Hydraulic Vs Mechanical Disc Brakes

by wheretheroadforks

At this point, disc brakes have pretty much replaced rim brakes across all categories of cycling. In the early 2000s, they became standard in mountain biking. The last holdouts were road riders. Since the UCI began allowing disc brakes in professional road racing in 2018, they have become even more common. When it comes to disc brakes, you have two systems to choose from. This guide outlines the pros and cons of hydraulic vs mechanical disc brakes.

hydraulic disc brake on a bike

What are Disc Brakes and How are they Different From Rim Brakes?

All bike brakes work by pressing brake pads against a surface on the wheel to create friction and slow the bike down. The main difference between disc and rim brakes is where the friction is created. In short, rim brakes apply braking force directly to the flat sides of the rim. Disc brakes apply braking force to rotors, which attach to the hubs.

Both hydraulic and mechanical disc brake rotors bolt to the bike’s hubs and spin with the wheels. The brake pads mount in the brake calipers, which mount to the fork and seat or chainstays, near the axles. The rotor spins between the pads as you cycle. The calipers house a mechanism which pushes the brake pads against the rotors with a piston when you squeeze the brake levers. The friction between the pads and rotors cause the bike to slow down.

Rim brakes stop the bike by applying braking force directly to the sides of the bike’s rims with brake pads. The brake pads attach the brake calipers, which mount to the top of the fork and the seat stays. The calipers have arms that reach around the bike’s tires. The pads mount to the ends of the arms with the wheel spinning between them. The brake arms pivot so the pads squeeze the rims when you squeeze the brake levers. This creates friction to slow the bike down.

rim brakes
Rim brakes on a racing bike

For more info check out my disc brake vs rim brake guide.

What’s The Difference Between Hydraulic and Mechanical Disc Brakes?

The main difference between hydraulic and mechanical disc brakes is how force is transmitted from the brake levers on the handlebars to the brake calipers near the hubs. Mechanical disc brakes use a steel cable. Hydraulic disc brakes use a fluid-filled brake line.

When you squeeze a hydraulic disc brake lever, a plunger pushes brake fluid from the master cylinder, which is in the lever body, into the brake line. The brake line is sealed and already full of fluid. This creates pressure in the line. This pressure pushes a piston in the brake calipers, which pushes the brake pads against the rotors. This is possible because fluids don’t compress. This is the same technology that you would find on a car or motorcycle with disc brakes.

hydraulic disc brakes
Avid Elixir 5 hydraulic disc brakes

Mechanical disc brakes, on the other hand, actuate with a steel cable, just like rim brakes. When you pull the brake lever, it pulls a cable that runs all the way to the brake caliper. The cable moves a lever on the caliper that pushes a piston. The piston pushes the brake pads against the rotor to create friction that stops the bike.

Mechanical disc brakes
Mechanical disc brakes. Notice the brake cable attached to caliper.

Hydraulic Disc Brakes: Pros and Cons

Pros

  • More stopping power/ More efficient
  • Less frequent maintenance and adjustment because the brakes self adjust.
  • The system is sealed which keeps contaminants out. This means less cleaning is required.
  • Smoother operation because there is less friction in the system.
  • Better brake modulation/control of the braking force
  • Lighter
  • More consistent
  • Easier on the hands because they require less force to operate
  • You can ride faster because you can stop faster
  • More technologically advanced/ Higher end

Cons

  • More expensive
  • Harder to service in the field because they are more complex. Specialty tools and fluid are required.
  • Spare parts are hard to find in remote regions and some developing countries
  • More difficult to maintain because you have to bleed the brake lines occasionally.

