Bicycle disc brakes: mechanical or hydraulic?

Choosing brakes for a bicycle is a decision that directly affects safety, riding comfort, and running costs. Mechanical and hydraulic disc brakes are the two most popular solutions, differing not only in price but primarily in how they operate and their braking characteristics. Each system has its advocates and specific applications where it performs better. Understanding these differences helps in making an informed decision when purchasing a new bike or upgrading an existing one.

How do mechanical disc brakes work?

Mechanical disc brakes use the classic cable system familiar from traditional brakes. When the lever on the handlebar is squeezed, a steel cable running through outer housing from the lever to the brake calliper is physically pulled. The cable moves a mechanism in the calliper that presses the brake pads against the disc mounted to the wheel hub.

Construction and operation

The entire system is mechanical — no fluids, no sealed hoses. The force applied to the lever transfers directly through the cable to the calliper. This means braking power depends directly on lever pressure and the cable mechanism's efficiency.

Callipers in mechanical brakes typically have one moving piston that pushes the pad against the disc. The second pad is stationary, so the disc is "drawn in" between the pads during braking. This is a simpler solution than hydraulic systems, but it has consequences for braking uniformity.

Advantages of mechanical brakes

Simplicity of service — anyone who can tension a derailleur cable can manage mechanical brake adjustment. No specialist tools or knowledge of bleeding hydraulic systems is required. Adjustment involves tightening or loosening barrel adjusters — it takes just a few minutes.

Reliability in the field — a snapped cable is a problem solved in 15 minutes with a spare. A damaged hydraulic hose in the middle of a forest? That's the end of the ride. For bikepacking tourists and those riding in remote locations, this is an invaluable consideration.

Lower price — a complete mechanical brake set costs £40–80. Decent hydraulics start from £100–120, whilst high-end models exceed £300–500. For those on a limited budget, the difference is significant.

Ease of component replacement — cables, outer housing, pads — these are all standard, inexpensive items available at any bike shop. No concerns about fluid compatibility or special tools.

Disadvantages of mechanical brakes

Less braking power — with the same lever force, mechanical brakes generate less pad clamping force than hydraulics. In practice, this means a firmer grip is needed to achieve the same braking intensity.

Poorer modulation — precise braking force dosage is more difficult. The cable system has greater resistance (friction in the housing), so the brake's response to subtle lever movements is less sensitive. This makes smooth, controlled braking on technical sections more challenging.

More frequent adjustment — cables stretch, housing compresses, pads wear. The result? Every few weeks of intensive riding, the cable needs tightening to restore proper lever throw. It's not difficult, but it requires attention.

Uneven pad wear — the single moving piston design causes pads to wear unevenly. One works harder, the other less so. This shortens their lifespan and sometimes requires earlier replacement.

How do hydraulic disc brakes work?

Hydraulic disc brakes use a sealed system filled with special fluid — mineral oil or DOT (depending on manufacturer). When the lever is pressed, a piston in the lever pushes fluid through a sealed hose to the calliper. There, the pressurised fluid moves pistons that press pads against the disc from both sides simultaneously.

Construction and operation

Hydraulic fluid has a crucial property — it's incompressible. This means every millimetre of piston movement in the lever translates immediately and precisely to piston movement in the calliper. There are no energy losses from cable stretching or housing compression. All the force applied to the lever reaches the calliper — without losses.

Hydraulic callipers typically have two or four moving pistons (in high-end systems, even six). All press the pads evenly from both sides of the disc, providing symmetrical, powerful, and controlled braking.

Advantages of hydraulic brakes

Powerful braking force — with the same lever pressure, hydraulics generate significantly greater pad clamping force. In practice, one-finger braking is sufficient even on steep descents. Less effort means less hand fatigue during long routes.

Excellent modulation — the hydraulic system responds instantly and proportionally to every lever movement. Braking force can be dosed very precisely — from gentle speed control to emergency stopping. This is crucial on technical descents where control is everything.

Self-adjustment — as pads wear, fluid automatically fills the increasing space in the system. Practically speaking, lever throw remains constant throughout the pads' service life. No adjustment is needed — only pad replacement requires attention.

Even pad wear — symmetrical clamping from both sides means pads wear evenly. This extends their lifespan and improves braking efficiency throughout the usage cycle.

Reliability in wet conditions — the sealed system isn't susceptible to contamination, water ingress, or component corrosion. A cable in housing can get wet, rust, and lose smoothness — hydraulics perform identically in rain and sunshine.

Disadvantages of hydraulic brakes

Higher price — a complete hydraulic brake set is an investment of at least £100–120, whilst high-end models exceed £400. Additional costs for potential repairs or hose replacement must also be considered.

More difficult servicing — fluid replacement, system bleeding, shortening hoses — these are tasks requiring specialist tools and knowledge. Many prefer to leave this to a mechanic, generating additional costs. Improperly performed bleeding results in a "spongy" lever and poor braking.

Leak problems — a damaged hose, leaky connection, worn piston seal — each of these faults requires mechanic repair. In the field, this often means the end of the ride, as improvised repairs aren't possible.

Sensitivity to air bubbles — air in the hydraulic system means power loss and a "soft" lever. Bubbles can form from leaks, fluid overheating on long descents (mainly with DOT fluids), or errors during servicing.

Key differences in practice

Theoretical considerations are one thing, but how do these differences translate to real riding experiences?

Power and braking control

On flat terrain and moderate gradients, differences aren't dramatic — both systems stop the bike effectively. The challenge appears on steep, long descents. Hydraulic brakes allow speed control with gentle one-finger lever pressure. Mechanical brakes require a firmer grip, leading to faster hand fatigue and less precision.

