bike mechanics

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Rim brakes or disc brakes – what’s the difference?

It’s a given that we see a lot of bikes in our shop and we’ve noticed that more and more modern bikes are being equipped with disc brakes. While once reserved for mountain bikes, disc brakes are now appearing on flat bar commuter and road bikes. So which is best? Rim brakes or disc brakes?

Let’s take a look at the pros and cons of disc brakes.

Disc brake
Disc brake

The pros:

  1. Better stopping power, especially in wet weather. Disc brakes are almost always more powerful than a similar quality level of rim brakes. This is more evident in the wet when rubber rim brakes don’t grab onto the braking surface of a rim as well as disc brake pads grab a rotor.
  2. The braking surface is kept away from mud and dirt. This is important with mountain bikes when you ride off-road, as debris gets on the rims and negatively affects braking.
  3. Your rims don’t wear out! As disc brakes don’t touch the rim you will never need to replace the rims due to wear from the brake pads. Every time a rubber rim brake pad makes contact with the rim it wears a very small amount of material off. Over time you slowly wear your rims away.
  4. No braking surface on the rims frees up wheel and rim designers to make rims and wheels that are strong and aerodynamic without any braking considerations.
  5. Braking power is tunable by changing the rotor size (the bigger the rotor the more power).
  6. Less hand strength is needed to brake compared to rim brakes, particularly true of hydraulic disc brakes.

The cons:

  1. They’re typically more expensive than rim brakes.
  2. They’re heavier than rim brakes. Disc brake frames are strengthened to withstand the braking force from disc brakes, which is what makes them heavier.
  3. They’re harder to work on. Particularly hydraulic disc brakes which need the fluid replaced periodically.
  4. Aesthetics. It’s hard to argue that disc brakes look better than a classic road rim brake.
  5. Rim brakes typically have better modulation. While disc brakes have more power, rim brakes tend to have more modulation. This refers to the ‘feathering’ of the brakes, the speed modulation, basically when you want to slow down for a corner rather than come to a hard stop or slow down a lot.
  6. Disc brakes can be noisier, especially if the pads get contaminated. Contamination occurs when grease or oil gets on the disc brake pads. The only solution to this problem is to replace the pads and clean the disc brake rotor thoroughly, so keep your chain lube away from your disc brakes!
Rim brake
Rim brake

In our opinion disc brakes are worth equipping on bikes over $1000. Particularly for a commuter, mountain or gravel bike. The exceptions are road bikes that won’t see any wet weather, such as your “nice weekend road bike”. For that style of bike rim brakes are fine, as the bike will weigh less and road bikes have so little rubber on the road that disc brakes can be overkill. The limiting factor in braking is the tyres traction, so with little rubber making contact on the road, you’ll just end up skidding (which can be fun!).

Thinking of changing your brakes? We’ve got parts for both systems here.

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Electronic vs mechanical gear systems

Electronic gear system

Let’s take a look at gear systems. Specifically, the difference between electronic vs mechanical gear systems.

The “Big Three” bike part manufacturers each have an electronic gearing system:

  • Shimano has Di2 for both road and mountain bikes;
  • Campagnolo has EPS; and 
  • SRAM has Etap which, along with being electronic is wireless! 
Left: Electronic rear derailleur (Shimano Dura-Ace R9150 Di2). Right: Mechanical rear derailleur (Shimano Tourney RD-TY500), note the electric wire going into the electronic derailleur vs the steel cables into the mechanical model.

There are, of course, the pros and cons of electronic gear shifting. 

The pros:

  1. No cables to stretch, rust or replace.
  2. Cable routing isn’t an issue, whereas mechanical cables don’t like to go around sharp curves, but digital wires can go anywhere. This frees up bike designers to make frames and handlebars weird and wonderful, which is especially evident in aerodynamic time trial and triathlon bikes.
  3. The shifting is done by a servo motor actuated derailleur rather than a cable actuated derailleur. This means electronic groupsets can cope with ‘heavy’ shifts and weird chainring combos better than mechanical groupsets. For example, sometimes when you’re on a steep climb (like Arthur’s Seat or Devil’s Elbow) where it’s more difficult to move to an easier gear under strain.
  4. There’s less hand strength needed to shift gears, which is great for people with smaller hands or arthritis.
Left: Electronic shifter (Shimano Dura Ace R9170, Di2). Right: Mechanical shifter (Shimano Acera 7 Speed ST EF500)

The cons:

  1. There is a battery to keep charged (or several if you have SRAM E-tap). If your battery goes flat the system automatically shifts you into the smallest chainring and the smallest cog on the cassette.
  2. It’s expensive. Typically electronic drivetrain parts cost 2.5x or more than the mechanical equivalent.
  3. The feedback from the shifters isn’t the same, think typing on a touch screen vs typing on a proper keyboard where the tactile feedback from the keyboard makes typing easier. This is especially true when wearing gloves.
The battery does need to be kept charged and in this case, is done via a USB charger.

Both systems are affected by chain and cassette wear as well as the derailleur hanger being straight and aligned correctly. So, regardless of which system you run, it does need servicing!

If your bike is due for a service you can book in at 1 of our 3 hubs, Monday to Friday.