Brose Drive S: efficient and quiet, but long criticised for its reliability
The Brose Drive S is one of the most appreciated central motors for its natural behaviour and extremely quiet operation. Launched around 2016, it has since evolved into several versions (Drive S Alu, Drive S Mag, Specialized 2.1 and 2.2 derived from Brose). It develops between 90 and 95 Nm depending on the versions and is notably used in bikes from brands like Specialized, BULLS, Rotwild, Fantic or BMZ.
Its main advantage is the use of an internal belt instead of a traditional gear train. This design significantly reduces noise but has also been the source of most problems encountered in the early generations.
The main flaw: the breakage of the internal belt
The most well-known issue with the Brose Drive S concerns the internal transmission belt.
The symptoms are generally:
- sudden loss of assistance;
- motor that seems to run idle;
- inability to transmit power to the transmission;
- sometimes a slipping noise before complete failure.
This problem particularly affected the first generation S Mag motors (2018-2020). Brose acknowledged the existence of premature failures and subsequently modified the design of the belt as well as the motor software to limit the torque spikes responsible for certain breakages.
Water infiltration: the second weak point
The second problem frequently encountered is the infiltration of moisture into the motor.
The observed consequences are:
- oxidised bearings;
- metallic squeaks;
- pedalling resistance;
- sensor degradation;
- long-term electronic failure.
Independent specialists consider that water is one of the main causes of failure in e-bike motors in general, but the Brose has been particularly monitored on this point during its early years of marketing.
Wear of bearings and freewheel bearings
With mileage, several specialised workshops report:
- worn main bearings;
- defective freewheel bearings ("sprag bearings");
- cracking;
- clattering noises;
- crankset difficult to turn backwards.
The first signs are often:
- a squeaking noise;
- a return of resistance in the cranks;
- less smooth pedalling.
Failures of the torque sensor
Some motors exhibit:
- irregular assistance;
- motor that operates in walk mode but not when pedalling;
- random cutouts under load.
Specialist repairers regularly identify the torque sensor as responsible for these symptoms. Unlike some competing motors, the repair can sometimes be carried out without replacing the entire motor.
Cutouts under heavy load
Users report :
- cutout on ascent ;
- loss of assistance after a few seconds of significant effort ;
- need to restart the bike to regain assistance.
These symptoms may be related to :
- a worn belt ;
- an internal clutch ;
- a faulty sensor ;
- or thermal protection.
Improvements made since 2021
Brose has gradually corrected the main weaknesses of the Drive S :
- new reinforced belt ;
- improved sealing ;
- modernised electronics ;
- software updates limiting torque spikes ;
- improvement of the internal transmission.
According to Brose, the teething problems observed on the early S Mag have been largely reduced in recent generations.
Conclusion
The Brose Drive S is often considered one of the most pleasant motors to use due to its smoothness and quietness. In contrast, the early generations suffered from a poor reputation mainly related to the internal belt, to water ingress and to the wear of the bearings. Since 2021, most of these defects have been corrected and the recent versions are significantly more reliable.
The Brose Drive S is therefore an excellent motor in terms of driving sensations, but for a second-hand purchase, it is preferable to prioritise a model produced after 2021 or with a known history of belt and bearing replacement.