WHY BUY A ROAD DISC BRAKE BIKE

In my earlier post, Why and When to buy a Road Disc Bike, I described the benefits that convinced me to recommend that road cycling enthusiasts get or build a bike with disc brake components and wheels when we buy our next bike.  I’ll summarize them those benefits here.

• Better braking is perhaps the most tangible and immediate benefit of riding a road disc bike.  With disc brakes, you can brake with more consistency, control, and feel (or ‘modulation’) than with rim brakes on carbon or alloy rims.  A road disc bike rides equally well on both dry and wet roads and without concern for brakes fading or carbon wheel rims overheating.

• If you can brake more consistently, confidently, and reliably, you can ride more aggressively on a downhill and into corners, both keys to faster riding.  This more than makes up for the slight and decreasing amount of added weight of road disc brake bikes which slow you down marginally when you accelerate or go uphill.  Of course, it’s up to you to ride faster; the bike doesn’t do it by itself but the opportunity is there to do so on a road disc bike.

• Lastly, having a road disc bike adds greater versatility to what and when you ride.  Beyond your typical dry, good pavement, rolling terrain rides, you can take one set of all-carbon, all-around disc brake wheels on wet roads, in the mountains, and on an off-road section or two without concerns.  Most enthusiasts riding rim brake bikes will have at least two sets of wheels – one with an alloy brake track and a second with a carbon one – to cover these situations.

The concerns about road disc bikes some people have raised are being addressed with either improved designs or better understanding.  Specifically:

• Performance – Road disc bikes are heavier and less aerodynamic than rim brake bikes but minimally and decreasingly so.  Current disc brake models are between 450 and 800 grams or 1 to 1.75 pounds heavier than a similarly equipped rim brake model.  If you add up the weight of an often unnecessary second water bottle or the amount of extra stuff you may carry in your saddle and back pockets, many people carry far more than this weight without recognizing it.  And I won’t even mention the extra weight some of us carry around our midsection. (Oh sorry, just did.)  Those who focus on (or even know) their bike’s weight typically are riding race, aero or climbing bikes rather than endurance ones.

That said, road disc bikes can get even closer to the weight of rim brake bikes.  We are already seeing that coming through added frame stiffness and in the design and selection of components like the choice of a 140mm vs. 160mm rotor or mechanical derailleurs vs electronic ones.

One of the biggest opportunities to rethink design and improve cycling performance with the advent of road disc bikes comes in changing the structure and shape of wheel rims.  Without the need for added thickness to support the braking forces on the rim, disc brake wheelsets can be lighter than rim brake ones.  The best disc brake wheelsets already are coming through with lighter rims than on rim brake bikes (see here).  Rims also don’t need to have parallel brake tracks and can carry the more aerodynamic toroid or rounded shape all the way to the edge of the rim that meets the tire.

Yes, road disc bikes have been shown to be less aero than rim brake bikes but not by very much.  Wind tunnel tests by Specialized, which sells both types of bikes, show that the difference is about 7 seconds over 40K or 25 miles.  Flat mount disc brake calipers, appearing on model 2016 bikes for the first time, tuck much more cleanly behind front forks and against rear chain stays and will likely reduce the aero difference even more.  Frankly, being able to ride a road disc bike faster downhill and into corners more than makes up any time lost from having a bike that is a few seconds less aero.

On the subject of performance, I’ve eliminated from consideration in this review those bikes that use cables rather than hydraulic lines that run from the brake levers the disc brake calipers.  I call these ‘cable-disc’ brakes; some call them ‘mechanical-disc’.  Same goes for ‘hydraulic-rim’ brakesets that use hydraulic lines that run to conventional rim brakes.

For me, cable-disc and hydraulic-rim are half-a-loaf-solutions that don’t provide you the full benefits of brake modulation or added versatility of true ‘hydraulic-disc’ brakesets.  You’ll typically only find cable-disc brakesets on bikes that cost less than those with hydraulic-disc systems, often on aluminum rather than carbon frame bikes.

• Quality – Initial concerns were that more service would be required with road disc brake bikes and that they’d be noisy and require more work to maintain.  Yes, you should bleed the lines each year and ‘bed-in’ new rotors.  I describe the steps to do both of these things in my post on disc brake components here.  It is pretty straightforward to do this and once done disc brakes should actually be easier to maintain than rim brakes.  Hydraulic fluid self-adjusts disc brake calipers.  With rim brake calipers, you need to manually adjust the distance between you rim and brake pads from time to time as the pads wear during the season.  Hydraulic lines also don’t require the cleaning, adjustment or replacement that dirty, stretching or fraying brake cables do.

• Change – UCI, the governing body of professional cycling, has not fully approved road disc bikes for racing yet. Some are concerned that until this happens, road disc bike and component designs will be in a state of flux and lacking standards.  Others don’t like the aesthetics of road bikes or see them as too different from what they have become used to over many years.

As to the concerns about UCI’s pronouncements, this isn’t even a case of the chicken and the egg.  Professional cycling is there to popularize the cycling industry that has been driving the move to road discs for several years.  Besides, the UCI’s technical committees that put forth the recommendations are supported and some would say heavily influenced by, you guessed it, people from the companies that make bike gear.

We’re already seeing movement toward common road disc bike hub widths (100mm front, 135mm rear), rotor sizes (140mm and 160mm), and rotor attachment standards (CenterLock and 6 bolt).  Bikes use either quick release or thru axle hubs and most wheel makers provide the end caps and axles that can work most any set up.

This range of ‘standards’ is not a whole lot different, and some would say far better than the bottom bracket, internal and external routing, cassette and chain, or clincher, tubeless and tubular options we already work with.

The pro circuit and racing oriented road disc bikes and components are following the lead of endurance bikes that most enthusiasts use.  The pro teams are currently most concerned about how to make pit-stop-speed wheel changes, something most of us amateurs enthusiasts will never have to worry about.

As to the look of the road disc bikes and concerns about what switching from rim to disc means for all the rim-based components and wheels you’ve invested in over the years, I get it.  My garage is full of sweet looking rim brake bike stuff.  Change can be expensive and can take some getting used to.  Each of us has to decide whether the benefits that disc brakes bring are compelling enough to make our next bike purchase different than the last one.