Ride report: New BMC Team Machine SLR01 is stiffer, lighter

Swiss company uses ACE software to design and test its new SLR01, which is lighter and stiffer than its predecessor

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ROUSSILLON, France (VN) — BMC’s new Team Machine SLR01 is markedly stiffer than its predecessor. So obvious is the change, in fact, that it is among only a small handful of bikes about which we are comfortable making such a statement — “markedly stiffer than before” — without a long test period and time in the lab. The improvement is that obvious.

The Achilles heel of the old SLR01, the one ridden to a Tour de France victory by Cadel Evans in 2011 and to a world championship last year by Philippe Gilbert, was front-end stiffness. It was no noodle, but it did not meet the standard set by the best in the industry, bikes like Cannondale’s SuperSix EVO, the new Trek Madone, and Specialized’s Tarmac SL4. Bottom bracket deflection was average, neither exceptional nor poor, and weight was hundreds of grams off the lightest available at 920 grams.

The new version is dramatically stiffer, and the change can be felt from the first pedal stroke. BMC claims a 25 percent improvement in torsional stiffness, a 25 percent improvement in bottom bracket stiffness, and a 10 percent increase vertical compliance; after test riding, the first two are believable while the last is less so. The new SLR01 feels just as comfortable as the previous model: about average within the industry, and completely acceptable for a race bike.

Descending, cornering, and generally aggressive riding are all more enjoyable now. The torsional and front-end stiffness is evident in hard switchbacks, and the geometry, identical to the last model, is refined and balanced. Overall ride quality is a vast improvement on the previous model, which was no slouch.

The frame is also lighter, a claimed 790 grams for a 54cm with all its paint and hardware — and the frame we weighed came in at 749 grams. That means bare frame weight, the figure often quoted by bike brands, likely hovers just above 700 grams.

In short, the SLR01 now has weight figures and a ride quality that place it among the top tier, up with the EVO, the Madone, the SL4, and Cervelo’s R5CA, among others. BMC now finds itself in such company for the first time in its relatively short history.

How did it get there?

That the new SLR01 rides like no BMC before it, despite having identical geometry to its predecessor, is not particularly surprising. The new frame was designed using methods that no BMC, or any other frame that we know of, has ever used before.

The development process is centered around a new software, shortened to ACE because its full name, Accelerated Composites Evolution, is a bit of a mouthful. BMC collaborated with a small company that spun off Swiss university ETH (Eidgenössische Technische Hochschule), which specializes in optimization algorithms originally developed for genetics research. By taking the optimization software and adding analysis tools used within carbon development, like finite element analysis, BMC was able to create a system capable of a sort of artificial intelligence, able to generate frame models and then analyze them for key attributes, all within the same software platform, and learn new lessons from each model. With each iteration, the software honed in on optimum tube shapes, tube placement, and carbon layup.

The goals were predetermined: weight targets, stiffness targets, and compliance targets were all plugged into the system. Likewise, initial parameters were also known: UCI regulations, industry standard measurements like front derailleur placement and tire clearance, and BMC design queues were all entered as requirements in the final design. It took 34,000 frame iterations, including eight “repopulations” (to borrow the genetics term) of initial data — starting over with minutely altered parameters, basically — to come up with a final model.

“You repopulate and then the algorithm goes another way,” chief project engineer Eric Juillard said. “That’s part of the optimization tool, rather than just look at the local level. That’s where we need this tool. You know, of course, that a bigger downtube is stiffer by itself, but it’s also heavier. The software hones in on the optimum better and faster than a human can.”

Not just looking at the local level was key, explained Juillard. “To simplify it, you can climb the highest mountain and look around you and think you’re at the peak. But far away there is another mountain that is even higher,” he said. “You need to repopulate [the software] and start from scratch and see where you end up. It’s evolution. If you start with all the same data, the algorithm will go in lots of directions and then hone in.

“We just give a range, say a tube needs to be between 25 and 80mm. Then the computer, using the algorithms, calculates the stiffness and weight and strength and then finds the optimum. Then you put in some new information to refine the process. You converge to the solution.”

Much like how computation fluid dynamics (CFD) has changed the way the cycling industry tests for aerodynamics, moving wind tunnel time from the early development stages to a period of final refinement and confirmation of theories, BMC’s software has removed much of the iterative design process and placed it within software, and out of human hands. For years, engineers have been building designs themselves and then testing them using computers; to have a computer build and test each design, and do it thousands of times, could change frame design much the way CFD changed aero wheel design — giving us the wide, stable rims that are popular today.

Indeed, perhaps the most intriguing element of BMC’s new software would be the future inclusion of a fourth parameter: aerodynamics. Adding aero to the list of goals complicates design and sets off an even more careful balancing act between weight, stiffness and compliance. It would be interesting to see what a computer would churn out.

The details

Nothing about the design of the new SLR01 is industry-shattering or wildly different. Bike engineers are rather good at what they do, and have already come up with most of the major design elements of a good carbon frame. Most of what is found on the SLR01 can be found elsewhere, as is true of just about every frame on the market. As BMC’s engineers pointed out, though, it’s the right combination of features and the smallest of tweaks that make all the difference.

Asymmetrical chain stays, with a narrower, taller right stay and more bulbous left, take advantage of all the space between wheel and crank to improve bottom bracket stiffness. Of course, Pinarello and others also have this feature.

Narrow, triangle-shaped (instead of square, as with the previous model) seat stays are compliance friendly; narrow stays can be found on most high-end frames these days.

The proprietary seatpost shape is interesting. It looks a bit like an aero Kamm-tail, but BMC’s engineers say it is actually a strength and comfort issue. The flat back surface reduces peak loads on a highly loaded part.

The down tube is massive, spreading all the way to the edges of the BB86 bottom bracket. Careful shaping, and the girth itself, both provide improved torsional stiffness.

The layup has been optimized by the ACE software, and the bike now features about 400 thinner carbon sheets, relative to the usual 200-300 slightly thicker ones.

The head tube is bulbous, flaring outwards from the bearings in a sharp contrast to the aero head tubes we’ve seen debuted lately, on the Giant Propel and Cervelo RCA, for example.

The top tube is wider, for improved stiffness, and the fork uses continuous fibers for increased strength.

The new frame features BMC’s DTI (Dual Transmission Integration) cable routing, which can be easily swapped from mechanical to electronic shift systems. A new, snap-in BB plug is cleaner and lighter than the last version.

And, finally, the prices: all SLR01 models will be sold with the same frame, and so there is no budget option. The cheapest is an Ultegra mechanical version, at $5,600 and 15.54 pounds. A SRAM Red build will set you back $8,000 and weighs 14.44 pounds, while the Dura-Ace mechanical model is a whopping $10,000 and weighs 14.08 pounds.

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