Bike tech: the arrival of the road disc


The long-anticipated move towards disc brakes on road bikes finally looks to be here. Iain Treloar explores the pros and cons of this consumer-driven change.

We’ve been talking about disc brakes on road bikes for a couple of years, but their adoption has happened in dribs and drabs rather than a flood. At first, mechanical disc brakes started appearing on touring and all-purpose road bikes, which was an important first step in their move to acceptance. With a demand and precedent established, it took a while for hydraulic disc brake options to be developed, but finally, in 2013, SRAM released the first hydraulic road system, closely followed by Shimano.

The requisite technology had been available on mountain bikes for something like a decade by this point, so you’d be excused for asking why it took so long for road bikes to catch up. The fact is that road bikes are, at the highest level, designed for professional athletes, and as such, have to fit within a rigidly defined set of rules laid out by the UCI (International Cycling Union). If a bike can’t be ridden (and hence, advertised) on the sport’s biggest stage, there’s limited potential for innovation and trickle-down.

Occasionally, however, a change is forced, and a technological shift is driven by what consumers want instead of what the pros are allowed. Disc brakes for road bikes are a prime example of this phenomenon, and as soon as the necessary gear was developed and then approved for use in cyclocross, the writing was on the wall. It was now no longer a question of if disc brakes would be introduced on road bikes, but when. When the UCI quietly announced that they’d be trialling disc brakes in the pro peloton at selected races, including the 2015 Vuelta a España, there was an almost palpable sense of relief.

Predating this, it was increasingly common to find disc brakes available on road bikes, particularly those of the ‘endurance’ category. The majority of brands will now offer models from this category with disc brakes; perhaps the clearest sign of their mainstream acceptance was when industry-juggernaut Giant rolled out disc brakes on all but the base two models of their popular Defy range. Specialized releasing their high-end Tarmac with disc-brakes in late 2014 was another important moment.

But there’s a difference between something being available and it being worthwhile, and you may find yourself questioning whether this is all an industry-led conspiracy to convince riders to part with their hard-earned money in the pursuit of the latest upgrade. Road bike traditionalists, for instance, will argue that there’s nothing wrong with the current crop of caliper brakes as indeed, there are still improvements being made. Shimano’s 9000-series Dura-Ace brakes, for instance, improved the performance of its direct predecessor by 20%. But while the benefits of disc brakes compared to rim brakes may be marginal in dry conditions, it’s in bad conditions that the former really shine.

The back and forth about the need for disc brakes (or otherwise) has uncanny parallels with the way the debate played out in mountain biking over the past couple of decades—and, spoiler alert, the benefits of the technology are now unanimously accepted in that application. While the demands on road bikes might be less physical than their off-road counterparts, the advantages remain.

  • More consistent braking across a range of conditions; brakes aren’t as affected by wet or dirty conditions
  • The potential for lighter rims (and hence, less rotational mass)
  • Less heat as a result of braking at the rim, and reduced risk of heat-related blow-outs on long descents.
  • Lighter feel at the lever with a hydraulic system, reducing hand fatigue
  • Cheaper to replace a rotor than a rim
  • If wheel is out of true, there is no risk of brake-rub at the rim
  • Self-adjusting for pad wear and no cable stretch on hydraulic systems
  • Wider tyres offer increased tyre clearance in dirty conditions

That’s not to say that disc brakes don’t introduce some other issues. Chief amongst these is that it greatly complicates the landscape of bicycle design, introducing a wide range of different variables to what once was relatively simple.

  • Widths of the rear axle may now be 130mm, 135mm or 142mm (sometimes with different interpretations of what 135mm might actually be, as seen with Specialized’s new SCS standard)
  • Quick release skewers may be used or through axles
  • The different standards of quick release and through axle diameters
  • Greater risk of heel clearance issues, especially with 142mm rear axle.
  • Heavier
  • ‘Uglier’
  • Less aerodynamic
  • More expensive
  • Different rotor sizes (140mm, 160mm)
  • Increased mechanical complexity, particularly in regards to brake bleeds
  • Slower to get wheels on and off when changing punctures, etc.
  • Potential lack of compatibility with aftermarket wheelsets
  • Potential compatibility concerns with bike-carriers
  • Increased width at the rear hub can have an impact on the chainline of the bike and its compatibility with gearing.

Some of these issues are more significant than others, of course, and they are, for the most part, far from deal-breakers if a bike has been cautiously designed to negate them. Furthermore, many of these arguments—particularly those related to weight, aerodynamics and the like—indicate the extent to which the consumer continues to be influenced by sports cycling. In reality, a better test of the true utility of disc brakes is considering whether they’re likely to positively impact your riding. In the case of disc brakes, which improve real world riding performance in a broad variety of conditions and encourage a mentality of exploration, the pros far outweigh the cons. Yes, rim brakes may be good enough—but disc brakes are great, and worth making the transition to.

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