MG4 X Power Vibe/Hum 65 to 75mph

[taltulon]

I should add up front that the vibration in mine is not significant and most people probably wouldn't notice it. However, I did a bit of down and dirty analysis just to satisfy my own curiosity. Vibration was measured with an iPhone on steering wheel. I took two samples, one at 70mph and one at 75mph.

There is a small peak at wheel rotation speed which I would expect as no wheel is perfectly balanced but there is a much larger peak at 45Hz (@ 70mph) and then 48Hz (@ 75mph). This is what I feel through the steering wheel. Taking into account errors within my non-calibrated measurement I would take a punt that that the vibration felt is exactly 3 x wheel rotation speed.

Take from that what you will.

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with all these calcs i couldn't resist but to create this meme...

 

[salty]

I should add up front that the vibration in mine is not significant and most people probably wouldn't notice it. However, I did a bit of down and dirty analysis just to satisfy my own curiosity. Vibration was measured with an iPhone on steering wheel. I took two samples, one at 70mph and one at 75mph.

There is a small peak at wheel rotation speed which I would expect as no wheel is perfectly balanced but there is a much larger peak at 45Hz (@ 70mph) and then 48Hz (@ 75mph). This is what I feel through the steering wheel. Taking into account errors within my non-calibrated measurement I would take a punt that that the vibration felt is exactly 3 x wheel rotation speed.

Take from that what you will.

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Looks impressive, but not got a bloody clue, what you are on about. ??

 

[Anon70]

From the science bit being based on wheel circumference that would imply changing the wheel or tyre combination to give a new circumference would make the vibes happen at a different speed?

It would also put the speedo out of whack but that's another issue

 

[murf62]

From the science bit being based on wheel circumference that would imply changing the wheel or tyre combination to give a new circumference would make the vibes happen at a different speed?

It would also put the speedo out of whack but that's another issue

It won't make a difference as the vibration you feel can't be coming from the wheels, driveshafts or any thing else spinning at the same speed. The wheel circumference was only relevant to illustrate the difference in frequency of rotating mass at wheel speed and whatever is causing the vibration we can feel.

In simple terms, don't bother changing brake discs, wheels, tyres or balancing any of these. It won't remove the 45-48Hz vibration.

It could easily be isolated by running one up to speed on a wheel free ramp with the wheels off. MG will have done this of course and are probably now trying to convince Xi Jinping to cough up some money to replace all the front motors once he's paid for the LKA fix.

 

[powerfulx]

It won't make a difference as the vibration you feel can't be coming from the wheels, driveshafts or any thing else spinning at the same speed. The wheel circumference was only relevant to illustrate the difference in frequency of rotating mass at wheel speed and whatever is causing the vibration we can feel.

In simple terms, don't bother changing brake discs, wheels, tyres or balancing any of these. It won't remove the 45-48Hz vibration.

It could easily be isolated by running one up to speed on a wheel free ramp with the wheels off. MG will have done this of course and are probably now trying to convince Xi Jinping to cough up some money to replace all the front motors once he's paid for the LKA fix.

This is interesting as it may play into my testing where I was able to have dead smooth driving when I fitted jubilee clips to the drive shafts, however it was on when the wheels were in sync, eg going into another lane or round a long corner would phase the smoothness and vibrations in and out. Pointing to the issue being reliant on an imbalance in the motor or transfer case. Or indeed some kind of motor cogging. When i run eco mode, vibrations are almost non existent.

 

[Soultrappa]

I should add up front that the vibration in mine is not significant and most people probably wouldn't notice it. However, I did a bit of down and dirty analysis just to satisfy my own curiosity. Vibration was measured with an iPhone on steering wheel. I took two samples, one at 70mph and one at 75mph.

There is a small peak at wheel rotation speed which I would expect as no wheel is perfectly balanced but there is a much larger peak at 45Hz (@ 70mph) and then 48Hz (@ 75mph). This is what I feel through the steering wheel. Taking into account errors within my non-calibrated measurement I would take a punt that that the vibration felt is exactly 3 x wheel rotation speed.

Take from that what you will.

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was this done in any particular mode as I have expressed before it seems to be more prevalent on quick acceleration in normal. I don't really feel it in sports or eco.

 

[Deleted member 11291]

was this done in any particular mode as I have expressed before it seems to be more prevalent on quick acceleration in normal. I don't really feel it in sports or eco.

For me its there all the time no matter the setting or accelerating or not.

 

[murf62]

was this done in any particular mode as I have expressed before it seems to be more prevalent on quick acceleration in normal. I don't really feel it in sports or eco.

I did it in Eco mode to prove to myself it's there all the time. It's not as pronounced as in normal. Next time I'm on a quiet motorway I'll do it in normal and sports modes for comparison.

 

[Fogey]

At 3x the rotational frequency, could this be pointing to the (probably inboard) CV joints - specifically "tripod joints" ?

Blog tripod vs. Rzeppa joint – KMP Drivetrain Solutions

n this blog, we would like to talk about the difference between the regular, ball-type CV-joints used in most passenger cars and the tripod joints that we use in our driveshafts.

www.kmpdrivetrain.com

In which case the vibration would be an intrinsic shortcoming of the implementation?

