Had another trackday today and it was pointed out by 2 separate people who drove my car that the rear suspension needs looked at. It's really soft and bouncy. Suspension is completely standard other than Eibach springs. Where is the best place to start looking for problems? Likely to be dodgy bushes? Ruined Shocks?
Handling issues
- Thread starter Easty-5
- Start date
Eibach lowering springs but you left stock dampers in place? That's a problem right there. They then probably wore out very quickly, so you're left with short, firm springs and shot shocks. Get a proper shock built for lowering springs (i.e. Bilstein Sports) and be happy.
CornishRob
Senior member
Bing said:Exdos is your man on this topic - he's done a shed load of work on his car. He'll tell you the OEM set up is unbalanced, and that the rear is way too soft as standard. Drop him a PM, he's a very helpful chap
I thought the rear was too hard and the front too soft hence it bobs on hard acceleration?
But yes, Exdos is the man with the knowledge
If the people who test drove your car are unfamiliar with the the unusual characteristics of the Z4M suspension, they may have misinterpreted what they could feel. Especially if they were driving only on the track.
I covered 25,000 miles (including over a thousand miles on the track) with Eibachs and standard shocks and the shocks were in perfect working order when they were removed from the car. This combination marginally reduced body pitch and roll compared with OEM and improved the inherent understeer. However, it was only once I'd fitted RTAB limiters did I realise how vague the rear of the car was without these. Unless you have collateral evidence that you have a failed rear shock or shocks, I would suspect that the soft front / hard rear spring setup and lack of RTABs was behind the problem your test drivers detected.
I've fitted RE rear top mounts, Turner RTAB limiters, KW Clubsports with camber/castor plates, and H&R ARBS front and rear as well as reinforced front strut towers, an OEM strut brace and Vibratech competition engine mounts. This has transformed the handling of the car on the track with balance through the bends and significantly shorting braking distances. However, you have to be committed to track driving as the car really lacks compliance on the road (and it was bloody expensive!).
I would suggest asking a competent mechanic to look critically at your rear shocks. If they are in good working order, spend your money on a RTAB limiting kit instead.
I covered 25,000 miles (including over a thousand miles on the track) with Eibachs and standard shocks and the shocks were in perfect working order when they were removed from the car. This combination marginally reduced body pitch and roll compared with OEM and improved the inherent understeer. However, it was only once I'd fitted RTAB limiters did I realise how vague the rear of the car was without these. Unless you have collateral evidence that you have a failed rear shock or shocks, I would suspect that the soft front / hard rear spring setup and lack of RTABs was behind the problem your test drivers detected.
I've fitted RE rear top mounts, Turner RTAB limiters, KW Clubsports with camber/castor plates, and H&R ARBS front and rear as well as reinforced front strut towers, an OEM strut brace and Vibratech competition engine mounts. This has transformed the handling of the car on the track with balance through the bends and significantly shorting braking distances. However, you have to be committed to track driving as the car really lacks compliance on the road (and it was bloody expensive!).
I would suggest asking a competent mechanic to look critically at your rear shocks. If they are in good working order, spend your money on a RTAB limiting kit instead.
CornishRob said:Bing said:Exdos is your man on this topic - he's done a shed load of work on his car. He'll tell you the OEM set up is unbalanced, and that the rear is way too soft as standard. Drop him a PM, he's a very helpful chap
I thought the rear was too hard and the front too soft hence it bobs on hard acceleration?
But yes, Exdos is the man with the knowledge
Good point, got it the wrong way round
RTAB limiters group buy though
The 2 people that drove my car - both extremely experience racing drivers and 1 who used to own a Z4MC. He said his MC was much stiffer at the rear than mine.
I have just had a look at the rear. Nothing glaringly obvious. I did however notice that my passenger rear tyre has been rubbing against the arch liner on the inside of the tyre. You can see in this pic just how low the rear of the car is going. Also, it's worth pointing out the the corner is on a dip.
Lastly, should I be able to push the shocks up by hand a bit when under the car?
I have just had a look at the rear. Nothing glaringly obvious. I did however notice that my passenger rear tyre has been rubbing against the arch liner on the inside of the tyre. You can see in this pic just how low the rear of the car is going. Also, it's worth pointing out the the corner is on a dip.
Lastly, should I be able to push the shocks up by hand a bit when under the car?
Thats the fastest pair of hairdressers I have seen in a while! 
Does look too low and must be if tyres are rubbing. Is the car really going up hill or a photographer jazzing it up?
I am not a suspension guru so sorry. Also from my experience of track day pictures photographers angle the camera quite a bit and you have flat bits of track looking like they have massive camber, going up / down hill. So impossible to tell how the suspension is loaded.
Your car will benefit from the Rear Top Mounts, The Rouge bushes or Limiter kit with new OEM bushes... There are lots of posts about it on here and some more info in my group buy..
I also went for the Vibratech Engine mounts and the all important Gruppe M induction kit to give it the CSL sound track.
Love the Z4M in red. Nice ride.
Does look too low and must be if tyres are rubbing. Is the car really going up hill or a photographer jazzing it up?I am not a suspension guru so sorry. Also from my experience of track day pictures photographers angle the camera quite a bit and you have flat bits of track looking like they have massive camber, going up / down hill. So impossible to tell how the suspension is loaded.
Your car will benefit from the Rear Top Mounts, The Rouge bushes or Limiter kit with new OEM bushes... There are lots of posts about it on here and some more info in my group buy..
I also went for the Vibratech Engine mounts and the all important Gruppe M induction kit to give it the CSL sound track.
Love the Z4M in red. Nice ride.
Yea the car is really going up hill there, that's why the rear looks so loaded. It bottoms out there which is pretty disconcerting and really unsettles the car. So need to address that. The rear is 100% too soft, which is strange as everyone usual states the rear is too firm and the front is too soft. My car is the opposite so something is certainly up.
I think first of all you should examine your car to see if something is actually broken before taking up the widely spread advice here and ordering all sorts of upgrade parts and whatnot...
It makes absolutely no sense upgrading stuff while some other part is on it's way out.
So that means getting it on a ramp and start poking around to see if all the bushings are still ok, see if the shocks are leaking, if the springs, roll bar droplinks etc are not broken etc etc.
Eibach springs on stock shocks are not a problem.
I don't know how many miles your car has but somewhere between 40k-80k miles shocks will start to loose some of their effectiveness. Sometimes caused by the N2 gas dissepating out slowly causing cavitation in the shock oil (pressureless oil)
Worn shocks will cause bouncyness but not altered geometry or sagging while going through long corners
It makes absolutely no sense upgrading stuff while some other part is on it's way out.
So that means getting it on a ramp and start poking around to see if all the bushings are still ok, see if the shocks are leaking, if the springs, roll bar droplinks etc are not broken etc etc.
Eibach springs on stock shocks are not a problem.
I don't know how many miles your car has but somewhere between 40k-80k miles shocks will start to loose some of their effectiveness. Sometimes caused by the N2 gas dissepating out slowly causing cavitation in the shock oil (pressureless oil)
Worn shocks will cause bouncyness but not altered geometry or sagging while going through long corners
Should I be able to compress the shocks by hand? I jacked the rear up, took the wheels off, lay on my back and I could compress both shocks a bit by pushing on the underside with not a great deal of force. I was also getting a bit of a "scushion' sound from the shock too.