DISC BRAKES
Like it or not, disc brakes are here to stay. We guide you through the ins-and-outs of the new breed of stoppers.
“AS THEY DON’T STRADDLE THE WHEEL, DISC BRAKES LET YOU RUN WHATEVER SIZE OF WHEEL OR WIDTH OF TYRE THAT YOUR FRAME WILL ALLOW”
WHY ARE WE DISC-IPLES?
We love disc brakes for a whole bunch of performance and practical reasons.
Consistent control
Because the braking is done by steel rotors at the centre of the wheel, riding in the rain or through muddy puddles doesn’t ruin stopping performance in the way it can with rim brakes. Rim material doesn’t affect braking either so you can use lighter carbon hoops without compromising control.
Direct feel
Presuming they’re properly bled, hydraulic disc brake lines don’t stretch and feel mushy when pulled hard, so you get very accurate braking feedback. Crystal-clear fingertip communication about the road surface and remaining grip translates directly into increased riding confidence, right up to the edge of your tyres performance. As one disc test virgin once memorably commented: “They don’t feel like brakes; they’re just levers that slow you down perfectly.”
Braking function isn’t affected by cables being bent around tight turns inside bars or frames either.
Self adjustment
Hydraulic brakes use fluid reservoirs to automatically adjust for pad wear, so you don’t need to fiddle with cable adjusters or realign the pads.
Then there’s tyre and rim clearance. As they don’t straddle the wheel, disc brakes let you run whatever size of tyre or width of rim your frame will allow. What’s more, as long as it’ll still wobble through the frame, a buckled wheel won’t rub on pads or affect braking either. Add the lack of drama if the rims get dirty and you can see why they’ve established themselves in the fields of mountain biking, cyclocross and gravel riding.
Tyre safety
Because they don’t heat up rims, disc brakes don’t have the potential to explode tyres or melt tub tyre glue on really long descents.
DISC-USSION
All the tech and facts you need to know about discs and how to get the best from them.
Setting up
Disc brakes need ‘bedding in’ to reach full power. By heating up the brakes progressively you transfer a layer of brake pad material onto the surface of the rotor to maximise friction. This is best done by accelerating then braking increasingly hard to the point where you’re almost skidding. Keep doing this until you stop feeling the brakes getting stronger with each start and stop sequence.
Hydraulics and hybrids
Fully hydraulic brakes are by far the best option as they have the most direct feedback and cleanest feel without any cable drag or stretch
“BASIC RULES OF LEVERAGE MEAN THAT A 160MM ROTOR CREATES ROUGHLY 20% MORE BRAKING FORCE THAN A 140MM ONE”
issues and they self adjust for pad wear. Hybrid brakes use a hydraulic calliper operated by a conventional cable brake lever. The shorter the cable, the sharper they feel and some self adjust for pad wear.
Fully cabled disc brakes have the weather, tyre size and rim condition independence of hydraulic discs but can suffer from cable stretch and contamination, which can leave them mushy. They feel different with different levers too (firmer with Shimano, softer but stronger with SRAM and Campagnolo).
Fluids and oils
SRAM and Hope brakes run on the same synthetic DOT 4 or 5.1 fluid as cars and motorbikes. Shimano and Campagnolo brakes run on mineral oil. Never get that mixed up as the wrong fluid will destroy the seals and other internal components and write your brakes off.
Rotors
Road bike rotors are typically 140 or 160mm in diameter. Basic rules of leverage mean that a 160mm rotor creates roughly 20% more braking force than a 140mm one and copes with heat better too. In other words, big riders and/or big hills need big rotors. ‘Two-piece’ rotors, that have an alloy centre are more expensive but a little lighter.
Pads
Most road bike brakes use organic resin pads, as they create less heat on long descents and run quieter too. Sintered pads include metal (normally copper) shavings, last longer and bite harder in wet/dirty conditions so work well especially on cyclocross bikes.
Mounts
Post-mounts use protruding stubs on the fork and frame that the callipers bolt onto from above. Direct-mount brakes bolt directly onto the fork/frame using bolts that insert from underneath.
DISC DONT’S
“EVEN NATURAL OILS ON YOUR FINGERTIPS CAN AFFECT BRAKING. IT SOAKS INTO THE PADS AND REDUCES FRICTION SO THEY DON’T WORK PROPERLY ANY MORE” If you’re looking for bombproof, maintenance-free brakes, pick SRAM
Never get lube or grease on your brake pads Even natural oils on your fingertips can affect braking. It soaks into the pads and reduces friction so they don’t work properly any more. Ignore the old wives’ tail about baking them in the oven to remove contamination too as you’re more likely to weaken the bond that holds the pad onto the backing plate and then you’re really in trouble.
Don’t drag your brakes Constant braking will build up excessive heat in the brakes and potentially cause pad and rotor overheating issues. It’s much more effective and speed efficient to brake harder when you need to and then release when you can to let the brakes cool down.
Never pull your brakes upside down The reservoir will be the wrong way up so any air is far more likely to leak into the master cylinder.
Don’t run less than six steel bolts We’ve seen racers trying to save a handful of grams by only running three bolts or lightweight alloy alternatives. Fewer or softer bolts are far more likely to come loose though. Alloy bolts are also more prone to seizing and then stripping when you try and remove them.
Don’t spray water on discs after descents Yes, making big clouds of steam is funny but rapid, irregular cooling like this risks warping the discs, which won’t be funny at all when you have to fix them.
Don’t touch discs after descents to see how hot they’ve got It’s quite common for rotors to hit 300°C on a long or steep downhills and speaking from idiot experience that sort of heat is going to hurt (and smell really bad) if you press your pinky against it.
Never fit lightweight rotors Saving a few grams with a fancy filigree rotor might be tempting, but lighter rotors generally can’t cope with heat as well as ‘proper’ rotors. It only takes a tiny amount of warp for the rotor to jam against the calliper and throw you over the bars or rip itself apart. Having hidden behind a safety screen while watching a rotor explode and embed razor sharp shrapnel into a lab roof during dynometer testing, it’s not a risk you want to take.
THE OTHERS
It’s not just the ‘big three’ groupset manufacturers that make disc brakes. Here are some of the alternatives, if you’re after a different kind of disc brake…
Giant
Giant’s Conduct hybrid system streamlines installation by building the reservoirs and master cylinders into an oversized stem face plate. This minimises the chance of cable stretch or contamination. Lever feel is good although the action of Giant’s own callipers is a bit on/off. It’s a cheap upgrade at £120 for both brakes but you’ll obviously need forks, frame and wheels that are compatible with rotors too.
Hope
Hope offers a ‘V-Twin’ cable to hydraulic conversion kit that uses a twin reservoir and piston system under the stem, as well as Hope’s own RX4 four-piston callipers that work with SRAM or Shimano levers.
Tektro Racing Products
TRP produces the single-speed hydraulic Hylex disc brake system, as well as the impressively powerful Hy-Rd hybrid system and the Spyre set-up, which we think is one of the best-feeling fully cable-driven disc brake systems.
FSA
FSA’s new K-Force WE RBD disc brakes are notable for low-profile levers with reach adjustment and different sized lever blades for small or large hands. We’ve not had much time on them yet though.