by Brad Culp; images courtesy of Argon 18

Ed. Note—keeping abreast of triathlon technology has never been easy. Triathletes, typically, are tinkerers and mad scientists, always looking for that next little tweak that will improve their times on the race course. When disc brakes appeared on road and TT bikes a few years ago, the triathlon world instantly decamped into two groups: stridently for and stridently against. Heather Jackson waited for a while before making the move this year with her new Argon 18 E-118 Pro. Guest Editor Brad Culp joins us today to walk us through how disc brakes have developed, and if they are here to stay.

There’s a seismic shift happening in the way we stop our bikes. When disc brakes began showing up on high-end tri bikes a couple of years ago, there was initially kickback. Many viewed it as a marketing ploy by bike and wheel manufacturers to push new product. Others argued that it was an unnecessary expense, because the goal should be to brake as little as possible during a triathlon.

But then triathletes began trying disc brakes, and they began telling their friends: There’s a better way to stop your bike—one that provides more stopping power, improved control and isn’t affected by the elements or rim wear. What was once considered a lavish upgrade for those with the deepest pockets is now becoming the industry standard. Not only is it helping athletes ride with more confidence; it’s helping engineers design better wheels and bikes.

A Better Rider

Among all sports that involve a bicycle, those who come from a triathlon background are notoriously bad at bike handling. It’s not entirely our fault. A triathlon bike isn’t exactly the best tool for learning how to ride well. Relative to road bikes, cross bikes, cross-country mountain bikes and even some commuter bikes, tri bikes are extremely unresponsive. They lack “pop” and they definitely don’t corner well. Triathlon bikes are clunky rocket ships that are made to go fast in one direction when steady power is applied, and the best ones do that extremely well.

Disc brakes have been the norm in mountain biking and cyclocross for more than a decade because they make the rider more agile, which is essential when you’re constantly trying not to crash. Discs are becoming a staple of every mid-to high-end road bike, and it’s only a matter of time until even entry-level tri bikes go away from rim brakes.

Triathlon represents a final frontier in the disc brake’s conquest of the bike industry, and it could be the segment that benefits most. That tri bike with deep-dish wheels may feel like you’re riding a rocket ship, but slowing it down isn’t easy—or smooth. Even the best rim brakes apply inconsistent stopping power, especially if there’s any water on the road. Disc brakes allow athletes to modulate their deceleration in a very precise manner, instead of squeezing rim calipers early and often into a curve or turnaround.

“There’s not really a learning curve when you switch to disc brakes,” says Heather Jackson, who only made the switch on her tri bike at the beginning of the year. “You’re more confident after the first time you try stopping your tri bike with discs. You can actually brake without squeezing the levers as hard as you can.”

A Better Rim

Squeezing brake pads onto your fancy carbon rims does plenty of damage over time, and it can become catastrophic if they become overheated on a long descent. Inevitably, every carbon rim will delaminate to the point it breaks, although the amount of time that takes varies widely by rider. Something that happens much more frequently than catastrophic rim failure is rain, and that might be the single biggest reason that discs are becoming the standard on nearly every kind of bike.

“Regardless of the discipline, having the confidence to control and slow your bike in any kind of weather is extremely important,” says Neil Shirley, Marketing Director at ENVE. “Properly functioning rim brakes are completely adequate for what a triathlete faces on a dry race course, but when you factor in training on roads open to traffic and the possibility of training or racing in the rain, the consistent performance of disc brakes should make them an easy decision.”

Moving braking forces from the rim to the hub is an easy decision for wheel engineers, too. As deep-dish, carbon rim technology has rapidly evolved over the past 20 years, much of the engineering focus has been on the brake track. Companies like ENVE and Zipp have literally spent millions testing ways to dissipate heat and ensure their wheels don’t explode whilst bombing downhill at 40 mph. By removing that concern, designers can now use the area that once was the brake track to improve the performance of the rim.

“We can build a lighter rim, but it’s about a lot more than weight,” Shirley says. “We can slightly change the shape of the rim at what was once the brake track. We’ve seen in testing that there’s a notable decrease in rolling resistance as rim width increases, and now we have bikes and brakes that make that possible.”

The interaction between wheel, brake and bike—especially on the front end—has wheel and bike manufacturers working together like never before. In 2017, Cervélo solicited ENVE to help design the front end of the P5X. The interaction between wheel, fork, handlebar, and rider became a major focus in the overall design of the bike, and engineers were able to think outside the box since they weren’t constrained by figuring out where to place rim calipers. By doing things like shortening the crown height and widening the fork legs, Cervélo and ENVE could work together to design a true super bike.

A Better Ride

Perhaps the biggest benefactors of the shift to discs are tri bike engineers, who can now design a bike around a brake that’s located where it should be: at the hub. Most designers are now operating under the assumption that rim brakes will not exist in five years—at least not on new bikes. Before we know it, spotting a pair of brake calipers will be as rare as seeing downtube shifters.

“There was a lack of standards with the thru axles, and that’s why it’s taken so long for triathlon bikes to shift to disc brakes,” says Dominique Fortin, Technical Representative at Argon 18. “Now we have a standard of 100 mm in the front and 142 in the rear, so brands can begin building around that.”

Thru axles stiffen both the front and the rear of the bike, and contrary to a belief that’s becoming less popular, they don’t make it any harder to change a flat than the quick release skewers used with rim brakes. And if there is an aero penalty at certain yaw angles, it’s beyond trivial in the big scheme of things.

“The bike only accounts for 20 percent of a rider’s drag,” Fortin says. “Disc brakes account for maybe one percent of that, and they help us make the bike itself better to ride. With caliper brakes, you need to add material inside the fork crown to resist the braking forces. By moving the braking force to the hub, we’re able to build a more comfortable fork.”

It’s a lot of small things that add up to something big: The faster you go—and the faster your competition goes—the more you have to benefit from making the switch to discs.

Fortin puts it this way: “Imagine you have a rider 300 meters in front of you who you’re trying to catch. If it’s flat or downhill, it can take forever to catch up by pedaling a little harder. But as soon as that rider taps the brakes, the distance shrinks in a matter of seconds. With disc brakes you brake later, get off the brakes sooner, and then accelerate faster. That’s where you can make up a lot of time.”