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Road bikes: all you need to know on disc brakes

It is appropriate to visually differentiatedisc brakes from pad brakes. Pad brakes put pressure directly on the wheels in order to slow down their rotation. Special pads must be used depending on the tyre’s material. The main technological constraint of pad brakes is in the wheels’ construction, often in aluminium or carbon material and of the proximity of the braking strip with the tyre. It is extremely difficult to produce an optimal braking surface while keeping the yield and the comfort property we need from the wheel.   …

It is appropriate to visually differentiatedisc brakes from pad brakes. Pad brakes put pressure directly on the wheels in order to slow down their rotation. Special pads must be used depending on the tyre’s material. The main technological constraint of pad brakes is in the wheels’ construction, often in aluminium or carbon material and of the proximity of the braking strip with the tyre. It is extremely difficult to produce an optimal braking surface while keeping the yield and the comfort property we need from the wheel.
 


 

The disc brake system is based on a disc (which is generally in steel), which is fixed to the wheel’s hub. There exist several technologies to activate the brakes by friction of the disc brake pads and the disc, which causes braking. While there exist several mechanical systems and even hydro-mechanic ones, it is the hydraulic one that is today the more common one on road tyres with disc brakes.
 
 
Disc brake advantages:
 
 


 

Braking power:

Using a steel disc as braking surface exercises a much higher braking power than standard braking pads. This is even truer for hydraulic disc systems. This way, the necessary effort on the lever is lower, allowing the cycling to be more relaxed. Braking distance is also reduced, which can be advantageous in turns’ entrances in order to perform. Power is clearly very much appreciated for security and serenity because the the cyclist is never sheltered from unpleasant surprises which demand great reactivity. Braking distance is 40% shorter with disc brakes. This indeed asks for good quality and large enough tyres to provide enough grip during braking: a minimum section of 25 mm, but 28 mm is highly recommended.
 
More homogeneous braking:
Disc braking is not only more powerful, but also more progressive. Touch on lever is more constant, the materials and surfaces which are in contact are of much higher quality than normal braking pads. This generates a high usage comfort and a higher serenity for the cyclist.
This is already the case when climate conditions are good, but when it rains or the road is wet the difference is very important. No more need to hope for the water to drain off the wheels to obtain adequate braking, disc braking is effective and has no surprises.
 
Better quality wheels:
Specific disc brake wheels have quickly appeared in wheel brands’ catalogues. Freed from the constraints of braking, of the employed materials, the produced heat in particular, disc brake wheels don’t necessitate braking strips and can be optimized to better satisfy their other functions. Weight, rigidity, aerodynamics and even comfort were improved.
 
No more wheel wear:
Indeed, under the effect of repeated braking, aluminium wheels are eroded little by little. For regular cyclists, braking quality is lowered after a few seasons. On disc brake wheels, the wear occurs on a consumable part: the disc.
 
No need to change pads when changing wheel material:
With disc braking, we can forget changing braking pads when we go from a carbon wheel to an aluminium one or vice versa.
 
 
Drawbacks :
 
 
Weight:
The extra weight generated by a disc brake group is around 300 to 400 grams, although braking systems are getting lighter and better. We also need to add generally heavier bike frame and fork as well as often larger tyres: we often recommend 28 mm. Furthermore, wheels are slightly heavier due to heavier hubs and more spokes. The overall weight difference is in the end around 500 and 600 grams. However this excess weight must be revised since for an equal tyre, the peripheral part (which has the highest impact on the bike’s inertia) is lighter on disc brake wheels.
 
Aerodynamic performance:
 


 

We all know how important aerodynamics are for performance. DT Swiss carried out tests between a disc wheel and the same one in the standard braking pads version. At a 45 km/h speed the disc bike consumes 4w extra. We must note that up to 25 km/h or 30 km/h the difference is lower. We must put these numbers into perspective as even if there is a loss on the wheels it is now possible to optimise bike frames and forks. Cannondale announced that the disc braking system allowed to obtain better aerodynamics on the new System Six thanks to the optimization that was made possible by the absence of standard braking pads structure: bike frame and fork shape were improved. Aerodynamics is in fact multifactorial, the loss on the discs can certainly be caught up with elsewhere with a well-studied conception.
 
