Z4 oversteers too much!

S

saitrix

Member
Hi,

Late last year I wasn't able to drive my car for a while but the MOT on the car ran out. The garage found both sides at the front to have excessive play on the lower suspension ball joints & excessive movement at the wishbone bushes. So I had the lower suspension arms replaced. They also gave advisories on the tread depth on the rear tyres so I decided to not mess around and replaced the rear tyres with identical to previously fitted and what is fitted to the fronts (Goodyear eagle f1 as2).

Now the problem is due to me having broken by back it meant when I first got back driving I was tootling around slowly but as it has healed I have been able to increase my speed on corners. This is where I found the car now does not understeer at all but instead it oversteers! Whereas before when I drove the same corners in the same manner it would always understeer. It has made it a bit of a pig to drive to be honest as it has lost its stability so currently DSC is never being even turned down at all.

So in short what should I be checking to try and sort this issue?

I have got another garage to check the geometry and everything is within BMW specs and I have checked the tyre pressures and they are all fine. I purposely waited to ensure the tyres are fully bedded in so it is not that. Has anyone else come across this? If I am honest it has lost any potential fun from the car due to this issue!
 
It could possibly be your driving technique, heard of lift off oversteer? Tuition can be useful, I've attended the "car limits" guys at North weald but I think they go to different areas as well-recommended :thumbsup:
Regards
 
Its probably your front toe, changing the TCA's for non oem parts can change the track and effect the toe angle, most tyre places do a free tracking check :thumbsup:
 
Smartbear, Don't worry about my driving style as I am driving in the same manner before and after so driving style is not an issue here! I am fully aware of lift off oversteer, what I am talking about though is on steady state cornering this is happening, ie no acceleration or decceleration.

TDJ, Tyre sizes are totally stock, 225/40/18 on the front and 255/35/18 on the rear, both axles running AS2 tyres.

jyonaudl, It unfortunately isn't anything as simple as the toe as I had the geometry checked recently (so camber, castor and toe was checked) and they did the tracking when fitting the suspension arms.
 
Ok, this is a long shot but check that the rear wheels haven't been put on the wrong sides, ie: tyres on backwards
 
Hmm that's a point, I have been thinking about this and on Saturday I think I will take the front wheels off and have an inspection of the arms fitted. I have had a nasty thought it could be the front anti roll bar not connected to the suspension arms, that would certainly give oversteer. I will also look for a snapped spring on the rear of the car, past that I am really struggling to think what it could be.
 
Just to clarify on the geometry check, did you have a proper four wheel alignment done on a Hunter machine (or similar) by a garage that knows how to use it properly? You should have a print out with before and after readings of all the settings and a final thrust angle.
 
I would have said its down to the GEO. My car is set up with far to much rear camber and not enough at the front. And my car is the same as you describe.
 
TomD, Yep to clarify I had it done at an alignment specialist using a Hunter laser alignment system and as you say I have the printout for before and after. They advertise they do trackday setups so I thought they should know well enough what they are doing. I will say when I went there they did not instil as much confidence as say Wheels in Motion or Roddinsons Motorsport (as you may guess I use to have an mx5) where they did none stock suspension setups. I will admit I don't care about keeping with manufacturer specs if that isn't right.

Machine monkey, I will review the setup later and have a look at the values again as I cannot remember off the top of my head. There is the chance the camber might be within manufacturer specs but on either end of each spec.

So overall I will still do a health check with my own eyes (now I can actually get under a car again!) to check the work carried out by the garage. Annoyingly normally I would have done all this work myself so it is frustrating that this has happened when I have had to use a garage. If I don't find anything then I will have a think about what to do with the geometry.
 
If you were saying that the car understeered before the changes and then since oversteers, the only things is could be are the arms and the tyres so that would be my first check.

Also, on a personal note.. I prefer oversteer as you can modulate where you want the car to be, it's nice to get movement in the rear end which for me feels a lot more safer than understeer which frankly scares the living daylights out of me!

