Your experiences of aftermarket suspension on the Z4 MC

[BMWZ4MC]

If you do updated arbs John be warned you must look at reinforcements on the front chassis ,this is a known area to fail with beefed up arbs.

Thanks for that. It's also a weak spot on the Z3MC, particularly at the rear end where the boot floor gets ripped apart

Is there a "how to" strengthen the Z4 chassis for ARBs anywhere?

I thought the problem at the rear of the Z3M was a torque-related issue?

 

[exdos]

I thought the problem at the rear of the Z3M was a torque-related issue?

I don't think anyone knows for sure if there's a single cause. It seems to be a combination of:
1. poor spot welds and/or too few of them during manufacture,
2. single-eared diff attached with a single mount to a relatively weak support.
3. diff bush bracket attached to an area under high loading from torque from the diff and of poor manufacture.
4. a lot of movement of rear subframe on "squishy" subframe bushes transfering stress via the diff to the single ear diff mount with high lateral loading.
5. excessive movement of the semi-trailing arms putting lateral loads on the rear ARB mounting points

The problem seems to mostly affect the earlier S50 variant and it can happen to unmodified cars that have never seen a track. I know of one case which was repaired by BMW under "goodwill" (costs around £4k) and which has failed again after only a few 1000 miles!

IMO the best way of attempting to eliminate the problem is to fit solid polyurethane subframe bushes so that the subframe can't move in the horizontal plane and offers the diff a more stable base.

I've not heard of torn front ARB mounting points and the uprated ARB (27mm adjustable), same as Z4 MC) is a very popular mod for the Z3MC.

 

[Franzino]

I've gone for the AC Schnitzer Racing suspension. I prefer not to have to fit spacers just to make a suspension system fit, which can cause rubbing issues and can be a pain with the MOT and the ACS set up isn't a coilover set up so is a straight swap for the OEM. I also want to keep the OEM top mounts and don't see any need for fitting camber plates because there is already some adjustability for camber with the strut towers. I know the AC Schnitzer Racing suspension for the Z3MC is very good, so I fancy trying this. It's essentially the Bilstein B16 PSS9 kit but made specifically to AC Schnitzer's specification for the Z4MC. I'll discover in due course whether I like it.

The Bilstein B16 PSS9 kit is something I'm maybe considering in the future. The AC Schnitzer kit is 500euro more expensive then the Bilstein donor and costs a massive 3.000euro... Will see what the future holds, for now I'm happy with the car. But the suspension is one thing that's could improve on track (on the street it's ok for me)... But first the driver (me) needs some time to improve :wink: And also I don't know of its a good thing to firm up the suspension on a roadster (the body it's not a stiff as a coupe)... Maybe it makes the car shake more?

 

[Franzino]

I live in the sticks and have to drive for at least 6 miles on the twisties with uneven surfaces to get anywhere, so my experience seems to be somewhat different to that of others. I've found that on the Z4MC the Strongstrut has made the steering so much more precise and has partially got rid of that floaty feeling on hard acceleration that I despised. Stiffer springs with my new suspension will sort out the rest of that problem. IMO, the OEM strutbrace is a bad design because it has a bend in the bar in the wrong plane and IMO the StrongStrut does what it is supposed to do and helps to preserve the static geometry in dynamic situations, which helps to make the car handle in practice more in line with the way that it was designed to do in theory. Does anyone else on here have a StrongStrut strutbrace?

I choose the OEM strut bar because it has a bend in the bar... In case of a crash on one side of the car the OEM strut bar bends and does not transfer the impact to the other side. I have a roadster and I also noticed some difference; sharper turning and a bit more body rigidity with less shakes and body movement.

 

[exdos]

If you do updated arbs John be warned you must look at reinforcements on the front chassis ,this is a known area to fail with beefed up arbs.

I've just been looking up reports of this problem and it appears that the failures (as reported on the zpost forum) all occur with the Ground Control ARB and with high front spring rates.

According to the Ground Control website it says for the Z4M ARBs: "Race front equivalent stiffness of 29mm front can be adjusted to be the equivalent of about 28-32mm"
The stiffness of a roll bar is proportional to the fourth power of the diameter of the bar, and the Z4MC OEM ARB is 27mm, so that gives a stiffness of (27x27x27x27=) 531441 units. and the Ground Control ARB set at 28mm equivalent is 614656 units and at 32mm equivalent is 1048576 units. Therefore the GC ARB is adjustable from 15.65% to 97.3% stiffer than the OEM ARB. I bet most of those failed ARB mounting points have occurred when the GC ARB has been set on the 32mm equivalent setting.

