What You Need to Know About Disc Brakes on Road Bikes
A disc-equipped road bike will serve you well, if you use it right.
Disc brakes on road bikes have been gaining popularity quickly over the past several years. Even the International Cycling Federation (UCI) has approved their use on pro race bikes in 2016. It’s likely only a matter of time until they’re the default option on most bikes.
So what do you need to know about them to use them effectively? We talked to experts to find out.
It’s all about power
“One of the primary benefits of going to discs on any bike is that you get nearly equal stopping power whether it’s wet or cold, regardless of conditions,” says Katie Teubner, customer service and warranty representative at TRP Brakes/Tektro USA. “In dry conditions, disc brakes aren’t more powerful than good rim brakes with good pads, but when the surface is wet, you don’t lose braking power with disc brakes [as you would with rim brakes].”
It’s possible to throw yourself over the bars by activating too much of any brake too fast—rim or disc—so give yourself time to adjust to your new disc brakes. If you have to suddenly grab a handful of lever to stop at a red light in the rain, you may be surprised at the power of your disc brakes. And don’t be fooled by occasional squealing—you’ll still get a lot more response than you’re used to with rim brakes.
More control for less effort
Nate Newton, of SRAM’s Road Technical Marketing Department, thinks that the biggest difference between rim and disc brakes is the increased amount of control the latter provide.
“A rim brake does a fine job of stopping you, but the power comes on right away,” says Newton. “With discs, you have so much power that you can stop on a dime, but that power builds up gradually. That makes them easy to modulate.”
It also means less hand effort is required to activate disc brakes relative to traditional rim brakes. “If you are descending for a long time, like in the Alps or in California, that effort adds up,” Newton says. “Your hands stay fresher throughout the ride because they don’t have to work as hard.”
Standard braking technique applies for both rim or disc systems: Apply your front and rear brakes evenly, with a slight bias to the front brake.
Organic vs. metallic brake pads
Pad material matters. Organic pads grip better and are more powerful than metallic pads; they feel easier to modulate; and they run more quietly during use. However, organic pads wear out faster than their metallic counterparts, especially when it’s wet or muddy.
SRAM recommends organic pads in all pavement situations and sells all of its road discs with organic pads; it only keeps metal pads on hand for cyclocross racers facing the nastiest of conditions. TRP advises choosing road-disc brake pads based on where you live and in the conditions in which you ride.
“Someone living in the notoriously wet Pacific Northwest might not want organic pads, or a bigger person might be better off with metallic pads,” says Teubner. “But the best thing to do is talk to someone at your local bike shop—they’ll give you good information about what works well for your local conditions.”
What about maintenance?
It may be a surprise that discs require less maintenance overall. “Yes, the initial setup of discs is more time-intensive due to having to cut lines and bleed the brakes,” says Newton, “but once your bike is ready to ride, you will have to fuss over it less on a weekly basis.”
After the initial installation and setup, check your pads regularly for wear—especially if you’ve been riding in nasty conditions. It’s tougher to see and feel brake-pad wear for disc brakes because of how they function. You may have to pull off the wheels and physically remove the pads to check wear. Fortunately, such inspection is simple and typically requires only one tool: a standard-sized metric hex wrench. (Not too confident in your wrenching abilities? Take our Quick & Easy Bike Maintenance course through RodaleU to become a more effective at-home mechanic.)
Most manufacturers recommend topping off brake fluid and doing a routine brake bleed once per year.
Bedding in your pads
Riders new to disc brakes will need to learn about bedding in new pads, but this will be a familiar task to mountain bikers. Bedding in brake pads is the controlled process of heating up the brakes and evenly applying some brake pad material to the rotors immediately after installation, but before regular use.
Taking 10 to 20 minutes to bed in your pads is important because it increases pad life, gives brakes a more consistent feel, and keeps them running quietly with less squealing and chattering. Every manufacturer has recommended bed-in procedures for its brakes—check with your local shop or a manufacturer's webite to find out what you should do.
Mechanical vs. hydraulic disc brakes
Disc brakes come in a few varieties: mechanical, hydraulic, or hybrid. With a mechanical brake, pulling the lever tugs on a cable, which actuates movement of the caliper’s disc-brake pads toward the disc. It’s similar to the way traditional rim brakes work, except the pads close in on a disc instead of a rim. When you pull a hydraulic brake, fluid pushes from the brake’s master cylinder into the system, which presses on the existing, effectively incompressible fluid already in the brake line, which forces the pads together around the disc. A hybrid system combines aspects of both systems' technology: Squeezing a brake lever pulls on a cable connected to the caliper, where the cable’s mechanical force is converted into a hydraulic force that then presses the pads together and against the disc.
“Hydraulic brakes are more powerful than mechanical brakes,” says Teubner. “That’s because in a mechanical braking system, there is cable stretch and the housing can compress. Yes, fluid can compress in a hydraulic system, but relatively less.”
Pad movement also differs. “With hydraulic disc brakes, both pads move at the same time,” says Newton. “While we’re starting to see some mechanical brakes do this, the traditional method for mechanical brakes is to use one fixed and one moving pad, resulting in less overall power.”
Another factor to consider is pad wear. As pads in a hydraulic braking system get thinner with use over time, the pistons creep inward to keep the pads close to the rotor. It means hydraulic disc brakes feel relatively consistent even as pads wear. In contrast, mechanical braking systems always move the same amount with each pull on the cable—they do not self-adjust as the pads wear down. Many mechanical brakes have a manual adjustment capability to compensate for such wear.
That doesn’t mean hydraulic disc brakes are always better than mechanical disc brakes. Mechanical disc brakes typically cost less and can be easier to maintain on the side of the road should problems arise.