Bike porn

I love the amount of thought and engineering that has gone into these. They are highly engineered to be light, stiff and powerfull, and it is interesting to see how that has led to trade-offs in other areas.

Stiffness demands the shortest possible lever arms, so: dual pivots down close to the pads and shorter than normal slots for the pad holders, with the rest of the adjustment achieved by an eccentric fixing bolt. Stiffness also demanded the depth and diameter of the main pivots.

Lightness machines away the material that is contributing least to stiffness, leaving a chunky ridged un-aero structure.

Power comes from the progressive advantage linkage - as more cable is pulled the leverage increases (and pad-motion reduces). This matches well the force profile needed to move the arms in initially against just the spring then also against the compressing pads. I don't know of any other brakes that do this as radically. The dual-pivot and cam mechanisms of other brakes increase the mechanical advantage more uniformly across the range of motion - something that could be done less compactly by just making the cable-arms longer.

But the linkage is also at the root of several niggles: you have to make sure the linkage is ramping up the leverage at the right point in the pad motion. The barrel-adjuster isn't in the right place in the mechanism to set this, so the brakes come with a variety of spacers to put between pads and the lever arms to adapt to different rim widths. That isn't a complete solution - as the pads wear down you'd have to change the spacers to keep the leverage profile the same.

The linkage combines with the dual pivots to create another niggle. The structure of two arms with fixed lower pivots and two upper pivots that are pushed apart is potentially unstable - if the upper pivots are closer than the lower pivots it will tend to flop sideways, one arm moving in and the other out. Springing the arms against each-other rather than the un-moving central parts exacerbates this, but it's putting the cable anchor on the lower pivot that guarentees the linkage would flop if not constrained.

So it is constrained, by a mini link - the little rod that runs from one arm of the main linkage to just in front of the central bridge bolt. This forces the arms to move symmetrically - consistant pad motion they call it.

Consistent pad motion sounds good, and inconsistant motion can be a real problem that frustrates setting up brake pads clear of the rim, but once the pads reach the rim what you really want is symmetrical force. If the rim is a little off-centre from the brakes, the diminutive mini-link will be struggling to make one pad push harder, trying uselessly to centre it. On other brakes it would be the springs that fight to centre an off rim, but springs are happy to loose and bend; the mini-link isn't. The brakes can be set up centred over incorrectly dished wheels, but that takes time and doesn't address poorly trued wheels.

The snap-in pad holders are a real innovation - it would be good to see other manufacturers licence them.

I'm not digging into these because i don't like them, i do. I'm digging just because they fascinate me.

excellent stuff!!!! lengthy, not quite as well written as a tester piece but passionate and commendably obsessive 9/10