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M3 Suspension Component Swap

Specific discussion about the E89 2009 Z4 (sDrive35is, sDrive35i, sDrive30i, sDrive23i)
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Player 1
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M3 Suspension Component Swap

Post by Player 1 » Thu Aug 16, 2018 10:21 am

Before going anywhere, the vast majority of the research work was done for me by this fine chap on E90 Post;
https://www.e90post.com/forums/showthread.php?t=230973

When looking underneath a Z4, the suspension is actually a bit of a mash up of it's own components, E46/E85 bits and E90 parts. The rear borrows heavily from the E85 with some upgraded bushings a heavier duty differential and bigger brakes, the front on the other hand is almost entirely lifted from an E90 3 series with the same aluminium subframe and suspension control arms which are the main focus of this post.

Numerous 3 series owners have been able to swap these control arms with items from the E90 M3 to improve the overall handling of the car without necessarily having to change springs/dampers and impacting the ride comfort. The main difference between the standard components and the M3 items (to the best of my knowledge) being ball joints in place of rubber bushings in the case of the lower control arms and much stiffer bushings on the front tension struts. These give much less deflex under cornering load resulting in a car that feels tighter, more predictable and offering better feedback.

The last item that the 3 series guys can swap is the M3 anti roll bar, I tried this on the Z4 however there is a plug on the electric power steering unit that fouls the M3 bar, the Z4 item is shaped differently in the middle to take this into account. The M3 roll bar will just about fit with a push however will rub this plug, therefore the only upgrade option here is a roll bar from H&R and the likes which is a shame because the M3 bar is significantly lighter and having made a short test run with both, there's little to no difference in the feel of either. (both are a massive improvement over the standard roll bar)

Options on the rear are slightly more limited, in terms of bushings there's only the lower bushing on the trailing arm where the wishbone connects that can be swapped for the ball joint from a Z4M or E46 M3, the upper bushing is already a ball joint on E89 Z4's (not so on E85's) and the main trailing arm bush that the E46 guys get trouble with and fit limiters from Turner to is also a different item on E89 Z4's. Visibly it's a wider item so presumably gives less deflex than the old ones.

That just leaves the rear anti roll bar for which any upgrade roll bar for the E85 will fit. M3/Z4M items will not fit here, as with the front H&R etc are the only options.

So which M3 parts can be used?
On the front suspension:
Left Tension Strut With Rubber Mounting - 31102283575
Right Tension Strut With Rubber Mounting - 31102283576

Wishbone Left - 31102283577
Wishbone Right - 31102283578

On the rear suspension:
Ball Joint (X2) - 33306852895

Thus far I've tackled the front suspension and fitted the control arms and a H&R anti roll bar, we took a copy of the cars alignment settings beforehand as the M3 wishbones are longer than the standard items meaning the toe will need to be readjusted afterwards. It will also add a small amount of camber however in my case it was still within BMW's recommendations (-0.1 to -1.1 on the front), my camber went from -0.25 to -0.7.
It is also worth noting that for reasons unknown to me, BMW decided to mount the headlight levelling sensor on the right hand side wishbone on the Z4 instead of the left hand side as on the 3 Series or M3. With the car on the floor I took a measurement of the distance of the sensor arm to the floor them made a small bracket to fit onto the M3 wishbone that'd maintain the same height.

The two front tension struts, visibly these are quite similar to the standard items albeit with a different bushing.
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Comparison of the M3 wishbone and standard item
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All fitted together on the left hand side
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I'll be having a go at the rear in the next few months but the result of all of this at the front is enormous. I'd changed the roll bar over a few weeks before fitting the M3 parts so was familiar with the improvement in front end response and reduction in body roll, the M3 components finally turn the Z4 into a proper sports car.
There is actual steering feel for a start, the initial turn in is slightly lighter than previously but the steering weights up as its loaded and give you little nibbles of information through the wheel about what the front tyres are doing at the same time, I'm finding this very addictive :D
Going through corners the whole car feels much much tighter with movements being far better controlled, instead of understeer and ploughing into the traction control it now just stays dead flat and outright grip is vastly improved. Along a twisting A road, the standard 35i wouldn't see which way this went :rofl:
One of the best parts of all of this is that there's been virtually no impact on ride comfort at all, being picky I'd say its a little more jiggly over really bad surfaces but the rest of the time it's still just as good a cruiser as before.
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Twin Turbo
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M3 Suspension Component Swap

Post by Twin Turbo » Thu Aug 16, 2018 9:02 pm

Firstly well done, I only know of a USA guy doing similar modifications to installing similar items.

https://e89.zpost.com/forums/showthread.php?t=950367

I did consider this but decided to go down the KW'3 route

However I can say from experience an E89 with Coilovers does not have the amount of Grip that a M2 has - there is more sway in the standard M2 suspension, but mechanical grip, is far greater.

