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Road Bike Brakes | Disc Brakes vs. Rim Brakes

road bike brakes

The triumphal march of the disc brake does not seem to stop in the road bike sector. It sounds logical somewhere, because those who fly down steep alpine passes are happy to reach 90 km/h and more. Here, of course, you want a reliable brake system, which is why the large component manufacturers have already brought numerous road bike discs onto the market. Nevertheless, most road bikes continue to be equipped with the classic rim brake. The low weight simply convinces sporty drivers. In this guide you can read why it is worth looking at disc brakes and what advantages and disadvantages the respective systems bring with them.

Road Bike Disc Brakes vs. Rim Brakes

The road bike brakes can be roughly divided into two categories: disc and rim brakes. As if the diversity would not be large enough, one has to differentiate further. Both disc and rim brakes are available in mechanical (i.e. with brake cable) and hydraulic versions.

Hydraulic rim brake systems are offered by SRAM and Magura, for example. These should offer a little more braking power and be more resistant to the weather thanks to the closed system. However, the spread tends to be low. The classic mechanical rim brake, as offered by traditional manufacturers Campagnolo, SRAM or Shimano, is still the top dog. Due to the slim and filigree optics, they simply fit best on road bikes in the eyes of many riders.

With disc brakes, however, it is exactly the opposite. Here hydraulic systems (e.g. SRAM and Shimano) are more common than the brake cable variants. However, there is quite a disagreement about the optics. Some racing cyclists find the brake discs on the streamlined racing bikes simply too beefy. Not least because it is also associated with increased air resistance.

Other riders, on the other hand, appreciate the look and the extra braking power, which can be crucial, especially at high speeds.

Disc Brakes vs. Rim Brakes Comparison

The subject of rim vs. disc brakes is quite complex and confusing. Here is a direct comparison of the two systems to have the most important advantages and disadvantages at a glance. If you need more detailed information afterwards, you can read each point in more detail in the following sections.

 Disc BrakesRim Brakes
Performance and Control– More braking power
– Constant braking power when wet
– Better braking dosing
– Enough braking power for most situations
– Braking power suffers clearly when wet
Weight and Aerodynamics– approx. 500g heavier than rim brakes
– no special aerodynamic integration possible
– approx. 500g lighter than disc brakes
– Special aero brakes on the aero wheel improve aerodynamics
Wear, maintenance and costs– Braking only wears off the brake disc, therefore lower follow-up costs
– Maintenance only possible with special tools
– Acquisition costs very high
– Braking wears out the safety-relevant rim
– Maintenance very easy and possible with standard tools
– Low purchase costs
Installation– First installation is very time-consuming, since it must then be vented with a special tool– Very easy assembly and possible with standard tools
Safety– Very heavy drivers or continuous braking can overheat the brake disc (brake pad glazed)– Tubes can burst due to extreme heat development (during continuous braking)
– Carbon rims can delaminate in extreme heat
Braking noises– Disks sometimes ring with minimal impact
– Disc brakes like to squeak when wet
– Carbon rims like to squeak in wet conditions and under heavy loads

Road Bike Rim Brakes

If you think of a classic road bike, then you think of a bicycle with rim brakes. Admittedly, the filigree stoppers on the streamlined racers may also make a better impression. But of course there are also some functional advantages that give the rim brake its legitimacy. The so-called side pull brake has prevailed on the road bike. Since the construction only allows very narrow tires, the side pull brake is almost only found on the road bike. You can read about the design-related restrictions and advantages that are decisive in the following sections. The most important advantages at a glance:
  • Rim brakes are about 500g lighter than disc brakes
  • Easy maintenance
  • Easy to integrate aerodynamically and optically
  • large selection of different components
  • cheaper to buy than disc brakes

Performance and Control

Way ahead: Of course, the braking power of rim brakes is completely sufficient in most cases. The stoppers convince even on long alpine passes, even if a disc brake offers a little more comfort and safety. It only becomes critical with rim brakes when it gets wet. Here the braking force drops very strongly, which is why it is worth taking a look at manufacturers like Zipp. These process the braking flanks specifically so that the surface treatment ensures a high braking effect even in damp conditions.

Another problem is that dirt and rain can severely impair the meterability and smooth running of the rim brake. No problem for fair-weather drivers, but you can be surprised by a sudden cloudburst, especially in the mountains. Closed hydraulic systems remedy this and also offer more braking power and better controllability than their brake cable brothers.

A problem that is usually underestimated in rim brakes is the problem of heat generation. On long descents, the braking flanks can heat up so much that the tubes burst inside. This happens above all for rims without rim tape. Not exactly ideal while plunging down a steep descent.

