New brake pads and rotors need to go through a wearing-in process called “bedding” before they can be used properly. Brake and pad manufacturers publish their own very similar pad bedding protocols and expect you to do this every time you install new pads and rotors.
Unfortunately, many mountain bikers don’t bed-in their brakes properly.
In general, all pad bedding recommendations call for a series of even and controlled brake events. During these, the brake pads are bed-in to the rotor by creating a transfer layer from the pads to the rotor through a process called thermal decomposition. Since brakes convert your kinetic [moving] energy to heat, brakes that are evenly cycled in a controlled manner are expected to apply an even transfer layer to the disc, resulting in the best braking possible for your setup.
Skipping the proper bed-in process can lead to lousy stopping power, damage to the pads and rotor, inconsistent bite or feel of the brakes, and noisy braking.
We did a survey on our Instagram and found that only 50% of respondents follow the manufacturer's bedding procedure every time they install new pads or rotors, with 31% only sometimes, and 19% not even caring enough to know what bedding is or does.
Most surprising of all was that 57% of respondents have bed-in their new pads simply by riding them down the trail! In terms of braking science, this is the antithesis of performance since uneven terrain and variable braking could lead to uneven bedding.
Given the widespread practice of skipping proper pad bedding and opting for trail-based bed-in methods, we decided to delve into the braking data. Our objective was to compare the braking during regular trail riding with braking during a controlled bed-in procedure. The aim was to identify any potential issues that riders who choose the trail method might face, and ultimately to see if there is indeed an easier way.
To get started, we installed BrakeAce PF2 wireless brake sensors on the front and rear brake mounts of a Giant Reign Advanced 29er. Brand new Magura Storm HC rotors in 203mm were installed, and Radic Kaha brakes were mounted with organic pads. Braking data was recorded wirelessly at 1000Hz using the BrakeAce app, and reported at 10Hz.
Tires were relatively new Maxxis 2.5 Assegai/2.4 DHR combo, in 3C compound. The bike also had a crank-based Quarq power meter which was recorded onto a Wahoo ELEMNT.
We followed Radic’s pad bedding procedure which called for us to accelerate up to moderate speed and brake moderately 20 times with each brake, and then to brake harder 10 more times from a higher speed. No skidding or braking to a stop were allowed. We did exactly this, and for the “harder” brake events, we simply used both brakes. (As you’ll see, we lost count a bit and did some extra braking).
We did all testing by riding back and forth across a relatively flat, paved carpark in Rotorua, New Zealand. It was a dreary day with light mist and 16°C temperatures - maybe not ideal bedding conditions, but this certainly created a real-world scenario.
PAD BEDDING STATS
The entire bedding-in ride took 12 minutes, and 3.5km of ground was covered.
All up, 62 brake events were completed during the bedding procedure. These 62 brake events absorbed 80kJ of energy over 1:52.4 of total brake time. The average brake event was 1.8 seconds long with an average power of 712W.
Event-by-event analysis showed us that the first rear-only event had an average brake power of 549W for 1.2 seconds, but increased to over 700W for 1.7 seconds by the 20th rear-only event. The same story was true for the front brake, with events increasing from 449W for 0.4s to 687W for 1.7s later on. In the final events with both brakes, total brake power increased to over 1,000W with a slightly higher bias towards the front brake.
Across the whole ride, Brake Balance was 53% (rear)/47% (front), and estimated max rotor surface temperature was 130°C(rear)/105°C(front). Toasty!
While it may have been possible to achieve a higher brake power in the very first event, the braking bite had what can be described as a “dead” feel, for lack of a better word. The brakes just didn’t feel like they wanted to do much. It may have been possible to simply squeeze harder to get higher power, but we weren’t explicitly heading out to ruin a set of braking bits, so we released the levers and squeezed based on feel.
