Changed sprocket 15T to 18T Performance CX, power cutting, speedo up and down.

[Voz]

Hiya.

I have a bike with a Bosch Performance Line CX with Intuvia display.

I have the latest firmware as at Feb 2018 with eMTB mode.

I also have the latest small version of the Speedbox 2 tuning module installed.

Everything was running fine although my top speed was making out at about 40-45km/h but with crazy fast pedalling.

I decided to pop on a new Bosch 18T front sprocket. Took it for a ride and noticed the Speedo running up and down, not stable at all. The speeds of 40-60 Km/h are now possible with this gearing, I recorded a top speed of 58 km/h on that short test run. Keeping up with inner city traffic is now a lot easier. You certainly get more of a workout on the bike with the 18T, that is good, I was getting too soft with the 15T. I will need to either add some links or replace the chain but it is rideable at the moment.

As I got closer to home it started to cut then bring back power as I was pedalling up a hill.

So, does anyone know if the Bosch motor setup needs to be configured for an 18T by a Bosch dealer? Or do I have some other issue?

Cheers

 

[Chris Nolte]

The Bosch motor has some internal sequences to detect motor manipulations. Although at it’s current state it’s often difficult to detect speed dongles, it can detect when you fit a larger chainring than the manufacturer spec’d. Technically this can be modified, but only by the manufacturer and it sounds unlikely that the manufacturer would be willing to do that in this case. Dealers don’t have access to make those changes.

 

[Voz]

Chris, thanks for that update. My selling dealer is clueless on the Bosch programming as they just don’t sell enough units.

So, it would appear that I will not be able to add a bigger sprocket then? I was wondering if the dealer had access to programming that would allow specific if a new front sprocket size but looks like this option is not available to dealers then?

 

[Chris Nolte]

That’s correct, it’s not possible to reprogram the bike on the dealer level. Some have swapped their front cog for a larger or smaller one with some success, but there is alaways a risk of it throwing an error. This risk will increase with future updates of the motor systems as Bosch works to stop speed modifications.

 

[Voz]

Chris, thanks. I will leave it with the stock 15T, Cheers.

 

[Durukan Devrim]

Chris, thanks. I will leave it with the stock 15T, Cheers.

I've installed 18T on CX motor and never had any issues. I don't have speedbox but I've re-positioned the sensor to pick up pedalling speed rather than the wheel. I did get 503 error frequently before I installed 18T because when your speed drop under 12km/h frequently motor shuts itself, with 18T my pedal speed won't go over 12 km/h as much as it did before. Your problem might be linked to the speedbox I'm afraid.