 

[salty]

At 3x the rotational frequency, could this be pointing to the (probably inboard) CV joints - specifically "tripod joints" ?

Blog tripod vs. Rzeppa joint – KMP Drivetrain Solutions

n this blog, we would like to talk about the difference between the regular, ball-type CV-joints used in most passenger cars and the tripod joints that we use in our driveshafts.

www.kmpdrivetrain.com

In which case the vibration would be an intrinsic shortcoming of the implementation?

Say what?

 

[Fogey]

Say what?

Post 640 refers to a measured frequency of vibration - the fact that it's at 3x the wheel's rotational speed is probably a significant clue. I'm surprised it hasn't already been leaped upon! If the CV joints are the tripod type, then there's the source of the problem (surely!)...

Not that it could be easily cured, I fear...

 

[Kermit]

I should add up front that the vibration in mine is not significant and most people probably wouldn't notice it. However, I did a bit of down and dirty analysis just to satisfy my own curiosity. Vibration was measured with an iPhone on steering wheel. I took two samples, one at 70mph and one at 75mph.

There is a small peak at wheel rotation speed which I would expect as no wheel is perfectly balanced but there is a much larger peak at 45Hz (@ 70mph) and then 48Hz (@ 75mph). This is what I feel through the steering wheel. Taking into account errors within my non-calibrated measurement I would take a punt that that the vibration felt is exactly 3 x wheel rotation speed.

Take from that what you will.

View attachment 27779View attachment 27780

Hi Murf62,

What app did you use to get the frequency/amplitude graphs? I run android but might be able to find something similar.

I used to investigate faults on large electrical machines (a very long time ago) and this reminds me of one case where part of the end winding has a resonant frequency of 100hz (2x mains frequency) and kept shaking themselves apart.

 

[powerfulx]

For me its there all the time no matter the setting or accelerating or not.

I drive mine into the show room and chuck the keys over the desk if it was all the time, how can you handle it ?

 

[Deleted member 11291]

I drive mine into the show room and chuck the keys over the desk if it was all the time, how can you handle it ?

I should clarify, the vibe is there between the speeds we are all talking about, not lower ones.

 

[WibbleWobble]

Well, well. The leasing company phoned me yesterday to say that my "steering damper upgrade" is available for my car and the dealer will call me to fix up a time for them to fit it. No call. I tried to call them but no answer left msg. for them to call me back. No call so far, CBA to chase them.

Finally had a call back, car booked in for Wednesday. We'll see what happens.

 

[murf62]

At 3x the rotational frequency, could this be pointing to the (probably inboard) CV joints - specifically "tripod joints" ?

Blog tripod vs. Rzeppa joint – KMP Drivetrain Solutions

n this blog, we would like to talk about the difference between the regular, ball-type CV-joints used in most passenger cars and the tripod joints that we use in our driveshafts.

www.kmpdrivetrain.com

In which case the vibration would be an intrinsic shortcoming of the implementation?

It's possible but if that's the source it would be a mechanical vibration rather than imbalance. I would expect that to be present regardless of speed. Balance vibrations are generally more pronounced at a certain speed like we experience on the XPower.

I tried mine yesterday in all driving modes and there is no noticeable difference between them.

 

[powerfulx]

Wow I'm so glad mine's not there when in eco. I've done some long trips, eco saves the day. It's only very very slight. Another drive mode and it's shake rattle and roll.

 

[Fogey]

It's possible but if that's the source it would be a mechanical vibration rather than imbalance. I would expect that to be present regardless of speed. Balance vibrations are generally more pronounced at a certain speed like we experience on the XPower.

I tried mine yesterday in all driving modes and there is no noticeable difference between them.

Well, both sources of mechanical disturbance would serve to excite a resonance, though I'd agree that out-of-balance would be proportional to the square of the rotational speed, so is more likely to behave as seems to be commonly the case. Does the vibration disappear at higher road speeds?

 

[Kermit]

The vibration on mine starts about 105kph maxes out at 110-115 and is completely gone by 120kph. So very much a resonance issue.
As to whether it's part of the drive chain or part of the steering that's resonating, I've no idea yet.
If we can narrow it down it might be possible to spoil the resonance with a bit of strategically placed extra mass .

 

[powerfulx]

Are we seeing any difference in left hand vs right hand drive ? This is the rear motor placed in the front and slightly detuned. Steering was never proposed in its original design.

Things tried so far by me,

• Full wheel balance.
• steering alignment
• swap to long range wheels
• jubilee clip balance ( caused phasing of vibration based on opposing wheels rotation point)
• eco mode (huge difference for me ). Others no difference.

Tried by others , all above apart from jubilee clip test.

Higher tyre pressures, ( made a difference to me) makes sense, vibrations go to ground rather than chassis. Think of a fish pump, on rubber feet, pump has more vibes, place on hard surface, less vibrations.

Next ill try just front tyres on high pressure, suspect same result.

Drive shaft angle, other cars worse angle than xpower. Not cause.

Other cars with drive shaft imbalance have similar issue. Right drive shaft smaller than left. Possible cause.