On technical sections — roots, rocks, sharp corners — the ability to precisely dose braking force is a matter not only of comfort but safety. Hydraulics have the advantage because they respond instantly and proportionally. Mechanical systems with cable resistance respond with minimal delay and less sensitivity.

Maintenance and running costs

Mechanical brakes require regular but simple maintenance. Every 2–4 weeks of intensive riding, the cable needs tightening; every 6–12 months, cables and housing require replacement (cost £6–10); every season, pads need changing (£10–20 per pair). Everything can be done personally with a basic tool set.

Hydraulic brakes require virtually no attention most of the time. Pads are replaced as frequently as with mechanical systems, but no adjustment is needed. Fluid is changed every one to two years (cost £6–12 plus £10–20 labour if done at a workshop). However, when something fails — a leak, damaged hose — repairs cost £30–60.

Reliability in various conditions

Mechanical systems excel in touring conditions where field repair simplicity matters. A spare cable can be carried and replaced virtually anywhere. For bikepacking expeditions, long-distance travel, or riding in areas without workshop access, this is a genuine consideration.

Hydraulics are more reliable day-to-day — no adjustment needed, consistent braking characteristics, weather resistance. But in the event of serious field failure, options are essentially limited. For those riding mainly locally with workshop access, this isn't problematic.

Who should choose mechanical, who hydraulic?

The choice isn't black and white — each system has its optimal applications.

Mechanical brakes suit:

• Recreational cyclists — relaxed rides on paths, in parks, and around town don't require extreme braking power

• Those on a limited budget — a new bike for £400–600 with mechanical brakes is a sensible proposition

• Long-distance tourers — field repair simplicity outweighs comfort considerations

• Those who enjoy tinkering — self-servicing provides satisfaction and savings

• Cyclists riding mainly on flat terrain — where long descents are absent, braking power is less critical

Hydraulic brakes are the choice for:

• Mountain bikers — technical descents, steep drops, and intensive braking are the natural environment for hydraulics

• Gravel cyclists — long descents on loose surfaces require confident, controlled braking

• Those valuing comfort — no adjustment, consistent characteristics, one-finger braking

• Fast riding enthusiasts — modulation on corners, confidence on descents

• Cyclists with workshop access — easy access to professional servicing minimises hydraulic disadvantages

Disc brake maintenance

Regardless of brake type, regular cleaning is fundamental to effective operation.

Why clean brakes?

Discs and pads collect contaminants from every ride. Chain oil sprayed during cycling, brake dust generated during braking, mud from puddles, dust from hardened roads — all settle on friction surfaces. The result? Reduced braking power, unpleasant squealing, and accelerated performance decline.

Dirty brakes also mean faster wear. Sand and dust particles act like sandpaper, abrading pad and disc material. Regular cleaning removes these contaminants and extends component lifespan.

How to clean disc brakes

The cleaning process is identical for mechanical and hydraulic systems — both use the same discs and pads.

Cleaning discs — use a specialist degreaser such as OC1 Brake Cleaner. Spray the disc on both sides, wait a few seconds for the product to dissolve deposits, and wipe with a clean cloth. Brake Cleaner evaporates quickly, leaving no residue, eliminating the risk of secondary surface contamination.

Cleaning pads — if pads are lightly contaminated, they can be cleaned with the same product. Remove them from the calliper, spray the working surface, wait for evaporation, and refit. When pads are heavily oiled or glazed, lightly sanding the surface with fine abrasive paper (240 grit minimum) is a better solution.

Cleaning callipers — callipers also collect dirt, dust, and oil spray. Regularly clean their outer casing and check that pistons move freely. With mechanical systems, lubricate calliper pivot points with light oil; with hydraulics, leave them unlubricated.

Cleaning frequency

After every ride in mud or rain — moisture mixes with dirt and oil, creating a sticky mass that quickly deposits on discs. A quick wipe after such routes prevents problems.

Every 2–4 weeks with regular riding — even in dry conditions, discs collect dust and oil spray. Brief cleaning keeps brakes in peak condition.

When noticing power loss or squealing — this indicates contaminated surfaces. Don't wait — clean immediately.

After accidental oil contamination — if chain lubricant reaches the disc, clean it immediately. Oil drastically reduces braking power and can penetrate pad structure, requiring replacement.

Frequently asked questions about disc brakes

Can mechanical brakes be converted to hydraulic? Technically yes, but it requires replacing the complete system — levers, hoses, and callipers. Discs and mounts remain the same. The cost of such an upgrade is £100–160, which often means purchasing a new bike with hydraulics makes more sense.

How long do brake pads last? This varies considerably. With intensive MTB riding involving heavy braking — 3–6 months. With recreational urban cycling — even 12–18 months. Check pad thickness every few weeks — when less than 1.5 mm of material remains, replace them.

What to do when hydraulic brakes feel "spongy"? This indicates air in the system. The brakes need bleeding — either personally with appropriate tools and fluid, or at a workshop. Bleeding cost at a shop is £10–20 per brake.

Are mechanical brakes sufficient for MTB? For gentle MTB on moderate trails — yes. For aggressive all-mountain, enduro, or downhill riding — probably not. The lack of power and modulation becomes frustrating and potentially dangerous.

How often should hydraulic fluid be replaced? Mineral oil — every 18–24 months. DOT fluid — every 12 months, as it readily absorbs atmospheric moisture. If brakes feel spongy or power seems reduced, replace the fluid sooner.

Summary

Choosing between mechanical and hydraulic disc brakes is a matter of priorities. Mechanical systems offer simplicity, lower costs, and ease of field repairs — a sound choice for recreational cyclists, tourers, and those on limited budgets. Hydraulics provide powerful braking force, excellent modulation, and freedom from adjustment — ideal for mountain bikers, fast riding enthusiasts, and those valuing operational convenience.