What is the difference between hydraulic and mechanical disc brakes?

Both types of disc brake have pistons which push brake pads onto a rotor. The difference is how the force applied on the brake levers is transferred to the brake rotor. Mechanical disc brakes function in a similar way to rim brakes in that they use a steel cable to move the pistons. Hydraulic disc brakes, on the other hand, use a fluid filled system so that when the braking lever is depressed, a plunger pushes fluid into the caliper and the brake pads are pushed onto the rotor to slow or stop the bike.

The following pros and cons of disc brakes apply generally to both types whether they be mechanical or hydraulic:

Pros of disc brakes

Better braking power - Disc brakes generate far more braking power than standard rim brakes. For the rider this means having to apply far less pressure on the brake levers, reducing muscle tiredness, especially on long descents where you are constantly having to check your speed.

Consistent braking - Depressing the lever of a rim brake is not always going to give you the same level of braking equal to the force you have applied, but with disc brakes braking force is much more consistent. This means as a rider you’ll be able to judge more accurately how much force to apply to the brake lever to get the desired amount of braking.

Reliability in wet weather - Compared with a rim brake a disc brake performs much better in wet weather. With a disc brake you don’t get that slight delay in braking which is caused on a rim brake as it first has to displace water from the rim before biting on the surface. Disc brakes by their position on the bike and the fact they are self-contained are generally protected from wet conditions, so wet weather performance is largely unaffected.

A faster ride - It is considered that disc brake bikes can actually provide a faster ride. As riders will have more trust and braking power on discs they can brake fractionally later than if they were using rim brakes. This will mean that they spend more time travelling at the higher speeds as they are spending less time on the brakes.

Reduced wear on wheels - Rim brakes inevitably cause wear on the rim surface, especially when combined with grit and dirt in winter, meaning that wheels will wear out far quicker than those on a disc brake equipped bike. Moving the braking point of contact away from the rim means that there is no heat build up on the rim and this minimises the chance of damage to the inner tube or tyre.

Brakes unaffected even when the wheel is not true -  As anyone who has damaged the rim on a wheel or their wheel is out-of-true will know, this can present problem for rim brakes will have to be slackened off (or the wheel straightened) to prevent them catching on the rim. Disc brakes don’t have this problem and continue to work effectively even if the wheel is slightly out.

Better clearance - Without the use of a brake caliper either side of the wheel rim, this has allowed the use of much wider tyres on road bikes. A wider tyre increases grip and comfort on a ride. Also more clearance also allows ease of fitting of mudguards for winter which typically would often have been much more of a nightmare task with certain types of caliper brakes.