Mechanical Disc Brakes: Pros and Cons

Pros

  • Cheaper
  • Easier to repair and maintain because they are simpler
  • Replacement parts are easier to find around the world because they use the same cables and levers as rim brakes
  • You can easily service them in the field with basic tools

Cons

  • Less stopping power/ Less efficient
  • They require more frequent adjustments as cables stretch
  • Harder to modulate braking force
  • Friction in the brake lines can make them feel less smooth to operate and less consistent
  • You have to clean them more often because the brake lines can get contaminated with dirt or debris
  • Heavier
  • Slower
  • Harder on the hands because it takes more force to apply the brakes
  • The pads are more likely to rub when they are out of adjustment
  • They are considered lower end and are less technologically advanced.
full suspension mountain bike with disc brakes

Hydraulic Vs Mechanical Disc Brakes

While both brake systems stop the bike quickly and safely if properly set up and maintained, they do have their strengths and weaknesses. In this section, we’ll compare hydraulic vs mechanical disc brakes.

Stopping Power

Hydraulic disc brakes produce more stopping power than mechanical disc brakes. The reason is that they are more efficient. Hydraulics multiply the initial force that you put into the system when you squeeze the brake lever. In other words, the hydraulic brake system creates more braking force than the force you applied to the brake lever.

The brake fluid also doesn’t compress and produces little friction while moving through the line so very little energy is lost in the system. The result is a very powerful brake system that takes little effort to operate. For more technical info, check out this guide about how hydraulics work.

Mechanical disc brakes are less efficient because less force makes it from the brake lever to the caliper. The reason is that some energy is lost in the system. When you pull the lever, some of the force that you apply is used to overcome the friction created by the cable running through the housing. Some energy is lost when the cable stretches or compresses. For these reasons, the brake pads can’t push against the rotors as hard to create as much friction. You can’t create quite as much stopping power so your stopping distance will be a bit longer.

Brake Maintenance

Hydraulic disc brakes require far less maintenance than mechanical. Once they’re set up, they just work. The main reason is that there is also no cable that stretches and needs to be adjusted. The only regular maintenance you’ll need to do is to replace the brake pads as they wear out.

Another reason hydraulic disc brakes need less maintenance is because the system is completely sealed. This means the brake lines can’t get contaminated with sand, dust, mud, dirt, and other debris. Hydraulic brake lines are pressurized and are air and water tight. There is also nothing to rust or corrode. For this reason, are ideal for off-road riding and mountain biking.

Hydraulic disc brakes are also self-adjusting. The pads align themselves in relation to the rotors and adjust as the pads wear down. There is no cable that stretches and needs to be adjusted or re-tensioned. There are no barrel adjusters to mess around with. For this reason, the pads are far less likely to rub on the rotor.

You will have to bleed hydraulic disc brakes periodically. Bleeding brakes means replacing the brake fluid. The average rider will have to bleed the brakes about once every 2-3 years. Some riders go as much as 5 years between bleeds. A racer may have to replace the fluid annually to keep the brakes operating at peak performance.

How often you need to bleed the brakes depends on the type of fluid that your brakes use (DOT brake fluid or mineral oil) and how much you ride. You will also need to bleed the brakes if they were opened up or leaked for some reason. If this happens, air bubbles can get in the system and reduce the braking force.

There is a bit of a learning curve when it comes to bleeding brakes. This job also requires some specialty tools. For example, you’ll need a bleed kit with syringes and adapters, a bleed block to hold the pistons in position, various tools like Allen wrenches and pliers and a screwdriver, as well as gloves and paper towels to keep everything clean. You’ll also have to take the time to learn how to do the job properly. Of course, you can also pay to have your hydraulic disc brakes bled at your local bike shop.

To get an idea of what the process involves, check out this step-by-step guide to bleeding hydraulic disc brakes from BikeRadar.

bike with disc brakes
A bamboo mountain bike with disc brakes

Mechanical disc brakes require more frequent maintenance than hydraulics. As the pads wear and cables stretch, the brakes go out of adjustment. They are pretty touchy. To keep them working properly, you’ll have to make minor adjustments every couple of thousand miles. Adjusting mechanical disc brakes gets a bit tedious. If they aren’t perfect, a pad rub, which is annoying and inefficient.

The cable housing can also get contaminated with debris. Sand, dirt, and dust can work their way into the cable housing. This is common when mountain biking or riding off road. The debris in the housing increases friction on the cable, reducing braking efficiency. You can’t pull the lever as hard because some of your force is going toward overcoming the friction. The debris can also cause the cable to snag and not run smoothly.