Summary:

  • the braking power of rim brakes is absolutely sufficient in most cases
  • the braking dosing is worse compared to disc brakes
  • Rim brakes (especially carbon rims) lose braking power when wet
  • Tubes can burst due to heat on the brake flanks

Weight and Aerodynamics

The biggest advantage of rim brakes over disc brakes is clearly the weight. You can save a whopping 500g if you don’t rely on disc models. Depending on the bike, this can be around 8% of the total weight. 250g is due to the higher system weight of a disc brake. Approx. 150g add up to the weight of the wheel and approx. 100g to the weight of the frame, since the mount for a disc brake requires more material and some areas are reinforced by the braking force that occurs.

Contrary to the expectations of many cyclists, rim brakes in the wind tunnel cannot win against the disc brake. The air resistance is approximately the same for standard brakes.

Special aero rim brakes, on the other hand, offer a marginal advantage. Here, the brake caliper is integrated into the frame or the fork, so that the air can flow past without interference. It is made possible by an almost flush surface consisting of the frame, fork and brake. This level of integration is unfortunately not possible with panes. So if you want to pursue pure-bred competitive sport, you are better advised with such rim brakes.

Summary:

  • Rim brakes save about 500g in weight compared to disc brakes
  • The air resistance of standard rim brakes and disc brakes is almost the same
  • Special aero rim brakes, on the other hand, offer a slight advantage in terms of aerodynamics

Wear, maintenance and costs

Brake linings on rim brakes wear out faster than with disc brakes, but the costs per pair of linings are significantly lower. Here it is important to choose the right covering for your own rim. There are differences in the hardness of the pads and the pad mix, single compound or triple compound, pads for specially designed brake flanks or carbon rims. Here you should definitely pay attention to the recommendations of the rim manufacturer. Care should also be taken when changing from aluminum to carbon rims: the used pads can be contaminated with aluminum chips, which would damage the carbon rims. Changing the impeller also means changing the pad.

With regard to maintenance, high costs can be incurred by the rider for rim brakes. Of course, this is less due to the fact that brake cables have to be replaced more often, but much more because rims wear out during braking. Due to the friction between the brake pad and the brake flank, material is permanently removed. If the side wall of the rim becomes too weak, the rim or the entire wheel must be replaced. The lighter the rim, the faster the wear limit is usually reached. Carbon rims can also delaminate due to frequent, strong braking. Delamination occurs when the individual carbon layers in the braking flank become detached due to the heat generated. This results in a total failure. Here, too, a new rim or a new wheel has to be bought.

Summary:

  • The cost of brake pads for rim brakes is lower than for disc brakes
  • Aluminum and carbon rims need different pads
  • When changing the wheel from aluminum to carbon, the brake pads should be replaced
  • Braking loads on the rims, which must therefore be replaced regularly
  • Carbon rims can delaminate due to “hot” braking

Installation

As always in the bicycle world, each component has its own standard. Side pull brakes must therefore be attached to special mounts. The brakes are usually attached to the fork / frame using a screw that goes into the center of the brake: this is known as the center bolt mount. A second option for side pull brakes is the direct mount standard. Here the brakes are not attached centrally, but each brake leg is individually attached to the frame or fork. The double support should be stiffer and thus offer better meterability. Both recordings are not compatible with Cantilever / V-Brake brakes.

In principle, no other fastening options can be retrofitted. There are all sorts of adapters and handicraft solutions, but please do not use them on a road bike. The function and safety cannot be guaranteed. You shouldn’t save when talking about brakes & safety.

Summary:

  • Rim brakes are suitable for center bolt and direct mount shots
  • V-brakes / cantilever brakes cannot be mounted on these mounts

Intended use

The mechanical rim brake is by far the most common, and rightly so. The braking power is simply sufficient for every amateur athlete and racer. Repairs are less complicated and compatible parts are in abundance. You simply can’t go wrong here. Rim brakes can therefore also be found on all kinds of road bikes.

Anyone who competes frequently is happy about the weight saved. In addition, proper aero bikes can only be achieved with rim brakes. How great the effect of the reduced air resistance is, however, remains to be seen.

Nevertheless, the rim brake is simply a well-functioning system that will not cause any problems for fair-weather riders.

