Terrible handling – (now a lot better)

I haven’t yet fitted my RTABs so can’t comment on comfort - the comparative ease of fitting was what swung me as a no brainer.

I also am not the best person to comment on comfort as I went from runflat 16” wheels on FK springs on original SE dampers (pretty horrendous) to 18” standard tyres on BC Coilovers (fully poly’d at the front). I think it’s sublime and can’t wait to finish off the rear.
 
Newbers said:
Darkangelv2 said:
If you replace with the Powerflex (or similar) RTABs it at least means pre-tension is no longer an issue :thumbsup:
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I didn't realise that. What's the verdict on them for the road? Would I be losing fillings? I've surrendered a lot of comfort with the coilovers and Powerflex ARB bushes already. If the thing was at least nice to drive I could over look some discomfort but I don't want it too much worse....
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My car has powerflex front arm, RTAB, front & rear ARB bushes, KW V1 coilovers & runflats and the rides not terrible.
 
That was the first thing I checked - I was pleased I did because two of the bolts were under torqued but that wasn't the issue.

My wife wrote off a wheel driving with loose bolts after her previous Mercedes had new tyres fitted and they weren't tightened.
 
Specialist cars have checked all of the suspension and say it is fine. They say next step is to get the alignment done but they won't do it because of the non-OEM coilovers (to be expected). Their guy did say I might want to look at replacing with shorter droplinks because it is quite a bit lower than stock (it original had the standard suspension) but I didn't get any more detail.

I haven't seen much on here about shorter drop links (may be something about some plastic Peugeot ones?) what is the accepted best practice?
 
Which KWs do you have? Not sure about other products, but the V3s and Clubsports for the Z4M come with shorter front drop links supplied. The rears are the same as OE.

Not convinced by the alignment suggestion - it would normally be a sensible idea, but I don't see how an alignment issue (on its own) can explain either of the points in your first post. You also don't want to spend money on an alignment if there's a chance you'll end up swopping out parts, because you might then need another one.
 
I have V2's. I haven't had the alignment done for two years (it's pothole central round here and I wasn't convinced it was right when they did it before) so I was planning to get it done any way. I'm not even that fussed about spending a bit more more on it - I've forked out a load already and would just like it to feel good - at the moment I'd rather take the Merc....

It's just had new Meyle HD droplinks on the front and I've got new Lemforders to go on the back but I'm thinking if they are too long I'll swap them for adjustable ones and if it'll help with the rear camber fit Powerflex adjustable lower control arms then everything is done and if I can find a specialist get someone to take the time to set it up properly.
 
Informative thread, following with interest. I feel my Roadster is rather wayward (at least more than I would expect) and especially squirmy under hard braking. Will get it looked at properly in the spring but for the time being am taking it easy.
 
... while you’re at it, check your rear drop links if you’ve done the RTAB’s & RTAL’s, as well as your front drop links, tierod ends & lollipops.

Am also wondering if a broken rear spring or knackered shock or rear top mount may also be the culprit...

I went for Rogue Engineering for both RTAB/L’s, was told was overkill but I find it perfect.

Good hunting
 
I had to drive in to work again today and I'm inclined to agree with the diagnosis of offside RTAB (possibly the other side is not great either). Turning left is more pronounced in its weirdness and I noticed a bit more of rattle (admittedly I'd have expected more of a knock) which appears to be coming from just behind me. I think it has probably just let go...

I don't totally trust Specialist Cars but yesterday they said they couldn't find a problem when inspecting. As was said before the one thing they couldn't inspect easily would be the RTAB's. I mentioned before they were only changed 2 years and <20k miles ago but I did have suspicions about preload.

Long story short I've just bought two new Meyle HD (ebay £13 for a pair) and also some adjustable control arms (Powerflex) + new bushes for the hub end of them. I'm going to take the pins out of the front top mounts then I'll get it booked in and they can do the whole lot + put the new drop links on, then I'll get the geometry done properly. They should now be able to get it spot on (either Z4M or M3 CSL).

If that doesn't work you'll see it on ebay and I'll buy a Panamera, if it does I'll spend the money landscaping my garden!

