BOSCH RIM MAGNET – TECHNICAL OVERVIEW FOR THE SMART SYSTEM (BES3)
Introduced in late 2021 and implemented across the 2022 model year, the Bosch Rim Magnet (BRM3400) is a core component of the Bosch Smart System (BES3). This system represents the 4th generation of Bosch e-bike drive units and introduces a significant change in speed sensing technology.
In contrast to previous Bosch motor generations (Gen2 and Gen3), which used external chainstay-mounted sensors and spoke / brake rotor magnets, the Smart System integrates the speed sensor directly into the motor housing. The corresponding rim magnet is mounted on the valve stem of the rear wheel—either tubeless or standard inner tube.
This integrated architecture improves both system precision and durability while reducing the risk of misalignment or sensor damage. The magnetic signal from the rim magnet is detected internally by the motor, enabling accurate speed calculations without the need for external sensor alignment or additional mounting brackets.
This design simplifies installation, enhances reliability, and supports a cleaner overall aesthetic—especially on modern e-bike frames designed for fully integrated electronics.
BOSCH (BES3) RIM MAGNET TUNING – RIM MAGNET TUNING SOLUTIONS
The Bosch Smart System Rim Magnet uses a new setup with an internal speed sensor and a rim-mounted magnet. This change makes older tuning systems incompatible, as they were designed for external sensors on the frame and magnets on the wheel spoke and brake rotor. To overcome this, new tuning solutions have been developed specifically for the rim magnet system, allowing them to work correctly even with the updated speed detection design.
Ebikes Parts and Accessories (EPA) offers some of the most popular and reliable e-bike tuning solutions on the market, backed by a proven track record of performance and durability. Below are our available tuning solutions designed specifically for the Bosch Smart System with rim magnet.
The BadassBox 5 is one of the world’s best-selling external e-bike tuning devices, and it is now available in a version compatible with the Bosch Smart System and rim magnet setup. It installs quickly, requires no tools, and can be removed just as easily. Legal for use on private property, it’s an ideal plug-and-play solution for riders who prefer a simple and reliable performance upgrade.
The SpeedBox is a popular tuning brand well known in the electric bike tuning industry. Indeed, SpeedBox Bosch tunings are available and compatible with all Bosch motors and models on today market, including the latest Bosch Smart System motors with the magnet on the rim. But there is more to add to the Bosch list of tunings since in 2019 SpeedBox released the more advanced B.Tuning series of tunings that connects with your mobile phone via Bluetooth connectivity. With the SpeedBox phone app now you can switch the engine on/off, lock the motor, save and share your trip data, monitor the speed, distance travelled, max speed, cadence, battery level, and much more.
Another excellent tuning is the VOLspeed which has been on the market for very long time and are well known for their reliability and unique features. Indeed, with the VOLspeed apart from setting up the maximum assisted speed to improve battery consumption you can also adjust the engine behaviour for a smoother engine engagement and disengagement and thus improved handling capabilities on technical terrains. All this features can be programmed via the keys on the display.
SpeedFun was the first tuning manufacturer to release a reliable wired solution compatible with the Bosch rim magnet system. With over 10 years of experience in the design and production of high-quality e-bike tuning devices, SpeedFun has built a reputation for innovation and reliability.
⚠️ IMPORTANT: COMPATIBILITY CHECK REQUIRED BEFORE PURCHASE
Before purchasing this device, please verify the “Product Code” of your Bosch Performance Line CX or SX motor. The product code is printed on the motor label.
In the example below, Bosch's two typical label formats are shown, with the product codes highlighted in red.
Compatible Motor Types:
• Performance Line SX – BDU314Y (manufactured from 2023)
• Performance Line CX – BDU374Y (manufactured from 2024)
• Performance Line CX – BDU384Y (manufactured from 2025)
❌ NOT COMPATIBLE IF YOUR BIKE HAS:
• Bosch ABS system
• Bosch GPS module (unless fully disconnected to prevent tuning detection)
Make sure to check your motor label carefully to ensure compatibility before ordering.
Here our list of tuning for the Bosch Rim Magnet engine configuration
Volspeed Bosch Rim Magnet BDU37 and BDU38
SpeedFun for Bosch Rim Magnet BDU36
SpeedFun for Bosch Rim Magnet BDU37
SpeedFun for Bosch Rim Magnet BDU38
