After installing the latest Bosch firmware update to my Bosch performance cx race version 4 motor, it seems to be noticeably louder...

[jbodnar]

After installing the latest Bosch firmware update to my Bosch performance cx race version 4 motor, it seems to be noticeably louder...is there an easy way to fix this?

 

[Greg Watts]

After installing the latest Bosch firmware update to my Bosch performance cx race version 4 motor, it seems to be noticeably louder...is there an easy way to fix this?

@jbodnar - increased noise after a Bosch firmware update is a known phenomenon, but the cause depends on which update you installed and what "louder" means specifically.

First, clarify what you're hearing: • Higher-pitched whine/mechanical tone - the Performance Update 2.0 (rolled out 4 May 2026) pushed the CX-R to 120Nm with 600% rider support. More torque delivery = more load on the drivetrain internals. Some riders report the motor sounds more "worked" under load. This isn't a fault - it's the motor doing more.

• Rattle or clunk at low power/cadence - this is a separate, pre-existing issue on Bosch CX motors generally. Worth noting that @DBSwiss found firmware updates didn't fix the low-power rattle - so if that's what you're hearing, the update likely didn't cause it either, just made you notice it.

Practical steps: • Check your chainring and crank are properly torqued - extra torque delivery will amplify any slop

• If it's a new high-pitched whine specifically under load at higher torque levels, that's expected behaviour post-update and not a symptom of damage • If it's a grinding or rhythmic knock, that warrants a dealer diagnostic - don't ride on it

I can't confirm official Bosch noise-level specs post-update (they don't publish those figures). If it's anything beyond a change in character rather than a new fault sound, worth getting it on a stand at your LBS and running through the Bosch diagnostics app.

What exactly does it sound like, and at what point in the ride?

 

[jbodnar]

@jbodnar - increased noise after a Bosch firmware update is a known phenomenon, but the cause depends on which update you installed and what "louder" means specifically.

First, clarify what you're hearing: • Higher-pitched whine/mechanical tone - the Performance Update 2.0 (rolled out 4 May 2026) pushed the CX-R to 120Nm with 600% rider support. More torque delivery = more load on the drivetrain internals. Some riders report the motor sounds more "worked" under load. This isn't a fault - it's the motor doing more.

• Rattle or clunk at low power/cadence - this is a separate, pre-existing issue on Bosch CX motors generally. Worth noting that @DBSwiss found firmware updates didn't fix the low-power rattle - so if that's what you're hearing, the update likely didn't cause it either, just made you notice it.

Practical steps: • Check your chainring and crank are properly torqued - extra torque delivery will amplify any slop

• If it's a new high-pitched whine specifically under load at higher torque levels, that's expected behaviour post-update and not a symptom of damage • If it's a grinding or rhythmic knock, that warrants a dealer diagnostic - don't ride on it

I can't confirm official Bosch noise-level specs post-update (they don't publish those figures). If it's anything beyond a change in character rather than a new fault sound, worth getting it on a stand at your LBS and running through the Bosch diagnostics app.
What exactly does it sound like, and at what point in the ride?

I installed the Performance Update 2.0 but I have the gen 4 motor BDU3760, not the newer gen 5 so the torque was not increased, but the motor seems louder going uphill in Race, emtb+, and auto modes (I currently don't use eco much; I believe my modes have not been customized).

 

[Greg Watts]

I installed the Performance Update 2.0 but I have the gen 4 motor BDU3760, not the newer gen 5 so the torque was not increased, but the motor seems louder going uphill in Race, emtb+, and auto modes (I currently don't use eco much; I believe my modes have not been customized).

@jbodnar - that's a useful clarification. If the torque wasn't increased (Performance Update 2.0's torque uplift is Gen 5 / CX-R specific), then the noise change on your Gen 4 is more interesting.

A few things worth considering: What the update may have changed on Gen 4:

• Assist curve behaviour - even without a torque increase, firmware can alter how sharply the motor responds to cadence and load, which changes the acoustic character under effort

• Motor management thresholds - Race and eMTB+ modes may now push the motor harder within its existing ceiling before backing off, which can manifest as a more strained sound on steep climbs

The modes you're noticing it in: Race, eMTB+ and Auto are all high-assist modes. If the update shifted how aggressively the motor applies power in those modes - even on Gen 4 - you'd hear it most exactly where you're describing: climbing under load.

Practical check: • Is it a higher-pitched working tone, or something more mechanical (rattle, grind, rhythm)? The former is likely just changed assist behaviour. The latter warrants a dealer diagnostic.

• Worth running a Bosch diagnostics check via the Flow app to confirm no error codes are lurking in the background.

I'd want to stress: I can't confirm the exact parameter changes Bosch pushed to Gen 4 in this update - that detail isn't published. If the sound is consistent and not deteriorating, it's likely behavioural. If it's getting worse ride-to-ride, get it on a stand.