Three disc brake road bikes
Credit: Robert Smith
Gear > Bike > Road bikes

Disc-brake road race bikes: 3 of the best reviewed for triathlon

Thinking about using disc brakes for triathlon? We test three £3k disc-equipped race bikes that can stop as fast as they go

With British Triathlon, the International Triathlon Union and Ironman all giving disc-brakes the thumbs-up for triathlon, the future of braking look set to be disc-shaped in multisport. And it’s a trend sweeping the bike industry, with some major brands already signalling that they’ll soon be stopping their production of rim brake bikes.

  

The top manufacturers have also made more cost-effective versions of their competition bikes with disc brakes, so you don’t need a pro team budget or a title sponsor to saddle one up. Matching lightweight or aero frames for smashing the climbs and dominating drag strip sections with powerful, precisely controlled, disc brakes makes a lot of sense.

Disc brakes offer an increase in stopping control, especially in bad weather, but successfully fitting them to a frame and fork isn’t easy. They move braking loads to the furthest ends of the chassis, which are typically the skinniest and most flexible. They need to retain as much of that flex as possible for a comfortable ride, while still being stiff and strong enough to cope with extra load at the end of long levers. Bigger, stiffer thru-axle dropouts potentially make this balance even harder
to achieve.

That’s why we see so many different – often asymmetric – disc frame designs. On the bright side, hydraulic disc hoses can be contorted through much tighter twists and turns than conventional cables. There’s no restriction on tyre size and no need for rim brake mounting/reinforcing stay bridges with discs. But does adding weight and stiffness to cope with braking stress to the fork and frame create too much of a compromise in ride quality? Can a bike be competitively aero with rotors and callipers disturbing airflow? How much extra weight does a disc brake system add and does that noticeably affect the ride quality?

These were the main questions we wanted to answer by taking three cutting-edge competition style, disc brake-equipped bikes and blasting them around the hills and valleys of the Yorkshire Dales in challenging winter weather. So, which of our disc jockeys are best suited to the conditions, and are we now total disc converts or happy to return to rim brakes now testing is done?

SHOCK ABSORBER

The Merida Reacto Disc 6000 (£3,000) is designed as a responsive and aggressive aero race bike and its geometric profiling certainly looks the part. The thru-axle fork deepens all the way up to a chunky crown that blends with a cut-out on the deep, rounded base, rectangular down tube.

The tall head tube uses a teardrop section, which is chopped off square at the trailing edge like most of the Merida’s other tubes. It’s tall for an aero bike, though, getting the less aggressive CF2 geometry compared to the flagship CF4 race bikes, so you’ll definitely need to lose the teardrop spacers under the stem if you want to get low.

The shield section top tube narrows towards an aero seatpost secured with a flush-fit wedge clamp. The rectangular, unbraced seatstays shelve back from a narrow junction, staying close to the tyre, and the wheel-hugging seat tube is barely broader than the tyre but the bottom bracket and chainstays are deep for stiffness.

A soft segment in the back of the aero seatpost is designed to absorb shock before it gets to the saddle. Both the saddle clamp pieces and the top of the seatpost can also be unbolted and reversed to subtly or significantly steepen the effective seat angle in triathlon/aero style. The front and rear flat-mount brake stations have finned heat exchanger extensions to keep brakes cooler on long descents. While the internal routing exit on the top side of the down-tube sends the cables out wide around the head tube to avoid
paint damage.

It’s not the tidiest looking arrangement, unless you trim the excess cable down slightly, and you’re not getting a full set of Ultegra (the cassette is 105 and the chain is from KMC), but it’s not noticeable in the slick shifting and power delivery. In contrast to the frame mounts, the Centerlock brake rotors don’t have any fancy heat-eating features. The Fulcrum rims are deep enough to add an aero edge without becoming too heavy, and the Continental Grand Sport Race tyres are dependable all-rounders. The Merida-branded cockpit is proportionally fine and the chunky saddle adds to the seatpost’s shock-absorbing effects.

It’s clear that the Merida is as edgy and angular in the way it rides as the way it looks. The head angle is relatively relaxed at 72.5° and the wheelbase long at 990mm, but the handling feels sharp and instant rather than lazy. It reacts the same way through the pedals, and that bar jumping hard whenever asked.