Road Bike Disc Brakes

The trend in the racing bike sector seems to be moving towards disc brakes. The brakes work basically the same as MTB disc brakes. The brake lever moves a membrane that transmits the force to the pistons through the incompressible braking medium (e.g. DOT or mineral oil). The pistons then extend and press the brake pads against the disc. But why did it take so long until the disc brakes, which have long been established in the MTB sector, were used on road bikes? For this you should look at some advantages and disadvantages. The most important advantages at a glance:
  • Disc brakes offer more braking power than rim brakes
  • The braking dosing with disc brakes is extremely good
  • Braking operations require less power, which increases safety and comfort on long descents
  • Disc brakes usually require little maintenance in the short term and work equally well even in bad weather
  • Rims do not wear out due to the braking process

Performance and Control

The braking performance of a disc brake depends on the disc size used. Mostly, 160mm disc brakes are used at the front and 140mm at the rear. For both disc sizes, there is more braking force compared to a rim brake. Before a disc brake can develop its full power, it must be braked down.

An important issue with disc brakes is so-called glazing. Heavy riders in particular can overheat the small discs on long passes. Solid steel disks with a diameter of 160mm help here. However, cooling fins on the brake pads are more elegant. Due to the enlarged surface, the heat can be better released into the air, which means that the coverings cannot be glazed so quickly. If you combine such brake pads with large brake discs with ventilation, even heavy riders shouldn’t have any problems.

Another advantage of disc brakes is that they can be metered. This is independent of the installation in the frame and external circumstances (e.g. dirty brake cables). This means that you always have the full braking power ready with one finger. This saves a lot of energy, especially on long descents. In addition, they hardly lose braking power when wet. But disc brakes tend to make annoying noises: brakes that are not properly braked like to squeak and brake discs often grind on dirty brake calipers. In addition, disc brakes usually have to be reset when the impeller is replaced.

Summary:

  • Disc brakes generally offer more braking power than rim brakes
  • Consistent braking dosing, regardless of the laying and environmental influences
  • Better braking performance in wet conditions, but tends to squeak when wet and grind when dirty
  • During long descents, heavy drivers run the risk of overheating, steel discs or cooling systems help here
  • After a wheel change, a disc brake usually has to be reset

Weight and Aerodynamics

The racing cyclist’s favorite units are grams and kilograms. The following applies: the less, the better. This is the biggest negative point of disc brakes. The entire system (lever, line and brake caliper) brings about half a kilo of additional ballast compared to rim brakes. Since in combination with disc brakes, thru axles are used, there is also a bit more weight here.

The larger weight is accompanied by a larger surface area of the components. One would therefore assume that the air resistance increases and that one has to consume the decisive extra watts for the wind. However, research in the wind tunnel show that disc and rim brakes have virtually the same air resistance.

Nevertheless, the integration of the disc brake is a big issue. By eliminating the braking flank on the rim, the rim can be made more aerodynamic and lighter, which could reduce the weight difference between rim and disc brakes somewhat in the future. At the same time, however, the disc itself provides more air resistance. This is where the so-called flatmount standard comes into play, which at least brings the brake caliper as close as possible to the frame. Aero road bikes are therefore also possible to a certain extent with disc brakes. It only gets really aerodynamic with special rim brakes.

Summary:

  • Disc brakes add approximately 500g additional weight
  • Aerodynamic properties are similar to rim brakes
  • Disc brakes can also make sense on aero bikes

Wear, maintenance and costs

Despite the higher braking force, the brake pads of disc brakes usually wear out somewhat more slowly than the counterparts of the rim brakes. However, this is more to be understood as a rough rule of thumb, since the results can vary significantly depending on the surface mix, riding style and weather.

Speaking of weather: once properly installed and vented, a disc brake works even in bad weather without grumbling. Further maintenance (e.g. venting) or maintenance are usually not necessary in the short term. Many manufacturers recommend changing the brake fluid regularly, but this is not a must. It is enough to replace the brake fluid if the performance deteriorates. A disc brake therefore has very low follow-up costs, unless a visit to the specialist is necessary. Bleeding both brakes costs around $50 and should definitely be done by a professional – if you mess around here, you risk bad consequences.

This is also one of the major weaknesses of the disc brake: if maintenance is required, it is relatively complicated and can only be done with special tools and oil. The topic of maintenance can also be reversed for a long time: if a wheel with hydraulic disc brakes stands still for a long time, you can almost be sure that you have to bleed the brake before you take off for the first time. On the other hand, you take a bike with a brake cable directly from the wall and drive off.

With regard to carbon rims, disc brakes offer additional advantages. On the one hand, you can switch between different wheels (e.g. from aluminum to carbon) without worrying about the brake pads. It is different with rim brakes. On the other hand, there is no need to replace the rims or wheels due to worn brake flanks, since you no longer have to brake on the expensive rim. As a result, it lasts virtually indefinitely. The same naturally also applies to aluminum rims. In the case of disc brakes, the wear limits of the brake discs must be observed. If these fall below a certain material thickness, it can happen that the discs collapse due to the braking process, which causes nasty falls.

