Bosch CX gen 4 swap for gen 5?

[nickf]

I'd be interested in swapping out a gen 4 Bosch CX for the new gen 5 in my 2022 Trek Rail. I know that the new Bosch model has different mounting holes so it is not directly interchangeable. However, the old gen 4 was actually fitted into the bike frame by means of intermediate fixing plates that bolted both onto the motor and also into the frame.

It seems to me that it should be possible to create a new set of fixing plates with new bolt patterns that would accept the gen 5 motor. Does anyone know if this has/can be done? I seem to recall that in one of Rob's podcasts they mentioned that the gen 5 motor was presented to the journalists at its launch in a Pivot Shuttle bike that normally ran a gen 4 motor. So the assumption is that Bosch had created precisely the kind of adapter plates that I am thinking of.

Given that it might be possible to mechanically fit the new motor into my old Rail, I am guessing that it would also be necessary to use the latest battery models and controllers which would probably require some additional fettling?

 

[RustyMTB]

Far as I know, the Gen 5 is a Gen four with some refinements. I'm interested in the idea but wonder if an adapter bracket might be the least of your problems if you see what I mean? If they've changed anything in the software, that would likely kill it off but I'm here with popcorn for the experience.

 

[megabobra]

I'm keen for this too!

 

[nickf]

My 2022 Rail was the last of the "non-smart" Bosch models. Bosch now has a range of batteries including the new 400, 600 and 800Wh formats that go with the gen 5 motor. But it looks as if the older format 625 and 750Wh batteries come in both "smart" and "non-smart" versions, so I'm guessing there's some special sauce in the BMS that makes them compatible with the smart system. If that's the case then I would probably also have to swap out my old battery and controller for "smart" versions, but maybe someone with a post-2022 bike wouldn't need to do this.

If it turns out that the gen 5 motor is only compatible with the new format batteries then that would certainly add significant complication because the dimensions and form factor of these batteries are quite different to the previous versions, so quite a lot of cunning fettling would be required to fit them securely into the down tube.

 

[RustyMTB]

Happy to be corrected but I'm fairly sure the 750 is smart system only. I'm also running a 625 non smart & would definitely fit a 750 if I could. If I'm right, then you are into a whole system swap at which point it becomes an exercise in fabrication to fit new stuff to an old frame.

 

[robbydobs]

Bosch do everything they can to stop you doing this. You can't officially even buy the motors, and even if you got one, you'd need a shop/dealer to contact Bosch to download a file to program the motor, unless you get one programmed for a different bike. But should you ever get problems with it, you'd need to visit a dealer and Bosch won't touch it.

You'd also need to buy new charger, display, controller, battery mounts and battery, and then fabricate a way to fit it all.

It's getting more and more difficult to do stuff like this, with encrypted communication protocols and stuff. Maybe they are worried about fires if people mess around with them too much.

It'd be easier to get an open source motor controller, like VESC, and then get a Pi/Arduino thing to control it all and replace all the electronics.

EBike / EScooter modular DIY OpenSource electronics and software

 

[nickf]

Bosch do everything they can to stop you doing this. You can't officially even buy the motors, and even if you got one, you'd need a shop/dealer to contact Bosch to download a file to program the motor, unless you get one programmed for a different bike. But should you ever get problems with it, you'd need to visit a dealer and Bosch won't touch it.

You'd also need to buy new charger, display, controller, battery mounts and battery, and then fabricate a way to fit it all.

It's getting more and more difficult to do stuff like this, with encrypted communication protocols and stuff. Maybe they are worried about fires if people mess around with them too much.

It'd be easier to get an open source motor controller, like VESC, and then get a Pi/Arduino thing to control it all and replace all the electronics.

EBike / EScooter modular DIY OpenSource electronics and software

Some good points. Essentially there are two elements to this project: the "technical solution" and the "Bosch support consequences".

For the former, you may be right that we'd need to replace all the electrical elements along with the new motor. That would be costly and require some ingenuity to mount the new format battery, but the new 600Wh is only a few mm wider/longer than the old 625Wh version, so in principal it should fit into the downtube. But we might just be lucky and find that the new motor is compatible with the previous smart batteries, in which case there would be much less work involved. I am still optimistic that some technical skills and a determined mind could make it work, even if that did indeed require swapping out the whole electrical system.

I am less optimistic regarding your valid points about the consequences for support from Bosch with this modification. And I haven't even addressed the issue of how I'd get my hands on a gen 5 motor in the first place! But many people choose to technically modify their bikes in various ways in order to overide the speed limiter, and they presumably are prepared to live with the hassle in the event that something goes wrong. Moreover, there is also a legal issue with overiding the speed limiter, whereas swapping to a newer model motor is just a commercial inconvenience for Bosch.

The reason why I am even considering this idea is because my high mileage 2022 Trek Rail will soon have effectively zero resale value. But otherwise I am totally happy with it, and the only reason why I'd change it for a newer bike is to have the quieter gen 5 motor. Buying an equivalent new bike is going to cost circa 8K euros, so there are 8000 good reasons to consider swapping the motor system!

 

[Weeksy]

A pair of 22p ear plugs will be £7999.78 cheaper and just as quiet

 

[Doomanic]

The charger/battery uses a different plug/socket so nothing you currently own would be any use. Pre-Smart System bikes are unlikely to have been designed with a bigger batter in mind so the 750 almost certainly won't fit. Better off buying a new bike.

On the flip side of that, there's a Powerfully HT in the Classifieds with Smart System and low miles that's tempting me at the moment, if only the aluminium Rail wasn't such a tank...

 

[BostonDye]

you will not be able to mount a gen 5. But if you have a dealer willing to sell it to you. You could go to a gen 4 cx with the smart system. Using a newer purion and smart system battery. You will spend close to 3000usd and that’s if you can even find someone to sell you a drive unit.