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[zian]

Hello everyone,

On my Zero S 2025, just following the change of the belt, a new strong strange noise appeared during acceleration, you can heard the sound on the video on 3 different accelerations.

It occurs only by accelerating with the max handle from the stop or from a low speed, otherwise it does not appear during the acceleration phases while driving. It is even more blatant in a climb, so when a strong couple is necessary.

I just went to the dealership to check the tension of the belt which was able to Freq at 62Hz, they tightened it to have at 68hz.

But the noise is still there.

With the old belt, I have a multitude of sound recordings taken in the same place just above the engine with my Bluetooth microphone, and there has never been this kind of noise type during acceleration.

The new belt seems well centered.

If someone has already had this problem or has an idea of ??the cause. Should we still tighten the belt ? The specification indicates between 62Hz and 82Hz.

We can heard that the noise can start at 15km/h to stop at 45km/h and resume 45 then up to 50, or start at 45 to stop at 75.

There is a resonance of the belt, it seems almost sure, but why?

[TheRan]

It almost sounds like something else nearby is resonating, perhaps a bit of bodywork or the rear mudguard. Have a check over the bolts and screws to make sure nothing's loose. If it's not that you might just have to accept it. From my experience trying to get rid of belt noise on my DS I've come to the conclusion that it's just something that happens when you have belt drive on an otherwise quiet bike. With the perfect combination of tension and alignment you can sometimes get it fairly quiet, until it gets wet or dirty or something shifts slightly.

[zian]

It almost sounds like something else nearby is resonating, perhaps a bit of bodywork or the rear mudguard. Have a check over the bolts and screws to make sure nothing's loose. If it's not that you might just have to accept it. From my experience trying to get rid of belt noise on my DS I've come to the conclusion that it's just something that happens when you have belt drive on an otherwise quiet bike. With the perfect combination of tension and alignment you can sometimes get it fairly quiet, until it gets wet or dirty or something shifts slightly.

Thanks, but I' can't accept this kind of bad resonating noise, the motorcycle is almost brand new (3 monthes) and was OK before the belt change.
I'll try to mount the first belt (just a little scratch on it) to proove it's a default on the new belt with a bad resonance of the belt itself.

[princec]

Mine makes all sorts of noises like that, and tbh, it's never bothered me much. The specific noises it makes depend on belt tightness, temperature, dirt, and water, and the belt itself (I suppose no two belts are totally identical).

Cas

[KuRi]

Mmm, that sounds weird. I'd find it annoying too. Are you sure is it a belt problem? My main concern with dealers is that they don't know what they are doing when working with modern electric bikes.

When I got my new DSR in 2020, the left peg had a terrible vibration at some resonance speeds. After visiting the dealer 2 times, I was told it was totally normal. Then I decided to buy the tools to check it by myself. The Rear wheel was not correctly aligned, causing the vibrations, and the belt was not tight enough. I fixed all by myself and enjoyed 5 full years of no noises, no vibrations, smooth driving. (Then I bought a new dsrx and everything started again with new problems xDDD)

[2020_SRS_Commuter]

Some starting things to look at:
1 is the  belt centered adequately on both the front and rear sprockets?
2 is the belt touching nothing else but the sprockets?
3 is the axle torqued to spec?
4 is a spacer missing/out of place on the axle assembly?
5 is the rear tire inflated correctly?
6 are the sprockets and belt undamaged, determined by visual inspection?
7 if you attempt to twist the belt by hand in the middle on the lower part of it, can you twist it more than 90 degrees easily?
8 all attachment bolts in the rear sprocket present and tight?

I wonder if the mechanic torqued the axle without fully seating the wheel against the stop on the non belt side.

[zian]

Thanks KuRi & 2020_SRS_Commuter for you answer, I'll study all these points.

The Rear wheel is correctly aligned, no problem with that.

