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Triathlon is in the midst of a bike revolution. Recommended tire sizes are moving from 25c to 28c, tubeless is the go-to over clincher wheels, and brake styles are moving from rim brakes to disc brakes at a rapid pace. While the new technology available to pros and age groupers alike is exciting, if you aren’t a professional triathlete who receives a new bike each season or an age grouper with lots of money to spare, it is easy to get “bike envy” these days.
Disc brakes vs. rim brakes is the jumping off point where many other bike upgrades, like bigger tire sizes, fall into place. But how much does this new brake tech really matter?
For the average athlete, not as much as you’d think.
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Get to know: Rim Brakes
Rim brakes are the decades-old way of braking on road and time trial bikes. A rim brake operates with two calipers in the front and rear of the bike. In those calipers sit thick brake pads. When a rider squeezes their brakes, a lever compresses, forcing the brake pads to push against the rim of the wheel, thus slowing the bike via friction.
Rim brakes come in two main types: aluminum and carbon. Aluminum rim brakes are not actually made of the metal, they are instead designed to work best on aluminum wheels. Same goes for carbon rim brake pads; they’re not made of carbon, but are designed to not scratch the carbon on race wheels. Over time, any type of rim brake pad will wear down from frequent use.
The market is trending away from rim brakes for a variety of reasons, but not everyone is sold on making the change just yet.
Professional triathlete Danielle Lewis nabbed a podium spot at 2022 Ironman Arizona on a rim brake bike and has found herself at the front of the pro field many times this past year sans disc brake bike.
“Personally, I don’t have an issue with rim brakes,” Lewis said. “I’ve raced in rainy and hilly conditions and performed well with the rim brake set up.”
Gustav Iden famously won the 2022 Ironman World Championship on a rim brake Giant Trinity bike. He was one of just a handful of male pros who opted to ride with rim brakes in Kona – and clearly, things turned out just fine for him.
Pros: Rim Brakes
- Easy to fix: Because of their caliper system, rim brakes can be fairly easy for a semi-knowledgeable home mechanic to fix if the brakes need an adjustment. Most rim brakes’ calipers are able to widened or narrowed with the twist of a screw, meaning a DIY’er would only need the correct size hex key to make that adjustment.
- Easy to swap out brake pads: When installing carbon race wheels for your big day, rim brakes are easy to swap from aluminum brake pads to carbon brake pads. All you need is a small hex key, and potentially some pliers to gently remove the pads.
- Travel-friendly: Because of their ease of adjustment, rim brakes make traveling quite easy. Patrick Brown, an engineer with Hunt Wheels, noted that this is one of the biggest benefits of rim brakes. “Rim brakes are easy to travel with. Most athletes can have confidence that they’ll have an easy time setting up their bike from the travel box when they have rim brakes.”
- Common parts: Rim brakes are the tried-and-true way of braking, which means many road and triathlon bikes still leverage them. If you need a new wheel or part last-minute, it is generally feasible to find what you need from another athlete or local bike shop.
Brown wanted to remind athletes that what matters is the rider feeling good about their setup instead of trying to accumulate the latest technology:
“There’s not one fastest setup,” Brown said. “It wasn’t long ago that all bikes were rim brakes, and some of the new [rim brake wheel] setups are still super fast.”
Cons: Rim Brakes
- Wear and tear: Rim brake pads will wear down over the course of a season. Some may need replacement after 500 miles while some can make it to the 1,000-mile threshold. Either way, riding on worn down brake pads is dangerous and can lead to wheel rim damage if not addressed. It is something to keep track of for sure during your heavier training cycles.
- Skidding to a stop: Rim brakes slow a bike by putting friction on the rim of a bike wheel. When the roads are wet, however, this makes it harder for the brake pad to grip the wheel effectively, meaning it’s easy to skid out or take longer to come to a full stop. Same goes for steep descents; when you have so much forward momentum down a high grade, you’re putting a lot of inertia behind a bike, making it harder for rim brakes to quickly slow you down.
- Stuck with 25: The caliper setup of rim brakes can only be opened so wide. This means that it can be difficult to use a tire size larger than 25c without the tire rubbing on the frame. With the newly-explored benefits of a 28c tire in triathlon, this can leave you lagging in the free speed department, although Brown from Hunt noted that “most rim brake frames will clear a 28c tire if you configure your setup that way.”
- Cable stretch: Because rim brakes use a metal cable to actuate the brakes from the lever to the caliper, the cable stretches. In the near-term, that can mean a loss of “brake feel”—the connection between lever and brake—in the long term, you’ll need to replace stretched out brake cables.
