Disc Brakes on Road bikes?

As disc brakes are appearing on more and more road bikes, I’d like to shed a little light from my experience on the subject.

The most common question is why would I want to have disc brakes on my road bike?   Disc brakes have made tremendous strides over the past few years, especially in the mountain bike arena.  Many more disc road bikes are on the market now, and many consumers are confused as to why.

First off a little brake anatomy.  Conventional road bikes use a rim brake, rubber pads providing friction at the rim of the wheel near the tire. Disc brakes are similar to what is common on automobiles and motor cycles, a disc, or rotor mounted to the hub, with resin compound pads pressing against the rotor to provide friction.  There are two ways that a disc bake can be activated, by a cable or hydraulically.  Cable actuated brake typically only push the pad on one side, slightly deflecting the rotor into the pad on the other side when they are actuated.  Hydraulic brakes typically actuate both pads at the same time, providing more powerful and smoother braking sensation.

A significant improvement that has trickled down from mountain bikes is the use of through axles on disc brake hubs.  Through axles are a substitute for the traditional quick release skewer.  The axle is a larger diameter (12 to 15mm) and threads through the hub and directly into the fork or frame of the bike.  This provides two main benefits, it reliably sets the wheel and rotor in the same position each time, and it stiffens the connection between the wheel and frame and fork.  This is a big improvement for mountain bikes with suspension forks but also subtly improves the performance and handling of road bikes.

Other design considerations for disc brakes include the diameter of the rotors (140mm, 160mm, 180mm), the attachment method of the rotors to the hub (six bolt or center lock design), the type of fluid used (DOT fluid or mineral oil), the ability of the rotor, pads and caliper to dissipate heat, the composition of the pads (sintered or metallic compounds), and mounting standards for the calipers to the frame and fork.

Maintenance issues are different for disc brakes, but similar, to rim brakes: pads and rotors must be checked and replaced for wear, and hydraulic brakes may need to be bled from time to time.  Similarly rims and brake pads wear out, and cables need to be replaced periodically.

Here is a breakdown of the pros and cons for disc brakes

Pros:

  • Better stopping power in wet conditions
  • Eliminates heat build up that rim brakes can cause (especially true for carbon rims, and for prolonged braking efforts)
  • Ability for the brakes to work effectively if the wheel is out of true
  • Requires less hand effort to brake, (especially hydraulic brakes)

Cons:

  • Adds weight to the bike
  • Adds expense to the bike
  • Provides only marginally better braking in dry conditions (there are various factors that affect this, including size of rotors, and hydraulic bakes stop better than cable brakes)
  • Prone to pad squealing / noisy

Can your current bike be converted to disc brakes?  Probably not, the bike frame and fork need to be specifically designed to mount the disc calipers, and accept the additional stresses that result from disc brakes.  The wheels also need to be specially designed to mount the rotors.

If you are an “all conditions” rider, commuter, cyclocross racer, gravel rider, plan to ride down long mountain passes, or want to use carbon fiber rims, then you should consider a road bike with disc brakes.  If you are concerned about weight, a fair weather only rider, or like to have options for wheel choices, then rim brakes are probably your best bet.

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