Disc Brake vs. Rim Brake Performance on Road Bikes

One of the most common questions we receive is whether disc brakes are better for road bikes than traditional caliper brakes.  It seems every company now offers disc brake road bikes.  So many marketing dollars focus on selling discs for every type of riding.  It's easy to understand why most people think discs are better for road bikes.  "Better" is a broad word that covers a lot of ground, just as "road bike" is a broad term.  We find that find each brake system has benefits and shortcomings.  These positives and negatives often get clouded by the latest bike review which may be influenced by what bike brands want to sell -- whether it's right for every rider or not.

We are agnostic about brake systems for road bikes.  We offer performance road bikes with three brake system options:  Calipers, discs, and even medium-reach calipers.  The reason we offer three systems is that each has strengths and weaknesses.  We just want cyclists on the right bike for their kind of riding.  We hate it when a rider ends up with the wrong bike for the wrong reasons. 

This article explores braking performance:  Which brake system lets you ride "faster" on various surfaces and in wet and dry conditions.  The answer is surprising.

The winding road and river.JPG

We're using the work done by the Global Cycling Network for the base data collection in this article.  Their videos are well thought through and their data is generally defendable.  To read more about our thoughts regarding GCN, read the end of this article.  Why use GCN's data?  We think riders find it most persuasive when we dissect other people's data rather than our own research so no one can claim that we are biased in our data sorting.  And, GCN says they are biased toward road discs.

In their video, "Are Disc Brakes Faster?  Disc Brakes Vs Rim Brakes" presenter Simon Richardson walks the viewer through their testing process and the results.  We're not going to summarize the video.  You should watch the video.

The question is:  Are disc brakes faster than caliper brakes on a road bike?

Short AnswerNo, disc brakes are not faster than caliper brakes.

In fact, in dry conditions rim brakes let you ride faster -- about 24 seconds faster on a 22-mile loop of constant climbing and descending.  In wet conditions, the data also concludes that caliper brakes are faster -- by about 4 seconds over the same loop.  We use GCN's own data to prove that conclusion.  There are a number of reasons for this counterintuitive truth.  Read on to find out why.

Long Answer:

First, the route we're using is "stitched" together from two of GCN's disc brake review videos.  One of the tests evaluates disc brakes on descending and one test evaluates disc brakes during climbing:

We put these two trials together to create a 22-mile theoretical route of constant climbing and descending.  It's a good way to maximize the differences in the performance of both braking systems -- with a world-class climb and a world-class descent.

As noted above, this fabricated route provides an advantage to the caliper brake bike over the disc brake bike:

  • In dry conditions, caliper brakes show about 24 seconds advantage or about 1 second per mile.
  • In wet conditions, caliper brakes show about 4 seconds advantage or about 1 second for every 6 miles.

Of course, these benefits are slim but they are real.  Anyone that says road discs are faster is going by perception rather than data.  In fact, Simon R., to his credit, acknowledges his bias in the GCN descending video. 

Here are the details about why calipers are faster in virtually every situation.

Faster Climbing

First the easy and logical part.  GCN found that caliper brakes provide about a 2-second advantage per mile.  GCN's video that includes an 11-mile climbing test on the Col du Tourmalet in the Pyrenees provides the data.  In short, the heavier the bike and wheels the slower the climb. 

On the 11-mile climb, they ran the math and found that the added "500 grams," or 1.1 lbs, for the disc bike equated to "about 20 seconds" slower climb.  So, calipers climb faster because they're a lot lighter than a hydraulic brake system.  To dig into the details of how it's possible for a disc bike to be more than a pound heavier, read the details below.  No one believes this until you dig into the details.  We find that actual weights of comparison bikes are more like 1.25 to 1.5 lbs heavier. 

On GCN's specific climb the rim brake bike provides about 2 seconds advantage per mile.  We're assuming this 20 seconds would hold true in wet or dry conditions because this is a climb.

Faster Descending

Descending in dry conditions:  GCN found that caliper brakes provide a slight advantage when descending, by 4 seconds over the "Stitched" 11-mile descent.  This is about a 0.5% advantage.  While small, the benefit would have been more substantial if they tested aluminum rim brake surface rather than carbon rim brake surface.

Descending in wet conditions:  GCN found that disc brakes provide a 16-second advantage on an 11-mile descent.  This shows that discs are better, right?  Not really.  Unfortunately, GCN chose to use carbon rims for all their tests.  Rim brake performance is noticeably worse with carbon rims than with aluminum rims -- this is true in both dry and wet conditions but very much accentuated in wet conditions.  If GCN tested aluminum rims in wet conditions, we're confident they would agree that the caliper brakes would have performed noticeably better than the carbon rims.  We can't say how much better, but given our experience, on an 11-mile descent, it's difficult to believe that aluminum rims wouldn't have been more than 8 seconds faster than carbon rims.  Regardless, even with a sub-optimal carbon rim, the caliper brake is still faster on the 22-mile loop because the 16-second deficit is overshadowed by the 20-second climbing benefit.

How can it be that disc brakes aren't any faster on a descent?

Hydraulic disc brakes have better stopping power.  There is no debate about that data.  However, this power doesn't make discs "faster" on a road bike.  To use GCN's own words, "You don't need better brakes on road bikes.  You need better tires that give you more grip."  This is true.  Nearly every road rider can easily lock up classic caliper brakes on a road bike because the tire contact patch is so small that there's not enough friction to avoid lockup and skidding when applying brakes in an emergency.  Contemporary caliper brakes have plenty of stopping power and modulation, even in wet conditions.

The lore of disc brakes allowing you to brake later into a corner doesn't bear out in GCN's testing.  Or, at least, whatever benefit there is gets offset by disc shortcoming.  We'll cover some of these shortcomings in future articles.

    Choosing the Best Brake System:  Considerations Beyond Just 'Fast'

    Both brake systems have numerous pros and cons beyond which is "faster."  There are plenty of examples where a road hydraulic disc brake is better than a classic caliper brake, but it's not usually related to performance.  The list of brake system considerations includes ride quality, traction, modulation, servicing difficulties, total cost of ownership, future-proofing, traveling ease, tire size compatibility, hand strength, weather and climate, and more.  Stay tuned.

    The Future

    At some point, disc brakes may become better in all situations:  lighter, better modulation, etc.  For now, that's simply not the case.  If we want road bikes to stop faster, it is the tire compound and casing that has to improve.  Stay tuned as component improvements occur.


    What is the Global Cycling Network?

    GCN is one of our favorite sources for cycling data.  They do a really good job of testing and explaining.  They collect a lot of data and explore multiple sides of an argument.  It's clear that they strive to be objective.  They do an excellent job of explaining complex ideas in ways that are easy to understand.

    No test procedure is perfect.  No test can cover every element of everything from every angle.  Simon Richardson acknowledges some of the shortcomings of their test procedures.  Doing what they do is really hard because no matter how thoroughly someone creates a test, some people will not be satisfied.  While we point out some nuanced procedural challenges with their work, we do not mean to be critical.  Their work is important and helpful to the industry.

    They're also doing a lot of work with these kinds of test.  They make it look simple, but it's not.  Many hours of research and preparation go into making each 10-minute video.

    We're really thankful for the work they do, and we support them to continue for many more years.