Picture you and your four best friends driving down the highway in a full blizzard with bikes on the back as you try to escape the sour weather in the mountains for some all-time desert riding. If you find yourself local to Ogden, Utah like we are, then dragging your bike through the snow or rain to find blue skies and dry dirt is a common occurrence. But have you ever stopped to think about the effect road grime, tire spray, mud, and dust can have on your brakes? Well, hopefully after reading this article you’ll start too and even pick up a tip or two of how to best take care of your brakes because in this TRP Technical Column, we are going to share some of our braking expertise from years of research and development with our professional athletes on World Cup tracks around the world by covering everything you need to know about cleaning and replacing wear parts on your hydraulic disc brakes.
When a disc brake is used regularly and exposed to mud, dust, or roadway grit, micro particles will naturally collect around the exposed parts of the pistons. If not properly cleaned, an excess of these particles will etch the outside of the pistons, degrade the delicate seals, and allow fluid to leak through thus compromising the hydraulic pressure of the system and giving you a one-way ticket to replacing the entire caliper. Along with this, these particles can congregate within the striations of the rotor and even embed themselves in the pores of the pads which can change the surface friction coefficient and heat characteristics of the system. This can lead to permanent glazing on the rotors as the system fights to burn through the contaminants which results in a decrease in stopping power and an increase in vibrations and noise. Either way, leave your brakes dirty and you will only encounter problems down the trail. Clean your brakes regularly though, and you will see a decrease in these issues along with an increase in the performance of the braking system by creating more pad surface friction and decreasing piston drag which allows for a lighter feel at the lever for more finite modulation and uninterrupted power. The choice between cleaning and not cleaning seems clear then, but how should you go about it?
There are two methods we like to promote: basic cleaning and advanced cleaning. Basic cleaning will simply consist of wiping the rotors down with a clean microfiber rag or paper towel and Isopropyl alcohol to remove any dirt, dust, road grime, or contamination from the surface of the rotors. At the very least, this should be done every time you wash your bike, lube your chain, drive through rain/snowy conditions, disassemble/reassemble your bike after travel, or replace the pads and rotors with new ones. If you consider yourself a go-getter and are not interested in doing “the very least” when it comes to bike maintenance, then you can actually do this after every ride to ensure your rotors are completely clear from debris. This will only increase the surface friction between the pads and rotor so make sure you always have a clean rag and some isopropyl in your toolbox and do not be afraid to wipe those rotors off once in a while, you might be surprised in how much gunk you find.
If you are interested in finding and removing more gunk, then try out the advanced method which consists of a full piston clean with isopropyl alcohol, and lubrication with mineral oil followed up by another clean of the calipers and rotors with isopropyl. As a rule of thumb, this should be done every time you change your pads since you will likely need to push the pistons back into the housing of the caliper which can damage those precious seals if not cleaned properly. This can also be done after severely muddy or dusty rides, after a bike wash, or during a bleed. In fact, on the UCI World Cup Circuit, a piston clean and lubrication is done every day for TRP Sponsored teams to ensure each system is operating smoothly and there is no alteration in the performance. By removing grime and lubricating the pistons, it ensures that all are actuating with equal pressure. With hydraulic brakes, fluid will follow the path of least resistance so if one of your pistons is moving more easily than the others, you will begin to feel a slight unresponsiveness when pulling the lever as that freely moving piston will push the pad to contact with the rotor before the slower moving ones catch up. And on the flip side of things, those freely moving pistons will retract quicker than the slower moving ones leaving the pads to contact the rotor for longer. This is what we refer to as piston drag and it can be quite a pesky problem as it allows more heat to build in that dragging quadrant which not only leads to pads being glazed, but it also a loss in rotational momentum as the system is creating friction to slow the wheel. Therefore, by lubricating the pistons with the same mineral oil that is found inside the brake, you are ensuring that all are able to actuate equally and accurately leaving you with a responsively light feel and no drag. Check out this TRP Tech Talk, which will walk you through how we recommend cleaning and lubricating your pistons.