Does anyones CX Gen4 make this noise/sensation? (Video)

[Akelu]

So I bought a new Focus Thron 2021 a few days ago. Has Bosch CX Gen 4 motor.

For first 70km or so I didn't notice this noise or sensation at all then all of a sudden it started happening. It happens at low cadence high torque (eg uphill). It makes a creaking noise and each time I hear the noise I feel a disturbance in the pedalling. Before it started happening it would just feel smooth going uphill now it feels bumpy through the pedals.

Video:

 

[Mikerb]

Not sure I can hear what you mean but it could just be pedal kick because you are in too high a gear. In effect the motor disengaged when it senses a momentary lack of torque on the pedals.

 

[Akelu]

In the clips, I am in a very easy gear, that is, easy to spin around. I'm not in a high gear. The noise I'm talking about is the low frequency thumping noise.

 

[StilusBoy79]

That noise isn’t something I’ve experienced within over 1k miles on same motor.

 

[Mikerb]

You need to isolate the motor from other parts of the bike by putting it on a bike repair stand and then rotating the pedals with the motor on and then with the motor off. If the noise is not there with the motor on it should rule out the motor. I hear the low frequency sound you refer to now ( PC instead of phone reviewing the video) .

 

[Akelu]

You need to isolate the motor from other parts of the bike by putting it on a bike repair stand and then rotating the pedals with the motor on and then with the motor off. If the noise is not there with the motor on it should rule out the motor. I hear the low frequency sound you refer to now ( PC instead of phone reviewing the video) .

It doesn't make the noise when the rear wheel is lifted off the ground and pedals spun with motor on or off. It only makes the noise when there's high pressure applied to pedals and lot of resistance generated which can't happen without the wheel on the ground.

Took it to another bike shop yesterday and they said they feel it and that it feels like what happens with a mismatched chain and cassette or old and new one. They pointed out some extra wear on certain teeth on the chainring and have suggested K try a new one and the included oem cheap one may not be especially suited to the chain. So I'm going to try that.

 

[Andrie]

Did you try to ride it with the motor off and if it still makes the same noise?

 

[Akelu]

Bike shop said it's same with motor off

 

[Akelu]

Update:

After recording several videos of the area, I realised that the chainring doesn't seem to be releasing the chain very well, causing the bottom chain to bounce. It seems the sound is in sync with each time this happens. We already ordered a new different chainring yesterday before I discovered this. So I'm hoping that the new chainring will resolve the problem.

 

[Mikerb]

It does look like the chain is bouncing on release from the chain wheel. If the chainwheel is worn/bent/damaged I would change the chain as well as the chainwheel.

 

[Akelu]

If the chainwheel is worn/bent/damaged I would change the chain as well as the chainwheel.

I'm not sure what's going on, it's a new bike. Bike store mentioned it looked like every second tooth (the wider ones) had a bit more wear on it proportionate to the rest. I will replace the chain at the same time as the chainring and see how it goes.

Going from a stock OEM FSA 34t "megatooth" to an ethirteen E*spec steel direct mount 34t narrow-wide chainring. Ethirteen says it's specifically compatible with 12 speed shimano, and Trek pairs it with the same slx 12 speed chain on their Rail 7 so hopefully it does the trick. Will be a big relief.

 

[Terrafirma]

I bought the 6.8 around 2 months ago. I had a similar noise not long after I got it. I was also suffering chain suck. My issue was the outside shield on the derailleur which was bent in a little and rubbing on the chain. Not sure how it happened but all good now. The bike is very comfortable and really climbs so well. The Bosch motor is perfect and love using EMTB mode. I note the bikes come with a standard Shimano 12 speed chain, not an E Bike chain so I will see how the standard chain holds up. I'm waiting on a 6 amp fast charger for mine which will come in handy for weekend trips and speeding up the charge time.

 

[Akelu]

I bought the 6.8 around 2 months ago. I had a similar noise not long after I got it. I was also suffering chain suck. My issue was the outside shield on the derailleur which was bent in a little and rubbing on the chain. Not sure how it happened but all good now.

Thanks for your reply.

Could you take a picture pointing out exactly where it was bent so I can check mine? Did you fix it yourself?

Thanks!

 

[Terrafirma]

I'll get a pic for you tomorrow some stage. I had a bike mechanic who I know to be very good look at it. This was not the place I bought the bike as it's a fair way away from me (Only place that had stock of the bikes in Victoria at the time). Typically with these noises it's nearly always something in the drive train IMO.

 

[Akelu]

Thanks, I actually have a post going at the moment over in the focus subforum for this problem.

