Hydraulic Vs. Mechanical disc brakes

  • What is the difference between hydraulic and mechanical disc brakes? Are hydraulics more reliable? Or more powerful? I'm curious since, hydraulics seem to get more attention and seem to be on professional bikes.

    I installed a pair of Shimano entry level hydraulic brakes in my MTB. Both calipers, front and rear, failed before 8 months of moderate use (like less than 1,000 kms). Pistons started to leak oil, pads got contaminated, braking was hard and the squeak deafening. I return to mechanical disc brakes; not so nice, but dependable and maintainable. How good is a brake if you can't trust it?

    Your individual experience with one set of brakes should not be generalized into saying you can't trust hydraulic systems.

    @super he said "entry level". Means cheap, right? Should serve as *valuable* input.

    @Det Shimano are a reputable company. Even their cheap components should be of acceptable quality and last longer than 1000km. Especially for safety-critical systems such as brakes: from a purely mercantile point of view, they can't afford the lawsuits and loss of reputation from thousands of dead cyclists whose brakes failed.

    @DavidRicherby well I get that, but "thousands" is a bit of stretch when there aren't that many cyclist deaths annually in the US as a whole.

    @Det Exactly. So most entry level Shimano brake components must be just fine. It must be that user5369 got a faulty brake, not that there's some systematic problem with Shimano's bottom of the range components. But your initial comment seems to be saying, "Well, he bought entry-level components -- of course they broke."

  • mattnz

    mattnz Correct answer

    8 years ago

    Hydraulics are used on higher end systems, cables are often a sign of a cheap brake set, so your observations are correct regarding "professional" bikes. However there are very good cable disc brakes (e.g. Avid BB7's) that are the exception that proves the rule. .

    Cables have the disadvantage of friction that hydraulics virtually eliminate. It is significantly easier to modulate hydraulic brakes, you get more force delivered to the pads, hence more stopping power for the same input, and faster/more reliable and predictable pad retraction when releasing the brakes. As the Hydraulic system is sealed, grit and grime cannot get in to jam up the moving bits, making them virtually maintenance free (replace worn pads is about all need doing) Hydraulic systems are also easier to set up and adjust (with the right tools - next to impossible without them). Cables have to the exact length, and need "tweaking" as they stretch from new.

    That said - a good quality and well maintained cable system will out perform a poor quality, cheap hydraulic brake set, so you cannot state "Its hydraulic therefore it's better".

    Disadvantages of hydraulics occur when you get a leak such as hole in a hose or blown seal. They are less "field serviceable" than cables, essentially the brake is rendered useless and unrepairable (in the field) by a minor fault - which fortunately happens very rarely, and usually caused by poor transport rather than while out riding.

    Another reported problem with hydraulics is boiling of fluid. This is more of a problem on road bikes where mountain descents of 100's of vertical meters in a very short time are more common. With overheated fluid initially the pressure in the system stops the fluid boiling. When the brake is released (even for a moment), the pressure comes off and fluid boils, and the brakes no longer work - at all - the lever just goes all the way in. Another thing that can happen is the rider stops with no problems, but the heat in the calliper (no longer being cooled by airflow) migrates to the fluid over the next few minutes, so when the rider rides off there are no brakes. (This is different to disc fade where the pads and disc overheat and brakes loss effectiveness slowly - both types suffer this equally.)

    Watch out in the future for Hydraulic shifters.... Available now if you have the big $$$$, lighter weight than XT and XX level components, almost certainly more reliable and easier to setup.... (Update 2015- Electric shifters mean these will not become main stream.)

    I've never even heard of hydraulic shifters! Are they currently available? Grip or thumb shifters?

    @mattnz That website, it hurts my eyes.

    @Kibbee : Sorry for not warning you. I think I am still a "deer in headlights" over the price....

    Re. "faster/more reliable and predictable pad retraction when releasing the brakes": Means for pad retraction (like a spring), are missing in older generations of hydraulic disc brakes (like Magura Julie)

    Grit and grim? I think you meant grime :) (I couldn't edit it myself because there apparently has to be at least 6 characters changed). Also, one potential disadvantage of hydros is that it's in theory possible to boil your brake fluid and render your brakes ineffective until they cool off. Unless you're into extreme mountain biking this is pretty unlikely though.

    Boil your fluid? Wow! Xtreme mtb'ing must involve lots of braking. (Though I live in good mtb country, and the NWCup is held at the Dry Hill Downhills, not to far a drive, I don't get out much.)

    Also, see a very good explanation of the pros/cons of mech vs. hydraulic: http://bicycles.stackexchange.com/a/12961/1502

    Bad braking technique can also overheat brakes, even to the point of boiling fluid. Specifically, being too scared of taking speed and thus pressing the brake cotinously. To avoid that, ( I ) use the brakes intermitently: Braking hard before corners and releasing on the curve exit and straights...

    From what I've read (I have no direct experience with this), hydraulic brakes now are designed so that lever pull remains constant regardless of pad wear. So that would be another pro to hydraulics.

    What's the point of hydraulic shifters when we have electronic shifting like Di2?

    Hydraulic was released about the same time as Di2 came out in Durace only, so at a price point it made sense, as it did for falt bars - MTB and tourers. I would not be surprised to find patant protections motivated some decisions. Rohloff do a Hydralic shifter for tourers, the Di2 Battery live is likely too short for that market. Aside for all that, in business sometime you have to do stuff to differentiate yourself from the big multi nations juggernauts.....

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Content dated before 6/26/2020 9:53 AM