BMC’s cross-country mountain bike has updated kinematics and new rear triangle design

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BMC has updated its Fourstroke cross-country mountain bike, with a new frame seeing refreshed suspension layout, updated geometry and increased water bottle capacity.

BMC has released three new Fourstoke models. The Fourstroke and Fourstroke 01 have 100mm of travel front and rear, and Fourstroke LT which has 120mm of travel front and rear. While these three bikes share the same frame, differences in carbon construction, suspension travel, and dropper post technology make each suitable for different types of cross-country riding.

A highlight from the range is the Fourstroke 01, which includes BMC’s Autodrop dropper post – the first-ever fully integrated automatic dropper seatpost.

BMC has introduced plenty of new specifications across the three new models. The Fourstroke has four specifications to choose from with prices ranging from £4,300 / $4,699 to £7,200 / $7,999.

The Fourstroke 01 has three models plus a frame kit. Pricing ranges from £5,800 / $5,999 for the frameset to £12,400 / $13,499.

Finally, the Fourstroke LT range includes three specifications with prices starting at £4,500 / $4,999 and going up to £11,499 / $12,499.

The most obvious change to the BMC Fourstroke from its predecessor is the bike’s new suspension layout.

BMC still uses its twin-link APS (Advanced Pivot System) suspension to drive the shock. However, the shock now sits horizontally underneath the top tube rather than vertically.

BMC says it updated the kinematics of the system to increase traction and suspension performance on climbs and descents. In addition, BMC believes the virtual pivot designs allow it to design complex kinematics with performance gains that outweigh those of lightweight systems such as flex stays and single pivots.

BMC has tuned the Fourstroke’s anti-squat to fall off through the travel to keep the suspension active deeper in the travel while maintaining pedalling efficiency nearer the sag point.

The new Autodrop dropper post technology is available on the Fourstroke 01 range of bikes. The two-position dropper post has 80mm of travel.

Unlike all other dropper posts, the Autodrop allows the rider to drop the post automatically without squatting on the saddle to lower it.

Inside the down tube of the frame is an air tank. This is filled via a port on the seat tube. When you press the dropper lever, the pressurised air runs through a hose to compress a spring in the dropper post, dropping the post without you having to sit on the saddle.

Pressing the dropper lever again returns the saddle to its pedalling height. No details were given on how many times this can be used before the tank needs to be topped up to keep the pressure correct for activation.

BMC claims Autodrop is for the race enthusiasts who want the maximum time powering on the pedals without having to sit down before dropping into a descent. If you’re using a dropper post dozens of times per race, the fractions of seconds saved by using the Autodrop post could amount to valuable time and energy savings.

The Fourstroke 01 bikes feature an additional port on the seat tube to provide easy access for Autodrop maintenance.

The Foustroke and Fourstroke LT use a conventional dropper post.

Frame stiffness is another area BMC addresses with the new Fourstroke. The rear triangle now uses a second strut that BMC says adds a 20 per cent increase in pedalling efficiency.

The bottom bracket area has also been beefed up to reduce torsional flex in the frame and aid power transfer.

BMC says it took feedback from its athletes when designing the bike and, as a result, the Fourstroke can now fit two water bottles in the frame. To fit two bottles, you’ll have to use side-loading bottle cages and they can’t be larger than 550ml.

Internal cable routing is guided through the front triangle, link, and rear triangle for ease of maintenance. An integrated fork stopper, chainstay protector and the lower link mud flap protect the frame further.

The rear stays have clearance for 2.4in mountain bike tyres. The rear hub is Boost 12x148mm spacing, and the frame uses a press-fit bottom bracket.

BMC has revised the Fourstroke’s geometry giving it the longer, lower, slacker treatment.

The Fourstroke and Fourstroke 01 share the same geometry. The Fourstroke LT has similar geometry figures but its longer suspension travel means it sits higher off the ground.

The head tube angle shaves a degree off the outgoing model to 66.5-degrees, and the effective seat tube angles have been steepened to 76.7-degrees.

Reach numbers have grown to 437mm on the smaller frames to a stretched-out 500mm on the extra-large. That said, the effective top tubes are slightly shorter than the outgoing Fourstroke due to the increased steepness of the effective seat tube angle and slacker head tubes.

Chainstay lengths are short and snappy at 432mm on all sizes. The bottom bracket drop is lowered by 9mm to 53mm on the Fourstroke and Fourstroke 01. It sits 38mm lower than the axles on the Fourstroke LT.

The new Fourstrokerange has 11 models. The bikes are specced with a mix of Fox and RockShox forks and shocks and Shimano and SRAM drivetrains and brakes.

There are four frame sizes to choose from, S, M, L and XL, which BMC says covers riders from under 172cm to over 188cm.

Luke Marshall is a technical writer for BikeRadar and MBUK magazine. He's been working for both titles since 2018 and has over 20 years of mountain biking experience. Luke is a gravity-focused rider with a history of racing downhill, previously competing in the UCI Downhill World Cup. Educated to a degree level in engineering and with a penchant for full-throttle speed, Luke is more than qualified to put every bike and product through its paces to bring you informative and independent reviews. You'll most likely find him on a trail, enduro or downhill bike riding the off-piste tracks around south Wales and the south west of England. He often makes an appearance on BikeRadar's podcast and YouTube channel.

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