BMC Launches the New Fourstroke With An Autodrop Dropper
BMC hasn’t exactly hidden the new BMC Fourstroke mountain bike. There were shots of an unmarked mountain bike under BMC-sponsored athletes for months before its initial drop. The new Roadmachine even won gold for Titouan Carod in the 2022 Val di Sole race.
And so here are the details: the new BMC Fourstroke mountain bike comes in three iterations, with further optimized suspension, even more radical geometry (for XC) than the outgoing bike, and with an automatic dropper post. BMC has always done their mountain bikes a bit differently than the consensus, and that continues here.
BMC Fourstroke Details
A few years ago, BMC dropped the Speedfox, a trail bike that had one unique feature: dropper post actuation tied to suspension settings. Not long thereafter BMC dropped the outgoing Fourstroke, which integrated the dropper post design into the frame. Needless to say, BMC has no hesitation in experimenting with how you raise and lower your seatpost for climbs and descents.
In short, the Autodrop setting that is found on the Fourstroke 01 models - read:race-centric models) allow the rider to extend AND drop the saddle at a push of a button without having to place their weight on he saddle. Why? BMC claims it leads to improved lap times, not only from adding a dropper post but also from having the split-second extra to pedal before hitting a downhill section of a course. Of course, if you come to a descent and need the saddle out the way, simply press the button and it goes away.
To note, this is not an infinitely-adjustable dropper but a two-position dropper that offers 80mm drop regardless of size. Part of that is the added compressed air tank underneath the dropper. It's inflated via a Schrader pump (and can be inflated with a shock pump). The air forces a piston down and the saddle drops. Press it again and it presses the piston again and the seatpost's spring returns to full extension. The seatpost is said to weigh just 350g, making it one of the lightest dropper posts on the market
Autodrop is currently only offered with the Fourstroke 01 models. Other models feature a standard 31.6mm dropper post, be it the standard Fourstroke or the Fourstroke LT.
Yes, there are now effectively three different models now. The Fourstroke 01 is the model that garners the most attention, with its integrated dropper post and slightly lower-weight frame. This is the XC race-specific model, with 100mm suspension travel. Then there is the Fourstroke, which has the same geometry and suspension changes but a simplified carbon layup that includes the swap to a standard 31.6mm dropper post.
Finally is the “downcountry” model of sorts, the Fourstroke LT. It takes the simplified carbon frame and adds just a slightly longer stroke shock for 120mm suspension travel and a 120mm suspension fork. It eschews the remote lockout that other Fourstroke bikes receive, and also comes fitted with Maxxis Rekon tires across all models. We reckon Fourstroke LT is the model folks without race-specific aspirations should go for
Standover heights are lowered on the new Fourstroke by as much as 45mm (more on that later). Fourstroke also accommodates two water bottles, though neither are on the seattube as one might expect. Rather, two standard 21oz bottles can be fitted as long as side entry bottles are used.
BMC offers some user-friendly changes that we’re happy to see. The Fourstroke now offers fully-guided cable routing through the front triangle, lower link, into the rear triangle, and to the brake caliper or rear derailleur. As before, there is an integrated bump stop to prevent the fork fork or handlebars from destroying the frame in an accident. The chainstay protector sees a bit more protection than before, though there is no included protection for the downtube.
BMC claims ample clearance for 2.4” XC tires.
BMC Fourstroke Suspension Details
BMC is using a new suspension layout, now ditching the linkage-driven suspension BMC used previously. Its still called APS - Advanced Pivot System - and it still features a twin-link layout like the previous bike. Doing so, according to BMC, allows them to be able to really fine-tune the suspension kinematics to do exactly what they want at every stage of suspension travel.
They’ve upped made the spring curve just a bit more progressive in an effort to improve small bump sensitivity. Improving that sensitivity means more grip on technical, loose climbs. Alongside that is a decreasing anti-squat curve, which BMC says is done once again for the sake of improving traction on climbs.
And they say everything you’d want to hear: more traction than other short-travel mountain bikes, all the suspension efficiency one could need on climbs, less pedal kickback deep in the suspension travel, and more predictable feel on the descents. It is interesting to note that BMC have continued with a dual link suspension in comparison to the more popular - but less sensitive - single pivot suspensions on other XC bikes. BMC is typically known to shave weight where possible, so any extra weight is there for a reason.
BMC Fourstroke Geometry
The previous generation Fourstroke received a whole lot of attention for its then-long reach, slack head angle, and a geometry chart that looked far more aggressive than its 100mm suspension suggested. BMC doubled down here, with a one-degree slacker 66.5 degree head angle and a matching 75.6-degree seat angle. Bottom bracket heights are dropped about 9mm for improved stability, and standover height is at 725mm across all sizes.
That number isn’t just among the lowest standover heights for any 29er XC mountain bike, allowing for plenty of space for shorter riders, but it offers a ton of space for a dropper post. Fourstroke and Fourstroke LT riders will likely be surprised by how much flexibility they’ll have in their dropper post sizing.
The Fourstroke also receives longer reach measurements, numbers that again feel more trail than XC racer. Reach measurements are bumped up about 15mm across all sizes, but stem lengths stay about the same. Chainstay lengths are a stubby 429mm, well on the short end of the spectrum. The result is a roomier cockpit and overall geometry numbers that would’ve been only in the BikeCAD dreams of a fervent Pinkbike commentor.
Frame geometry of the Fourstroke and Fourstroke 01 are the same despite the small frame changes. The Fourstroke LT offers the same frame angles thanks to the longer 120mm fork and matching shock. The big difference here is the 15mm taller bottom bracket height that comes with the additional suspension travel.
Who Should Ride the BMC Fourstroke?
There are so many good cross-country mountain bikes out there, and a slightly narrower list of fantastic “downcountry” mountain bikes. But those looking for a bike at the forefront of technology will really come to appreciate the BMC Fourstroke. It might be best optimized for the increasingly-technical cross-country courses, but its slack geometry provides plenty of confidence on faster descents.
The Fourstroke isn’t necessarily for weight weenies, as its APS suspension system exchanges some weight savings for improved sensitivity and overall performance. BMC claims they’ve used “extensive testing” to show their bike is faster than others that feature weight-saving suspension systems. That said, it is still lightweight, as top models are every bit as light as the likes of the SCOTT Spark RC or Cannondale Scalpel Si.
A top-spec BMC Fourstroke 01 LTD is said to weigh in at just 23 lbs, making it light, but not the the lightest option. Those looking for something lighter might consider the Orbea Oiz mountain bike, a featherweight that also offers more traditional geometry. The SCOTT Spark RC should definitely be on the shortlist for anyone looking for a fast XC mountain bike, and those looking for heaps of traction from their short-travel bike might look at a Cannondale Scalpel. But none of these bikes have the lightweight integrated dropper, the aggressive geometry, and the sophisticated suspension of the Fourstroke.
While the BMC Fourstroke sees a considerable change to its suspension that redefines how the Fourstroke looks, the performance has taken a step forward. Its forward-thinking geometry takes another step ahead of other XC bikes, and the inclusion of an Autodrop dropper seatpost is a novel addition to the bike. And if that’s not your cup of tea, BMC offers a version with a standard dropper post. Want a lightweight mountain bike with a bit of the edge taken off? The 120mm BMC Fourstroke LT is the ticket.
There’s no shortage of great cross-country mountain bikes out there, but BMC’s latest Fourstroke might just be one of the best.
Words by Alvin Holbrook. Images provided by BMC Switzerland.