To disc or not to disc, it’s one of the most hotly debated topics in social and professional cycling circuits the world over. Already commonplace in the mountain bike world, the tech still remains largely polarising in the road bike world. However, with more and more of the world's largest bike brands embracing disc brakes on road bikes wholeheartedly, there’s little denying the industry shift at play.
To help you make an informed decision on your next road bike purchase, we've sifted through the jargon and heresay and created the ultimate guide to buying a disc brake road bike with all the information you need when considering a shift in stopping power.
How Disc Brakes Work: Hydraulic vs Mechanical
Disc brake systems require many parts to work efficiently and effectively on the bike and there are two different ways in which disc brakes are actuated. These include cable and hydraulic, with some manufacturers that offering a hybrid of the two.
Hydraulic disc brakes are largely becoming the norm on performance road bikes from the entry-level through to top of the line options, mostly due to the better braking consistency on offer and less maintenance they require. When pulling the lever on a hydraulic disc brake bike, a plunger is activated at the master cylinder located in the lever itself, this pushes fluid through a hose, and onto the calliper at the wheel. The pressure of this oil operates pistons in the caliper that clamp the brake pads onto a rotor at the wheel's hub.
The advantage of hydraulic systems is that they are a closed system, meaning that water, debris or dirt have an extremely low chance of compromising the brakes. Also helping with low maintenance is the fact that the hydraulic systems self-adjust to gradual brake pad wear. Additionally, a full hydraulic system is lighter and isn't affected by tight bends or twists in the bike's cable routing (a big bonus for aero and time trial bikes). Lastly, and most importantly, hydraulic systems offer a smooth braking feel at the lever and easily controlled stopping power with less hand effort required.
Mechanical systems are cable actuated, meaning that you pull on a lever, which then pulls a braided stainless steel cable (housed in some form of outer cable housing) which is then used to apply braking force to the rotor.
Much like rim brake systems, the main drawback of mechanical systems is that they are susceptible to cable stretch resulting in a loss in braking power and a spongy feel at the braking lever. As well as cable stretch, mechanical systems are also susceptible to rust, dirt and debris build-up that can bind the braking system. Additionally, mechanical systems need semi-regular adjustments as pads wear. It’s worth noting that these issues are absolutely avoidable courtesy of a maintenance schedule.
Rim vs Disc Brakes: The Differences
The most obvious and fundamental difference between a traditional rim brake bike and a disc brake bike is how and where the braking forces are applied. A rim brake bike applied braking force directly to the rim, or sides of the wheel. On the flip side, a rotor that sits separately in the centre of the wheel handles the stopping power on a disc brake bike. The rotor is typically mounted directly to the hub much like a motorcycle or the car in your (or your neighbours) driveway.
The caliper itself (that holds the brake pads) will either be Post Mount or Flat Mount. Post mounting a caliper has carried over from the mountain bike world and is where mounting posts are integrated into the fork or chainstay for the caliper to be bolted onto. This design means the caliper is set out to sit parallel with the disc rotor, whilst also having the ability for side to side adjustments to solve brake rub.
As its name suggests, a flat mount caliper sits flat to the frame itself for a much cleaner, low profile interface that more efficiently works with the tighter space clearances that exist at the rear of a road bike over that of a mountain bike. Flat mount brakes work in a near opposite fashion to Post Mount, with the bolts running through holes in the frame (or adaptor plate) and then threaded into the caliper. Flat mount is a relatively new road-specific standard and is fast being adopted across the majority of road, gravel and cyclocross disc-equipped bikes on the market.
Another key difference lies in axle differences. Rim brake wheelsets almost exclusively use classic quick release skewers in order to hold a wheel in place.
On a disc equipped bike, the axle standards are different, with quick release skewers often eschewed in favour of thru-axles. Thru-axles get their name from the fact that they simply run through the wheel. To remove a thru-axle, riders must first unscrew the axle to pull it out. Whilst taking a marginally longer time to remove a wheel, the addition of the thru-axle itself provides a stiffer hold of the wheel and a consistent tightening method to ensure the wheel is done up to the same torque each time. For more information on the differences between rim and disc brake bikes, check out our Can I fit disc brakes to my road bike? article.
