Trek Allant+ 7S: Slight Vibration Emitting from Bosch Performance Speed motor

webcurl

Well-Known Member
It's very difficult to describe a problem that does not seem to have a definitive pattern to it.
He tried to explain it, with what seemed like a bit of panic about his purchase :)
Somebody else chimed in with the same experience.
He mentioned 2 exact bikes having the same problem.
Not everyone pedals all the time at the correct/most efficient RPM's for the motor's or battery's sake, sometimes i do that because i feel a bit lazy, occasional benefit of an ebike i say!
I've had a similar experience with my Performance CX Gen 2 and that has a Rohloff & Gates carbon drive and i believe different internal gearing to the Gen 4.
In my situation the only way i can explain it is when the motor is close to the cut-off speed and a slight constant force is applied to the pedals going up a small hill or after going over a small hill & pedaling (beyond assist limit) BUT not every time!
In fact it's frustrating to try and pin down and explain because many things must be in the correct position for it to happen and wind resistance, assist cut-off, the incline/decline, speed heading in & out, etc. all determine if it's going to happen.
In my case it's vibrations through the pedals and a vibration sound being slightly amplified by the frame, nothing major though.
Is it a particular area where the motor is being pulsed due to it being close to disengage or engage coupled with a certain amount of rider torque, i don't know.
Is 45km/h the general upper limit of the CX Gen4 HS? Where he mentioned it happening a few times?
 
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William - Bosch Team

Active Member
It seems like (2) different topics are being discussed here, so I'll attempt to provide some clarity. I believe the original post was regarding pedaling vibration under load, which can be caused by chain vibration (assuming all else is well on the bike.)

The published article(s) refers to the "clacking" noise that both Bosch and competitors eMTB DUs may emit on fast, bumpy descents, and is something different than pedaling vibration. When rolling fast over bumpy terrain, with cranks level (not pedaling) the internal gears may essentially rock back and forth in unision with the slight rocking motion of the cranks. For smoothness and efficiency while pedaling, the gear mesh it not under pressure, so there is a little bit of play. The noise heard on bumpy terrain, at speed, and with cranks relatively steady is the noise of the metallic Performance Line CX gears lightly tapping each other as they rotate slightly, each on their own respective axis. If they were snug against each other, efficiency would be reduced. Bosch chose gear-on-gear transmission of power for the reliability it provides over different methods.

This gear "clacking" noise is much less likely to be heard with a CX DU ridden on pavement as the conditions won't really be right.

I hope this helps!
 

Alaskan

Well-Known Member
Chain vibration is something that all bikes electric or acoustic can have under certain harmonic conditions depending on the frame, chain length, cadence and force or torque being applied. There are many people with belt driven bikes who report experiencing the same thing.

It can't be made to go away but lubrication chain condition can make it more or less pronounced. It is physics and it is the law.

It seems we may be dealing with a "The Princess And the Pea" situation with someone who is just hypersensitive to a phenomena common to all bicycles.

After all this back and forth, it sounds like something we all experience, on many different bicycles, at the certain point where the harmonics are just right. It is not a flaw but a feature that bugs some more than others. If a person just cant stand it, another bike might help but it also might do the same thing, just under slightly different circumstances.

It would be a stretch demand a warranty replacement under these circumstances. If the bike is returnable at this point that is probably the best option. Just know whatever different bike you get could end up doing the same thing. In that case a biking may just not suit you and it would be best to go back to driving a car. I hope it does not have any squeaks or rattles.
 
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webcurl

Well-Known Member
It seems we may be dealing with a "The Princess And the Pea" situation with someone who is just hypersensitive to a phenomena common to all bicycles.

In that case a biking may just not suit you and it would be best to go back to driving a car.
And then there's the occasional expectation that with the likes of Trek, Bosch, R&M, etc. the "Green" Pea's are a little less pronounced! :)
 

MrLibraryMan

Member
Region
USA
I stand corrected further research shows Bosch has acknowledged this noise/vibration issue to their new motor -
This explains why the Trek Allant 7 could be unfortunately particularly sensitive to picking up and amplifying this motor noise. So really a design flaw from Trek to not make allowances for this Bosch feature.
Excerpt from :

The 4 Best 2020 eMTB Motor Systems Reviewed - Bosch vs Brose vs Shimano vs Fazua Ridden & Rated​


Talking about noise, the absolutely biggest downside of Bosch’s latest design is a metallic clacking noise when the engine is unloaded and rolling over uneven ground, not unlike that of bad chain slap, coming from the motor itself – something I’ve never experienced with any competitor’s product. On some bikes equipped with the new Performance CX it’s more noticeable than on others. We checked in with Bosch and got the following explanation:

When encountering technical terrain on an eBike or eMTB, a vibration of the chain/chainring can occur. Those vibrations can be transferred to the frame, the drive unit and to the inner gear wheel (inside the drive unit). How much vibration is transferred depends on the type of bike (for example hardtail vs full suspension and aluminum vs carbon). In some cases, when freewheeling a metallic sound can be generated when the inner gear wheel is not under the stress of pedaling.

We have been able to recreate this occurrence with different drive units – both from Bosch and competitors of Bosch. The new Performance Line CX is possibly a little more sensitive and the noise is slightly louder than the noise of the other drive units. The CX has a high power density, a highly efficient gearing mechanism and incredibly smooth-running gears. Paired with reduced weight, lower wall thickness and improved heat release it is easier for mechanical noises to be omitted. But performance, efficiency, heat removal and heat-resistance are more important to us.

Usually this noise is drowned out by the sounds of the bike on the trail when descending. Knowing the occurrence, it is easy to reproduce the noise, but the noise does not have any influence on the performance, functionality or reliability of the motor.


