Disc brakes conquer the road bike: problem solver or new problem?

It's been 20 years since the attempt was made to transfer mountain bike technology to racing bikes with the "Rock Shox Ruby" suspension fork model. After a short hype, however, the attempt failed miserably. Today the disc brake wants to conquer the racing bike. Problem solver or new problem? We try to analyze the strengths and weaknesses of the braking system, which is undisputed on mountain bikes, for road bikes.

One thing is already clear: disc brakes have a much higher level of acceptance than suspension has ever had in racing bike circles. Many racing bike manufacturers already have models with it in their range, and the number of buyers has long since escaped the exotic status. With a view to the existing strengths, one should not forget that disc brakes are not a panacea and certainly have their weaknesses.

Advantages of disc brakes

1. braking effect

Anyone who is used to a good disc from a mountain bike knows that the pure braking effect is far superior to that of a rim brake. When switching from rim brakes to discs, you don't notice this so much, but if you take a step back, you'll be really shocked by the differences in braking performance. Whether a narrow, non-profiled racing bike tire can then transfer this braking effect to the road is another matter, because the wheel cannot do more than block. Every plus in braking effect is actually superfluous.

2. Wet / weather independence

The greatest advantage of disc brakes is that they deliver almost the same braking performance even in wet or bad weather conditions, while rim brakes suffer massively here. Everyone knows the feeling of hitting the brakes in the rain, and for one or two revolutions of the wheel almost nothing happens until the water on the rim has been displaced and the brakes take effect.

With disc brakes, on the other hand, full power is available immediately. This fact is probably responsible for the fact that, after initial reluctance, the disc brake on cyclocross bikes has prevailed across the board. The cross bike also benefits from the fact that the disc brakes are also less susceptible to dirt during mud races, but this is unimportant for the racing bike.

3. No stress on the rims

Since the disc brake no longer brakes on the rim, there is no longer any need to consider the braking surface of the rim. Rim manufacturers are therefore more independent when it comes to the shape of the rim, which could benefit not only the stability but also the aerodynamics of the rims. Since there is no abrasion of the rim, there is no longer any wear, which increases the service life of the rim. Mountain bike experience has also shown that this can result in weight savings at the rim, and as this sits very far out on a rotating component, this is significant for acceleration.

Disadvantages of disc brakes

1. heat

You can't avoid the feeling that some of the problems from the early days of disc brakes on MTBs are being repeated on racing bikes. It is often the people who brake a lot who believe that disc brakes are a panacea for them. This is exactly where the problem lies: there is one thing that disc brakes don't tolerate very well: HEAT!

Just as with mountain bikes in the past, relatively small brake discs are installed on racing bikes today. Diameters of 140 millimeters at the rear and 160 millimeters at the front are often seen. However, the small discs get hot very quickly during continuous braking. This leads to some problems:

Episode 1: Fading

Fading means that the braking effect decreases during continuous braking due to the heat that occurs, sometimes extremely.

Consequence 2: glazing of the brake pads

If a brake is not run in over a few kilometers but is braked very hot when it is relatively new, the brake pads can glaze over. These will then no longer be able to achieve their optimal braking effect.

Consequence 3: Total brake failure

A total failure of the brake is also possible if the temperature is too extreme.

Consequence 4: Damage to the frame or fork

Carbon is ubiquitous in today's cycling. This applies to racing bikes as well as mountain bikes. Carbon fibers get their strength from resin, which "glues" the fibers and hardens them after lamination. But resin has a melting point. If a disc brake is braked so hot that the temperature rises above this, and heat dissipation is not successful, then delamination, i.e. the resin “softening” with corresponding damage to the carbon component, cannot be ruled out.

Especially this problem of the softening resin at high heat has already led to defective rims with carbon rims (especially with carbon clinchers). The above-mentioned frequent brake users are therefore not automatically better off with a rim brake. However, the rotational speed of a rim (wheel outside) is significantly higher than that of the brake disc (wheel inside), so the rim gets significantly better cooling from the wind. In general, it is better for any type of brake to brake briefly and sharply than to keep the brake applied permanently. Even if you have to brake a lot, you should always release the brakes briefly from time to time.

bigger = better?

You can counteract the temperature problem with larger brake discs, which of course not only affects the look, but also leads to disadvantage number two.

2. stability

Due to the high braking effect that occurs in connection with the one-sided load, higher forces are generated for the components involved. Both the frame and fork, as well as the hubs and quick release skewers have to be significantly more stable and stiff in order to work well with disc brakes.

3. Weight

To compensate for this lack of stability, the frame, fork and wheels are often slightly heavier than rim brake models. In addition, the brake itself is usually a bit heavier than a rim brake.

4. aerodynamics

From an aerodynamic point of view, there is a disadvantage of about eight watts compared to a rim brake. However, since the disc brake is only mounted on one side, the differences will be very different depending on the angle of attack. A cladding or integration would be possible, but would only massively aggravate the heat problems already described due to poorer ventilation.

5. squeaking / grinding

Unfortunately, annoying noises cannot be completely ruled out even today.

Disc brakes are certainly the first choice for bad weather drivers due to their superior wet braking properties. An option for everyone else, but not a must-have.

TIP

(from Bike-Base Schliersee): Especially for triathletes who use a time trial or tria machine as a pure competition bike, disc brakes can be a very interesting option for their training bike that also saves money and space.

A disc cyclocross bike can be transformed into a competitive disc road bike in seconds with a second set of wheels. The frames of disc crossers and disc racing bikes are identical for many manufacturers anyway. Provided you have the right brake disc, you don't have to worry about the right brake pads or adjusting the brakes, just change the wheelset and you can use a bike either as a racing bike or as a cross bike, depending on your mood, weather, season, terrain, etc , and thus has an extremely wide range of training options with just one additional bike (in addition to the competition bike).

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