In conjunction with the calipers, rotors are a critical aspect of a disc brake system.
When considering a disc brake bike, it's important to understand that brake rotors aren’t a one size fits all type set-up. Whilst there is no set industry standard, many manufacturers will use either 140mm rotors, 160mm rotors or a combination of the two (large on the front wheel) for optimised braking where it counts. So what’s the difference? In a nutshell, the bigger the rotor, the more braking force they can generate and the greater heat they can dissipate. This isn’t without always the case, however, as rotor design and material also have a large say in braking performance.
Centrelock vs Six Bolt Rotors!
When looking at purchasing a disc brake road bike, or upgrading the rotors on your existing disc brake road bike, buyers will be faced with choosing between either centrelock and six bolt disc rotors. The two rotor designs themselves are largely the same and perform the same function as each other, however, it is how they are mounted to the hub that differentiates the two designs.
As per their name, six bolt rotors attach to the hub using six bolts whereas the centrelock rotors attach directly to the hub and locks using a special key. Whilst centerlock hubs were initially introduced into the market by industry leaders Shimano it's possible to use other brand rotors with centrelock hubs with use of an adapter. The 6 bolt rotors use a standard Torx wrench to attach them to the hub. When it comes to potential performance benefits between the two differing styles, centrelock rotors are easier and faster to remove and are centered more accurately on the hub. This is as a result of not having to worry about evenly torquing the six bolts when installing the rotor.
Materials and Construction
Typically rotors will be made out of stainless steel, however, some manufacturers have started integrating alternate materials into their rotors. Shimano is one of many manufacturers who have done this, sandwiching aluminium at the core of its stainless steel “Ice-Tech” rotors to aid with heat dissipation.
Whilst popular on high-end road cars, composites are yet to make their way to the cycling world. This is largely due to the fact that carbon ceramic rotors require an immense amount of heat to work effectively, much more than can be generated on a road bike, regardless how long the descent. The materials that the pads themselves are made of will likely have an impact on the performance of your brake set also. Typically brake pads will be either of the following:
Metallic (aka sintered): More durable and with more braking bite. The downside of metallic brake pads is their tendency to squeal under load or when heated. Resin (aka organic): Made up of organic materials and bound with resin, this type of pad is more commonly used due to the fact that they are quieter and offer better brake modulation. Resin pads will wear quicker, but take less time to bed in initially.
Many different companies produce brake pads, even if the company does not produce a whole braking unit. When shopping for replacement brake pads, make sure the shape and style match the ones you removed. A good idea is to take the old brake pads into the bike shop and find a match.
Also available from Shimano are pads that are ‘finned’ - the compound of the pads is no different, but the fins act to draw heat away from the pads under extensive braking load.
When it comes to pads wearing on the rotors, its worth noting that pad material is always softer than that of the rotor. Expect the rotors to outlast many sets of pad replacements.”
Rim vs Disc Brakes: Performance Differences
One of the key advantages of disc brakes are the performance benefits. Whilst, in reality, there is nothing wrong with rim brakes, in fact, the force required to lock a wheel is exactly the same for the two but with disc brakes allowing for greater modulation during the braking process. This is particularly handy when riding in wet weather or tackling long descents. So what is modulation you ask? Simply put, brake modulation is the ability to feather or control the brake force being applied without locking the wheel – effectively being in control of your brakes.
Another key advantage of discs is the freedom that it allows frame, fork and wheel designers. This is largely due to the increased wheel and tyre clearance on offer. This allows for more aerodynamic, comfort-increasing or weight saving design queues to be integrated into a frame or fork. Disc brake specific wheel and frame composition is also slightly different and typically beefed up. In order to cope with the additional braking forces generated by disc brakes, bike and wheel manufacturers will often have to redesign a fork or chain stay with additional carbon, or alloy for added strength and increase spoke count with increased stiffness in mind.
