Vibration on HARD highspeed acceleration

[Pho3niX90]

So as the title suggests.

Since I bought the M5 there has been an issues bothering me, on hard acceleration around 150kmh the car would have a vibration, and recently discovered on a dyno it is worsen 20x. All other times the car is perfect and no sign of vibration.

Has anyone ever experienced something similar and found a solution?

Car has been taken in for balancing a couple times now, and bmw cannot reproduce it therefore leaving it in my hands to fix.

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[TurboLlew]

Had this issue before. Wheel was very slightly buckled. The Supa Quick machines re-balanced it time and again for me with no luck (150-170km/h and noticeable with high speed braking too - was driving me nuts). I know your immediate thought becomes a bushing or shaft or diff or something like that... Couldn't really see much on the wheel in terms of damage when on the machine but I know my fronts were previously repaired which may have contributed...

Took it to TWT and it was sorted. Maybe machines were not calibrated or TWT had brand new machines (I don't know).

 

[Dewald Basson]

My bet would be on a wheel that is slight out of round.

 

[Pho3niX90]

My bet would be on a wheel that is slight out of round.

Shouldn't it be all the time then? Even when not accelerating? I have balanced them a couple of times now already at 3 different places.

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Had this issue before. Wheel was very slightly buckled. The Supa Quick machines re-balanced it time and again for me with no luck (150-170km/h and noticeable with high speed braking too - was driving me nuts). I know your immediate thought becomes a bushing or shaft or diff or something like that... Couldn't really see much on the wheel in terms of damage when on the machine but I know my fronts were previously repaired which may have contributed...

Took it to TWT and it was sorted. Maybe machines were not calibrated or TWT had brand new machines (I don't know).

Thanks, mine is literally just accelerating hard, not on braking or even cruising at those speeds.

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[TurboLlew]

I think it might be a combination of the force acting on the wheel that amplifies the effect when accelerating together with the actual rotational speed that causes this. I also didn't have the issue when constantly at that speed (or gently accelerating between that range)

If it is a small enough imperfection, the wheel will balance perfectly on the machine but will still have issues at high speed in practice. They don't balance at high enough speed to pick up issues.

 

[Dewald Basson]

Shouldn't it be all the time then? Even when not accelerating? I have balanced them a couple of times now already at 3 different places.


The imbalance is so small that it only become noticeable or amplified once the wheels rotates at insane rpm's. Imagine if the car is move at 160km/h how many rotations each wheel has to make. I am do doff to do the maths on that but it must be a bucket load. Additionally the faster you go the more force is apply to the wheels, pushing them away from the axle(imagine a F1 car with a puncture the tire swings away from the axle). It is this motion/force that must be balanced, if it is not the wheel will start to wobble, causing vibrations.


Even a out of round tire can cause vibrations, think slightly oval but only on one side.


I hope that makes sense :hammerhead:

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I think it might be a combination of the force acting on the wheel that amplifies the effect when accelerating together with the actual rotational speed that causes this. I also didn't have the issue when constantly at that speed (or gently accelerating between that range)

If it is a small enough imperfection, the wheel will balance perfectly on the machine but will still have issues at high speed in practice. They don't balance at high enough speed to pick up issues.

Sorry I just repeated what you said :hammerhead:

 

[Peter@AEW]

I would start looking at gearbox mounts prop couplings and diff mounts.
Just thinking out loud

 

[JayDrft]

Ever considered crack testing the rims...? Given rotational forces, combined with frictional heat - a crack might open up...there are some fancy spray on products.

I know spoked rims that have a bit of "power" behind them, tend to give up on the weakest point, spokes.

I hope it helps...

 

[Pho3niX90]

So ran the m5 on kar's dyno, ran until 240 without any vibrations. So I don't know anymore

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[JayDrft]

Tyres pressures? Have you checked the pressures before and after a run, one might be running a bit thinner(material) and causing it to heat more rapidly than others, hence giving you an uneven setup

 

[FerdiBotha]

So ran the m5 on kar's dyno, ran until 240 without any vibrations. So I don't know anymore

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I’d have the front wheels inspected for cracks, buckling etc.

 

[Dewald Basson]

Avoid uneven roads then :tease:

 

[cOlDFuSiOn]

So ran the m5 on kar's dyno, ran until 240 without any vibrations. So I don't know anymore

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Then the rear is fine, the front is the suspect then.. :thumbs:

 

[Pho3niX90]

So ran the m5 on kar's dyno, ran until 240 without any vibrations. So I don't know anymore

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Then the rear is fine, the front is the suspect then.. :thumbs:

Yeah at most the vibration is very hard to reproduce. Accelerating hard from 100 to 180 doesn't produce the vibration. It seems downshift around 150 and accelerating causes the vibration albeit feint. However my causr of concern was on the first dyno whete the car sounded like it wanted to explode. However today on kars dyno it didn't happen.

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[TurboLlew]

So ran the m5 on kar's dyno, ran until 240 without any vibrations. So I don't know anymore

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Then the rear is fine, the front is the suspect then.. :thumbs:

Yeah at most the vibration is very hard to reproduce. Accelerating hard from 100 to 180 doesn't produce the vibration. It seems downshift around 150 and accelerating causes the vibration albeit feint. However my causr of concern was on the first dyno whete the car sounded like it wanted to explode. However today on kars dyno it didn't happen.

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What did it sound like on the first dyno? Were wheel bearings ever changed? Any other noises (The cabin is very well insulated so you only notice when windows are down and you are driving next to a wall sometimes)

 

[Pho3niX90]

So ran the m5 on kar's dyno, ran until 240 without any vibrations. So I don't know anymore

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Then the rear is fine, the front is the suspect then.. :thumbs:

Yeah at most the vibration is very hard to reproduce. Accelerating hard from 100 to 180 doesn't produce the vibration. It seems downshift around 150 and accelerating causes the vibration albeit feint. However my causr of concern was on the first dyno whete the car sounded like it wanted to explode. However today on kars dyno it didn't happen.

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What did it sound like on the first dyno? Were wheel bearings ever changed? Any other noises (The cabin is very well insulated so you only notice when windows are down and you are driving next to a wall sometimes)

The best way to describe it is a fast vibration, sounds like the small speedhumps near a tollgate or offramp.

Wheel carrier bearings have been changed on motorplan before.

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