What’s The Deal With Disc Brakes?

Ah, yes, remember the days (just a few years ago) when so many people were saying that disc brakes didn’t belong on road bikes? That they weren’t necessary, or that they would never find their way into the pro peloton? Well, there’s nothing like a dose of market reality to prove the naysayers wrong.

Despite some initial hurdles, bike manufacturers across the board have come to embrace disc brakes as the sensible, value-added components that they are. Sure, we still hear people say they don’t need disc brakes, and we agree. Old-school caliper brakes have been slowing and stopping bikes just fine for decades. What the modern world has come to accept, however, is that disc brakes just happen to work so much better. And, the most important thing to consider about a better-working brake is not how much heavier they are but how much safer they are.

THE LONG, SLOW ROAD

Despite all the initial opposition (the complaints from so many Euro pro riders being the most dishonest and uninformed), disc brakes have slowly made their way into the world of skinny tires and even—gasp—used to win stages at the Tour de France. While mountain bikers have been all the wiser, having embraced the technology over 20 years ago, most road biking traditionalists have seen the comeuppance of disc brakes as some sort of alien invention.

Although Phil Wood was making disc brakes (for tandem use) as far back as the mid-’70s, the breed has finally come into their own with performance-oriented hydraulic designs replacing cable-operated versions, all with thru-axle compatibility. No matter how you see it, disc brakes are a marked improvement when it comes to rider safety, and while they may be a touch more complicated than your average rim brake, the benefits are tough to ignore.

All the major component-makers are now players in the disc brake game, and each offers unique characteristics that will appeal to different types of riders. In this article, we break down the ride quality and technology of each brand, along with some helpful tech tips on how to troubleshoot your brakes.

SHIMANO

When it comes to disc brakes, Shimano has a strong reputation in the mountain bike world with some of the best riders leaning towards their offerings. On the road side, they have been a go-to for most of the Road Bike Action test riders.

Shimano offers five levels of disc brakes, starting with the cable-operated version used in their Sora groupset followed by the hydraulic models used in the Tiagra, 105, Ultegra and Dura-Ace kits. Until the release of Campy’s disc line, Shimano had the most ergonomic hydraulic lever on the market, but the new 9170 and 8070 shifter offerings are leaps and bounds smaller than anything else on the market for those with small hands.

The feel: There is a fine balance between modulation, stroke length and total power, especially during emergencies. Shimano brakes offer riders a comfortable amount of modulation with adequate stopping power under efforts that come on quickly and plateaus at the end of the stroke. In other words, it is easy to lock up the rear wheel if needed. The levers also tend to have a lot of free stroke and can get awfully close to most bars as they reach the end of their travel.

SRAM

The American brand started out with a cable-operated disc brake that was a leftover from the early mountain bike days that proved popular with early adopters. In 2013 they were the first to go all in with a hydraulic road-specific brake, and while they did have a massive recall out of the gate, SRAM made the necessary fixes to provide hydro brakes that are consistent in delivering reliable performance.

SRAM offers a four-model line (Apex, Rival, Force and Red) of hydraulic brakes, each offering solid performance. To make better sense with their 1x drivetrains, SRAM has gone the extra distance to make a left-side brake lever sans any shifting duties. Nice! With their tower-like hood shape that provides something firm to hold onto, SRAM brakes are hard to miss.

The feel: SRAM brakes have plenty of power, and a very active free-stroke adjustment to control the modulation starting point. The bite between the pads and rotors is a bit more progressive, but SRAM doesn’t lack any power when it’s needed.

CAMPAGNOLO

The Italians were the last to enter the hydraulic brake game, but as the old saying goes, “He who laughs last…!”  We have ridden the highest- and lowest-end versions, with each level boasting incredibly comfortable ergonomics and a sleek hood shape that is the closest of all hood designs in mimicking the size of a caliper brake hood. Campy offers disc brakes at four different levels, including their top-level Super Record EPS, but all share the same caliper and brake technology. The differences are found in the shift mechanism and materials used in the construction of the hood and lever.

