Undoing the lockring and changing the chainring: avoid the costly mistakes
Changing the chain and chainring is part of normal maintenance. On a mid-drive motor, however, the chainring sits behind a lockring. That is where the costly mistakes happen: the tool slips, the splines get damaged or the ring is turned in the wrong direction.
Typical mistakes and how to avoid them
- Wrong direction of rotation: On Bosch, the threaded connection has a left-hand thread. This is stated explicitly in the Bosch assembly instructions for the 3rd-generation drive units (BDU310 to BDU386), and the chainring manufacturer KMC also states it for Gen2 and Gen4. Left-hand thread means: to loosen it, you turn clockwise. Check the information for your system before applying force.
- Unsuitable tool: A universal spanner only grips individual notches and slips easily. A precisely fitting tool for your system distributes the force across all the notches of the ring.
- Wrong tightening torque: Bosch specifies 30 Nm for the spider of the 3rd generation. For the Brose lockring, retailers state 28 Nm (magnesium housing) or 25 to 30 Nm (aluminium housing). For other systems, the manufacturer's specification or the marking on the ring applies.
- Dirt in the thread: Sand and dried mud make loosening difficult and can damage the thread. Clean the area thoroughly before applying the tool.
Which tool fits?
On Bosch, the 2nd generation needs a different tool from the 3rd and 4th generations because its ring is larger (around 50 mm compared with 40 to 45 mm). Our guide Bosch motor: identify the generation explains which generation you have. There are dedicated versions for Brose Drive, Yamaha PW and PW-X as well as Specialized.
The right tool for each drive (prices at bikely as of 10 October 2026):
| Drive | Assembly tool (spider) | Lockring |
|---|---|---|
| Bosch 2nd generation (BDU2xx) | Spider for Bosch Gen2, €24.95 | |
| Bosch 3rd generation | Spider for Bosch Gen3, €29.95 | |
| Bosch 4th generation | Spider for Bosch Gen4, €29.95 | |
| Brose Drive S / C / T / TF | Spider for Brose Drive, €29.95 | Lockring for Brose, €14.95 |
| Yamaha PW | Spider for Yamaha PW, €29.95 | Lock nut for PW / PW-SE / PW-ST / PW-TE, €14.95 |
| Yamaha PW-X / 2X / 3X | Spider for Yamaha PW-X / 2X / 3X, €29.95 |
Matching parts: Assembly tools (spider) · Lockrings for Brose and Yamaha
Sources: Bosch assembly instructions BDU310–BDU386 · KMC assembly instructions Bosch Gen4 · KMC assembly instructions Bosch Gen2 · Park Tool: lockring tools · Retailer information Brose lockring. As of: October 2026.
