Bosch CX - tip for owners

[Phil Dryden]

While out for a recent ride on my Cube, I became aware of a rasping noise coming from the motor area, especially when in the higher gears. Fearing the worst I got the bike up on the work stand and sure enough there was a rasping noise in the smallest 2 sprockets. Closer inspection, however revealed that the bottom of the moulded plastic chain guard ran very close to the chain in the smallest sprockets, and was in fact rubbing against the chain in the smallest one. Maybe I had caught it with my foot, or somehow disturbed the alignment of the chain guard to cause chain rub. A bit of levering and manipulation and hey presto, sorted with great relief. Incidentally, at the same time I gave the chain a thorough, thorough clean using the Park tool till it gleamed; lubed it, and cleaned/lubed the derailleur - running like a Rolls now. Every 500 miles seems about right for my riding.

 

[soundwave]

https://www.ebay.co.uk/itm/BCR-70e-Sprocket-Electric-Bike-Bosch-E-Bike-E-Bike-Cog-Sprocket-16-Tooth/113470517215?hash=item1a6b5eafdf:g:OA4AAOSwpHpbKRAb:rk:5:pf:0

these sprockets are offset so will give better clearance if needed and cheap

 

[Phil Dryden]

Thats a helpful pointer, Soundwave - many thanks . I also see that they can supply larger chainrings, which is useful as I may fit a bigger one next year; never use the bottom 5 gears and sick of spinning out on the existing 15T chainring.

 

[soundwave]

you can run two sprockets as i have 20t and 18t just run the above on the outside and a normal one on inside.

 

[soundwave]

 

[Phil Dryden]

Nice set up! Food for thought.

 

[John5001]

Happened to me I thought the engine had gone..phew.. Just replaced, as the guard was chewed up. The guard was replaced with another, cost about a fiver.

 

[Phil Dryden]

How did you remove the chain guard? There's the obvious screw in the top, but there seems to be 2 hidden fixings behind the guard which I could not get at. Don't think they were clips as I manipulated the guard as much as I dare but could not release them.

 

[John5001]

Used a hub puller for the crank and levered off.

 

[cdm]

you can run two sprockets as i have 20t and 18t just run the above on the outside and a normal one on inside.
View attachment 28199View attachment 28200

How do you shift from one to another?

 

[Fat Rat]

How do you shift from one to another?

You don’t
You swap them manually

 

[cdm]

Interesting, Thank you,
I currently have 15T at my bosch performance line CX, what is you suggestion for 2nd option, 18T ?
https://www.ebay.co.uk/itm/BCR-70e-Sprocket-Electric-Bike-E-Bike-E-Bike-Cog-Sprocket-18-Tooth/123322851625?hash=item1cb69d6129:g:OA4AAOSwpHpbKRAb:rk:20:pf:0

Do I need special holder for two sprockets? and what tool I need to mount 2nd one?

 

[soundwave]

you need a crank puller to remove the crank arm and a bosch lock ring tool, socket or spanner to remove that.

you then just put them both on and fit the lock ring thats it.

 

[Phil Dryden]

Ultimately, I think I would prefer to stick with a single front chainring for simplicity, but not sure how many extra teeth would be appropriate for me. I just want to stop spinning out at the small sprocket end, and be able to do most of my riding using the middle rear sprockets rather than the smallest 2 or 3. Better for chain alignment, anyway. Do you reckon 20 teeth (existing 15T, Bosch Performance CX) would make the difference I'm looking for without pushing me too far down the rear sprockets? Would I still be able to use the plastic chain cover with a slightly larger chainring? Many thanks for any advice.

 

[soundwave]

no idea what guard you have but 17-18t would get you of the bottom of the cassette and more in the middle.

 

[Phil Dryden]

Hi Soundwave. Its the existing manufacturers outside plastic guard going round the chainring and top of the chain. Probably better to gauge it with the new chainring on. I don't suppose for a relatively small increase from 15 to 18 teeth any extra chain links would be needed?

 

[soundwave]

tbh id just take off the guard you might get away with the chain you have but you dont add links to a chain esp a ebike lol thats just asking for it to snap.

 

[Phil Dryden]

Many thanks for your help, SW.