Buying a Disc Brake Road Bike: Everything You Need to Know

To disc or not to disc, it’s one of the most hotly debated topics in social and professional cycling circuits buy and sell road bikes 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 Systems
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
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.

Calipers
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.

Axle Differences
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

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.