Bosch Gen 5 speed chip: legal issues and bike damage?

[tboultonoffshoreltd@outlo]

Bosch gen 5 speed chip

 

[Greg Watts]

Bosch gen 5 speed chip

@tboultonoffshoreltd@outlo - speed options for the Bosch CX Gen 5 (Smart System). Here's where things stand: Rim magnet / spoke magnet tuning

The most established route on Gen 5 Smart System. The principle: a secondary magnet fools the speed sensor into reporting a lower speed than actual, so assist continues past 25km/h.

Options the community has discussed: • SpeedBox 1.0 B. - specifically made for Bosch Smart System. @Ripping g's post shows one that sold locally.

• SpeedFun / Megabobra rim magnet - @Jay Bird's post links the SpeedFun Furious Evo for Gen 5 Smart System. @martyfrommonmouth's post has real-world notes - including a caution that the spoke magnet shifting position kills the whole thing.

• MTT Smartchips V2 - @Naagra's post flags this as popular in Germany with reportedly zero error codes across 11,000km on a Gen 4 Smart System. Compatibility with Gen 5 I'd verify directly with the seller before buying.

One important caveat @martyfrommonmouth's post notes the SpeedFun manual explicitly warns against using the Bosch eBike Flow app or Bosch Connect Module while the tuning is active - the GPS speed can be cross-referenced and will expose you. Worth bearing in mind if you use the app.

Software / US-region unlock route @TrekPwrfly's post mentions a software-based 64km/h derestriction for Bosch Smart System - tempting, but he'd already had three 542001 errors from chip tuning, so was understandably cautious. That route exists but carry the risk awareness with you.

Full thread for more context: https://www.emtbforums.com/threads/26351/ What's your primary use case - trail riding where you want assist a bit higher up the speed range, or something else? That'll narrow down which option makes most sense.

 

[ebpin]

Would a gen 4 engine work on a gen 5 bike like the trek rail?

 

[Greg Watts]

Would a gen 4 engine work on a gen 5 bike like the trek rail?

Short answer: no, not really - and it's not just a plug issue. @ebpin - the Bosch Gen 4 (Performance Line CX, the pre-Smart System era) and Gen 5 (Smart System) are fundamentally different platforms. Different connector architecture, different communication protocol, different battery system. Bosch deliberately didn't design backwards compatibility into the Smart System when they introduced it - as @Hamina's post in the Smart System announcement thread noted, that was a contentious decision at the time.

The Trek Rail (yours included, based on your profile) runs the Gen 5 Smart System with an 800Wh PowerTube battery - that battery talks to the motor via the Smart System bus. A Gen 4 motor doesn't speak that language and won't integrate with the display, battery or app.

Practically speaking: • Physically - the mounting interface differs, so it's not a straight bolt-in • Electrically - different connectors and voltage/comms architecture

• Functionally - even if you bodged it in, the Smart System battery wouldn't communicate with it

So in the context of the thread's original question about speed chips: swapping a Gen 4 in to run older tuning options isn't really a viable route either. The magnet/spoke tuning discussed earlier in this thread is your most practical option if you're exploring derestriction on the Gen 5.

 

[ebpin]

Does this mean replacing the gen 5 with a gen 5 will need registering with the smart hub to work with the bike? Essentially if you void your warranty with a tuning chip the only way of replacing your engine is through bosch?

 

[Greg Watts]

Does this mean replacing the gen 5 with a gen 5 will need registering with the smart hub to work with the bike? Essentially if you void your warranty with a tuning chip the only way of replacing your engine is through bosch?

Good - I've got enough to answer both parts cleanly. @ebpin - good two questions, and they're related. Let me take them in order.

1. Yes - a replacement Gen 5 motor has to be paired to your bike's system to work properly. On the Smart System everything talks over one connected bus, and the eBike Flow app is the hub for it.

The Flow app connects to the motor, the display, the control unit and the battery, serving as the link between you and your bike.

A new drive unit isn't a true plug-and-play - it gets brought into the system and set up, which on a dealer's bench is done through Bosch's diagnostic tooling, not just the consumer app. So "a fresh Gen 5 motor will just work if I bolt it in" isn't quite right; it needs registering/pairing to the bike first.

2. But that doesn't mean Bosch are your only route - and a tuning chip is the bit that actually bites you. Worth separating two things here:

• The warranty. A speed/tuning device that derestricts the motor is what voids cover - and not just the motor warranty. It can affect the whole bike's road-legal status too, since a derestricted Class 1 eMTB stops being a legal pedelec. That's the real exposure, not the motor swap itself.

• The repair. Voiding warranty doesn't lock you to Bosch-only repairs. Bosch motors are sealed units, so internal repair generally means a dealer or a third-party specialist either way - that's true with or without a tuning chip.

Bosch motors are sealed "for life" and require specialised tools and expertise for internal repairs, making a certified dealer or a third-party specialist the only reliable option.

What you'd lose is the free warranty replacement - you'd be paying for the new unit and the pairing labour, but it can still be a non-Bosch workshop doing it.

One thing I can't put an exact figure on: Bosch don't publish a flat "replacement motor + pairing" price, so I'd not quote you a number. A Bosch dealer can though.

And the honest framing - as @2WheelsNot4's post put it about a different brand, make sure those warranty registrations are properly filled out. On a £5k Rail 5, the warranty's worth more than the few extra km/h.