P.S. I'm sure I won't find such a friendly and helpful bunch on any Panamera forum!
 
I (visually) checked the rear top mounts (as I happened to have the boot open). Couldn't see anything wrong. They are Meyle HD which I've heard can rattle - wondering if that might explain some of the noise.
Powerflex control arms + all the Mehle bushes arrived this morning. Love it when the postie brings me some bling!
It's booked in on Friday for fitting and alignment.
 
Just picked the car up. One of the track rod ends was seized so both got replaced. RTAB's replaced (they thought they were OK though), adjustable control arms with new bushes fitted and new droplinks on. Alignment completed. £705 for labour + track rod ends. I supplied the other bits. :cry:
I went for the Z4M alignment in the end. I figure that gives me a benchmark. Ignore the diagnosis, parts had just been changed:
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I only went for a quick ride and it's better but there is definitely still something going on. The front is fine but the rear is still very lively and doesn't seem to want to follow, particularly when the road surface is not great. I find this surprising given how much toe in there is....
 
What tyres are on the car?

Have thought about getting a free alignment check elsewhere just in case the new alignment is a bit out?

Other than that is there anyone local that has the same car to give it a test drive to see if they feel the same issues. Not saying it's all in your head but another owner might tell you it's fine, or not!
 
I'm not sure your alignment is helping much, that is a helluva lot of toe in, especially on the rear. That much toe in is really going to wear your tyres on the inner edge, the rear is going to be slow to turn in (toe out will make it very quick to turn but will be unstable in a straightline). I went for z4m as a starting point but front camber at 1.20, reduced front toe in to total 0.04 and rear to total 0.08, this is a very stable set up in a straight line, no issues under braking (too little toe in on the front can lead to toe out under braking and instability) I get zero bump steer and zero tramlining with neutral handling.
Reduce the amount of total toe in and I bet you will be much happier, if it doesn't fix it at least your tyres wont be worn out in 6 months
 
Good idea getting an alignment as a reference point. Seems to be a decent job too - converted to degrees/minutes, the toe values look nearly bang on (0deg11 front and 0deg28 rear).

When you say “rear is still very lively and doesn't seem to want to follow”, would it be fair to interpret that as the car having a strong tendency to understeer overall, with the rear remaining stubbornly planted before breaking away suddenly? Because that is just the factory Z4MC feel - it’s a bit rubbish! Personally I found tyre wear patterns ok with stock geo, but it does depend on how you drive.

What’s happened to the weird behaviour where the car seemed to steer itself and turn in more than one movement? If that’s gone, then as [ref]Davz[/ref] says, you could now just dial out that toe and see how it goes. I’ve done similar and it’s brilliant. If not, then you’re still probably looking at some kind of mechanical wear or failure.

For what it’s worth, I replaced my RTABs last year and they looked fine externally but were total mush inside. A deflection (e.g. pry bar) test is the only way to really tell what condition they are in and that needs and expert arm/eye.
 
Davz said:
That much toe in is really going to wear your tyres on the inner edge, the rear is going to be slow to turn in (toe out will make it very quick to turn but will be unstable in a straightline). I went for z4m as a starting point but front camber at 1.20, reduced front toe in to total 0.04 and rear to total 0.08, this is a very stable set up in a straight line, no issues under braking (too little toe in on the front can lead to toe out under braking and instability) I get zero bump steer and zero tramlining with neutral handling.
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It's weird, if I didn't have the figures there I'd swear the rear was toeing out a bit because of the nervousness over any undulations in the road. (This is the new phenomenon that I started the post with). Even with tired Bridgestone Potenza's and broken rear springs when tramlining was at it's worse I was never really troubled by rear - it was the front that wanted to kill me!

What I would say is that under hard braking the car now seems to be much more stable. (I can now be relaxed standing on the brake without having to be ready for a fight).