Maintenance:
The ease of maintenance is nearly equivalent between disc and standard pads. Changing disc brake pads is comparable to replacing standard brake pads. Brake bleeding is slightly more complex than replacing a cable for inexperienced cyclists. However this operation is quite easy to perform. Otherwise, you’ll be able to find several mechanics who are able to do that, once a year or every two years according to frequency of usage, cyclist’s weight and difference in height.
Disc brakes have a several assets. For any non-professional cyclist, disc braking is with no doubt the right choice. It provides a much higher security level and usage comfort than standard braking pads with no big difference on the yield. For a professional cyclist purely seeking performance, the choice is questionable depending on the used material and the terrain profile. It is today difficult to affirm which system is faster than the other one.
 
Disc pads overheating and freezing (if inadequate material):
Manufacturers and users were quickly confronted to this issue. Transferring the disc technology from mountain bike to road is not very easy as the constraints are very different. During a descent from a col on road, cyclists will perform very long braking, which will increase disc, hydraulic oil and pads’ temperature. In extreme cases, disc brake pads can freeze and the hydraulic braking system can lose its efficacy.
Today, we can say that the main fabricants such as Sram or Shimano provide serious solutions and that risks are very low if we use the recommended material for our practice and build.
Shimano extends its Ice Tech technology, which is already applied to disc brake pads, to discs in order to improve heat evacuation. Using this type of technology allows for realising important temperature gains.
Sram has a different approach by using DOT 5.1 brake liquid, which can withstand higher temperatures than mineral oil. Furthermore pad supports are equipped with small heat-blocking parts in order to protect the oil. Finally, Sram recommends using larger diameter discs than Shimano: 160 mm as opposed to 140 mm.
 


 

Other interesting solutions appears as in this Mérida Scultura Disc, whose base is equipped with a cooling fin on the brake support, reducing temperature by roughly 35%.
 
 
Trends :
 


 

Bike fabricants have highly enlarged the offer over the last two years. On the cyclosportive and racing bike segment there is at least as much choice of disc brake than standard ones. Specialized even considers completely switching to braking pads on its road bikes. A model like the Roubaix, an endurance cyclosportive bike is already solely available in the disc braking version. Clearly, disc brake bike sales are increasing considerably and it’s a safe bet that it is only the beginning.
For wheels and groups the offer is now substantial, as there is no longer just one brake for a bike of this type. Big brands like Mavic, DT Swiss or Campagnolo have a well-developed product range.
The same can be said for the groups (see paragraph on the available groups at the end of this article). Shimano, Sram, Campagnolo offer the large majority of their braking groups in standard and disc versions.
 
 
Several standards:
 
Braking Systems:
The mechanical system activates the calliper pistons with a standard brake cable. Conventional levers are thus employed. It is the most economical system.
The hydraulic system activates the calliper pistons by means of a hydraulic hose filled with Dot or mineral oil (depending on the brakes). It is the best-performing system. Shimano, Campagnolo, Magura, Hope and others function with mineral oil whereas Sram functions with Dot 5.1.
 


 

Finally, the mecano-hydraulic system activates the calliper with a brake cable. This system is interesting in that it allows to keep standard levers while improving braking power.
 
Disc fixing:
 


 

On road as on mountain bikes we’ll find: 6 holes and Center-Lock. Center-Lock is the most common standard on road bikes as it is very simple and easy to convert to 6 holes if needed.
There alto exists the AFS: Axial Fixing System of Fulcrum, which is very close and also compatible with Center-lock discs.
 
Calliper fixation:
Two types of fixation are available for a disc brake calliper for road bikes: the postmount and the flatmount.
The Postmount: the calliper has a small leg which can be tightened with two screws in the frame (back brake) or fork (front brake).
 


 

The Flatmount: the threads are located in the calliper. For the back brake, the screws pass through the frame and are then screwed in the calliper. Mounting a front Flatmount calliper on the fork is done with an adaptor Postmount. There is no Flatmount fork as their conception would make them too fragile.
 
Discs:
 


 

Shimano and Sram propose 140 and 160 mm diameters for road. It is customary to use a 160 mm front disc and a 140 mm back disc.
However, Sram recommends using a 160 mm back disc for better heat evacuation. For Sram, the 140 mm disc is compatible with light builds and cyclo-cross.
On Shimano’s side, a large R&D effort was made in order to improve the dissipation of heat produced by braking; Shimano’s discs evacuate heat thanks to the Ice Tech Freeza technology: aluminium fins (which better dissipate heat than steel) from the braking surface to the center of the hub. From this results a 50% temperature reduction during braking as well as an over 20% higher durability of the pads. For this reason, Shimano recommends its 140 mm discs at the back and even at the front for light builds;
 