SRAM specifies a minimum thickness of 1.55mm, Shimano recommends 1.5mm. The brake pads should also always have a certain thickness to ensure safety. SRAM speaks of 3mm including the carrier plate, Shimano of 0.5mm excluding the carrier plate.

Some manufacturers (e.g. Magura) include a simple tool with their brakes, with which you can determine whether the limit values are undershot. So you always stay on the safe side.

The acquisition costs of a disc brake usually exceed the costs of a rim brake. A road bike including a disc therefore costs at least $300, sometimes even up to $1000 or more. It also gets quite complicated when a disc brake needs to be repaired. Nothing can be done here without special tools that can be problematic on tour.

Summary:

  • Pads on disc brakes usually wear out slower than with rim brakes
  • Carbon and aluminum rims are not worn out by braking
  • Disc brakes usually require little maintenance and care …
  • … however, if a repair is due, special tools are needed
  • Acquisition costs are significantly higher than for rim brakes

Installation

A special bracket must be available to mount a disc brake. Postmount and flatmount recordings have become established on the road bike, whereby the latter standard wins more and more shares. Flatmount is closer to the frame because the brake caliper simply moves along the frame or fork with the disc size instead of growing away from it. This improves the aerodynamic properties and also fits better with the look of sleek road bikes.

Since aerodynamic reasons often rely on internally routed cables, disc brakes are a bit tricky to assemble. To move it, the closed system has to be opened. A subsequent venting (with special tools) can usually not be prevented.

Once passed through the frame, both post-mount and flat-mount calipers are simply attached using two screws. Please always use a torque wrench here and take the corresponding torques from the instructions. With suitable adapters, 140mm or 160mm discs can be used. It is important that attention is paid to the approval of the frame and fork manufacturer. A too large pane can damage a component while riding, which can lead to serious falls and injuries.

Summary:

  • There are two common standards: Postmount and Flatmount
  • Flatmount improves the aerodynamic and optical properties
  • There are adapters for 160mm discs for both standards. 140mm usually works without adapter.
  • Installation on internally routed cables often requires bleeding the brake
  • The torques and approvals of the manufacturers regarding the size of the disc brakes must be observed

Compatibility

Basically, a road bike frame and the fork must be designed for a disc brake. Retrofitting the appropriate recordings is practically impossible. It is also important that post-mount and flat-mount brakes cannot be interchanged with one another. Although there are adapters with which post-mount brakes can be used on flat-mount recordings, the reverse is not possible.

Even individual components cannot be exchanged between different manufacturers. A Shimano brake lever does not work with a SRAM brake caliper via plug & play, since the connecting pin differ. Internal leverage ratios and various braking liquid (mineral oil at Shimano, Dot at SRAM) also cause incompatibilities. This means that a new brake caliper usually means a completely new system including brake lever and the like.

Summary:

  • The frame and fork must be prepared for the installation of a disc brake
  • Postmount brakes fit on flatmount adapters using an adapter, but the reverse is not possible
  • The selection of compatible disc wheels is currently not as numerous as for rim brakes

Intended use

So who should use disc brakes on road bikes? Some riders will eventually claim that their rim brakes work so well that they don’t need any improvement. And in fact you have to say that the question of disc or rim brakes is more a question of personal taste. You cannot choose a clear winner.

Disc brakes always make sense when driving in wind and weather. The braking performance is consistently high even when it rains, while rim brakes weaken extremely here. In addition, wider tires can be installed because the rim brake sets limits due to the installation space, which are not applicable to disc brakes. That is why gravel bikes and touring bikes are often equipped with disc brakes. The wider tires offer more traction and safety.

The disc stoppers also show their strengths on long descents: not just because they offer a little more braking power, but because each braking process requires less power. This protects the forearms and hands. They are also easier to dose, which means that corners can be braked more precisely. So important seconds can be won here, which makes disc brakes also interesting for competition drivers. But be careful: Before every race you have to check whether disc brakes are approved. Otherwise there is a risk of an unexpected technical disqualification. 

So if you don’t care about every gram and instead enjoy high braking power, good meterability and more comfort, then you are exactly right with a road bike with disc brakes.

Summary:

  • Disc brakes make sense for all-weather drivers
  • Wider tires can be installed
  • You benefit from long descents
  • Curves can be braked more precisely due to the better meterability
  • You should always pay attention to the competition regulations: disc brakes are not allowed in every race