When you say “rear is still very lively and doesn't seem to want to follow”, would it be fair to interpret that as the car having a strong tendency to understeer overall, with the rear remaining stubbornly planted before breaking away suddenly? Because that is just the factory Z4MC feel - it’s a bit rubbish! Personally I found tyre wear patterns ok with stock geo, but it does depend on how you drive.
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I've never known my car to understeer but I would agree with breaking away suddenly (and on the road at least). I only did a few miles down a straightish but bumpy, fast road and it was very busy so I can't really comment yet on the whole package. What I was struck by was coming off a roundabout the uneven surface had kicked the rear (quite significantly) off-line and it (the rear) had also felt twitchy at a couple of other points in a straightline (whilst the front was planted and fine). This bothers me more than anything because a lot of my driving is straight roads (often with less than ideal surfaces).

Tomorrow I'll have 60 miles on the M25 (at varying speeds so should get a better sense of the straight line behaviour). I really need to find somewhere with a bit of room to take a few fast bends to see what happens if I push it hard. I'd really like to be able to compare left to right because I'm convinced it's more pronounced in a left turn (rear right loaded up).

I've had the car for 10 years and drive it pretty hard so I'm really familiar with it's peccadilloes.

I am mindful of the fact that I've gone from Avons to Uniroyals (on the rear only). Our cars are sensitive to tyres but I've noticed this much more on the front than the rear in the past. I'm going to double check pressures tonight to at least be aware of any impact that's having.
 
This may seem like pointing out the obvious, but I went through quite a bit of this recently too......

Having changed up to a new set of FK510's I found my 3.0 Si bouncing around all over the place. I got the alignment done for a 3.0 Si with M-sport suspension and the numbers were also high, with a lot of toe-in and rear camber. As with Davz, I too knocked these back a bit to reduce tyre wear but this was not my issue.

Mine was all based on tyre pressure - the tyre shop put in 40 psi and this made it feel like you were driving with four over inflated footballs on each corner. A reduction down to 32 psi completely transformed the car.
 
Still haven't had a chance to properly test the car (mostly <10mph on the M25 :| ). That said one incident that really well illustrated the issue - getting on to the M25 (towards Heathrow) at St Albans, the slip road is long with a left then a right then another left curve. There are two lanes which are both a bit rutted. With no one else around the spirited driver takes a straight line through this curve crossing from one lane to the other and back at motorway speed. In my car, crossing the lanes (in particular the worn tyre ruts) is really hairy. It's a bit like the front and the rear are different cars or perhaps like there is another person steering the rear wheels. It's less extreme in a straight line but same sort of thing.

I stumbled across this post https://z4-forum.com/forum/viewtopic.php?f=9&t=52424 from six years ago and particularly "The real culprit was finally revealed on the Mercedes SLK launch last month. Mercedes brought in a Z4 for evaluation during the SLK's development and had noticed the same strange chassis behaviour that we'd experienced. After putting the car on a chassis rig, the explanation seemed to be a noticeable change in rear toe angle when the Z4's rear suspension moved up and down, meaning it would start to 'steer' from the rear on undulations. Now, increased toe-in on compression is great on track as it tucks the car into the apex, killing understeer in the process, but pretty useless on our lumpy roads as the change in toe angle can cause the constant wandering we'd experienced as the rear wheels steered their own independent course to the fronts."

I seem to have developed an extreme case.....

All of the suggestions above have been sensible and I have checked them all. Liam22's suggestion "The handling woes sounds like rear bump steer. The loaded rear wheel goes into toe out during compression" seems to sum it up.

Question - are our cars known to suffer the same body shell cracking where the subframe is mounted as apparently happened in the e46 3-series? Google led me to this https://speed.academy/bmw-e46-cracked-subframe-fix/2/. Link is to page two which is the more interesting but action starts page one.
 
I've had my rear wheels off this afternoon looking around for anything that BMW might have missed twice or my independent whilst they were doing the rear control arms. One thing I notice is that I can quite easily rock the upper rear wishbones from side to side (as in twist them around the axis between the bushes at each end). Given that there are bushes on either end, the spring and the ARB bush I was surprised how easy this was. This does coincide with the bushes on this arm being the only ones (apart from engine and subframe) that I haven't changed. Is this normal? Could the combined wear in these bushes be responsible for the dodgy behaviour in my rear( :o)
 
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