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|Easy to fix||Relatively quick wear and tear|
|Easy to replace brake pads||Less accurate stop time and distance|
|Travel-friendly||Limited wheel size to 25cc (can extend to 28cc in some cases)|
|Parts for rim brakes are common||Stretching cables|
Get to know: Disc Brakes
Disc brakes are the bike upgrade most triathletes are lusting after. After being used in the mountain biking world for many years, disc brakes were approved for use in draft-legal and non-drafting triathlon in 2016.
Disc brakes operate via the use of hydraulics. Two small brake pads (much smaller than rim brake pads) sit millimeters apart on the bike frame. A disc on the bike wheel slides in between them. When the brake lever is squeezed, there’s an increase in pressure on hydraulic fluid in the brake lines, which then compresses the brake pads, forcing the disc on the wheel to cease rotating, thus stopping the wheel and bike.
“The biggest benefit of disc brakes is you have so much more [on the bike] to play with aerodynamically,” Brown said. “You aren’t limited by having a vertical [rim] brake track, so you can run a wider tire and get creative with front end and fork setup.”
Pros: Disc Brakes
- Safer stops: A dedicated rotor, with cutouts for air to help cool, means less heat buildup on the braking surface. This means more consistent braking, but more importantly it means no added heat on the rim—which contacts the tube and tire.
- Better braking: A larger braking surface, with less heat buildup and the direct, hydraulic connection between lever and caliper all adds up to better, harder, and more consistent braking in all conditions.
- Room for creativity: As Brown noted, disc brakes allow riders to be creative with their wheel and bike setups. Disc brakes remove the limitation of caliper width and allow riders to run 28cc (or larger, in some cases) tires, which improves ground contact time and permits more aerodynamic wheel profiles to be used.
- Improved frame aerodynamics: Disc brakes allow bike frames to be designed in a more aerodynamic way, too. “With disc brakes, bike forks can be moved away from the wheel rim a bit, giving more room to create the optimal design with wheel profiles,” Brown said. “You have three separate bodies interacting with the wind [frame, fork, wheel], and with a disc brake setup, you have more freedom to control the way that each of those bodies behave.”
- Easier wheel swaps: Because you’re not dealing with rims of different sizes and materials, swapping a disc wheel across bikes—even a carbon to aluminum wheelset—is a piece of cake. No caliper widening or readjustment required.
- Less expensive wheels: This is an odd one, but a side effect of not having to deal with heat buildup on a rim braking surface saves a lot of R&D expense for companies making disc-only models. Not only that, but wheels companies have less exposure to braking malfunctions and catastrophic crashes.
Cons: Disc Brakes
- Difficult to DIY: Unless you are an engineer or skilled mechanic with experience in hydraulics, it is inadvisable to attempt to adjust disc brakes on your own. There is a strong chance you could accidentally drain the hydraulic fluid, introduce air bubbles, or clamp the rotor pads together without the proper knowledge.
- Cross your fingers for parts: Although disc brake bikes have soared in popularity in the triathlon world in recent years, it is still more difficult to source replacement parts for disc brake bikes, especially on the fly. If you are traveling to an exotic race location, be sure to bring any spare parts to fix disc brakes with you.
- Slightly less aerodynamic: In some cases, disc brakes can be considered as less aerodynamic than rim brakes. This is because the disc brake rotor juts out a bit into the windstream moving over the fork and wheel. “That is a very messy area with the spokes chopping the wind, it can have some drag,” Brown said. “You can make up for this small drag with the efficiencies of the wheel rim profile and bike setup.”
- Weight: Though not as big of a deal for triathletes, a hydraulic disc brake system (including lines, fluid, calipers, and rotors) weighs a bit more than a cable-based rim setup.
|Better stop time and accuracy||Difficult to DIY|
|Allows for creativity in bike design||Can be hard to source parts on the fly|
|Improved frame aerodynamics||Disc rotor less aerodynamic than rim brakes|
|Easier wheel swap|
|Cheaper wheels (theoretically)|
Rim Brakes vs. Disc Brakes: Conclusions
If saving a few watts here and there is your goal, it may make sense to splurge on the ultra-accurate disc brake bike models. But keep in mind, the rim brake isn’t dead yet. If you have an existing rim brake bike setup you are confident and comfortable riding powerfully during a race, that may outweigh any benefit you would get from changing to a disc brake bike. Like with most things in triathlon: there is the “optimal” way, and then there is the way that suits the individual athlete and their goals. When it comes to brakes, there are “optimal” answers, and then there is the answer that allows you to ride with confidence. Always choose the latter.