25-35 MPH - Wobble/Bounce.

M

Maniac

Elite
From the moment I had this car I've felt a subtle bounce/oscillation from the rear on smooth roads between 25 and 35 mph. It's like you're running over a slightly ribbed road.

Anyhow I put this down to stiff suspension and either a slightly out of shape rear tyre or wheel, or perhaps a very slight ribbing in the road surface as its not always detectable.

When I had the tyres changed a year ago I really hoped it would go and it didn't this slight bounce at a certain speed was still there.

So I recently changed wheels as some of you know, thinking it must be a wheel. No. It's still there. Took it to the dealer and got a 'that's how this car is' response, at certain speeds the suspension can set up a harmonic type of thing, particularly on the active suspension. Didn't believe a word.

Still not happy... I over inflated the tyres last night and I could really feel this bounce on smooth road surfaces, reduced the pressures and it got less but is still there.

At this point I'm thinking wheel bearing perhaps (but there's no discernible bearing type noise) or final drive / diff / etc but again no noise or other behaviour to give me a clue (though I do think I can hear a very faint rotational thump but it could be my imagination as the road really does need to be like glass to feel this).

So before I spend good money on diagnosis to be told there's nothing wrong again, does anyone have any thoughts what this might be?

FYI I have the adaptive suspension. I've also had this car on a Dyno and you could see the rear of the car bouncing up and down around 1/2cm at 30mph but as you slowed or speeded up the car settled down. So I'm fairly sure its not road surfaces given a rolling road allowed me to see it outside the car. It was too small a movement to believe it was anything other than a flat spot on a tyre or wheel and this was before the new Pirellis and 313's.

Its yet another minor annoyance as most roads are too imperfect to feel it... but its really bugging the hell out of me to know what it might be...

Thoughts?
 
I have a similar feeling from my front wheel but again only on certain road surfaces. I have the rotational type noise you describe as well. Mine is due for MOT next month so I was going to get them to take a look then. I suspect mine is wheel bearing.
 
Wheel bearing is a guess only because I really can't see it being anything else now unless a drive shaft related fault which i doubt. Early on in the world of 19" run flat concrete tyre ownership I hit a pothole with a real whack. Wouldn't surprise me given how hard these tyres are if it also resulted in some damage to the wheel bearing. Darren Wood (stockport) are 10 minutes from me so I may see if I can get it there as I'd trust their opinion rather than the dealer given the good reports I hear about Darren Wood. Still, its more money drained from me for diagnostics. Not sure its that bad to warrant it... I am a bit of a perfectionist and where do you stop?
 
Maniac said:
Wheel bearing is a guess only because I really can't see it being anything else now unless a drive shaft related fault which i doubt. Early on in the world of 19" run flat concrete tyre ownership I hit a pothole with a real whack. Wouldn't surprise me given how hard these tyres are if it also resulted in some damage to the wheel bearing. Darren Wood (stockport) are 10 minutes from me so I may see if I can get it there as I'd trust their opinion rather than the dealer given the good reports I hear about Darren Wood. Still, its more money drained from me for diagnostics. Not sure its that bad to warrant it... I am a bit of a perfectionist and where do you stop?
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I've only ever heard good things about Darren Wood. As for the perfectionist bit, I know exactly what you mean. Mine has been annoying me for months, even though it has zero impact on the driveability of the car, hence the reason I'm going to do as you are, and pay the diagnostic fee to get it sorted. I assume wheel bearings are replaceable under warranty? I'll have to check my Mondial documentation.
 
I think the bearings are... Having taken mine into Williams Manchester to be told 'its normal'.. I'll be paying Darren Wood to investigate and if they find anything, I'll then try and claim for the work at the dealer via extended warranty. I may well not get the money back from the diagnostic but I'm willing to pay that knowing (hoping) Darren Wood will probably do a better job on the diagnostic than Williams.
 
I was out for a pint with Darren Wood over Christmas....Im sure he will sort it for ya.


Where abouts are you by the way,cant be too far from me ?
 
Is it more on one side than the other ? Could it be an out of balance wheel giving a vibration ?
Know its obvious but sometimes these things can be missed.
Would have thought a wheel bearing would rumble and when wheel lifted off of the ground there would be discenable movement at the hub.
 
I doubt it's wear. The car has just 20,000 miles on it. I'm guessing pothole damage but quite what is another matter...
 
Do you have any uneven tyre wear then that would show an alignment problem ?
Maybe worth getting the rear tracking checked to see if something has gone out of kilter ?
 
I'm not sure but I think the bounce on a dyno is to do with the centrifugal force of cambered wheels. When they hit a certain frequency the kinetic energy is transferred and causes the shocks to bounce until the frequency is passed. There is probably nothing wrong, just blame Newton.
 
Out of balance driveshaft?,do they have a damper on the exhaust to dampen out vibration / sound that's possibly missing? I don't see it can be a wheel bearing,the noise would of developed in some way surely? My money is on a driveshaft. GoodLuck :)
 
Perhaps get the wheels balanced on a dynamic hunter machine. It will be the cheapest thing to try..
 
Z4M-2006 said:
Perhaps get the wheels balanced on a dynamic hunter machine. It will be the cheapest thing to try..
Click to expand...

Already done that ... 'road force balancing'. Its deffo not the wheels or tyres as I've said, because I have 313s with Pirellis now and the feeling is the same as when I had 296 with Bridgestones (which I originally blamed). Has to be something from the diff onwards,half shaft, bearing, something... guess I'm going to have to bite the bullet and get it into the indy... not this weekend it looks though as the weather's going to be shocking.
 
Just spoken with Darren Wood and I'm taking the Z over there in the morning for a quick road test. I guess I'll have to book it in sometime in the next few weeks as this is going to be something tricky to find...
 
Hmm.. Seems this issue lessens as I make the suspension stiffer. I'd expect it to get worse on a rotational issue with stiffer suspension. I'd go with a harmonic of the suspension if I hadn't seen the car move on the Dyno.

It's booked in on the 6th at Darren Wood so ill see what they say.
 
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