My problem is exactly the same as this one : https://www.electricmotorcycleforum.com/boards/index.php?topic=12714.0

By testing the frequency of the belt with different positions of the wheel with the motorcycle on the lateral crutch, I find between 58 and 68 Hz. So now I have just understood that the cause is the crown which cannot be perfectly circular and have its center perfectly in the axis of rotation of the wheel.

The old belt (which has a small tear) has been mounted again yesterday, the sound of resonance is much less, there is therefore clearly a frequency of resonance specific to each belt, which must come to resonate with the couple gable / crown and their respective shapes and centering.

The average tension adjustment of the belt is secondary for this problem, it plays, but not a lot (to tighten the belt aggravates this resonance problem a little too), while the difference between 2 different belts therefore plays a lot on the phenomenon.

I was able to have a belt to go and an another belt on the return, so the comparison was easy: the set of belt noises is very different from one to the other at different speeds / acceleration / decelerations => It is obvious, it is not embarrassing apart so this big resonance and 1st acceleration in the maximum, rolling it then does not come, except at the start of the climb so, so it comes back to a strong couple required.

There will be other handles by the dealership to try to resolve this resonance with the new belt. I will post at that time.

[TheRan]

There was someone else here who also had a fairly off-centre rear pulley, they tried rotating it on the rear wheel (you have four possible positions, 90° apart) and found the best one. It sounds like it could be a difficult and long process though unless you have a truing stand and a some kind of gauge to measure the runout of the pulley (at the peak of the teeth), to avoid having to remount the wheel on the bike each time, tension the belt, and then check the frequency at different rotations.

[2020_SRS_Commuter]

That was me. There should be a thread about it here somewhere. Rotating the rear sprocket and reattaching significantly reduced the runout. Now at 64k miles I can say for sure... never had that problem again.
Im on my phone now but later this evening when I get to one of my laptops Ill find it. Originallly I had a 10hz difference in tension 180 degrees apart, and that was reduced after what I did.

[zian]

You told about that here :

This may or may not help, or even be the same issue, but I had a similar problem I resolved by rotating the rear sprocket.
https://www.electricmotorcycleforum.com/boards/index.php?topic=11202.0

Do you remember the final result (range in Hz) ? From 10Hz to ?
So that I will have a aim.

Rotating the rear sprocket can't change the oval form, but it can change the center axis for sure and make it closer to the wheel rotation axis.

First I'll let my dealer try what Zero recommand, and if the bad noise is always there, I'll recommand to rotate the rear sprocket too as you.

[2020_SRS_Commuter]

No, but coincidentally I am replacing my belt soon, maybe even in the next few days.
I'll take a look when I do that and let you know.

[2020_SRS_Commuter]

Sorry but I decided to keep the belt for the full 25k after tightening and inspecting, so this data is not as accurate as I would like. It appears there is a variance of only a  3, maybe 4hz 180 opposed but its difficult to tell for sure from a belt with 20k miles on it and here's why... ( this will take a bit to explain ) :

A thing Ive noticed with these belts as they age is they crack on the toothed side, between every tooth, but they also crack on the outside, not between every tooth but at a few scattered places on the belt.. Examine a used belt off the bike  once removed and its easy to see these cracks. Under tension on the bike the cracks between teeth are almost impossible to see unless they are severe.  The cracks on the outside however can be seen, if you look closely on the sprocket on the motor and roll it slowly.
It appears to me that each of these exterior cracks lowers the tension a few hz when they are on the motor sprocket.

So on a used belt, you will see the hz going up and down at several points as the exterior cracks roll over the motor.
And with a new belt, you will only see the offset in the sprockets reflected in the hz measurement because the belt is uniform.

So... long winded but thats why I cant be sure right now. Maybe 3 maybe 4 on the offset.

[zian]

Thanks a lot for these good infos.
Zero recommand to change the small sprocket in my case, so we will see next week after the change...

[TheRan]

That will be a nice little earner for them, surprised they didn't suggest changing the motor. The front pulley is much less likely to be off centre just because of the way it's made.

[KuRi]

You are lucky Zero is willing to Help. When I ask about noises, vibrations, etc... they say everything is normal... always...