Event though this noise is not at a level that would cause me to not ride a Bosch equipped bike anymore, you simply cannot unhear it. With every development from derailleur to chain protector over the past few years to keep a bike as quiet as possible, hearing the clacking noise when rolling over uneven terrain without the motor being engaged is simply annoying.
Very interesting and revealing article. It verifies some of my initial thoughts and experiences I had posted at the very beginning of this thread. However, discussing this among ourselves doesn't really resolve anything, unless the decision-makers at Trek receive our concerns and genuinely care to address the issue with its customers.
 

Alaskan

Well-Known Member
Very interesting and revealing article. It verifies some of my initial thoughts and experiences I had posted at the very beginning of this thread. However, discussing this among ourselves doesn't really resolve anything, unless the decision-makers at Trek receive our concerns and genuinely care to address the issue with its customers.
Exceept that is a different noise that occurs under totally different circumstances than what is being discussed here and the reason for it was a design choice explained in post #62
 

Alaskan

Well-Known Member
And then there's the occasional expectation that with the likes of Trek, Bosch, R&M, etc. the "Green" Pea's are a little less pronounced! :)
Indeed. There are expectations and there are expectations. Some are reasonable and some are not. Whether this one is or not is what we have been trying to ferret out. That the OP feels vibration is not in question. That the source of the noise is the motor is still very much is in question. Also, the noise in the link he cites as proof is, just that, a noise, not a vibration felt through the feet...totally different than what he is experiencing. I think the question as to the source of the vibration and whether it is "normal" or not still remains to be determined here.
 
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MrLibraryMan

Member
Region
USA
It seems like (2) different topics are being discussed here, so I'll attempt to provide some clarity. I believe the original post was regarding pedaling vibration under load, which can be caused by chain vibration (assuming all else is well on the bike.)

The published article(s) refers to the "clacking" noise that both Bosch and competitors eMTB DUs may emit on fast, bumpy descents, and is something different than pedaling vibration. When rolling fast over bumpy terrain, with cranks level (not pedaling) the internal gears may essentially rock back and forth in unision with the slight rocking motion of the cranks. For smoothness and efficiency while pedaling, the gear mesh it not under pressure, so there is a little bit of play. The noise heard on bumpy terrain, at speed, and with cranks relatively steady is the noise of the metallic Performance Line CX gears lightly tapping each other as they rotate slightly, each on their own respective axis. If they were snug against each other, efficiency would be reduced. Bosch chose gear-on-gear transmission of power for the reliability it provides over different methods.

This gear "clacking" noise is much less likely to be heard with a CX DU ridden on pavement as the conditions won't really be right.

I hope this helps!
 

MrLibraryMan

Member
Region
USA
You’re absolutely correct about two topics being discussed in this thread. Somehow the topic moved away (or evolved) from my specific title of this thread. Nevertheless, there seems to be notable problems with some of the Trek Allant+ 7S’s (or other Allant+ model’s) components and how they behave with each other. When Trek’s customers invest approximately $4,000 US dollars for a top bike manufacturer’s e-bike, we should expect a solid, problem-free product to enjoy. It’s a expected and sensible.
There— now I moved off the topic a bit.
 

Akrotiri

Well-Known Member
Region
Europe
As far as I’m concerned after reading and participating in this thread no problems have been revealed with the allants and/or the motors.

Their have been complaints and observations (myself included) that there is vibration under specific circumstances that is very likely emitted from the chain and felt through the pedals.

If the unlikely turns out to be true and it is coming from the motor this is easily fixed with more applications of grease at the motor mounts as many riders have done and documented over at emtbforums.com
 

MrLibraryMan

Member
Region
USA
As far as I’m concerned after reading and participating in this thread no problems have been revealed with the allants and/or the motors.

Their have been complaints and observations (myself included) that there is vibration under specific circumstances that is very likely emitted from the chain and felt through the pedals.

If the unlikely turns out to be true and it is coming from the motor this is easily fixed with more applications of grease at the motor mounts as many riders have done and documented over at emtbforums.com
Akrotiri, could you please post the link of that discussion? Thanks!
 

Johnny

Well-Known Member
From time to time I feel a slight, intermittent vibration coming from the Bosch Performance Speed Motor as I travel around 10-15mph (or faster) on level surface streets and on uphill surface streets. At first I thought it was the OEM tires, but discovered that they were not creating/contributing to the problem. It's not from the pedals either. The slightly annoying and irksome vibration is definitely coming from the Bosch motor.

Whenever I feel the subtle vibration from the motor, it tends to lessen or even disappear when I increase the mode from tour to sport or even turbo and while I'm in 3rd, 4th, or 5th gear. So my question is, is this slight and intermittent vibration an unintended indicator or warning that the motor is laboring or that it cannot adequately handle the demands I'm placing on it? Of course, if I am going up a hill, I'll drop to 3rd or 2nd or 1st gear to lessen the demands on the bike (and on me). (By the way, I weigh 215 lbs., and I don't have any heaving loads on the bike other than my Kryptonite New York U-Lock and a small frame bag for bits and pieces.)


At which cadences are you getting this vibration? The motor torque depends on motor output and cadence not the speed of the bike, so you may want to replicate a similar case at different cogs/speeds to make sure that it is the motor not the bike itself.

Find a flat and safe road, use a gear to keep your effort (you will be in the smaller cogs), support level and cadence close to the case where you get the vibration. Find an uphill where you can repeat while riding on larger cogs.

Do you get the same vibration for both cases?
 

MrLibraryMan

Member
Region
USA
I was referring to this very thread.

You’re the OP and your title is:

Trek Allant+ 7S: Slight Vibration Emitting from Bosch Performance Speed motor​

Yes, very good, Akrotiri, but you mentioned emtbforums.com.

Now can you tell me the link of where you found the discussion of adding grease to the motor mounts on that forum?