Twitchy/nervous/vague steering at speed

ocrx8

Active member
 Essex
Hi all

I've had my Z4 for several months and am loving it, although can't shake off this odd feeling I get through the wheel!

I first picked up the car at the end of July and it drove beautifully. All tyres were Bridgestone RFTs. The front right required replacement (MOT advisory) so two weeks after purchase I replaced both fronts with Vreds non-RFTs and at the same time, got the camber and 4-wheel alignment done. All of this was done at Elite Tyres, who I've always rated very highly. They use Hunter equipment.

Drove a couple of hundred miles and all seemed fine - the main difference being less tramlining, I suspect due to the non RFTs on the front. However, I then began to notice a twitching/wobble above 50/60mph - almost like a constant side to side movement - along with a light/vague feeling at these speeds. More noticeable on smooth roads and quite tiring after driving for more than 30 minutes. Also, it is more noticeable when the car in in Sport mode (I assume this is because the steering is tighter). I find the steering on the car light in general so I prefer using Sport mode, but sadly this makes the problem worse.

I took the car back to Elite and mentioned this problem. They rechecked the balance and found on the front wheels was buckled - this could be seen quite clearly on the balancer, so I thought this was the root of the problem.

Fast forward several weeks and I got a new set of 108s from FA Wheels to replace my damaged set. Mine needed a refurb badly anyway so this the wheel swap worked out well for me. Driving home afterwards, the car seemed much smoother as a whole - turned out both left wheels were buckled, so this is no surprise! However, the twitchy feeling remained.

Next stage was to replace the rears to Vreds non-RFTs (I know, I was naughty for mixing and matching) to have the same all round - I thought this would be the end of the issue. I also asked for the alignment to be rechecked. After the new rears were fitted, the ride improved significantly but sadly the twitchiness still was noticeable!

I've attached a print out of the alignment - this was the result of the check after it was originally adjusted (roughly 2 months). I am told it is normal for the rear camber to settle in a negative position for Z4s, so I am not worried about this. For all of the experts out there, is there anything drastically wrong with the results?

Has anyone else had a similar problem and subsequently cured it? I've had wheel balance issues before on previous cars and it doesn't feel the same, but I guess as the wobble only appears at 50+mph it could be related. It just seems strange the problem only occurred after the run-flats were taken off and the alignment was done. To add, a rear spring was replaced at the MOT in July as it had snapped, and to my knowledge all 4 are now fine.

Thanks in advance (and sorry for the essay!).

2873AAB1-FAEC-4E9B-8547-C42EE8543F16-8624-00000AE8A18F6D8B.jpg
 
DId the twitchiness arrived with the new front tyres?

if if did, are the new tyres directional?

DArio
 
What Dario said^^

Also, how are your front control arm bushes?

The ones on mine went so I replaced them with Powerflex thinking I was doing the right thing. They ended up giving me the EXACT symptoms you describe.

I changed the arms for Lemforder OEM ones (really cheap job) and the car returned to being utterly perfect.

You will need another four wheel alignment afterwards unfortunately, even if the garage tell you that you won't.
 
I noticed it after the new tyres were fitted - but only after driving several hundred miles! Vreds are directional as far as I am aware. I would get a picture but it's raining at the moment (!). I'm fairly sure they have been fitted the right way around as two garages have seen the car (Elite and FA Wheels) and nothing was said, but it is something to eliminate.
 
Blue said:
What Dario said^^

Also, how are your front control arm bushes?

The ones on mine went so I replaced them with Powerflex thinking I was doing the right thing. They ended up giving me the EXACT symptoms you describe.

I changed the arms for Lemforder OEM ones (really cheap job) and the car returned to being utterly perfect.

You will need another four wheel alignment afterwards unfortunately, even if the garage tell you that you won't.

Thanks - Is there a way to tell if the bushes are shot? I have wondered if this could be the cause. Have you got a link to these Lemforder items?
 
Here you go-

http://www.eurocarparts.com/ecp/c/BMW_Z4+Roadster_3.0_2005/p/car-parts/suspension-and-steering/suspension/suspension-bushes/?618110295&1&dee5515e6cb7ed583bee5b8b8c2e91ab26705a70&000437

They always have 25% off though :)

The garage demonstrated mine were shot by putting the car on the ramp (wheels off the ground), standing in front of the car and pushing the whole wheel back towards the rear. The wheel could clearly be seen to move backwards (which it shouldn't do at all) and you could see the control arm moving about in the bush.

To give you an idea where the bush sits, it's number 1 in the diagram here-
http://www.powerflex.co.uk/products/Z4+%28E85%29-1203/1.html
 
ps. I was with a geometry specialist recently and he blamed directional tyres for all sorts of woes!

his trick was to swap the tyres over side to side, but not turn them on the rim for a trial. that way the directionality was negated.

if the car has done 40K+ miles with out lower control arms....... then its likely that it wont harm the situation.

Dario
 
Apologies for the shoddy pictures. Here's the driver side:

D3F41CFD-C3F5-444C-BBFB-C1E7BBEDB2B8-9102-00000B4EE93A97B9.jpg


and the passenger:

2B8541F6-D0F9-4B7C-AE22-2D4AEEE5A920-9102-00000B4EF359F522.jpg


I've PM'd a few people and I might get the springs checked out... will jack the car up tomorrow and see if that's the issue.
 
I know nothing about directional tyres but why is the off side tread pattern running up /from the outside edge to the inside and the nearside tyre tread pattern is running down / from the outside to the inside in the pics? So the pattern is / /. I would have expected / \ or \ / if you get my drift? Any one got a take?
 
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