Over the past few months, we’ve been vigorously riding a Whyte 29 C test bike for review in our latest issue of Enduro Magazine. Whilst the lightweight carbon 29er hardtail is incredibly quick and has impressed us with its sure-footed stability, throughout the testing period it hasn’t quite been all apples and roses. The 29 C is the base model of the 3-tier lineup, and as such features the basic Elixir 3 hydraulic disc brakes that sit near the lower end of the Avid range. Despite their no-frills appearance however, these are actually a great performing brake when setup properly, with heaps of power and a level of modulation that avoids the ‘bitey’ sensation that some other brakes can be guilty of.
Although we have plenty of experience with the Elixir range, on our Whyte test bike the brakes began to develop quite a bit of audible vibration from both wheels after the first few rides. Despite the squeaky noises going on, the brakes still performed well enough, but there was also an ever-so-slight pulsing sensation through the levers that was pretty dam annoying. The issue we experienced with the brakes on the Whyte was almost exactly the same that we had with the Formula R1 brakes we tested in the previous issue. Although we had some idea of what was going on, we decided to speak to a handful of different bike shop mechanics and riders to hear their thoughts on the issue and whether they had experienced anything similar on their own bikes. On top of that, we got in touch with both SRAM and Formula to hear their thoughts on brake noise, what causes it and how best to fix it.
It has to be said firstly that there are quite a few factors that can cause a noisy disc brake, and that one persons ‘sure-fire fix’ will not necessarily address the issue that your brakes are experiencing. Here are some examples of what might be going on:
Contamination: Commonly caused by a wayward squirt of chain lube or an accidental grab of the rotor with greasy hands, contamination of your brakes will result in noise of varying levels and deterioration of overall braking power. In most cases, once the pads and rotors are contaminated, you’ll likely have to throw them into the bin and start afresh. A clear indication of contamination is if your front and rear brakes are providing different levels of stopping force (i.e. the one with less force is contaminated). However, it is possible for both to be contaminated at the one time.
Glazed Pads: Caused by excessive heat from sustained downhill braking, glazing involves your brake pads heating up to a point where the surface becomes shiny and smooth. This smoothness can cause a high-pitch whining noise, a lack of overall power and can also affect the rotor surface too, which will show discolouration like the pads. This is symptomatic of a setup that is under-gunned for your weight and/or riding style.
Poor Bed-In: If your new brakes are not correctly ‘bedded-in’ from the start, they can cause noise, poor power and a ‘shuddering’ sensation at the levers. Bedding-in brakes involves applying a consistent layer of pad material to the rotor surface. It is the interaction between this layer and the brake pads themselves that provides you with the friction that slows you down.
Improper Application: Having experienced our fair share of bike shop time during previous lives, we have found this issue is a particularly common complaint amongst riders who are using their MTB for commuting or for lighter duties on bike paths and rail trails. Disc brakes are designed to operate in some pretty full-on conditions, and their principle design is to work on friction. Sometimes that friction results in noise and there’s not a lot you can do about it. However, the lighter you are, and/or the more ‘gentile’ your riding is, the less you will be working your disc brakes to their full potential and the more chance there is for noise to occur.
After some discussion with Dylan Coulson at SRAM’s technical service centre, DSD, it appeared that our brakes were experiencing the 3rd issue, caused by improper bed-in. The vibration and shuddering we were experiencing was due to an inconsistent braking surface on the rotor, caused by dragging of the brakes during their first few outings. These microscopic ‘ripples’ along the brake rotor are magnified during hard braking, resulting in a bloody awful noise and vibration at the levers.
The steps that we will take you through today are part of a process that essentially ‘resets’ the rotor and pad surface so that you can begin bedding-in the pads as if the brakes were new again. What needs to be said here is that depending on how badly the brakes have been bedded-in in the first place, you may actually have to replace both the rotors and pads, which is what both Avid and Formula recommend. We would also recommend this if you’re guilty of a short temper or are not renowned for amazing mechanical abilities amongst your mates. Of course, if your brakes are contaminated, this process has limited effectiveness depending on how bad the contamination is. Unless you are 100% sure on the issue you’re experiencing, this may be the point where your local qualified bicycle mechanic will be better equipped to fix the issue and get you back out on the trails. We shouldn’t need to note how important brakes are whilst riding off road, but if you’re not sure – hand your steed over to the experts!
In order to carry out this procedure, you’ll need some bicycle/automotive disc brake cleaner, some clean lint-free rags, gloves, Wet ‘n’ Dry sandpaper, and the necessary Torx/Hex keys to remove your rotors and pads. A clean work surface is essential, along with ventilation.
Step 1. Remove the Disc Rotors from the wheels.
Step 2. Remove the brake pads.
Step 3. Clean both brake rotors by blasting with disc brake cleaner
Step 4. Using a small wooden block, wrap around the sandpaper so that you have a flat surface to work with.
Step 5. Begin rubbing the brake track of the rotor with the sandpaper, making a circular pattern and applying a medium-firm pressure. You should be able to see a visible change in the surface (below). After sanding, give the rotor surface a blast with disc brake cleaner to ensure all contaminants are removed.
Note the difference in the rotor surface on the left (after) and the right (before).
Step 6. Now to clean the pads. Blast the brake pads with disc brake cleaner, then rub the pad surface along a clean rag to remove any contaminants off the surface.
Step 7. Using a clean piece of sandpaper, rub each pad in a circular motion in order to remove any microscopic patterns on the surface. After this step, give each pad another blast with disc brake cleaner, wipe along a clean rag and allow to dry.
Step 8. Mount the rotors back onto the hubs and fit the pads back into the brake callipers. Ensure all hardware and mounting bolts are torqued and tight.
Step 9. Bedding In.
Depending on the brake manufacturer, this process can vary from brand to brand. If you speak to mechanics, there will likely be a range of techniques to accomplish this task properly, but the fundamental thing to remember is that you want to apply an even and smooth layer of brake pad material to the rotor surface. Here is a fairly standard step-by-step procedure that you can carry out with your freshly reset brake rotors/pads. This process is also the same if you have brand new brakes.
- Find yourself a long stretch of road, and better yet a nice long downhill road.
- Ride up to a moderate speed of around 20km/h
- Apply both brakes firmly till you are at a walking pace, but DO NOT COME TO A STOP
- Continue riding up to speed and repeat steps (2) and (3) approximately 20 times
- Continue riding, but this time at a quicker pace of around 30km/h
- Apply both brakes firmly till you are at a walking pace, but DO NOT COME TO A STOP
- Continue riding up to speed and repeat steps (5) and (6) approximately 10 times
This procedure should allow for the brakes to heat up sufficiently to ensure that pad material is evenly displaced onto the rotor surface. During the process, you should feel a notable increase in braking power by the end. In addition to the above, here are some further tips:
- Do not overcook the brakes in the bed-in process (by going too fast), otherwise you’ll simply glaze the pads.
- Do not ‘drag’ the brakes or be overly gentle about it, as that is another way to develop an overly smooth pad surface that will create noise.
- Avoid trying to bed-in brakes on your very first ride off-road.
- If the noise or vibration begins to return during the bed-in process, then unfortunately your brake rotors & pads will likely need replacing, though you can attempt the entire rotor/pad reset process again if you have the patience.
For the most part, we’ve found the above process to be very effective. You should note that if you bed-in brakes properly from day one, you should have quiet, smooth and strong braking with minimal issues. Reseting the pad/rotor surface should only be necessary if you haven’t managed the bed-in process correctly.
For the full details on the process that SRAM recommends, check it out here: Avid Brake Bed-in Theory-3.
And for Formula brakes, head on to their website here.