I have heard that people say the Z understeers a lot but since I have had mine I have only had it twice, which was my fault for entering a wet roundabout way too quickly, however I have lost count at how many times I have had the rear end moving around.

The only other thing to take into consideration is that around this time of year the roads are more greasy and less predictable than usual due to them being a bit damp and cold although the sun is out the ambient temp isn't all that high, so this could be a factor?

Also the Eagle F1 Assy 2's I have the same tyres that I use in the summer months and I find them crap for the first 2 miles or so but once worn in they seem to grip a lot better.

Let us know how you get on as I am quite interested as to what you find.

Cheers
Dan.
 
I'm sorry to go off-topic a bit here, but I would love to see your geometry setting. Maybe some would appreciate your oversteer setting :)
AFAIK Z4's are prone to understeer, but drive it like you stole it and they will oversteer bigtime. Things do change with addition of LSD though.
 
coupedan, I purposely waited until we had some better days for that reason before jumping to conclusions but yeah I agree it still isn't ideal weather.

RenoRaines, Here are what they measured:

1zh1d7b.png


Now since the last time I looked at this I have found some specs people have banded around on this same board (linked below). As you can see the major thing sticking out to me is the rear camber being a lot lower than the stock -2.5. The other thing is the large mismatch in camber at the front axle. What is adjustable on Z4's suspension wise? Looks like I probably won't find anything wrong visually, seems like it could be geo.

suspension0001.jpg
 
Looking at your numbers I would look into front/rear camber and toe. With your rear camber setting at ~1,35 (factory is supposed to be -2,5) I would expect that a car would be more planted or understeer prone. But taking into account the whole construction of the car and geometry this could cause your over-oversteering issue. Try to get rear axle as close to factory spec as possible, at least camber, at your shop and do a test drive.
BMW's factory specs which you attached are for sport (M) suspension.

There could be though numerous reasons why your car behaves as it does.

http://www.thesmokingtire.com/2012/massive-list-of-solutions-to-understeeroversteer/
 
I thought all 3.0 prefacelifts had the sport suspension setup? I have a 3.0 prefacelift with the 18" wheels so staggered tyre sizes so I thought that is the spec I should be working to.

So today I checked the following:

Tyres - All fitted correctly in the correct rotational direction. Fronts were 0.1bar low and rears 0.2bar low.
Antiroll/sway bars - All attached correctly to the suspension.
Springs - All complete with none of them snapped.
Dampers - No leaks or knocks could be seen.

So it really is pointing towards the geometry setup of the car causing this as I can't think of much else I can inspect. So I guess its time to try and find a specialist that knows more about what they are doing on BMWs. Does anyone know what is possible to adjust on the Z4, ie do I need to buy any shims to do the camber at the rear?
 
saitrix said:
I thought all 3.0 prefacelifts had the sport suspension setup? I have a 3.0 prefacelift with the 18" wheels so staggered tyre sizes so I thought that is the spec I should be working to.

So today I checked the following:

Tyres - All fitted correctly in the correct rotational direction. Fronts were 0.1bar low and rears 0.2bar low.
Antiroll/sway bars - All attached correctly to the suspension.
Springs - All complete with none of them snapped.
Dampers - No leaks or knocks could be seen.

So it really is pointing towards the geometry setup of the car causing this as I can't think of much else I can inspect. So I guess its time to try and find a specialist that knows more about what they are doing on BMWs. Does anyone know what is possible to adjust on the Z4, ie do I need to buy any shims to do the camber at the rear?
Click to expand...

Where are you based? Is it worth meeting up with another member and let them drive your car, you drive theirs to get a second opinion?
 
It seems like my alignment was not done with the correct ballast in the car so I have now got it booked in for alignment at a place I have used on a previous car and have done a good job.
 
Now as I am expecting for my alignment out am I right saying that I may need some new nuts if the camber requires being changed as they are single use? Does anyone have info on the procedure and whether I should go with any parts.
 
How many miles have you done on your new rear tyres?

Most tyres don't work 100% straight out of the box!


If the problem only started after the new rubber was fitted I wouldn't be looking for a complicated fix just yet?
 
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