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After giving my bike a good wash and deep cleaning of drivetrain components, I like to clean my disc rotors as well. I typically use a small spray bottle full of 90% isopropyl alcohol and a clean cotton rag.
After cleaning rotors with alcohol, should I need to bed in my brake pads again? Should I do anything special before riding again?
MY personal opinion, based solely off experience and guesstimations is that they do to a degree but not to the extent that a new rotor and pad combination would.
My reasoning is that one of the main components in brake pad bedding in is heat. The heat build up helps to evenly distribute pad material to the rotor surface. One of the reasons many people say you should not come to an abrupt halt while bedding in new pads/rotors is it can make an uneven distribution of material where the pads come to a stop.
The tiny particles that are transferred, spread and disperse more evenly when heated and become harder to remove once cooled which accounts for the poor performance when the disc pad comes in contact with a non level surface resulting in micro vibrations and horrible noises.
While a full bed in procedure is not necessary, the surface of the rotor has taken on a slight change and will require a few passes of the pad to essentially resurface the rotor on a microscopic level. While the rotor feels clean to the touch and looks shiny and new, microscopic sediment is still left behind where the alcohol has carried it and then evaporated. Therefor a decrease in braking power occurs until that sediment has found its new home in the microscopic nooks and crannies of the rotor and or pads.
This however does not require the same about of heat as bedding in an all new rotor does though as the majority of the surface has already been heated, cooled and smoothed down by the general use of the brake, but there has been a microscopic change to the surface.
So while i don't think it is necessary to go through the entire bedding in process, i would just air on the side of caution and use your best judgement for the first couple of miles/stops ridden/performed after cleaning.
