How can you improve on a bike designed by a supercomputer? Add disc brakes, of course
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Cadel Evans knows the BMC Teammachine better than most. ‘I reckon I’ve done 150,000km on every iteration of the SLR,’ he says. ‘I would say this, of course, but this new bike is exceptional. It has the same geometry as the original, that same nimbleness that allows you to hit a 46cm gap with 44cm bars, but it’s got discs. And as I’ve always said, if you can’t go fast, at least look good.’
As a BMC ambassador, the 2011 Tour de France champion has a vested interest in talking up BMC’S redesigned flagship, but he might just have a point.
The previous generation of the Teammachine SLR garnered praise across the board for its sharp handling and impressive stiffness, yet many pedigree race machines have suffered as a result of the addition of disc brakes. Changes in geometry to accommodate wider hub spacing and smooth chainlines, not to mention heavier components, left many early disc brake fans disappointed – ourselves included. With the SLR Disc, though, BMC appears to have blended in disc brakes almost seamlessly.
First up, geometry is unchanged save for the chainstays, which have increased from the 402mm of the rim brake model to 410mm. That’s less than the 415mm or 420mm stays of many other disc bikes, and crucially, says BMC engineer Tobias Habegger, it’s not enough to make the handling discernibly different to the previous generation: ‘We knew that generation was good, so we wanted to keep that bike’s characteristics. It was hard to improve on that as a rim-braked bike, but the discs threw up a whole lot of other challenges.’
Those challenges have been met thanks to a prototyping process BMC calls ACE – Accelerated Composites Evolution – which it used to great fanfare for the previous Teammachine. Using supercomputers, BMC ran an algorithm it had designed that generated and tested different prototypes of the bike virtually. Engineers provided the parameters – for example, tubes must be no bigger than the UCI’S 3:1 ratio – then they hit ‘go’. One year and 34,000 prototypes later, the computer generated the ‘perfect’ bike.
‘We changed the parameters for the inclusion of disc brakes,’ says Habegger. ‘That led the computer to run through a further 18,000 new iterations before we came to the new Teammachine. ACE also now combines shape and laminate, meaning it simultaneously works on the shape and the best carbon fibre lay-up
process, instead of first defining the shape, then defining the best lay-up for that shape.’
The result is a disc bike whose frame weighs a claimed 815g, which built up as pictured weighs 6.8kg (painted, size 56cm), which BMC says handles like a nimble race bike but with the added benefits of disc brakes.
Same but different
The trademark BMC gusset under the top tube has now been filled in, partly to save weight and partly to accommodate the new clamping mechanism, which is neatly hidden in the underside of the top tube. The seatstays lose the brake bridge, again saving weight and allegedly aiding compliance, while the fork gets an oversized left leg.
‘What most manufacturers do is add extra material to reinforce the fork against disc brake loads,’ says Habegger. ‘This typically makes it 4050g heavier. What ACE told us to do was to build the fork asymmetrically, so the left leg has a much wider cross-section but very similar wall thicknesses to the right leg, so overall the fork is only 18g heavier than before.
‘We haven’t changed much with the tube shapes, as they were optimised already within the UCI rulebook,’ he adds, but says advances in composites have helped increase stiffness by 10% at the bottom bracket, without adding significant weight.
As an aside, Habegger also says the paint on a frame ‘accounts for around 10% of the frame’s weight’, but that a ‘naked’ version of the frame is available, albeit specced with Shimano Ultegra. The upshot is that, somewhat counterintuitively, the lower-spec Teammachine has a lighter frame.
Elsewhere, the junction box and charge port for the new Shimano Dura-ace Di2 has been integrated into the down tube and the frame uses Shimano’s new direct-mount calliper mounting. BMC has also specced its own integrated stem with a recessed underside to hide the cables, and a fork steerer with flattened sides to let cables run inside the head tube without inhibiting the rotation of the bars.
Whether the new Teammachine Disc really does ride as well as its forebears remains to be seen when we do a full test in an upcoming issue of Cyclist.
BMC Teammachine SLR01 Team Disc, €11,499 (pictured, approx £9,989). Entry level Teammachine SLR02 Disc from €3,699 (approx £3,223)