Whilst a disc brake frame and fork is designed to be stiffer in order to deal with the additional forces generated, the offset of this is weight. When looking at frame weights alone, the weight gains are negligible. However, when you factor in the heavier groupsets and wheelsets required for disc specific bicycles, a fully built bike will typically tip the scales around 500 grams heavier than its rim brake counterpart.
Rim vs Disc: Wheel and Tyres
As previously mentioned, one of the key benefits of discs is the additional tyre clearance that is afforded by the lack of rim brakes. As a result of this, it's not uncommon to see a disc specific bike roll out of the factory with 25c or 28c tyres as standard. As detailed in our guide to road bike tyres, the additional rubber on offer will do wonders for compliance when riding over imperfect roads or performing light offroad / gravel duties on your next all day adventure. In addition to tyre clearance, wheel design has been altered. With a brake track no longer required, disc specific wheels will often feature a more aero-friendly shape, a lower rim weight and an increased spoke count. For more information on rolling stock, check out our ultimate guide to road bike wheels.
Disc Brake Road Bike Maintenance
Just like any road bike, disc equipped models require maintenance to operate at their best. Instead of a cable change once or twice a year, disc maintenance sees users giving their bike an oil change (brake bleed). Most manufacturers recommend bleeding and replacing the oil once a year, with bleed kits costing as little as $25.
As disc brake systems uses pads to bite onto the rotors, slowing the bike, these also need to be routinely inspected and replaced as necessary. Much like rim brake pads, disc brake pads are available in a variety of different materials each carrying their own benefits in durability and braking power. Prices for disc brake pads are typically slightly more than that of a decent set of rim brake pads, however, they also typically last longer. Riders are encouraged to routinely check the pads for wear (done by looking the thickness of pad material available), as failing to do so can cause premature wear to the rotor itself.
Finally, and arguably most importantly, when performing maintenance on your disc brakes, always ensure that correct lubricants and cleaners are used. Oils, such as those present in degreasers, chain lube, bike cleaners, or even your fingertips are enough to compromise the braking performance of your disc brake road bike. Pure Isopropyl alcohol is a commonly recommended cleaning agent for safely shifting both grime and oil from disc brake systems
When travelling with your hydraulic disc equipped steed, or removing a wheel for cleaning purposes, it is important to not pull on the lever when there is no rotor or spacer present between the pads. Most, if not all hydraulic disc brakes available on the market are self-adjusting, this is to account for pad wear, ensuring that the pads are an optimal distance from the rotor at all times. Pulling on the lever when there is no rotor to bite into, means the pads themselves will creep further and further in seeking a point of contact, eventually leading to leaked fluid and an unuseable brake. To overcome this, most new bikes (bike shops typically have them if you ask nicely) are supplied with little plastic spacers to insert between the pads to prevent accidental pad squeezing when the wheel is out.
Top Care Tips
- Regularly inspect pads and rotors for wear, particularly when riding in wet conditions
- Never touch a rotor with bare fingers (oil)
- Never use spray lubes around them
- Don’t use anything to clean them other than disc brake specific products or pure Isopropyl alcohol
- Ensure you use a spacer for the brake pads when the wheel is removed
- Just like with rim brakes, consult your local bike store if at any point your braking performance or brake feel at the lever changes from what you're used to
First ride tips
Already purchased a disc brake road bike? Awesome work! Here are a few simple tips to ensure you get the most out of your new ride.
- Bed in your pads and rotors
Bedding in your pads and rotors is simply the process of mating the brake pad and rotor surfaces together, without doing it, disc brakes are likely to be noisy and not deliver full performance.
Upon taking delivery of your new disc brake bike, bed-in those brakes by repetitively getting up to speed (approx 25km/ph), then performing a number of hard stops (without locking the wheel or coming to a complete stop). Repeat this 10-15 times (Expect them to squeal progressively less during this process). Easy!
If your first ride (or any ride for that matter) is a wet one, don't be surprised if you hear squealing coming from your pads and rotors when feathering the brakes. This is simply due to the fact the water creates a layer between the rotor and the pads which should dissipate after a few rides, or when the rotor is heated up during braking.