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. 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 to 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. 


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  • Dave on

    Tim – I’ve only experienced blue and red Campy pads. Blue are really similar to BXP, and red are a carbon specific pad that’s probably a bit hard for alloy (but that I’ve heard work great with ceramic/not ceramic rims).

    Scott – BXPs are good pads and kind on rims.

    Matt – With carbon rims, the big rule is stick with the recommended pads. We supply blue pads with current Rails, and Campagnolo red pads have also been tested well with them so you can use those. On the open road, I wouldn’t use cork because really they’re terrible at stopping but at adjusting speed they’re killer.

    Cat – The variability of rim wear is endless – weather, hills, rider weight, braking style, what pads you use, how clean you keep your bike, etc. That’s why predicted rim life is somewhere between under 5000 miles (Seattle riders were the first to embrace discs because it’s a perfect storm for rim brake wheels) and infinity.

    Weiwen – We supply a blue compound pad with Rails, but if and when people are able to race crits if they want to use cork, sure. Just take them out before you go anywhere that might require an actual stop.

    Ted – The rotors should be fine, they are 2 piece which I way prefer, and other than that they are a hunk of steel. There’s some in the rotor discussion, but not much. The pads that come with your brakes are resin pads, while (spoiler alert) I generally prefer sintered though I may be weird for doing so. I’d say use them and wear the pads out and see how you like them.

  • Ted on

    Thanks for the tips. I know the disc pad entry is coming soon, but I have a new bike build going on, with November wheels, and was hoping you could throw me some advice. Are the pads and rotors for the Shimano GRX 812 groupset any good, or should I replace them from the get-go? If I should replace, can you let me know what you like for a gravel bike?

  • Weiwen on

    Very interesting info about rim brake pads. I’m not sure I necessarily would have agreed on Shimano’s stock brake pads, at least for 105 and higher brakes, but I now realize that I’ve been on PEO rims with BXP pads for the last year, and I didn’t ride in the rain the year before. So, I wouldn’t necessarily know how they do in the wet.

    What you say about BXP pads being good on alloy rims in general matches what Boyd Cycling told me – I was asking because the PEO coating on my rear rim got scraped off by grit. That was annoying.

    I just realized that it’s not clear what stock pads you’re supplying. It sounds like you’re saying you can use cork pads with your rims, you just won’t stop very fast (same with cork pads on any carbon rim). So, I’d assume you’re not sending cork pads out with your Rails. Am I off-base?

  • Cat on

    Am I very gentle on brakes or just recklessly speedy? I’ve run two rims on my main bike over the course of 20 years- the OG CXP30s (which are still in great shape) and the current set. Neither rim has any visible wear to the braking surface which still looks almost new and I’ve maybe gone through to or three sets of koolstop pads.

    That same bike also has super limited clearance- it just (really not) fits 28mm and I’m wanting to rebuild it’s ancestor which is from 1988 and is probably one of those frames- the rims on that were OEM and sucked to begin with.

    Meh…. I guess I’ve reached that age where change starts to seem arbitrary and annoying.

  • Matt on

    I might have missed it, but did you say what pad you think is good for use on carbon rims when you are not using cork pads for criteriums?

    I never knew Shimano pads are so bad. Maybe that is why I don’t think I have ever replaced a OEM Shimano pads and I do ride a decent amount (although majority flatlander)?

    Thanks!



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