Brose Drive S Mag
Magnesium-housing base unit. Belt drive, dual freewheels, 410% assist. OEM platform for Specialized 2.1/2.2, SRAM Eagle Powertrain, many open-system eMTBs.
Brose Drive S Mag is the magnesium-housed flagship of the Brose Drive S family, an open-OEM full-power eMTB unit that has underpinned everything from the Specialized 2.1/2.2 drive to SRAM's Eagle Powertrain. Headline numbers are 90 Nm nominal torque, 565 W claimed peak, 250 W rated continuous, 36 V architecture and 2.9 kg on the scale. It launched in September 2018 as a lighter, more compact replacement for the aluminium Drive S, and despite an eight-year run it still anchors current 2024/2025 bikes from Fantic, Rotwild and BH. As one community thread put it, the Brose lineage is described as "a cultivated powerhouse with a real Brose feeling", a useful framing for a motor that has always traded outright aggression for natural delivery.
The numbers. Brose claims 90 Nm and 565 W peak; an independent dyno pulled 493 W under sustained load, with Velomotion's bench recording 575 W at the chain in short bursts, which lines up with the claimed figure once drivetrain loss is accounted for. Assist tops out at 410%, up from 380% on the Drive S Alu, and Brose's Flex Power Mode modulates output by cadence and pedal force rather than running a flat power ceiling. There is no separate boost-torque figure: 90 Nm is the headline number across all modes, with Specialized's Shuttle tune being the most aggressive variant in the wild. A 2020 software update fixed early belt-failure behaviour and Specialized later pushed firmware to a 20-amp ceiling, with @Zimmerframe noting Specialized progressed through Drive T, Drive S and Drive S Mag with their own firmware on top.
Character and feel. The S Mag's defining trait is silence and zero drag above the 25 km/h cutoff, courtesy of the Gates belt and twin sprag clutches. @Rob Rides EMTB described it on a Levo as the "Smoothest motor with 90Nm" and "Quietest motor both up and down", and Velomotion's lab work backs that up, calling it "by far the quietest engine in its performance class" with little pitch variation under load. Eco and Trail feel almost imperceptible to engage; the 25 km/h decoupling is "so smoothly that the transition is almost imperceptible". Push it into max Flex Power on a hot day, though, and you will see thermal rollback. Community testers consistently rate it quieter than Bosch CX Gen4 and Shimano EP801, though @emtbeast notes the newer Brose Drive³ Peak is quieter still than the S Mag.
Compatibility and ecosystem. As an open platform the S Mag accepts third-party batteries (most OEMs spec 500-750 Wh in-tube cells; Rotwild pairs it with a 750 Wh pack on the R.X750), with Brose's own system using a 630 Wh InTube. Displays range from the BLOKS 14d remote-and-display combo to the Marquardt Just Drive 3 and Specialized's Mastermind TCU. The Brose eBike app handles firmware updates and per-mode power tuning between 0-100%, while Specialized riders use Mission Control with the BLEvo community app on top. Standards are conventional: ISIS interface, 55 mm chainline, and both threaded and press-fit mounting options across two housing variants. @PaoloBLEvo's archival find on firmware 7.1.1 showing no cutoff at 30 km/h on the early Drive S Alu is a reminder that firmware history matters; current Specialized tunes are properly speed-limited.
Reliability and known issues. Early S Mag units (2018-2019) had a genuine reputation for belt and tensioner failures, which is exactly why @emtbeast notes the "main culprits for the most of the Brose motor failures on the Levo was the belt and the tensioner". Post-2020 software and a mechanical revision largely closed that out. The other failure mode is sensor-side: @fm4711's teardown of a "no motor" error on a Drive S found a clean belt and planetary gear with no burned components, suggesting torque ring or hall sensor failure, and crucially the circuit board is custom-programmed per motor and not swappable. Plan for a full unit replacement rather than a board-level repair. @MNCraig had a 2024 Levo Alloy Comp delivered with electrical failures that couldn't be resolved by parts swaps and required a complete bike replacement, which fits the pattern.
Bikes you'll find it on. Trail riders should look at the Fantic XTF 1.6 Carbon Factory 2025 (160/160 mm) or the lighter BH AtomX Lynx Carbon 2025 at 150 mm. For enduro the Fantic XMF 2024 at 170 mm is the sweet spot, while the Fantic XXF 2024 pushes to 200 mm of travel for park use. Rotwild R.X750 2024 is the integration benchmark, mated to a 750 Wh pack and Rotwild's own tune. The Transition Repeater 2025 (now discontinued) used the most raw, least-filtered tune in the lineup. Fantic's firmware leans aggressive on initial bite; BH runs a noticeably softer Trail map.
Verdict. The Drive S Mag suits riders who prioritise quiet, drag-free pedalling and natural modulation, and who accept that 90 Nm and 565 W peak now sit below the Bosch CX Gen5, Brose's own Drive³ Peak (95 Nm) and the Avinox M2S (120 Nm). The real trade-off is housing bulk: at 2.9 kg the unit is competitive on weight, but its physical volume creates a visible down-tube bulge that modern frames hide less elegantly than 2024-generation rivals. Current production motor, in market since 2018, succeeded at the platform level by the Brose Drive³ Peak from summer 2024 but still shipping on 2024/2025 model-year bikes.
