Z4 Rear Suspension

[HaiderGill]

Hi,

From the Evo car magazine review of the Z4 E85 has always kept me from buying as I drive on A or B roads rather than smooth tracks:-


"the Z4 seemed to wander from bump-to-bump, sending confusing messages to the driver as to what was really going on. It felt like an advanced form of tramlining and became christened the 'Thrill of Writhing' in the office. At first I thought it had to be the fault of the standard run-flat tyres, so after the Z4's disappointing performance at last year's eCOTY (063), we swapped the Bridgestones (having covered 11,000 miles, they were around 60 per cent worn) for a set of Vredestein Ultracs. The initial ride coarseness certainly improved on the Ultracs, while wet grip was transformed. But even so, the Z4 never felt really relaxed unless the road was glassy smooth.

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."

Can this behaviourbe overcome?

Thanks
Haider

[ZStig]

Its never been an issue or bother for me. Guess other cars I've owned had similar "issues"

[HaiderGill]

You haven't seen our B roads, snakey, twisty, up and down gradients but as they are B roads out in rural places the tarmac is not smooth. It's a patch work with pot-holes, rippled, worn tarmac. There are some that you go on and you are the only driver on them if you are going up to down you can see the snakey couse is free for a couple of miles. Brilliant roads to drive on though.

[Finnegan]

I have the ///M version of the Z4, and it can be a bit of a handful on very poor roads like the ones you describe. Twisties, up/down, off camber, are not really an issue. However, bumps mid-corner do upset it a bit, potholes, really bad cracked and worn asphalt mean you have to be on your game and ready. It's a quirky car. (But I wouldn't trade it for the world!)

If you're interested in something that will handle that kind of road with more composure and is in the same vehicle class as the Z4, I'd recommend looking into something like a Cayman. I had one, it was brilliant in those conditions. The ride is still really stiff like the Z4, but you can get the adjustable suspension, and sticking to 18" wheels helps too, and it's a focused car. It's more composed, pretty forgiving (up to the limit), very predictable, very consistent, and isn't upset by bumps, potholes, and the like. (You will feel them, but the car tends to stay on target.) It doesn't have the same quirks as the Z4.

BTW, stay away from the Gen I Cayman and only look at Gen II--the engine in the Gen I is a real problem (as in self-destruction). Those issues, and the attraction of the Z4 (still kept driving my wife's Z4 when I had the Cayman) steered me to the Z4. The Z4, for me, is just more fun. Guess I like quirky cars!

[HaiderGill]

All is not lost the 3.0si Coupe SE comes without the sport suspension and doesn't have this dodgy track setup of the toe-in increasing. Worst case I'll to get Birds Auto to develop me their proposed Z4 setup.

This what they (Birds) have done for 335i
http://www.birdsauto.com/content/col...ar_201006.html


and 130i hatch: -
http://www.birdsauto.com/content/col...ar_201012.html


Thanks
Haider

[beta]

Sounds interesting, looks like they use soft suspensions with beefed up roll bars. I'd be hesitant to install a thicker roll bar without reinforcing the mounting points so this doesn't happen.

[Finnegan]

Originally Posted by HaiderGill

All is not lost the 3.0si Coupe SE comes without the sport suspension and doesn't have this dodgy track setup of the toe-in increasing. Worst case I'll to get Birds Auto to develop me their proposed Z4 setup.

This what they (Birds) have done for 335i
http://www.birdsauto.com/content/col...ar_201006.html


and 130i hatch: -
http://www.birdsauto.com/content/col...ar_201012.html


Thanks
Haider

Very interesting! Thank you for posting these articles!

If you go this route, please keep us informed about progress. It looks like they've not only improved the "B road" performance but made the car better cruising on nicely maintained roads as well.

Two forum members are at present considering a different car (E9x M3) due to back issues (Z4 not being especially kind in that regard). This type of mod would be attractive to many as it would let you have your cake and eat it too.

[v3.0si]

what issue of EVO is this from?

[The HACK]

The E85 hasn't been produced for nearly 4 years now, why would Mercedes use it as a benchmark to develop their SLK? Something does not compute here.

Plus, the E85 has the same identical rear suspension, in fact, borrowing every single parts from the E46. I've never heard of this complain on the E46 before about the toe changing dramatically in the rear due to camber changes.

Now...if you want to talk about the front McPherson strut changing toe when compressed? That's been known to happen on ALL BMWs, not just the Z4s.

[v3.0si]

^whs...

i was wondering if maybe the article is about the e89 rather than the e85... although that still doesn't explain mb's involvement.

[HaiderGill]

Originally Posted by Finnegan

Very interesting! Thank you for posting these articles!

If you go this route, please keep us informed about progress. It looks like they've not only improved the "B road" performance but made the car better cruising on nicely maintained roads as well.

Two forum members are at present considering a different car (E9x M3) due to back issues (Z4 not being especially kind in that regard). This type of mod would be attractive to many as it would let you have your cake and eat it too.

Wilco will let you know how I go with the suspension. In essence a sports car should resist able to resist roll, be grippy and supple inorder to be able to put it's power down.

[HaiderGill]

Originally Posted by v3.0si

what issue of EVO is this from?

Hi,

I don't have the issue number but it's on their site: - http://www.evo.co.uk/carreviews/evol...mw_z4_30i.html

[HaiderGill]

Originally Posted by The HACK

The E85 hasn't been produced for nearly 4 years now, why would Mercedes use it as a benchmark to develop their SLK? Something does not compute here.

Plus, the E85 has the same identical rear suspension, in fact, borrowing every single parts from the E46. I've never heard of this complain on the E46 before about the toe changing dramatically in the rear due to camber changes.

Now...if you want to talk about the front McPherson strut changing toe when compressed? That's been known to happen on ALL BMWs, not just the Z4s.

The article is dated April 04, so it would probably be around that time. Have a butchers: -
http://www.evo.co.uk/carreviews/evol...mw_z4_30i.html

[HaiderGill]

Originally Posted by beta

Sounds interesting, looks like they use soft suspensions with beefed up roll bars. I'd be hesitant to install a thicker roll bar without reinforcing the mounting points so this doesn't happen.

It's not just softer at the rear but from my chats with Kevin Bird vis-a-vis my 1er hatch and now the Z4. He said also the stock springs at the back were far to stiff compared to the stock front springs. This creates an imbalance. The added stiffness in the rear is to help remove the need for an LSD. I am not saying it is the only way but I'm looking for a set-up for the road (not track) and as we say being able to 'put the power down on good and poor roads'.