When you release the brake lever, the brakes may not disengage instantly if there is debris stuck next to the cable. If the housing gets wet, the cable can also rust. This adds more friction and prevents the cable from running smoothly. If your cables get rusty, you’ll want to replace them.

One positive is that the maintenance required to keep mechanical disc brakes running is pretty simple. You can easily adjust and replace the cables with basic tools like a couple of Allen wrenches.

Modulation and Precision of Braking Force

Hydraulic disc brakes give you more control over the braking force. This is possible because the brakes take so little effort to apply. You can gently squeeze the lever and apply exactly the exact amount of braking force that you need for the situation. The brakes are so sensitive that you can control them with your little finger. This allows you to stop faster without locking up the wheels. When you let go of the lever, the braking stops almost instantly.

Because mechanical disc brakes require you to use more force to pull the brake lever, it’s harder to control the braking force. You can’t move your hand as accurately when you’re squeezing hard. If you’re not careful, you can lock up the wheels. You can also shed more speed than you wanted, which is inefficient.

Weight

Hydraulic disc brakes weigh less than mechanical disc brakes. The calipers are lighter because they have fewer moving parts. If you’re the kind of rider who weighs every component before installing it, you’ll probably prefer hydraulic disc brakes. Having said this, the difference in weight is very minimal and won’t matter to most riders. The difference is probably less than half a pound.

Smoothness of Operation and Braking Consistency

Hydraulic disc brakes offer smoother and more consistent operation. When you squeeze the brake lever, it always feels smooth because there is nothing in the system that can snag or get hung up. The brake fluid moving through the line creates very little friction. Because the system is sealed, it can not get contaminated with debris. This makes the braking force incredibly consistent and predictable. Every time you pull the brake lever, you get the same result.

Mechanical disc brakes, on the other hand, create friction when the cables run through the housing. They can also snag and rub. Particularly if the cable begins to rust or the housing gets contaminated with dirt or debris. This creates resistance which can make the brakes feel a bit less smooth. You may have to apply more force than expected to overcome this resistance. This makes the brakes a bit less consistent.

Having said this, a clean and well adjusted mechanical disc brake operates very smoothly and consistently. It takes a bit more effort to keep them performing at their best.

Parts Availability

Spare mechanical disc brake parts are much easier to come by than hydraulic disc brake parts. The reason is that mechanical disc brakes use the same cables and levers as rim brakes. These are the most common parts that need to be replaced. Levers and cables are available in pretty much every bike shop in the world. You can find parts in remote regions and the developing world. Parts availability is the reason that most bicycle tourists prefer mechanical disc brakes over hydraulic. Even high end touring bikes still use mechanical disc brakes.

Hydraulic disc brake parts are a bit harder to come by. If you ride in the developing world or remote regions, finding replacement levers, calipers, brake lines, brake fluid, or the required tools to maintain them will be difficult or impossible. If you need to make a repair while traveling from Cairo to Cape Town, you might have to order parts online and wait for shipping or travel to the nearest capital city to find a high-end bike shop.

Some countries don’t even import hydraulic disc brake parts. In that case, you might have to fly home to buy what you need. Of course, hydraulic disc brakes run for many miles without issues. If you’re touring in the developed world, the only spare you would need is brake pads.

Touring bike with mechanical disc brakes
A fully loaded touring bike with disc brakes

If you’re touring somewhere very remote, you might want to avoid disc brakes all together and use rim brakes instead. Disc brake rotors, pads, and calipers are not widely available in some parts of the world. This is the reason that most expedition touring bikes still use rim brakes.

Serving and Repairing the Brakes in the Field

Mechanical disc brakes are easier to service in the field. You can maintain and repair them with basic tools and just a few spare parts. All you need is new cables and a few Allen wrenches that probably come with your multi-tool.

If one of your brake cables gets damaged or starts to fray, you can easily replace it and get back to riding. Even if you’re a hundred miles from civilization. If you encounter an unknown problem, you can completely disassemble a mechanical disc brake caliper to diagnose it and attempt to make a repair if you have the know-how.