The feel: Late to the party as they were, the Italian component-maker has found the right balance of modulation throughout the pull of the lever. The power is easily controlled by the longer lever shape offering even and predictable progression through the travel. The hood profile provides the best ergonomics and closely matches the size of those not housing hydraulics. No matter, from the shape of the lever to overall braking performance, the Campy binders offered the best experience for a road disc setup.

TRP

TRP might not be the first name that comes to mind when it comes to disc brakes, but this company has some reliable offerings. They have focused on the entry-level side of things in mountain bikes, but had big success on the downhill circuit with riders like Aaron Gwin winning the 2017 World Cup sporting TRP stoppers. Since TRP is not in the drivetrain business, their disc brakes are best utilized for single-speeds and bikes without integrated brake/shift levers.

The feel: Several months ago we tested a Turner Cyclosys that came with a set of TRP’s Hylex RS brakes with an adapter slot for a Di2 climbing shifter. TRP sells this adapter as a set or individually. The Hylex brakes have a very comfortable feel and range of modulation, with the power coming on as gradual as any rider would want. We like that there is reach adjustment, but the lever shape has an awkward curve that some of our test riders weren’t as friendly with. If TRP were able to integrate their brakes into mainstream drivetrains, they’d be a serious contender outside of the single-speed hipsters and a few Di2 converters.

DISC BRAKE TECH TIPS

Are rotors interchangeable?

There are two types of rotor mounts—six-bolt and center lock (CL). Most hub manufacturers offer both mount options, and DT Swiss offers adapters from CL to six-bolt. Shimano and SRAM will tell you that their rotors can only be run with their calipers, but you can cross over each brand, and there are plenty of great aftermarket options too.

What’s the difference between metallic and organic pads?

Companies offer two different types of brake pad compounds—metallic and organic (resin). Metallic pads create more friction between the rotor and have more stopping power. The metallic pads also last longer since they are metal, but can be more prone to making noise and a darker residue on surrounding areas. Organic pads are preferred by many as they use a softer compound that doesn’t last quite as long, but is much quieter than their metallic counterparts. Organic pads are usually more expensive and have a less touchy initial contact. For most road circumstances, having a quieter ride is worth the extra coin.

What is bedding in your pads and rotors?

Bedding your pads and rotors is arguably one of the most important aspects of disc brakes. There is a slight glaze on brand-new rotors and pads that has to be worn off for your brakes to stop properly and minimize noise. The process of bedding in your brakes is applying heavy pressure on your brakes several times while moving without completely stopping. This glaze can burn off evenly, and a small amount of material from your pads can rub off onto the rotor surface. This creates the friction needed to stop and, in our opinion, is the most overlooked but important process.

Why are my brakes squealing?

Pads and rotors have to be kept clean from contaminants like lube or degreaser. If your brakes are squealing or honking, chances are there is something on the pad or rotor. Most of this noise can be cured by cleaning the rotors and pads with a microfiber cloth and rubbing alcohol. As stated above, if brakes are not bedded properly, the glaze will create an uneven contact surface, also causing vibrations and noise. In some cases front brakes can squeal due to fork flex after hard braking efforts, misaligning pads as they retract. This has become less common thanks to the support and stiffness that thru-axles provide. The last source of noise is low pad material or none. If you are down to the back plate of the pad hitting the rotor, chances are it will sound terrible. Campy pads implement two ways to identify when your pad is low, while the rest of the brands rely on regular inspection.

When should I bleed my brakes?

The process of bleeding your brakes is to eliminate air that is in the brake hose or that is caught in the caliper or lever. If your lever pulls all the way to your handlebars, this is a clear sign that there is air in the line and your brakes need to be bled.

It is also important to understand the type of fluid used in your system, as they react to moisture differently. Shimano uses a mineral oil that is hydrophobic and does not absorb moisture but instead separates it. The moisture is heavier and usually settles in the caliper and leads to a very distinct and total loss of lever feel. Most other brands use some type of DOT fluid, which is regulated by the Department of Transportation (hence the name) and is a mixture of many different substances. DOT fluids absorb moisture, thus distributing it evenly throughout the system. This leads to a slower and progressive performance drop that is usually overlooked.

