If the BMC Fourstroke name looks familiar, but the suspension layout doesn’t, that’s because the Swiss brand has totally revised their cross country and marathon platform, and in case you didn’t notice, they’ve also added a TQ-HPR50 motor to the system, hence the AMP suffix on the model name.
The 120 mm travel Fourstroke LT AMP frame design houses the same visually undetectable and nearly silent TQ motor that Trek uses in their Fuel EX-e that we tested back in July
• Carbon fiber front & rear triangles
• APS dual-link suspension design
• 120mm front and rear travel
• TQ HPR50 drive, 360 Wh battery
• 66.5° head tube angle
• 77° seat tube angle
• Sizes: S, M, L, XL
• Pricing: $7,299 - $14,999 USD / €6,899 - €13,999
Not wanting to limit the hydration capacities on the bike despite the 360 Wh battery in the downtube, BMC rearranged the orientation of the shock on the dual-link carbon fiber frame to hold two water bottle inside the front triangle, while nestling an integrated display into the top tube and ditching the integrated dropper used on the unassisted version of the Fourstroke.
The Swiss aren’t known for creating affordable products, but they are known for their high standards. BMC offers four models in the range beginning at $7,200 USD and climbs to a price that will leave a hole in your bank account - $14,999 USD. The bike will be delivered in Europe first, starting in December 2022 with the highest priced model. A few months later, they will be available in the USA. From there, the pattern will continue as the less expensive models trickle in.
Frame and Motor Details
Straight, sharp lines make for a clean outline on the Fourstroke AMP LT with no sign of a battery or motor visible from the side view. If you take a top-down view of the frame though, you'll see the integrated TQ display screen and likely pick up on the charge port at the top of the downtube, safely tucked out of harm's way. In the theme of creating clean lines, BMC has routed the rear brake line, and other necessary cables on the three lower-priced models, through a port on the side of the headtube.
In order to fit wider variety of seat posts, BMC moved away from the integrated and proprietary fit of the their in-house, oval-shaped dropper post that the standard Fourstroke features. By using a 31.6mm seat tube, consumers can run with the stock post or choose from an assortment of options on the market.
As for the motor, the system is identical to the HPR50 unit that so easily snuck past unsuspecting trail users during out previous test. In total, the assistance from the mechanical system weighs only 3.9 kg and produces 50 Nm of torque. All of the modifications to power output, controls, and visuals will be accessible via the TQ Motor app.Suspension Design
Judging by the lines of the Fourstroke AMP LT and the short, upper rocker link, you might wager that this frame could have been subject to a flexstay pivot, but BMC stuck to their kinematic objectives which were only achievable by using the APS dual link configuration. BMC states that the new kinematics decrease the anti-squat to reduce chain growth and pedal kickback deeper in the stroke. At the same time, they've added more progression to increase small bump sensitivity and more support towards the end of the travel.Geometry
Although this lightweight, marathon-style eMTB is built with similar components that you’d see on the XC World Cup circuit, it does receive a steep 77-degree seat tube and marginally slacker 66.5-degree head tube angle. The four sizes have smaller gaps between each reach number, starting at 437 and jumping up roughly 20mm per frame size, however, the chainstay lengths remain at 435 across the board.Specs
The Fourstroke AMP LT LTD is complete with Fox Factory suspension, including a 34 StepCast fork, and carbon DT Swiss XRC 1200 wheels, leaving little to be desired on the $14,999 top-end package that also includes full matching purple paint to the wireless oil slick SRAM XX1 AXS components. Dropping down the pricing ladder, the suspension on the AMP LT ONE moves over to RockShox, with a SID and Super Deluxe Air in the Ultimate trim, and alloy DT Swiss wheels, but keeps the SRAM G2 RSC brakes with 180mm rotors at each end.
From there on out, the two lower price points of the Fourstroke AMP LT TWO and THREE continue with RockShox suspension, but shifting and braking duties are covered by Shimano. Throughout the range, Maxxis Rekon 2.4" EXO tires are the choice for rubber and Praxis takes care of the cranks with alloy options.