Hydraulic disc brakes, on the other hand, require some specialty tools and knowledge to repair and maintain. This makes them harder to service in the field if something goes wrong. For example, if an accident severs a brake line or a blown seal causes all of your brake fluid to spill out, your hydraulic disc brakes become useless. You can’t repair them with a basic tool kit. It wouldn’t be practical to carry all of the necessary tools and brake fluid to make major repairs while you’re out riding.

If your hydraulic brakes fail catastrophically while you’re out riding, you’ll just have to call it a day and go home to make the necessary repairs. This is one reason that many bicycle tourists and bikepackers avoid hydraulic disc brakes.

Disc Brake Fade and Failure

Brake fade is a reduction of stopping power. Both mechanical and hydraulic disc brakes experience brake fade if too much heat builds up in the system. This is common on long steep descents.

The friction between the brake pads and rotors causes heat to build up. When the pads overheat, friction is reduced and you lose braking power. This can happen with both hydraulic and mechanical disc brakes.

Brake fade is more common on road bikes because they generally have smaller rotors which don’t shed heat as quickly. Road riders also tend to ride faster. High speeds also require more braking force to slow down. Bicycle tourists carrying a heavy load may also experience brake fade. After all, it takes a lot of braking force to slow down a 300 pound fully loaded touring bike.

If you feel your brakes beginning to fade, the best solution is to stop to let them cool off. After the brakes cool off, the stopping power is restored and they’ll work perfectly again. This is true of both hydraulic and mechanical brakes. Also, don’t touch the rotors as they get hot enough to easily burn your hand.

If you experience brake fade regularly, one solution is to install larger rotors. These shed heat more quickly. You can use them longer before brake fade begins.

Excessive heat can cause hydraulic disc brakes to completely stop working if the brake fluid overheats. When the fluid gets hot enough, it begins to boil. This boiling is caused by heat buildup from the friction created by the brake pads rubbing on the rotors.

While you’re actively braking, the pressure in the hydraulic brake system prevents the fluid from boiling. The reason is that a liquid’s boiling point is higher when it is under more pressure. When you release the brake lever and reduce the pressure on the fluid, it instantly begins to boil. At this point, the brakes stop working.

You’ll know when your brake fluid is boiling because the brake lever will move all the way in and provide no stopping force when you squeeze it. If this happens when you’re in the middle of a descent, you could be in trouble.

This problem can also occur after you’ve stopped. The caliper and rotor stay hot because there is no air flowing over them. This heat radiates to the brake fluid and causes it to boil, resulting in no brakes. If you stop mid descent, you should check your brakes before proceeding to make sure they’re working.

The best way to avoid boiling brake fluid is to install larger rotors that can shed heat more quickly. During particularly long descents, you should stop periodically to let your rotors, calipers, and brake fluid cool off. Some hydraulic disc brake calipers have fins to help them cool. These work just like the fins on an air cooled engine

Speed

Hydraulic disc brakes allow you to ride faster. This is possible because they allow you to stop faster. You can wait longer to begin braking before going into a turn. For example, instead of starting braking 40 feet before a turn, maybe you can start braking 30 feet ahead. This allows you to maintain a higher average speed. This is important for competitive riding.

With mechanical disc brakes, you have to start braking a bit sooner because the brakes can’t stop you quite as fast. This slightly reduces your average speed. For most riders, the difference in speed is insignificant.

Hand Comfort

Hydraulic disc brakes are easier on the hands because they take very little force to apply and modulate. They are so sensitive that you can brake with one finger. This allows you to tackle a multi mile long descent down a steep mountain pass without your hand getting tired. It’s also great for certain types of mountain biking where you have to brake hard and frequently. Your hand won’t cramp up or go numb from braking.

Hydraulic disc brake lever
A hydraulic disc brake lever

Mechanical disc brakes are harder on the hands because take much more force to use. The reason is that the system doesn’t provide as much mechanical advantage. You really have to squeeze the levers with all of your fingers to apply the brakes hard. During a long and steep descent, this can get quite tiring. When your hands get fatigued, you can’t modulate your braking as well.

