Disc brakes or rim brakes? This is the question that every cyclist encounters probably at least once in his life. To answer this question, we will take a closer look at and compare both brakes today.
Which system is best for mountain bikers and road cyclists?
While the question of disc brakes or rim brakes is still hotly debated on for racing bikes, disc brakes have been firmly established on mountain bikes for many years and are indispensable for downhill, Enduro and freeride cycling.
When the mountain bike was designed in the 1980s, the bikes were equipped with rigid forks and cantilever brakes, which used cable pull and later on occasionally hydraulics on the rim for braking. Alongside the increasing spread of suspension forks on mountain bikes and full-suspension bikes, disc brakes largely displaced rim brakes. Both systems were adopted from motocross motorbikes and adapted to the bicycle dimensions. The suspensions allowed better damping, higher traction and thus also much higher speeds off-road. Therefore, the development of disc brakes for mountain bikes was the next logical step in order to be able to optimally control the high speeds and strains.
The advantages of disc brakes on MTBs
On long and steep descents, rim brakes tend to heat up the rims a lot. This can lead to reduced braking performance or even damage the rim, tyres and brake pads. Even in wet conditions, disc brakes are vastly superior to cantilever brakes or V-brakes. Disc brakes for mountain bikes are sometimes equipped with cable pulls for power transmission. High-quality brakes, however, are usually hydraulic systems that use a special brake fluid to transmit power. The following overview shows the positive effects of a brake system with disc brakes on MTBs:
- Mountain bikers need less finger force for the same braking effect. The brake levers are often designed so that they can be operated with one or two fingers at most. This means that the other fingers remain on the handlebars and the bike can be ridden safely.
- The rims are not abraded by the brakes and even a slight imbalance (“eights”) will never cause the brake to wear out on the rim.
- In wet conditions, the pads of the disc brake achieve significantly better brake values due to a higher surface pressure.
On long descents, the rims do not get hot and cannot be damaged. The heat development is concentrated on the brake discs.
- Usually the brake pads on disc brakes last longer. Changing the pads is very easy as well. Brake discs are also very durable.
Thicker tyres are no problem for the disc brake compared to the rim brake.
In addition to the immense advantages for mountain biking, disc brakes also bring with them some small disadvantages:
- They are heavier than rim brakes and also more sensitive (e.g. when transported with wheels removed).
- The entire brake system is technically more complex and requires more know-how, more experience and more time for maintenance and care.
- Brake pads for disc brakes must be run in to develop their full braking power. This requires a little patience, but can be done easily by any mountain biker.
- Hubs and spokes are subject to greater strain with disc brakes than with rim brakes.
Good disc brakes are more expensive than rim brakes.
Different disc brakes: brake discs, brake pads, brake fluid
Even though mountain bikes systems may look very similar at first glance, there are some fundamental differences that are particularly important when converting and modifying the braking system.
Most brake discs are made of stainless steel. Besides differences in design, they also differ in their diameter. This in turn changes the braking power of the entire system. Simply put, this means: larger brake disc equals stronger braking power. However, larger brake discs also weigh more and cannot be combined with any suspension fork on any bike. The general standard constitutes 180 mm discs or 203 mm discs. There are two different types of mounting for the discs on the hubs, known as “IS2000” and “Centerlock”. With the IS2000 system (6-hole), the brake disc is attached to the hub with six M5 Torx screws. Shimano’s Centerlock system, on the other hand, uses a special locking ring with a multi-tooth profile. With the Shimano Centerlock, the brake disc is mounted and dismounted in no time. The 6-hole mount, on the other hand, has the advantage that an M5 Torx screwdriver is often available more quickly than the special tools for centre lock systems.
Depending on the brake system, mountain bikers can choose from a wide variety of brake pads. In principle, there is usually a choice of sintered pads or organic brake pads. The metallic pads (Sinter Brake Pads) are insensitive to heat and very durable. However, they need more time to run in and put more strain on the brake discs. Organic brake pads (resin brake pads) consist of organic fibres and synthetic resin. They are particularly quiet and can be run in very quickly. In wet and sandy conditions, however, they are usually somewhat inferior to sintered pads.
The brake fluid in disc brakes for mountain bikes is either mineral oil or DOT. The guidelines for brake fluids laid down by the Department of Transportation (DOT for short) actually refer to cars and motorbikes, but are equally valid for mountain bikes. Different brake fluids are used for hydraulic disc brakes (e.g. DOT 4, DOT 5.1), which are not always compatible with each other. Other manufacturers, such as Shimano or Magura, rely entirely on mineral oil. These brake systems require very little maintenance and the brakes often do not need to be bled for many years. Brakes with DOT filling, however, are different: since the fluid is hygroscopic (i.e. it “draws” moisture from the air), these brake systems must be serviced at regular intervals.
Disc brakes on a road bike
While disc brakes have long been established on high-quality mountain bikes, disc brakes on road bikes are still far off from being established to the same extent. However, the interest of road cyclists in disc brakes is growing continuously and the range of sophisticated braking systems offered by manufacturers is increasing accordingly.
Light and reliable rim brakes have been standard on road bikes for amateurs and professionals for several decades. Road bike rims are therefore equipped with a special braking surface for the brake pads to press against. Mostly, these surfaces are made of aluminium – but sometimes individual alloys or carbon are used instead. Carbon fibre is known for its high strength and low weight. In wet conditions, however, the braking power of an aluminium braking surface is noticeably more powerful. One disadvantage of the rim brake is the restriction in the choice of tyres, because road bike tyres for rim brakes must not be too wide. Road bikes are made of increasingly stiff materials to ensure ideal power transmission. At the same time, the cyclist’s comfort always lessens. Wider tyres promise better damping and adapted riding comfort – but cannot be fitted with rim brakes.
The advantages for road cyclists using disc brakes are therefore:
- Freer choice of lightweight rims and wider tyres. The braking surface is no longer attached to the rim. This makes the wheels more durable (no wear on the brake flanks and no heat build-up through braking).
- Better riding comfort through wider tyres without creating more rolling resistance.
- By shifting the weight from the brake flanks (which are omitted) to the centre of the wheels (brake discs), the rotating mass shifts towards the centre of the wheel. In terms of total weight, there is only a slight difference depending on the brake. However, the wheels are easier to accelerate with disc brakes and require less effort to steer.
- The braking performance is also very good in wet and dirty conditions.
In addition, there are advantages and disadvantages that also apply in the area of disc brakes for mountain bikes. Easy operation and very good braking performance stand opposite higher purchase costs and greater maintenance effort. When searching for the lightest combination of wheels and braking system, rim brakes are still ahead. However, the weight of setups with disc brakes decreases from year to year. The question of absolute weight will therefore become superfluous in the near future. The trend towards using disc brakes on road bikes is unmistakable and affects amateurs, recreational road cyclists as well as professional cyclists. At the very latest since German sprint specialist Marcel Kittel caused a stir with disc brakes on his road bike at the Tour de France 2017 and at the Dubai Tour 2017, the topic has been the subject of hot debate more than ever before.