The E46 M3 CSL has a front OEM ARB of 30mm (810000 equivalent), which is 52.4% stiffer than the Z4MC's front ARB: I wonder if the CSL's mounting point has been strengthened more than the Z4MC's?

 

[Beedub]

If you do updated arbs John be warned you must look at reinforcements on the front chassis ,this is a known area to fail with beefed up arbs.

I've just been looking up reports of this problem and it appears that the failures (as reported on the zpost forum) all occur with the Ground Control ARB and with high front spring rates.

According to the Ground Control website it says for the Z4M ARBs: "Race front equivalent stiffness of 29mm front can be adjusted to be the equivalent of about 28-32mm"
The stiffness of a roll bar is proportional to the fourth power of the diameter of the bar, and the Z4MC OEM ARB is 27mm, so that gives a stiffness of (27x27x27x27=) 531441 units. and the Ground Control ARB set at 28mm equivalent is 614656 units and at 32mm equivalent is 1048576 units. Therefore the GC ARB is adjustable from 15.65% to 97.3% stiffer than the OEM ARB. I bet most of those failed ARB mounting points have occurred when the GC ARB has been set on the 32mm equivalent setting.

The E46 M3 CSL has a front OEM ARB of 30mm (810000 equivalent), which is 52.4% stiffer than the Z4MC's front ARB: I wonder if the CSL's mounting point has been strengthened more than the Z4MC's?

Correct all reported failures have been with the ground control unit...

Wonder if the csl unit fits our cars?? I'm pretty certain they don't have beefed up mounts compared to our vehicles.

 

[exdos]

Correct all reported failures have been with the ground control unit...

Wonder if the csl unit fits our cars?? I'm pretty certain they don't have beefed up mounts compared to our vehicles.

If the CSLs mount points aren't beefed up, then we should be able to increase ARB stiffness up to 50% safely. I've found a way that the Z4 MC's OEM front ARB can be modded relatively cheaply, this effectively will shorten the lever arm length, by about an inch or so with no cutting or welding. I've got a manufacturer of the part looking into making the appropriate part to fit a 27mm bar.

 

[Aliv6]

ouch, bang, rattle, ouch, wallop, spine breaking, physio...

Looks good though...

 

[exdos]

ouch, bang, rattle, ouch, wallop, spine breaking, physio...

That's a great description of the Z4MC's OEM suspension.

I'm trying to create something far better than that. My initial test drive with the ACS suspension has proved that the ride has been considerably improved and that front end lift/pitching has been considerably reduced too. It's now a case of finding the best geometry and damper settings to give the handling that I want.

 

[aerobod]

I like 0 toe front as well but thinking of trying some toe out next time i have it aligned. Don't ask me figures, i haven't researched it yet.

You'll find that toe out makes the steering "exciting", to say the least!

I find that slight toe-out puts quite a bit of feel back into the steering. Currently I'm running 0.03° toe out (still within BMW spec that allows up to 0°02', or 0.033° toe out), car feels very responsive to turn-in and has lost the slight straightahead dead feeling I had from the front 245/40-18 Michelin PSS tyres when running 0.06° toe-in. This works well with the 1.55° front camber I'm running, with absolutely even tyre wear, throwing in monthly auto-x sessions in the summer to scrub the tyre shoulders a bit.

 

[exdos]

UPDATE

After my initial drive last weekend to check for any problems, unwanted noises and to get a feel for the car with the set up advised by ACS, I was able to put the car on level ground to allow the suspension to settle so that I could then check/adjust the geometry.

We had a decent day on Thursday and decided to try the suspension on stiffer settings than recommended with less toe-in at the front. The handling was better with the front set a bit stiffer than the initial recommended setting, but I had set the rear just a tad too firm which made the car jump a bit on a fast but bumpy road, although it wasn't uncomfortable, so I feel that with the rear settings backed off by 1 position, I've found the near optimum settings for road use. I'll stick with my new settings for a while to see if they need any more adjustment under a wider variety of road conditions.