Pricing

Mechanical disc brakes are cheaper. Low-end sets start around $35. This includes rotors, calipers, cables, levers, and everything you need to install them. Mid-high end mechanical disc brake sets run around $150. This is about half the cost of comparable hydraulic disc brakes.

Maintaining mechanical disc brakes also costs less. Cables cost just a few dollars. With a little bit of know-how and a few basic tools, you can perform all of the necessary maintenance and make repairs by yourself. No need to visit an expensive bike shop.

Hydraulic disc brakes are a bit more expensive. Lower end models start around $100 for a set of front and rear calipers, levers, and hoses. Mid-high end hydraulic disc brakes cost $300-$400 for a set. They are usually sold pre-bled and ready to install and use.

Maintenance on hydraulic disc brakes is also more expensive. When it’s time to bleed the brakes and replace the fluid, you’ll need some tools. You’ll also need brake fluid. These will cost you $40-$50. If you want to pay a shop to bleed your brakes, it will cost $60-$100 for parts and labor. Of course, you’ll only need to bleed the brakes every year or two and once you have the tools, the cost is much lower if you do the job yourself.

Replacing brake pads costs the same on both types of brakes. The pads are exactly the same. Both systems also use the same brake rotors.

Disc Brake Technology and Quality

Hydraulic disc brakes are considered higher-end and more technologically advanced. These days, all mid-range and high-end mountain bikes use them. Since the UCI started allowing disc brakes in the pro peloton in 2018, many teams have made the switch. Because of this more and more manufacturers are releasing road compatible hydraulic disc brakes. Hydraulic brakes have been the standard in competitive mountain biking for years already.

Because they are used in racing, much more research and development goes into designing hydraulic disc brakes. The technology is more advanced. If you’re the type of rider who races or simply likes to use the newest and highest end gear, hydraulic disc brakes are a great choice.

Mechanical disc brakes, on the other hand, are often considered lower end. These days, many low-end bikes and department store bikes use them instead of rim brakes. Manufacturers do this to make the bike look more premium than it really is. Low-end mechanical disc brakes don’t work any better than rim brakes.

Of course, not all mechanical disc brakes are bad. There are some high models that provide almost as much stopping power as hydraulics if they’re properly set up and adjusted.

Electric bike with disc brakes
Disc brakes on an E-bike

A Few Similarities Between Hydraulic and Mechanical Disc Brakes

Both hydraulic and mechanical disc brakes use the same pads and rotors. These are the two most common parts that need replacement.

The pads are a wearable part that needs to be replaced periodically. Friction from rubbing against the rotor wears them out. How long they last depends on the material that the pad is made of, the weather, how hard you brake, and the terrain. Resin pads, also called organic pads, often last 500-800 miles. Sintered brake pads often last 1000-1300 miles. When there is about 1 mm of brake surface left on the pads, it’s time to replace them.

The disc brake rotors are one of the easier parts to damage on a bike. If the rotor hits a rock or gets knocked hard during transport, it can bend. Heating and cooling can cause a rotor to warp over time. Once a rotor is bent or warped, even if it is bent slightly, the pads will rub. You can attempt to bend the rotor back or just replace it. The fact that both hydraulic and mechanical rim brakes use the same pads and rotors makes it pretty easy to find replacements.

Another similarity with both hydraulic and mechanical disc brakes is in the way they function. Usually, one brake pad is fixed in place and the other moves to push the rotor against the fixed pad. This system is common on lower-end and mid-range mechanical and hydraulic disc brake systems because it is simpler. There are fewer moving parts.

Some higher-end disc brake systems use a dual-piston system which moves both pads toward the rotor at the same time. This system is more complex but may perform slightly better.

A Couple of Common Problems with Hydraulic Disc Brakes

Hydraulic disc brakes can leak. If a seal fails, brake fluid can begin to leak out of the line and onto your brake pads and rotors. When the pads get covered in fluid, they no longer work and need to be replaced. The fluid damages the brake pad surface. If you get brake fluid on your rotors, you’ll need to carefully clean them, making sure you get all of the fluid off before reinstalling them. If you missed a spot, you could ruin your new brake pads.

