Unstable at high speed

[decalwren]

Sorry to post this here, only really being a lurker after recently acquiring my z4. I have been having issues with steering when travelling at motorway speeds, so naturally I took it to have the alignment checked. It seems definitely improved but still not 100%. Do these alignments look correct? This is for 3.0 coupe si sport.

https://goo.gl/photos/mZGpgomNQ2DRDLUT8

Thanks in advance for any expertise you can share on this.

 

[synthedup]

Sorry to post this here, only really being a lurker after recently acquiring my z4. I have been having issues with steering when travelling at motorway speeds, so naturally I took it to have the alignment checked. It seems definitely improved but still not 100%. Do these alignments look correct? This is for 3.0 coupe si sport.

https://goo.gl/photos/mZGpgomNQ2DRDLUT8

Thanks in advance for any expertise you can share on this.

Hi, are you running run flat tyres?

If so thats your problem I reckon oke:

 

[Bing]

+1

Run flats catch ruts in the road on these cars really easily, makes the steering wheel feel like it's randomly moving. Once you know what it is you do get used to it... Mostly. Changing to normal tyres will almost certainly solve this as long as all the rest of the suspension components are ok.

 

[decalwren]

Thankfully the previous owner ditched the run-flats. This definitely feels different to tram-lining though. Prior to having the alignment changed it was a lot more severe and you could feel the steering wheel move left then right at regular intervals once above a certain speed, since then you can still feel it, but it is much lighter and kicks in at a higher speed.

Can you guys see the printout from the alignment that I linked, not sure if google photo links work on forums?

 

[Darkangelv2]

I wouldn't be too happy with that front right after alignment even if it's within tolerance.

 

[Tom_j_l]

Drive it down a back Road at speed now that keeps you on your toes lol

 

[Bing]

Here's mine - bear in mind it's an M. The fronts look on the edge of tolerance, but he was really concerned with getting the steer ahead and thrust angle at 0.

The only other thought I've had is that maybe you've lost some wheel weights, or one of your wheels is slightly buckled from a pothole. I had both problems on mine, and new tyres / rebalancing got rid of an annoying vibration I had.

 

[Zikim]

On the Roadster the rear toe-in is 8' to 14' whereas yours are at 5' & 3' . The rear toe-in aids the stability. Your rear camber looks low if you have the M Sport suspension, I would expect it to be 2deg 50'

 

[Rorybeanbutler]

I had a lroblem with instability and it was due to diff tyres on front and rear axles. Once they were the same brand it was fine.

 

[decalwren]

On the Roadster the rear toe-in is 8' to 14' whereas yours are at 5' & 3' . The rear toe-in aids the stability. Your rear camber looks low if you have the M Sport suspension, I would expect it to be 2deg 50'

Thanks for this, I do have the M Sport suspension on the coupe. I found the specs below which seem to agree with you:



Is this the correct spec for my car (M Sport suspension, 56 plate coupe on 18" wheels)? If so, it looks like I need to go back to the garage and ask them to do it again.

 

[Raj_UK]

Sport suspension should be stated at the top in the car model. I've actually got a very similar rear camber to you (had mine done yesterday) but it shows as red. The garage told me the camber adjustment was maxed out so couldn't adjust it any more! They didn't put any weight in the car and fuel level was also low! Don't mean to highjack your thread!!

 

[decalwren]

Thanks a lot for the feedback , I have gone back to the garage and asked them to double check the spec as I also found this:

http://workshop-manuals.com/bmw/z_s..._alignment_e86___low-slung_sports_suspension/

This again seems to suggest that I need more negative camber and toe at the rear, although I thought that increasing camber would actually create less stability at high speeds so needing more positive toe is more likely to be the culprit? I think either way I am going to try and get it set up as BMW intended and go from there. I just hope the alignment shop can find the correct settings this time as I don't trust random things I find on the internet. I will report back with how I get on.

 

[jeffers]

Is it a bit like an oscillation of the steering wheel, like the EPS is trying to mess around with the wheel angle? I have a similar problem on my '08 coupe.

 

[85genius]

I had similar have a play around with the tyre pressures I've got mine at 32 front and 35 rear and more more high speed scariness or tramlining

 

[decalwren]

Sorry it has taken me so long to get back, I have been away in Europe the last few weeks.

I got the car realigned somewhere else after the last people used the wrong specs and generally didn't seem to know what they were doing when I called them about it, apparently they had failed to secure the steering wheel when they did the alignment and the new place had specs that were similar to the ones I posted. The car has behaved much better since then, it still feels a little less planted than my last z4 at autobahn speeds, however the last one didn't have the sport suspension, 18" wheels and low profile tyres, so at this point it feels mostly like tram lining rather than a regular oscillation like it was before.

I will have a play with the tyre pressues as suggested as this could help make the last bit of difference.

Thanks all for your help, hopefully my experience is helpful to someone else in future.

 

[ben g]

I got mine done this week as it felt awful at speed. My rear toe is less than yours but the camber is maxed out (lowered) and it drives lovely now. Slight wheel wobble, more like fidgety which may be the wheel weights, but other than that, perfect.

Here's a graph for you to compared. It also says M roadster at the top. I had it done with just sport suspension last year and it feels about the same.



sport settings and lowered suspension:

 

[Philmor]

Hi, I've just experienced the same thing with my 2003 3.0i E85. Mine was do bad it destroyed thd rear tyres. Fitted new tyres and took it to my local garage for 4 wheel alignment, also asking thwm to check the rear bushes. It was a lot better, but still kicked out on the rear when driving over drain covers.

I then noticed my new tyres were wearing very badly, so I took the car back to the garage, they then said the bushes must be bad. I took the car away from there feeling very pissed off and took it to my mates garage, who advised the alignment was miles out of spec.

They changed the rear bushes and checked everything out, realigned the suspension and what a difference !! I love the car to bits now !!

Moril of the story, get the bushes checked makes a huge difference

 

[hopz121]

I have set mine up with M settings and it is now alot more stable at high speed, i think the M uses Less Rear camber which helps alot with this.

 

[Dean'o]

Hi, I have the same problem with mine. I upgraded to 18" from 16" was told my wheels are slightly buckled. It does it more at 60 - 70 mph.

 

[MKZ4000]

Had this. Lowering the tyre pressures to 30 all round helped no end