BMC have released an all-new Fourstroke, their full-suspension cross country platform. The biggest news is the race-ready Fourstroke 01 model has what BMC call "the first ever fully integrated, automatic dropper post."
Pinkbike photographer Andy Vathis spotted this prototype version back in 2019.
By "automatic", they mean it can extend and drop at the push of a button, without the rider having to compress the seatpost manually by squatting down on the saddle. BMC call this Autodrop, and the advantage is obvious. Come into a descent and need the saddle out the way? Just press the button and it's gone. No need to stop pedalling, squat down on the saddle and stand back up before you can attack the descent. That's probably not a big deal to the average rider, but used many times over the course of a World Cup race it could add up.
During a race, we activate Autodrop up to a hundred times allowing us to focus entirely on the track and giving us the gold-medal-winning advantage.—Titouan Carod, BMC MTB Racing Team
A normal dropper post gets the energy it needs to return from a spring, which is compressed by the rider pushing down on the saddle. In technical engineering terms, dropper posts are ass-powered. BMC's Autodrop post, however, is air-powered. There's a tank of compressed air in the down tube, which is inflated via a Schrader valve to 14 Bar (200 psi). When the remote button is pressed with the saddle up, the compressed air pushes on a piston which forces the post down and compresses a small coil spring. When the button is pressed again, the air is released and the coil spring returns the post to the extended position.
BMC say the seatpost can do this up to one hundred times; when the pressure drops below 4 Bar (50 psi), it can no longer drop automatically, but it will still function like a regular (ass-powered) dropper post. BMC say that "During a race, BMC riders activate Autodrop up to a hundred times", suggesting they might use the full Autodrop capacity over a long race, perhaps finishing with effectively a "normal" dropper.
The seatpost offers 80 mm of travel and only has a high and a low position - it cannot be set to an intermediate height. There's no word on the weight, but it's based on BMC's RAD seatpost, which shares the same integrated design and oval cross-section. That post is claimed to weigh just 345g, but BMC admit the air tank alone adds 120 grams to the frame weight.
The top-spec Fourstroke 01 LTD's total weight is claimed to be 10.5 kg (23.1 lb). That's not the lightest by race bike standards, but the company acknowledges this. They say their dual-link APS suspension system is heavier than the flex-stay-single-pivot layout that's become nearly ubiquitous in the category. But BMC say their approach more than makes up for the weight penalty: "Extensive testing shows that the Fourstroke and APS suspension are faster than lighter bikes that feature weight-saving suspension systems, proving that superior traction and pedalling efficiency are more important than weight." Obviously, take any company's claims of "extensive [internal] testing" with due scepticism, but it's interesting to see BMC openly sacrifice lightness for overall performance in the XC category, both with the suspension design and the Autodrop feature.
The top-of-the-range Fourstroke 01 LTD
BMC's naming convention is more than a little confusing. The Fourstroke 01 is the no-compromise race bike, and is the only model to use the integrated Autodrop seatpost. It has 100 mm of travel at each end, with 32 mm stanchion forks. There are three spec levels under the Fourstroke 01 banner, all of which offer Autodrop. These are the Fourstroke 01 LTD (€ 12,999), the confusingly-named Fourstroke 01 ONE (€ 10,999), and the Fourstroke 01 TWO (€ 8,999). There's also the Fourstroke 01 FRS V1 frame, shock, fork and seatpost (€ 5,499).
The Fourstroke ONE. (Not to be confused with the Fourstroke 01, obviously.)
Then there's the Fourstroke (minus the "01" part). This is similar to the Fourstroke 01, except it has a regular 31.6 mm diameter (round) seat tube, and so cannot take advantage of the integrated Autodrop or RAD droppers, which both have an oval cross-section. There are four spec levels: ONE (€ 7,499), TWO (€ 6,499), THREE (€ 5,299) and FOUR (€ 4,299).
The Fourstroke LT LTD
Finally, there's the Fourstroke LT, which of course stands for long travel. With a longer shock and fork, it delivers 120 mm of travel at each end but is otherwise similar to the regular Fourstroke. There are three spec levels: LTD (€ 11,499), ONE (€ 5,899) and TWO (€ 4,499).
All three versions have similar geometry. For an XC race bike, the numbers are decidedly on the progressive side, with a 66.5-degree head angle and a 76.7-degree seat angle. The frame geometry of the Fourstroke and Fourstroke 01 are identical, though the cockpit proportions of the 01 are more aggressive. The LT version is near identical too, with no change to the frame angles. Instead, a longer fork and shock create a 15 mm increase in bottom bracket height when the suspension is fully extended.
The Fourstroke 01 LTD and ONE are available from June 2023, TWO from October 2022 and FRS VAR1 from February 2023, and cost 12,999 (13,499 USD), 10,999 (11,499 USD), 8,999 (9,499 USD) and 5,499 (5,999 USD) euros respectively.
Fourstroke ONE is available from October 2022, TWO from April 2023, THREE from June 2023 and FOUR from September 2023, and cost 7,499 (7,999 USD), 6,499 (6,999 USD), 5,299 (5,799 USD), and 4,299 (4,699 USD) euros respectively.
Fourstroke LT LTD is available from April 2023, ONE from January 2023 and TWO from September 2023, and cost 11,999 (12,499 USD), 5,899 (6,399 USD), 4,499 (4,999 USD) euros respectively.