Disc brake pads:
As for mountain bikes, you can choose between different linings: organic, semi-metallic, metallic.
Organic lining, also called resin: the disc brake pads have a high braking power even when cold from the first brake once the brakes have been run. They are particularly silent and well-performing. They wear out quicker than the others and are also a little less resistant to overheating.
Metallic lining: the pads are very durable. They make more noise with humid weather. They are less well-performing than organic pads.
Campagnolo and Sram even advise against them for road bikes.
Semi-metallic lining: it is a mix of the two types of linings, organic and metallic. Some disc brake pad brands offer this type of lining which can combine several advantages depending on their composition. The pad support is sometimes neglected, however it plays a very important role in heat evacuation. Often in steel, more effective aluminium ones are available on the market. Shimano developed the Ice-Tech technology: an aluminium fin on top of the pad in order to evacuate the produced heat.
The Shimano Ice-Tech pads with aluminium lining are an excellent choice for several users, combining maximum braking effectiveness to good heat evacuation.
 
 
Available groups:
 
The offer is now large and allows all types of cyclists to find what they are looking for.
Shimano offers disc options from the Tiagra group to the Dura-Ace group, by way of intermediate range groups 105 and Ultegra. The Ultegra and the Dura Ace levers have the Free Stroke technology which has already proved its worth on mountain bike levers, allowing to adjust the pads attachment. Shimano is 100% concentrating on this technology.
 


 

In terms of hydraulic disc brakes with cable transmission, the choice is between the following groups: the Dura Ace R9100, the Ultegra R8000 and Ultegra 6800, the 105 R7000 and 105 5800 as well as the Tiagra 4700 which is the entry-level model for road disc brakes.
The disc option is also available with the Di2 transmission on the Dura Ace R9170, Ultegra R8070 and Ultegra 6870 groups.
 


 

For triathletes and time trial bikes, we must turn to Dura Ace R9180 levers.
Sram offers a large range of hydraulic brakes. There exist 3 Sram technologies on this range.
 

 
The Hydro R platform which we can find on the majority of the range: Red, Force 22, Rival 22, Apex 1 in 11 gear versions as well as the 10-gear S700 group 10 vitesses. It is possible to regulate the Hydro R levers.
 

 
Today, the Hydro HC platform is only available on the Sram Red etap HRD group (electronic transmission). It is Sram’s top of range system, allowing to regulate lever guards as well as regulating the contact point at the calliper’s level (Contact Point Adjustment technology).
 

 
For triathlon and time trial, Sram offers the S-900 Aero HRD brakes.
Campagnolo, the other leading brand on the transmission sector has also followed on the disc for road wheels.
The mechanical transmission / hydraulic braking range goes from the12 gears Super Record and Record to the 11 speed Chorus and Potenza.
The Super Record EPS and Record EPS 11 gears with electric transmission are also available in hydraulic disc braking.
 


 
If on one hand the levers differs according to groups, Campagnolo disc brake callipers are identical on the whole range.
TRP is the fourth brand offering different products.
 

 

The Hylex RS is unique in its genre as it is an hydraulic disc brake with road-type levers for singlespeed transmission. TRP offers the possibility to install buttons on the lever in order for them to function with a Shimano Di2 transmission.
Hy-road is a mecano hydraulic calliper. The lever activates the hydraulic calliper by means of a classic brake cable.
 


 

The Spyre and Spyre SLC callipers constitute an eccellent option for a disc braking system with mechanic cable.
Finally, like Sram and Shimano, TRP offers a solution for triathlon and time trial with the HD-T910 hydraulic brake.
Other brands offer interesting products:
 


 

Rotor with its Uno Group Set: a hydraulic transmission as well as a hydraulic braking system in partnership with Magura, the specialist German brand. For the disc version, Rotor uses the top-end MT8 calliper of Magura.
 


 

The English brand Hope has developed a special calliper, named RX4. It has 4 pistons and exists in 6 colours as well as different versions compatible with Sram or Shimano callipers as well as Postmount or Flatmount.

 
 

Conclusion:
 

We can say that the disc brake road bike market is in full expansion. The offer for components is now substantial with numerous alternatives for consumers. Braking elements were adapted to road practice following the first experiences which showed more overheating than in mountain biking due to higher speed and longer braking but also due to using very (even too?) small discs. Disc brakes appear more comfortable and predictable than standard brakes. Bike manufacturers work hard on this market segment where we expect to see other innovative products aiming to improve even more disc braking for road bikes. It’s a safe bet that even more cyclists will be equipped with these in the future even though standard brakes seduce more cyclists today.

 
 
 

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