I look forward on this project with interest

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M3 Suspension Component Swap

Post by buzyg » Thu Aug 16, 2018 10:27 pm

Good read. :thumbsup:
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M3 Suspension Component Swap

Post by Player 1 » Fri Aug 17, 2018 7:58 am

Twin Turbo wrote: Thu Aug 16, 2018 9:02 pm Firstly well done, I only know of a USA guy doing similar modifications to installing similar items.

https://e89.zpost.com/forums/showthread.php?t=950367

I did consider this but decided to go down the KW'3 route

However I can say from experience an E89 with Coilovers does not have the amount of Grip that a M2 has - there is more sway in the standard M2 suspension, but mechanical grip, is far greater.

I look forward on this project with interest
Thanks both, and thank you for the link Twin Turbo. I haven't seen that car as yet, he really went to town on it! Quite interested about what he's done with the brakes but might wait until my existing ones are worn before doing anything as the standard 35i brakes aren't bad at all.
Also what he has to say about the electronic simulated locking differential working effectively, I did have reservations about stiffening the rear end without putting a proper locking diff in there however it's got to be worth a go for sure :D

Very interesting what you have to say regarding the M2, I took part in the bmw club's Welsh weekend earlier this year so having spent a good deal of time chasing different M cars, M2's included, I'd came to the same conclusion that they have far more mechanical grip than the E89.
Would you say the KW coilovers affect ride quality in a negative way? As the car gets used for long trips quite often I don't want to do anything that's going to have a big hit on NVH as at the moment it's very good, just need to figure out how to get rid of the tyre noise :wink:
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M3 Suspension Component Swap

Post by R.E92 » Fri Aug 17, 2018 9:02 am

The M2 has wider and stickier tyres than the Z4 by default. I upgraded to 275/30 Pilot Sport 4S from 265/30 Pilot Supersport and the increase in grip was huge.

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M3 Suspension Component Swap

Post by Twin Turbo » Fri Aug 17, 2018 8:17 pm

Player 1 wrote: Fri Aug 17, 2018 7:58 am
Twin Turbo wrote: Thu Aug 16, 2018 9:02 pm Firstly well done, I only know of a USA guy doing similar modifications to installing similar items.

https://e89.zpost.com/forums/showthread.php?t=950367

I did consider this but decided to go down the KW'3 route

However I can say from experience an E89 with Coilovers does not have the amount of Grip that a M2 has - there is more sway in the standard M2 suspension, but mechanical grip, is far greater.

I look forward on this project with interest
Very interesting what you have to say regarding the M2, I took part in the bmw club's Welsh weekend earlier this year so having spent a good deal of time chasing different M cars, M2's included, I'd came to the same conclusion that they have far more mechanical grip than the E89.
I did a similar one in the peak district and found I was shouting at GT-Rs to go quicker on the B roads. But only really realised the grip the car had on my first track day in the M2 - and compared it to the Z4.

However in the M2 - I know I can go quicker - I estimate another 3-5 sec.

Would you say the KW coilovers affect ride quality in a negative way? As the car gets used for long trips quite often I don't want to do anything that's going to have a big hit on NVH as at the moment it's very good,
[/quote]

I went for Kw'3 as my E89 was a daily driver and track toy, so I was able to change the ride quaility - but I found it to been more firm than stock sports suspension.

However I have a few mates with Mlights with adaptive suspension, and the Z4 was definitely better on country b roads.

Video of my long lots love, around donnington

https://youtu.be/0n7gLJg7ACk

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M3 Suspension Component Swap

Post by Player 1 » Tue Aug 21, 2018 6:02 pm

Haha, I'd suggest trying the Welsh Weekend out, there's not a lot of hanging around with those guys :wink:

For now I think I might stick with the standard dampers, where I am it's a couple hundred miles to get to the nearest track so it's very much a road car.

Having had a chance to get some more miles with the new suspension on now, what's standing out the most is the total lack of understeer which brings about a lot more confidence when pressing on. Thus far I can't recommend this enough!

Looks like a lot of fun at Donnington too! :D
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