashland removed his Echo cylinders and Echo lever because they had even less travel than the HS33 for his Schlumpf 36. He installed the prototype version of the brake I posted about because he needed the huge pad travel distance. (I know he also trimmed the pads and two of the wheel cylinder metal “horns” to clear the rim better . . . yes, his Schlumpf wheel/frame seem to flex a lot, but I think he has now eliminated unwanted brake pad contact and . . . he said he’s actually riding faster.)
I don’t have an Echo brake set here to actually measure how much pad travel they provide, but based on what I’ve seen, I wouldn’t think its going to give more pad travel than a stock HS33 Magura. Echo does claim that thier cylinders are shorter than Magura, but how much, I really don’t know.
So, how much rubbing do stock HS33’s give on a standard KH36 w/ Nimbus?
And, forgive my ignorance (I’m new to hyd brakes), but how precisely does this mod fix that issue? Does it somehow let the pads seat back farther against the stops/slave cylinders?
EDIT: Okay, re-read. So you’re saying standard HS33’s can’t have their pads set all the way down on the stops and still be driven all the way to grab the rim, so you’re increasing the fluid reservoir, thereby allowing more travel, facilitating a wider neutral position for the pads?
On another note, the lever I have on my KH36 is a TWP (regular maggie slave cylinders); the lever is really light weight, but I’m not sure if its reservoir and/or plunger size/travel is significantly different than on my other 4 unis. I have an old HS33 in my parts box that looks, size-wise, more like the 22 (I only know it’s a 33 from the TPC on the lever). What I can say about the TWP is that it seems to provide enough travel to grab the rim when needed, and I haven’t had a bit of brake rub on hills as of yet. So I’m pretty happy with it.