While it can start getting sketchy in violent wind conditions, the cut and shut aerodynamics of the frame don’t have any directional agenda in average conditions. This urgency is great if you’re feeling similarly aggressive, and on short crit-style rides the Reacto was a blast.

Despite the CF2 being the shape for civilians it’s still a relatively long bike, which makes it stretched and race ready in feel. Add the ability to shunt the saddle forwards for a steeper seat angle and it’s a natural home for clip-on triathlon bars for multisport work in terms of ride position. The stiffness of the frame comes at the expense of a firm ride over rougher surfaces so you’ll want to relax your grip and ‘hide’ in the saddle when things gets properly pockmarked.

AFFORDABLE ARISTOCRACY

Bianchi might be the oldest continually active bike company in the world, but the brand-new Aria Disc 105 (£2,750)  is a totally up-to-date, high-control, high-performance machine. The aero chassis borrows drag-reducing tricks from the Aquila time-trial bike and Oltre XR series, and the geometry is the same as the flagship Oltre XR4, but it’s still affordable by aristocratic Italian standards.

Opinions on a bike’s looks are subjective, but the contemporary yet classic Aria got more than its fair share of complimentary cosmetic comments from fellow riders when out on the roads. Subtly curved and tapered fork legs bow out around the wheel to reduce conflicting airflow, in a trick first used on the Aquila time-trial bike. Separate brake and gear cable insertions behind the head tube keep control lines low and neat, and the short head tube has flat-back ride position potential.

There’s a flush-fit seat clamp for the teardrop seatpost and the upper part of the seat tube uses a smoothed diamond section before cutting away for wheel room above the broad, bulged bottom bracket. Deep rear rectangular chainstays end with neat axle recesses for easy wheel location. Seriously muscular seatstays follow a fork-matching flared curve up to a low level junction with the seat tube. The big rear stays also hide the brake calliper sitting in the angle between them for a clean look.

With the Ultegra bike (£3,150) unavailable when we were putting the test together, our Aria came with a Shimano 105 spec that comes in £400 cheaper. Functionally there’s very little to tell between them but 105 is around 300g heavier, and the 505 shifter levers have a different shape with an awkward lump under the palm.

The colour-coded Fulcrum aero wheels are wrapped in 28mm Vittoria tyres and the Selle San Marco saddle is also colour-coded, with a Bianchi cockpit supplied in size specific proportions. While the reach and stem dimensions aren’t radically long on paper, the Aria feels stretched for speed. The longer shifter hoods naturally pull you further forward, which is good as the shallower hand angle makes the lumpy bits less noticeable.

Add a 72.5° head angle and the large diameter tyres, and the Bianchi likes to take corners with grand sweeping gestures of confidence that feel fantastic at speed. But it’s stubborn and slow to correct if things go wrong or you need to tweak your line for traction. And there’s enough weight at the front to make it lurch from side to side if you come too far forwards out of the saddle.

You’ll adjust to the handling quickly, though, and it suits the overall character of the bike well. While you’ll get a spirited shift if you dig the spurs in for a climb, the Aria’s natural character is of a high-speed cruiser, where it performs beautifully. With none of Bianchi’s vibration damping Countervail technology deployed in this affordable frame, bigger hits and sharper edges can come through with a slap and a sting.

Smaller chatter and buzz is muted well by the frame and bigger tyres, though, and combined with the low drag tube profiling it carries speed over flat or rolling terrain with a real flywheel feel. Frame tubes and rims aren’t so deep that it gets sketchy when the wind gets gusty, and, overall, the Bianchi is a great place to be when you’ve got a few hours to spend in the saddle and want to cover plenty of miles.

SUPERBIKE SPEC

The Cannondale CAAD12 Disc Dura-Ace (£3,499.99) alloy frame has a string of awards to its name and is a superb showcase of just how far you can take metal tube technology. The hourglass head tube backs onto a super-thin wall down tube that morphs and reshapes regularly before reaching the BB30 bottom bracket shell as a flattened oval.

