Swiss brand BMC’s latest cross-country race machine has fresh geometry, tweaked suspension kinematics and an integrated seatpost that drops at the touch of a button. While the updated geometry contributes to a riotously fun ride, how well does all this new tech work? And, with just 100mm of rear-wheel travel on offer, how does the Fourstroke stack up against the 120mm-travel bikes that are becoming commonplace in cross-country racing?
BMC Fourstroke 01 TWO frame details
BMC says it focused largely on increasing stiffness when redesigning the Fourstroke frame. It’s constructed from the brand’s premium carbon fibre, with extra volume added around the bottom bracket to reduce torsional flex and aid power transfer. The rear triangle now has strengthening struts on both sides (before, there was only one on the non-driveside), which are claimed to increase pedalling efficiency by an astonishing 20 per cent.
BMC still uses a twin-link suspension system, but the shock now sits horizontally rather than vertically. While this ‘Advanced Pivot System’ design is heavier than a single-pivot setup, the brand say it provides greater traction and pedalling efficiency, resulting in a faster bike. The frame is longer and slacker than the previous model for improved performance on steeper, faster descents, with a 477mm reach and 66.5-degree head angle on the large size I tested. However, the chainstays have been kept short (429mm) to aid power transfer and agility.
BMC has added mounts for two water bottles on the down tube – ideal for marathon racers and longer rides. Internal, guided cable routing and a large port to access the Autodrop seatpost mechanism should allow for hassle-free maintenance. A small chain guide keeps the drivetrain in check, while a chainstay protector, lower-link mudflap and integrated fork stopper protect the frame and shock.
|Seat angle (degrees)||76.7||76.7||76.7||76.7|
|Head angle (degrees)||66.5||66.5||66.5||66.5|
|Rear center (mm)||432||432||432||432|
|Seat tube (mm)||420||440||470||510|
|Top tube (mm)||574||597||621||649|
|Head tube (mm)||83.8||93.5||101.3||117.6|
|Fork offset (mm)||44||44||44||44|
|Bottom bracket drop (mm)||53||53||53||53|
|Crank length (mm)||170||170||175||175|
|Stem length (mm)||50||60||60||70|
BMC Fourstroke 01 TWO specification
The fork and shock can be locked out on the fly for greater climbing efficiency. The race-focused RockShox SID SL Select+ fork and SIDLUXE Select+ shock contribute to the bike’s light, stiff and efficient feel, and can be firmed up using a Grip Shift-activated lockout. SRAM’s Level TLM brakes and GX Eagle AXS drivetrain provide sufficient stopping power and smooth wireless shifting. The DT Swiss XR 1700 wheels are fitted with fast-rolling Vittoria Mezcal 2.35in tyres. The cockpit comprises a BMC bar and stem, plus a Fizik saddle.
The most notable addition for this year is the Autodrop seatpost. While other dropper posts extend at the touch of a button but have to be compressed by your body weight, this one drops without any downward pressure, thanks to an air tank in the down tube. BMC say this saves vital energy and time when you’re between the tapes. Pressurising the tank to its maximum of 14 bar (about 200psi) should give you around 100 actuations. When the pressure drops below 4 bar, the post is designed to continue to work like a standard cable-operated dropper.
BMC Fourstroke 01 TWO ride impressions
SRAM’s GX Eagle AXS wireless shifting works a treat. It’s hard not to smile when you throw a leg over the new Fourstroke. It’s surprisingly capable on techy descents for a 100mm cross-country bike, yet eats up climbs for breakfast. Its handling is exceptional, the progressive geometry helping it to conquer the most technical ascents and gnarliest downhill sections. The long front end and 760mm-wide bar enable efficient use of your lungs, while the steep 76.7-degree seat tube angle keeps you centred over the bike and makes it easy to manoeuvre when things get technical.
With 53mm of BB drop, the BMC has a low centre of gravity, which helps it feel planted and well-balanced, no matter how rowdy you get. The suspension handles impacts impressively well, and I never felt I needed more than the 100mm of travel on offer, even on the steep, rough trails of north-east Scotland.
The suspension handles impacts impressively well. Directed in a straight line, this bike flies, feeling stable and giving you the confidence to point and shoot. The low BB caused a few pedal strikes on rocky, steep climbs and tight, rooty descents – especially towards the end of long rides, when I was starting to flag. I also found the steering a little twitchy at times, with the light front end becoming slightly overreactive when speeds decreased and the trails got tight.
The Mezcal tyres performed well in the dry and held their own in the wet, though, only letting me down when conditions got sloppy. While the Autodrop seatpost was a treat, working well and increasing confidence on descents, I had to pump it back up on a regular basis, and ended several rides with an empty air tank. I can see the benefits for racers, though.