Of course as the braking continued and the pads started to bed-in, the brakes felt much better and we felt more comfortable getting the power we needed. By about midway through the bedding process, the brakes really started to feel good. You can see the upward trend in brake power across the bedding process. Since the brakes felt better and better, it was encouraging to go faster and faster knowing that slowing down would be no problem. Brake power increased partly due to the higher speeds of the later events, but these later events were also longer, therefore allowing a few final cycles of heat into the brakes.
As you might have guessed, accelerating over and over again on flat ground with heavy trail tires takes quite a bit of work. We analyzed the power meter data in TrainingPeaks, which showed that we had to pedal up to 400-500 watts ahead of every braking event, essentially turning the pad bedding process into an interval session.
It actually turned out to be quite a pain, so it’s easy to see why someone might look for an easier method to get their brakes trail-ready.
TRAIL BRAKING STATS
For comparison, we rode the same bike setup post-bedding on a nearby grade 5 trail called Minerals. Had we done this all wrong, we could have bed-in some new pads on this trail, however we suspect similar results to those below - though in this case the rider didn’t need to pull the lever as hard and the brakes were predictable (plus our teeth and rotors lived to ride another day).
All up, the trail was just over 800m long and took 4:25 with 235m of elevation loss. Total brake time was 1:03.2 across 37 brake events totaling 21kJ. The average event duration was 1.7s with an average power of 332W.
Brake Balance was 78%r/22%f. Interestingly, max estimated rotor temperatures of 90°C and 33°C, respectively, were lower than what we saw during proper bedding. However, peak brake power on the trails was 2100W, which blew the doors off what we did in the parking lot.
A quick glance at the raw data showed that the braking was anything but “even and controlled” when compared to the bedding results and what manufacturers expect you to do. Closer inspection of the Event Types showed that 2 brake events were highly Modulated, 10 were Critical (extremely heavy braking), and one had 6.8 seconds of straight braking!
We’re assuming here that anyone going for the on-trail bed-in method might brake similarly, but there is huge variation across riders or trails. Steeper trails or less experienced riders may tend to use the rear brake more (yes, more than 78%!), while advanced riders may end up braking less overall but more intensely in certain sections. And of course each trail has its own unique braking demands, which varies according to conditions.
Based on what we know about proper pad bedding, the data revealed that we might run into some issues if we decide to bed in our pads on the trail. Some potential issues are:
Lack of bite in the first few events, potentially leading to loss of control of the bike
Higher bias towards the rear brake, which could result in the front brake not getting hot enough or bedding in properly at all (we've seen as high as 99% rear brake!)
Higher brake modulation, which could lead to an uneven transfer layer
Trail sections with overly long braking events compared to controlled bedding
Trail sections with overly heavy braking compared with controlled bedding
As you can guess, some of these things could lead to problems with your brakes later on, such as extreme noise on a poorly bedding front brake or inconsistent bite on the rear brake from over-modulation. Of course safety is a serious concern too.
While being able to skip out a mini sprint/bed-in session and save some pre-ride time are pretty big draw cards, the potential impacts on future braking performance should be enough to follow proper procedures - especially if we only replace pads a few times per year.
Do we need a solution? Well, given that a surprising majority of riders may not be getting the most out of their brakes, it would make sense to have a simplified process to bed in our new pads or rotors every time.
From what we've seen, the best and most likely to succeed brake bedding solution is to follow the procedures that your manufacturer recommends. We were really happy with the way the brakes felt and performed after following the proper bed-in procedure, and we think you would be happy too. Just make sure to set aside an extra 12 minutes to get your pad bedding done before you hit the trails.
It's worth noting that during our poll, we asked riders if they had any pad bedding processes they swore by. A number of riders claimed to have had good results using water on the pads, but since this wasn't recommended, we didn't try it. This and other bedding hacks leave us plenty of options for future testing, and we're always interested to hear what others are doing.
All this being said, we were curious to see how it felt bedding in some new pads down a long, straight road descent. Aside from getting to the top of the hill, there was not much additional pedaling needed to speed back up between braking. We’ll leave this as a ‘DON’T TRY THIS AT HOME’, but this is what it looked like with the brake power overlaid on the GoPro: