The Up Side

Despite all its focus on rugged terrain, climbing that rugged terrain is relatively harsh on the Fourstroke 01. Its travel is progressive enough that the tire wasn't tracking our shelfy grunts. Smoother and sprint-worthy bits, on the other hand, were quick and rewarding.

Down Time

Though we never forgot that the Fourstroke 01 is a race bike, it is as capable as a race bike can be. Its stiffness kept it from feeling too vague and its relative stiffness kept it from being too twitchy. Some meatier tires would help, though.

Dollar for Dollar

This may be the most expensive bike we've ever had at Bible. And it really has only one purpose: racing. If you're concerned with winning, this is the bike for you. If you're concerned with value, it is not.

Next year may be the year XC rigs finally get real. It's about time. The descents on some XC courses could easily pass as segments on enduro courses. And some of today's cross-country bikes could easily pass as trail bikes. The BMC Fourstroke, though, is not one of them.

Sure, a few of its bullet points are on the progressive side: It's got a 75.6-degree seat tube angle, 67.5-degree headtube angle and a reduced-offset fork. Plus, BMC designed the new Fourstroke around an integrated dropper, taking cues from the small but growing number of racers who know when it's time to stop counting grams. But those notes just add texture to a tune that's playing much louder in the background. The Fourstroke is still for racing and only racing. And as you might expect, that's not always a good thing.

Those 100 millimeters of travel are incredibly progressive, so the Fourstroke was as unyielding on flat-out sprints as it was on those gut punches southwest Utah calls climbs.

Any elevation gained on our test track was not gained easily. Climbs were shelfy, steep and sudden, and we got a little hung up powering through them on the Fourstroke. That's not an indictment of the linkage itself, though. There was no unwanted pedal feedback, so the suspension stays ready but firm, regardless of wattage. But the Fourstroke's trail-bike-like lines and numbers didn't make it a trail-bike-like technical climber. Mid-travel models like the Giant Trance 29 or Specialized Stumpjumper ST carry momentum up the rough stuff better. Even the Yeti SB100 was a cloud compared to the Fourstroke, though both bikes have the same rear travel.

An 80-millimeter integrated dropper post is perfect for a race setting.

But they are not the same bike. The Fourstroke is not meant to be a cloud. It's meant to be lightning. Those 100 millimeters of travel are incredibly progressive, so it was as unyielding on flat-out sprints as it was on those gut punches southwest Utah calls climbs. Enough so that none of us used the dual-remote-lockout switch. Also, it weighs 23.5 pounds. Factor in the ultra-quick DT Swiss wheels and light-duty Vittoria tires, and you get a bike that encourages and rewards you to mash and sprint in a way no cloud ever could. And none of the aggressive numbers made it feel unwieldy at slow speeds. Granted, we're used to mind-bending cockpits like those of today's Transitions and Yetis, but the non-traditional front end didn't pack any surprises in traditional XC scenarios.

Geometry: BMC Fourstroke 01

It did pack some surprises on the descents. Namely, it didn't scare us. That's not to say we were relaxed, but compared to other fully dedicated race machines like Giant's Anthem 29, the BMC feels remarkably calm. We had to be careful with our line choices, but the Fourstroke made those choices intuitive. In fact, once we started comparing notes, the tires had as much to do with the Fourstroke's dedicated-XC feel as did the bike itself. The extra grams of some extra rubber would be worth it if you want this bike to save you seconds on the downhills. But aside from that, the frame feels remarkably stout. Straight-lining into a rock section didn't set up the flexy feedback loop that it might on other 23-pound bikes. And the short stem and slack head angle meant we could get farther behind the front wheel than any true XC bike has ever allowed.

If you want to go far, fast, the Fourstoke will answer the call.

That dropper post helped too. It only offers 80 millimeters of drop, but that's perfect in a race setting. The effort needed to stow a 125- or 150-millimeter dropper isn't worth it. Eighty millimeters is enough to get it out of the way and keep you safe. And the three-position mechanical design is reliable and fast-acting. When you want it up, it's up. We might have wanted the middle spot to be 20 millimeters off the top instead of off the bottom, and the design is only 50 grams lighter than a 30.9-millimeter KS LEV CI, the lightest mainstream traditional offering. But the Fourstroke is not about mainstream thought. When we approached it from the perspective of a dedicated racer, the Fourstroke is the perfect weapon. It's familiar enough to play by the rules, but radical enough to break a few.

