Until recently, when contemplating buying new wheels the main choices triathletes had to make were: tubular or clincher; alloy or carbon rims; and what rim depth? Yet the introduction of tubeless wheels and now disc brake-equipped bikes hasn’t only provided more options, but also changed the road cycling wheelset and braking landscape forever.
Driven by the cycling industry, the use of and support for disc brakes is increasing in triathlon and this upward trend looks set to continue. Currently, similar to the pro-cycling world, in both drafting and non-drafting events the pro-triathlete field is using a mixture of disc and rim brakes. Yet it’s noteworthy that all of the major steeds launched at Kona 2018 – and ridden to notable success by Ironman athletes such as Daniela Ryf, Lucy Charles, and Cameron Wurf – were disc-equipped.
Although not as divisive as the arrival of disc brakes, another innovation from mountain-biking has found its way to triathlon – tubeless tyres/wheels. Thanks to their claimed puncture-evading capabilities, it’s possible that over time ‘going tubeless’ will also become viewed as game-changing.
Broadly, wheels are available with rims of 30mm, 60mm, and 80mm. The general rule of thumb is that the deeper the rim, the more aerodynamic the wheel. But at the same time the cost goes up so does the weight, and handling stability drops. Swapping from a pair of low spoke-count training wheels to standard 60mm carbon wheels can make substantial aero gains, says aerodynamics expert Xavier Disley of AeroCoach Ltd UK. Over an Olympic-distance bike course of 40km and at 40km/h with the same tyres, says Disley, the saving would be 8-12 watts or 45-70secs, even more when multiplied for a 180km Ironman bike leg.
Here we assess the multiple options and their race-day effectiveness when it comes to choosing your race wheels, from braking options to tyre types, rim depths and disc wheels.
DISC BRAKE PROS AND CONS
Compared to rim brakes, disc brakes offer greater braking power, superior modulation (feel), more consistent and reliable braking, and can accommodate wider tyres. Furthermore, it appears that the weight and aerodynamic negatives of the first-generation, disc-equipped bikes are reducing.
“For a like-for-like comparison and the exact same bike, discs will be a little slower but it doesn’t take a lot now to design a bike around disc brakes to reduce or remove that penalty,” explains Disley.
The most popular wheel brand at Kona 2018 were, once again, Zipp. The American brand is committed to disc brakes and this is where the majority of its recent development has been focused. “The braking is better and, as we look ahead, our engineers are free to explore new aero concepts without having to design around the restraints of rim-brake calipers or brake tracks,” says Dan Lee, Zipp’s PR content manager.
Lee also says that many of Zipp’s sponsored athletes are making the transition to disc brakes, with the feedback that they allow them to brake later into corners, which helps maintain overall speed. In response to the increasing clamour for disc brakes, and reflecting the ITU’s position, British Triathlon has permitted disc brakes in all domestic and international competition since January 2018.
Mechanical and hydraulic disc-brake systems are available, the latter being more popular and offering far better performance, but requiring more careful initial set-up. There are two common sizes of disc rotor, 140mm and 160mm, and the rotors are attached to the wheel with either a six-bolt or centrelock mount. Mike Cook, mechanic and owner of Tunbridge Wells’ Velo Works advocates the use of the larger rotor despite the slight weight disadvantage. “I always recommend 160mm for the improved performance (braking power) and a
larger disc will cool down quicker.”
Nearly all disc-brake frames come with 12mm bolt thru-axles front and rear. Compared to classic quick-releases, thru axles are much stiffer and ensure rotor-alignment. Leading ITU athlete Kristian Blummenfelt believes that disc brakes are here to stay, but admits that there remains room for improvement. “When the disc-brakes work, it’s fantastic! When they don’t work, then the old fashion rim-brakes would be easier to fix. Disc-brakes are the future for sure, but perhaps they need a few years on the road market to improve all of the small problems.”
There are two common mistakes made by those new to disc brakes. The first is failing to ‘bed in’ new pads. “Bed in basically means taking a very fine amount of [brake] pad material off and, once bedded in, the brakes will become sharper,” says Cook. Equally fundamental is avoiding contaminating the pads when cleaning your bike, for example when lubricating the chain.
Although disc brakes look to be the dominating set-up in the coming years, in the short-term, at least, rim brakes have a future. Despite its commitment to disc brakes, in 2018 Zipp updated many of its rim brake wheels and now offers more rim brake options than ever before.
Rim brake wheels come with alloy or carbon rims. Historically, alloy rims have tended to provide more reliable braking and are more robust, but come with a weight penalty. However, many wheel manufacturers claim that, following substantial research and development, their carbon braking track performs as well as the alloy competition.
Matt Bottrill, our bike performance expert, and cycling coach to top Brit Ironman athletes Lucy Charles, Tim Don and Will Clarke, believes that alloy rims are no longer necessary. “The days of alloy rims are numbered. Carbon wheels have come down a lot in price over the years. They offer better rider comfort, lightness and stiffness.”
Regarding disc versus caliper brakes, Bottrill says that when bunch racing he always opts for disc-brakes, but he doesn’t think they’re needed for time trials. Coming from an ITU-bunch-racing perspective, pro Tom Bishop is open to
disc-brakes but is still confident with rim brakes. “I’ve done a fair few technical courses and some testing conditions and I still coped on rim brakes.” As he’s also his own mechanic at races, he likewise favours the simpler maintenance of rim brakes.
TUBELESS, TUBS AND CLINCHERS
A clincher tyre has a bead that runs around the edge and hooks into the clincher wheel’s rim. The tyre houses a separate inner tube that can be replaced in the event of a puncture. A tubular (or tub) consists of a tyre and integrated inner tube, which is taped or glued to the rim. The tubular tyre/wheel combination is lighter than the equivalent clincher, and can be run at a wider range of pressures with less risk of getting a pinch flat. However, to get the best rolling resistance performance, a tubular needs to be glued on and this isn’t straightforward to remove (just ask Normann Stadler!).
In a tubeless set-up, the tyre (not all tyres are tubeless) and rim form an airtight seal, there’s no inner tube and sealant is inserted to block/fill any puncture holes. Many clincher wheels are now tubeless ready and come with a simple tubeless conversion kit. In addition to eliminating flats, tubeless tyres have, in theory, lower rolling resistance than both clinchers and tubulars. But a couple of words of caution: installing tubeless tyres requires patience, the sealant needs to be replaced/topped up every few months, and the sealant may not fill bigger holes/slits.
DISC WHEEL MERITS
Disc wheels are comparatively expensive, their use is likely to be limited to race day, and they’re normally heavier than other wheel options. So, are they worth it? To Disley the merits are clear.
“Rear disc wheels are always faster, unless you’re doing a pure hill climb and finishing at the top of the hill. The rear disc wheel would need to be many, many kilos heavier than a normal rear wheel to outweigh the aero benefit.”
Pro triathlete Mark Buckingham shares Disley’s view. “I’d always go for the disc option with deep front for non-drafting unless it’s super windy.” Yet there’s always the risk of disc wheels being banned at a race due to strong winds – as they were for 2018’s ITU Age Group World Champs on the Gold Coast. To avoid a potential DNS, Buckingham recommends a mixed-depth combination. “Maybe a better choice would be to purchase a deep rear wheel with a slightly shallower front so you could use them in any conditions.”
Alternatively, at a fraction of the price of a disc wheel (although not as aero), you could buy a cheaper disc cover (Aerojacket do them for around £90) to convert your normal rear wheel to a full disc when the conditions are suitable.