This moisture naturally finds its way into each system through microscopic holes or pores in the hose and connections. It is good to bleed your brakes twice a year, just to keep the fluid fresh and your brakes performing consistently. Also note that when bleeding brakes with pads installed (not recommended), use brand-new pads as to not overfill the system.

Does rotor size matter?

Although we have had good results running 140mm rotors front and rear, for all-around road use, most bikes spec a 160mm front rotor with a 140mm rear rotor (SRAM says a pair of 140mm rotors are safe for closed-course riding). Mountain bikers (and tandems) will use up to 203mm for the added braking power. Larger rotors allow for more stopping power, so if you don’t feel like you’re getting enough power, a larger rotor will help but adds to the chances of having noise from deflection.

“While mountain bikers have been all the wiser, having embraced the technology over 20 years ago, most road biking traditionalists have seen the comeuppance of disc brakes as some sort of alien invention.”

What is free stroke?

Most of these brake systems all have a free-stroke adjustment screw, and it changes the point that the lever pulls before the pads are engaged. This doesn’t mean the pads move as the screw is adjusted, but instead changes the volume space between the piston and when it pushes the fluid and is housed in the hood. So, on one end of the adjustment the lever will initiate pad movement the moment it is pulled, and on the other end of the adjustment the lever will not do anything for maybe 5mm (each brand is different). This can help simulate that open-caliper-style brake setup that many crit racers like on their rim brakes.

Is it bad to pull the brake lever when the wheel is removed?

Yes, and it can lead to many problems, including moisture entering the system. Hydraulic systems are different from mechanical versions, because they employ an auto-adjusting pad-wear function. This is part of the reason Shimano and SRAM both say you should only use their rotors on their system. The rotor has a specific thickness that mates with their pad-retraction distance. What this means is that if the rotor is too narrow, the brake may automatically adjust when it shouldn’t, or, on the flip side, if it’s too wide the pad may not move enough to disengage completely.

If the rotor is not present between the pads, the system will not retract completely, thinking the pad material is low. Too many pulls on the lever in a case like this will either make the two pads on each side contact or the caliper piston to overextend and disengage from the caliper shell.

In the case you do mistakenly pull the lever, simply use a clean tire lever or flat, thin object to pry it open, being careful not to score or contaminate the pad material. To minimize risk while the wheel is removed, get a caliper pad block or, in a pinch, use a small piece of cardboard between the pads, but make sure it is clean.

Is it bad to pour water on your brakes to cool them off?

Yes and no. Brakes are designed to exceed 200 degrees Fahrenheit easily as you are converting kinetic energy to heat through the friction of pad on rotor. So, if you have been running your brakes for 30 minutes down a steep hill, chances are they are hot. But, if you just gently apply them to stop at a light, they will normally only be warm. Both are normal circumstances and do not need assistance cooling as long as the system is functioning correctly (no moisture in the fluid as it will boil at 100 degrees Fahrenheit).

If you feel the need to cool them down, remember that some materials that go through an accelerated cooling cycle can alter their integrity. Also, many people use their bottles to carry water that has or may have previously had a drink mix. Those can affect the pad material and cause more problems than help. Now, if your brakes get splashed or you ride in the rain, chances are the water is not concentrated around the caliper and rotor, so this will just help to lower the total system temperature.

So what are the current standards on disc brakes?

This could change in the blink of an eye, but at the moment it’s flat-mount calipers, 12×100 front thru-axle, 12×142 rear thru-axle and 160mm front rotor. The rear rotor is usually 140mm, but many frames can only fit 160mm minimum due to geometry restraints.

It’s also worth noting that there is a growing number of aftermarket brake rotors (e.g., Galfer, Ashima) that are often lighter than those offered by the brake companies. But it’s all physics, and with less surface area (more or larger cutouts on the brake surface) means more time needed to achieve the same amount of friction leading to more heat, so don’t always let weight or aesthetics be the determining factor for rotor choice.