Brake pad tech: rim brakes

We put so many blogs on the fire (see what I did there?) this spring and early summer that the content got depleted, plus it being summer and a few personal things happening and all of a sudden it's a couple of weeks since we've posted. 

Though the industry is all in on disc brakes, it seems that the market is not. Yesterday, we were asked to spec a wheel set for a classic titanium bike that doesn't have room for bigger than 23mm tires. The universe of available rims, and I'm going to understate this, is evaporating. Of course this is all a huge part of the impetus for the Rail rebirth. The Rail 25 suits this guy's needs nearly perfectly, while more people are into the deeper Rail 55. We've always envisioned November as somewhere near the leading edge of bike stuff, but now in a hot second the definition of retro has gotten all spun around. It's crazy.

In my experience, people talk a lot about the braking of different rims and brakes, and they place a lot less emphasis on the pads they use. Whether for rim or disc brakes, the pads are a huge contributor to braking performance. The pads that come with most Shimano brakes are nearly criminal in their performance. They're rock hard blocks designed I guess to never ever wear out or be too harsh on the rims, but good lord trying to stop with them when there's even rain in the forecast is impossible. SRAM, on the other hand, uses SwissStop black compound pads in all of their brakes that I've seen, and they are relatively good pads. 

I am far from a brake pad expert but in my position you have to be aware of these things. My observations are that there are three characteristics brake pads can have - hardness, flakiness, and abrasiveness. Softer pads like BXPs give excellent modulation - as you brake harder, the pad compresses and engages more with the rim, developing more friction. Hard pads like the Shimano OEMs just don't create any friction. I think to some degree flakiness and abrasiveness oppose each other; BXPs flake off and wear away, while Kool Stop Salmon pads are more abrasive. That makes Salmon pads excellent for stopping in wet conditions, but they're not gentle on your rims. BXPs sacrifice themselves and in doing so are a bit gentler on your rims, but on regular alloy rims they're not as "lock 'em up!!" as Salmons. On ceramic (not ceramic) rims that are abrasive, BXPs develop a LOT of friction, which means that you get a lot of braking power, but the pads wear more quickly. If you want to slow down, something's got to give. 

Our favorite pads for alloy rim brakes are Kool Stop dual compound and SwissStop BXP. BXPs are primarily sold for ceramic (not ceramic) rims, though their area of expertise is all alloy rims. For most people in most situations, BXPs are a perfect pad. You'll wear through them on a somewhat accelerated schedule compared to other pads, but the performance is outstanding. For people in wetter environments, the KoolStop dual compounds are it. The softer and less abrasive black part is more like a BXP, and the more abrasive Salmon part means you stop better in the wet. The kicker is that these will wear your rims more quickly than BXPs will.

For carbon rims, you're more limited to what the rim maker lets you use, in terms of warranty, but there is also a broad range of what works. If you're racing crits with carbon rims, cork pads are the absolute money. You don't stop worth crap with them, but they're sublime at adjusting your speed. If you use Rails, you can use cork pads whenever you like in a race. Carbon is really hard, far more than aluminum, and so the pads have to be a bit harder to match that. SwissStop yellows, which were like the OG carbon pad that we all thought were great 12 years ago, are way too soft. The hardness and heat of carbon braking turns them into silly putty and they leave crap all over your rims and they'll probably overheat and destroy the rims to save you the hassle of cleaning that crap off. The good carbon pads for general use these days are fairly hard and fairly flaky.

As with everything, there's some maintenance involved. Don't mix pads between alloy and carbon rims, or else your pads will all of a sudden become very abrasive as alloy bits get embedded in the pads. Keep your pads clean, as dirt and gunk turn any pad into an abrasive pad. After any ride where you've smelled the brake pads, drop the wheels out and hit the pads with some 80 grit sandpaper to knock the glazing off. Glazing is like gristle on the pad surface, and it makes the pad surface rock hard and non-abrasive. If you use cork pads, you have to be vigilant about glazing. And please, be aware of how worn down your pads are - metal pad holders are worse pads than any pads I've ever seen!

That's it for rim brake pads. We'll look at disc pads (and rotors) soon.