I think Focus is using non-optimal chainrings on some of their e-bikes (jam², thron²)

I'm having some troubles with the stock FSA chainring on my Thron 6.9. I think Focus is using non-optimal parts on this bike (also noticed they use the same chainring on Shimano drivetrain Jam²) On my new Thron2, with a FSA G4 34t megatooth chainring, When pedelling uphill mainly...

www.emtbforums.com

 

[Terrafirma]

Sorry forgot to mention I replaced my chain after my issue as it had damaged the chain enough and for the sake of a new 12 speed chain it made all the difference.

 

[Akelu]

Since I posted the video in this thread, I did more discovering and found the noise is coming from the chain not being released from the chainring properly. (You can see the video in the link above your last post), so my noise isn't coming from the derailleur area. But I can check that anyway, maybe the derailleur is bent causing the problem at the chainring area, compounding the issue with the chainring not being a Shimano 12 speed chainring.

 

[Terrafirma]

Since I posted the video in this thread, I did more discovering and found the noise is coming from the chain not being released from the chainring properly. (You can see the video in the link above your last post), so my noise isn't coming from the derailleur area. But I can check that anyway, maybe the derailleur is bent causing the problem at the chainring area, compounding the issue with the chainring not being a Shimano 12 speed chainring.

My noise wasn't coming from the derailleur area either. It was coming from the chain ring and pedal area. Isn't the chain ring specified by Bosch and part of the Bosch motor kit?

 

[Akelu]

My noise wasn't coming from the derailleur area either. It was coming from the chain ring and pedal area. Isn't the chain ring specified by Bosch and part of the Bosch motor kit?

No, chainring is seperate from Bosch motor. The Bosch gen 4 is the "standard" much like a certain crank type, and different companies make different chainrings for it for different drivetrains.

It is very interesting that your sound came from the chainring area too and was actually the derailleur so I eagerly look forward to your post tomorrow, maybe the same thing happening to me.

 

[Akelu]

Is it a norrow / wide chainring, and the chain is not placed appropriately?
It is the correct chain and chainring I take it?

Correct chain and chainring, so far as what focus selected for the bike. My theory is that my problem is at least in some part due to the fact that focus selected a chainring that does not specifically support 12 speed shimano chain as the tolerances are much tighter for Shimano 12 speed compared to others.

 

[Terrafirma]

Correct chain and chainring, so far as what focus selected for the bike. My theory is that my problem is at least in some part due to the fact that focus selected a chainring that does not specifically support 12 speed shimano chain as the tolerances are much tighter for Shimano 12 speed compared to others.

Isn't the chain ring specified by Bosch?

 

[Akelu]

Isn't the chain ring specified by Bosch?

No, the Bosch motor is just the 'standard' much like a crank type, and then different manufacturers make different chainrings for it. IE FSA makes spiders + direct mount chainrings for Bosch gen 4, E*thirteen makes direct mount for it, many companies make them with varying chainlines, teeth profiles and teeth counts.

My original chainring was an FSA megatooth direct mount Bosch Gen4 chainring, the replacement they sent out was an FSA Bosch gen 4 spider, with a FSA megatooth 104bcd chainring bolted to it.

They are both officially 1x11 chainrings (the tooth profile), so that's why I'm thinking the E*thirteen chainring will fix the problem because its tooth profile specifically supports Shimano 12 speed and thus it has more headroom for the chain to come from different angles. (Shimano specifies this, they say that boost and non boost chainlines will work on the same crankset because of the Hyperglide+ tooth profile is more forgiving on the angle of the chain relative to the chainring)

 

[Terrafirma]

No, the Bosch motor is just the 'standard' much like a crank type, and then different manufacturers make different chainrings for it. IE FSA makes spiders + direct mount chainrings for Bosch gen 4, E*thirteen makes direct mount for it, many companies make them with varying chainlines, teeth profiles and teeth counts.

My original chainring was an FSA megatooth direct mount Bosch Gen4 chainring, the replacement they sent out was an FSA Bosch gen 4 spider, with a FSA megatooth 104bcd chainring bolted to it.

They are both officially 1x11 chainrings (the tooth profile), so that's why I'm thinking the E*thirteen chainring will fix the problem because its tooth profile specifically supports Shimano 12 speed and thus it has more headroom for the chain to come from different angles. (Shimano specifies this, they say that boost and non boost chainlines will work on the same crankset because of the Hyperglide+ tooth profile is more forgiving on the angle of the chain relative to the chainring)

Let me know how you go with this. When I am due to replace my chain ring it will be handy to know

 

[Akelu]

Got my bike back from bike shop today, got the Ethirteen espec Bosch direct mount steel chainring installed. It's like a whole new bike. The pedalling is very smooth now, absolutely no chain suck at all. I checked with FSA and the chainring included with the bike does not support Shimano 12 speed. Very happy with the new chainring.