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Check out the rest of the Short-Travel 29 class


Q&A With Antoine Lyard, BMC mountain bike product manager

Where did the inspiration for the Fourstroke 01 come from? Was it a reaction among BMC designers to XC course design getting more aggressive? Or feedback from your athletes?

The inspiration for the new Fourstroke came from the mission to create the ultimate, elite-level, cross-country race bike. We look at it purely from the evolution of World Cup XC racing and what's needed to be fast on those technical courses. Therefore, the Fourstroke attributes are clearly focused on XC racing at the World Cup level, where every second counts. Today's World Cup events feature technical, high-speed descents so the new Fourstroke has a slack head angle and frame-integrated dropper seatpost for navigating downhill terrain, a steeper seat tube angle to position the rider perfectly on the bike on the climbs, plus the simplicity and efficiency of one-by-specific drivetrain.

A few other brands have gone even more aggressive with their XC bikes. Adding travel and bigger tires until they could double as trail bikes. The Fourstroke 01, on the other hand, could not double as a trail bike.

What made BMC land where they did on this bike's travel and geometry? Why not go even further?

It's undeniable that many of the latest XC bikes borrow from trail bikes, and you can look at it from different angles. To us, it all comes down to intended use. Some brands (mostly North American) follow the trend of short-travel trail bikes and claim some XC-race capability. We respect that but don't necessarily follow the same path. Could we have built 2.6-inch-tire clearance? Sure, but the frame would have been heavier, the geo would have been affected, besides XC racers don't run 2.6-inch rubber. Could we have increased RAD dropper travel to 125 millimeters? Yes, but we would have not achieved the same weight savings, and the benchmark was to be lighter than the current lightest XC-specific post on the market. The list goes on from there. When designing a product, there's always a decision on where you want to make the compromise. For the Fourstroke, we had a clear idea of what we wanted to achieve and there was little room for compromise to open up to other types of riding. Keep in mind, BMC does offer the Agonist, which is a 110-millimeter-travel XC bike that utilizes a 'conventional' dropper post. We see a lot of riders running a 120-millimeter-travel fork on their Agonist to create an even more trail-capable XC machine, so that's quite comparable to other trends we're seeing in trail-bike-influenced XC bikes in the states. That said, the new Fourstroke has great potential to influence the future of our mountain bike range.

Where did the motivation to design the RAD dropper come from? Did you have team members using (or wanting to use) a dropper post before the introduction of the Fourstroke 01?

It all started with Julien Absalon. His career began in the era of cross-country when it was all about power-to-weight ratios. Both the bike and athlete had to be as light as possible in order to win in the climbs. Back then, race tracks were made of long climbs and not-so-technical descents, some racers could win World Cups even if they walked steep sections of the main descent. Races were two-and-a-half hours long and consisted of four big loops so it was primarily an endurance effort. Because of XC being in the Olympics, things started to evolve toward a more TV-friendly format with shorter loops, reduced riding time, short and punchy climbs and challenging technical sections. A new breed of racers emerged, Nino Schurter being at the forefront of this. Julien started to be challenged by this evolution because he was still riding a super-lightweight hardtail, he didn't do much core strength training, nor work on his bike-handling skillset. He first went to the full-suspension Fourstroke in 2014, under the pressure of his team manager, and he then won the World Championship that same week. That was a huge shift for him—he now understood there were others ways to be fast than power-to-weight. Then he changed everything related to his training regimen and equipment, and that's when he adopted dropper posts to compensate for his handicap to Nino. He became competitive again, other racers started to mimic his bike setup and training choices, and it snowballed from there. From that moment in 2014 we knew there was no going back from droppers in XC racing. To quote Julien: "With a dropper post, you're not adding 300 grams to your bike. You're adding speed to your bike." With RAD, we just delivered speed in the lightest package possible.