The asymmetric Delta seat tube flattens and expands sideways as it drops onto the top of the bottom bracket shell, locking in anti-twist stiffness when you pedal hard. Together with the brace-free seatstays and a top tube that tapers dramatically from head tube to seat tube, it’s clear to see where stiffness or comfort-boosting flex are concentrated.

All cables and hoses are fully internal with a tidy dropout exit point for the rear gear line. With a weight under 1.1kg, the frame is light and the fork is fully carbon with a 12mm thru-axle for security and a front-of-crown brake pipe entry point keeping things clean. And with the metallic flake paint finish, it looks more like an exotic carbon frame rather than an off-the-peg model.

The spec you’re getting is superbike level with an almost full set of Shimano Dura-Ace gearing, the cassette is Ultegra, cranked round by Cannondale’s own hollow-armed SpideRing chainset. Cannondale branded kit forms the cockpit and skinny shaft, cutaway top seatpost, while Fizik provides the premium Antares saddle. The wheels use Cannondale Hollowgram carbon rims, using licensed Stan’s No Tubes technology to come tubeless as standard, using liquid sealant and a rim-mounted valve rather than a separate inner tube.

The wheelset creates a huge weight saving advantage for the Cannondale, and acceleration is in a different class to the rest of the pack. Even at full 90psi front/100psi rear pressures, with relatively narrow 19mm internal rims, the wheels have a richly connected feel compared to the conventional, lower grade tyres and deeper, alloy rims on other bikes on test here. While it doesn’t dampen vibration like carbon can, the frame itself is surprisingly forgiving of rougher surfaces considering how alive and precise it feels.

The result is a bike that just disappears underneath you on climbs or whenever you hit the gas coming out of corners, and begs you to go on the attack to rub that in at every opportunity. Handling is sharp and precise but that surefooted wheel and tyre connection meant it was never nervous, however late we left braking or hard we leaned through tightening turns. We can’t think of a bike at this price point that we’ve enjoyed as much.

The overall verdict

If you want a carbon fibre, Shimano Ultegra disc-equipped bike, this test makes it clear that there are some great options for most types of rider. Despite weights and geometry being very closely matched across two out of three bikes, they feel surprisingly different on the road.

When it came to the aero bikes, the Bianchi Aria despatches miles easily with a cultured feel and stable handling that fat tyres and disc brakes make the most of. In contrast, the Merida Reacto Disc feels urgent and snappy. In terms of actual speed over a long rolling ride we couldn’t get a decisive preference from our test team, especially once you add price disparity complications into the mix.

But there was one thing every tester agreed on – the Cannondale CAAD12 is brilliant if you want a bike that lights up every part of every ride. It’s not the mellow or relaxing option, but its effervescence is perfect for attacking short-course triathlon rides. Cannondale has nailed the component package to add fatigue-reducing tyre float and surefooted security to maximise the gains from disc brake control. And it’s done it for an awesome price, whether you go for this superbike spec or the Ultegra/Mavic sibling.

Buy the Merida Reacto Disc 6000 from www.merida-bikes.com

Buy the Bianchi Aria Disc 105 from www.tredz.co.uk

Buy the Cannondale CAAD12 from www.evanscycles.com

Have a little less cash to spend?

The Bianchi Aria 105 (£2,300) rim brake version of Bianchi’s affordable aero bike comes in £450 cheaper than disc brake option. It has more comfortable levers, too. The Merida Reacto 5000 (£2,000) sticks with 105 rim brakes, but slices a third off the cost of Merida’s angular aero weapon. Downgrading to an Ultegra groupset and Mavic Aksium wheels saves a chunk of cash on the Cannondale Caad12 Disc Ultegra (£2,199)

Have a little more cash to spend? 

For £400 extra, you get a Bianchi Aria Disc (£3,150) with the same smooth speed of the Aria Disc but loaded with the latest Shimano Ultegra. The next rung on the Merida ladder, the Reacto Disc 7000-E  (£3,850), will get you the Di2 electric shift version of Shimano Ultegra driven through an FSA Energy chainset. A Cannondale Supersix Evo Carbon Dura-Ace (£3,699) swaps to rim brakes but you get the same kit on the SuperSix Evo carbon frame for a 6.1kg rocket.

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