Another problem is that the pads can get stuck together and the pistons can stick out too far. This problem occurs if you accidentally squeeze the brake lever when the wheel is off the bike. The reason this happens is that the rotor isn’t there to act as a spacer to hold the pads apart and prevent the pistons from coming too far out of the caliper.

hydraulic disc brake levers
Don’t squeeze your hydraulic disc brake levers when your wheel is removed.

The easiest way to correct this issue is to pry the pads apart with a blunt object like a flat head screwdriver. When you do this, make sure the tool you use is clean. Also, be careful not to scratch the pads. If you introduce debris or knick a pad, you can damage the rotor when you brake.

If the pistons came out too far when you squeezed the brake lever, you’ll have to remove the pads and push them back in. There will be some resistance from the hydraulic fluid in the system. A wrench can usually do the job. Be very careful when doing this so you don’t damage the seals and create a leak. Try to push the pistons straight back in. After the pistons are in place, you can replace the pads and your brakes should work as good as new.

A Note About Disc Brake Rotor Sizes

Rotors are available in a range of sizes from 120mm-205mm. All else being equal, larger rotors allow you to slow down faster than smaller rotors. Larger rotors also shed heat better than smaller rotors so brake fade or boiling brake fluid is less likely.

Generally, road bikes use smaller rotors than mountain bikes. On most bikes, the front and rear rotor sizes are the same. Some riders us a larger front rotor because the front brake provides the majority of your stopping power.

The most common rotor sizes are 140 mm and 160 mm. For most riders, 160 mm rotors on both the front and the rear works well for road and mountain biking. Lighter riders can get away with 140 mm rotors. Heavier riders may feel safer with a 180 mm rotor on the front for additional stopping power. The only benefit of a smaller rotors is that they weigh a bit less.

Rear disc brake rotor

For cyclists that need extra strong stopping power, like bicycle tourists carrying a heavy load or gravity riders, larger rotors may be a good idea. In these cases, 180-200mm rotors might be the best choice.

A Note About Tires and Stopping Power

The brakes aren’t the only factor that determines how fast you can stop. Your tires also play a major role. Most modern bike brakes, including rim brakes, have more than enough braking power to lock up the wheels. When the wheels lock up and your tires skid, it doesn’t matter what kind of brakes you’re running.

Generally, narrow tires have less grip than wide tires because less of the skinnier tire makes contact with the road. They create less friction with the ground when you apply the brakes. For this reason, they can’t stop as fast. Wider tires have a larger contact patch with the road so they can create more friction and stop faster.

A wide tired bike with disc brakes
A fat bike with disc brakes

Of course, there are trade-offs. Wider tires create more friction with the ground while you’re riding. They are also heavier and create more drag. This makes them less efficient. This means you’ll burn more energy and cover less distance when using a wider tire.

Another consideration is the condition of the tire’s tread. Regardless of what kind of tire you’re using, it won’t be able to get as much traction and stop you as fast when the tread wears down. Keep an eye on the condition of your tires and replace them when the tread starts to get worn down.

Final Thoughts about Hydraulic Vs Mechanical Disc Brakes

This choice really comes down to your budget and where you ride. For those who ride in a region where parts are readily available, hydraulic disc brakes are the better option all around. Even though they cost a bit more, the increase in braking performance and brake feel is worth it for most riders. The smoothness and consistency are nice as well.

For those who plan ride in remote areas where finding spare parts may be a challenge, or those on a lower budget, mechanical disc brake may be the better option. Modern mechanical disc brakes provide excellent stopping power.

With the recent acceptance of disc brakes in the professional road racing, I expect the technology to continue improving. Pro road cycling has a major influence on the cycling industry as a whole. More research and development will go into building the best hydraulic disc brakes. More companies will begin manufacturing their own models. Mechanical disc and rim brakes will always have their place but hydraulic disc brakes seem to be the future.

Where do you stand on the hydraulic vs mechanical disc brake debate? Share your experience in the comments below!

For more info on bike brakes, check out my disc brake vs rim brake pros and cons list.

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