I've got 10mm spacers all round on my Z3MC but I've never previously experienced the change from fitting spacers on their own, because the KWV3 on the front wheels of that car needs the spacers for clearance to fit. So, I wanted to try increasing the front track width on my Z4MC to see if there is any tangible difference. I removed the spacers from the rear of the Z3MC and fitted them to the Z4MC and they really do make the front end feel much more planted and with reduced bodyroll, especially at higher speed. The Z4MC is now beginning to feel more like my Z3MC, which I think is near-perfect. So, I'm now intending to fit spacers all round to the Z4MC.

The ACS Racing suspension has definitely cured the two major problems of the OEM suspension that I'd identified and the car is now so much more comfortable and with better handling. ACS Racing suspension certainly wasn't my first choice, and I only decided to buy it because I got it for a price that made it too attractive to ignore. Since the ACS suspension has solved the problems provided by the OEM suspension, I have to say it has certainly passed that test already. I must take the Z4MC to The Ring and try the car with a stiffer set up there to form my full opinion of the suspension, and be able to compare it to KWV3 on my Z3MC, but so far, I very much like it.

 

[exdos]

I find that slight toe-out puts quite a bit of feel back into the steering. Currently I'm running 0.03° toe out (still within BMW spec that allows up to 0°02', or 0.033° toe out), car feels very responsive to turn-in and has lost the slight straightahead dead feeling I had from the front 245/40-18 Michelin PSS tyres when running 0.06° toe-in. This works well with the 1.55° front camber I'm running, with absolutely even tyre wear, throwing in monthly auto-x sessions in the summer to scrub the tyre shoulders a bit.

I'm sure that will work well for your auto-x sessions.

I doubt that you have the kind of public road "twisties" in Canada that we have here in the UK, particular the sort in my part of the UK. They can be very tight and narrow with very undulating surfaces with lots of bends. I found that when I was running any toe-out on public roads, the turn-in could be too sharp to account for some of the bump-steer inputs you get from the poor road surfaces, particularly with negative camber in the order of -1.5 degs or above. I find it's just too tiring to drive like that all the time. Toe -in can make the steering feel "dead", as you say, and I've found that 0 toe gives a best compromise setting where you can have sufficiently quick steering for relatively slow speed cornering but also sufficient self-centreing and straight line stability at high speed (i.e. over 140mph at The Ring). If you've ever played around with caster, you'll also find that increasing caster can give quick turn-in without the need for toe-out or much negative camber and gives good self-centreing. I'd fit caster/camber plates on the Z4MC if someone made "streetable" ones, but all those I've seen are of race spec with no damping bushes in them.

 

[Beedub]

UPDATE

After my initial drive last weekend to check for any problems, unwanted noises and to get a feel for the car with the set up advised by ACS, I was able to put the car on level ground to allow the suspension to settle so that I could then check/adjust the geometry.

We had a decent day on Thursday and decided to try the suspension on stiffer settings than recommended with less toe-in at the front. The handling was better with the front set a bit stiffer than the initial recommended setting, but I had set the rear just a tad too firm which made the car jump a bit on a fast but bumpy road, although it wasn't uncomfortable, so I feel that with the rear settings backed off by 1 position, I've found the near optimum settings for road use. I'll stick with my new settings for a while to see if they need any more adjustment under a wider variety of road conditions.

I've got 10mm spacers all round on my Z3MC but I've never previously experienced the change from fitting spacers on their own, because the KWV3 on the front wheels of that car needs the spacers for clearance to fit. So, I wanted to try increasing the front track width on my Z4MC to see if there is any tangible difference. I removed the spacers from the rear of the Z3MC and fitted them to the Z4MC and they really do make the front end feel much more planted and with reduced bodyroll, especially at higher speed. The Z4MC is now beginning to feel more like my Z3MC, which I think is near-perfect. So, I'm now intending to fit spacers all round to the Z4MC.

The ACS Racing suspension has definitely cured the two major problems of the OEM suspension that I'd identified and the car is now so much more comfortable and with better handling. ACS Racing suspension certainly wasn't my first choice, and I only decided to buy it because I got it for a price that made it too attractive to ignore. Since the ACS suspension has solved the problems provided by the OEM suspension, I have to say it has certainly passed that test already. I must take the Z4MC to The Ring and try the car with a stiffer set up there to form my full opinion of the suspension, and be able to compare it to KWV3 on my Z3MC, but so far, I very much like it.

interesting read Re the spacers..... in general actually.... im using special hexagonal super lightweight billet units with every single piece of unwanted material removed from them.... they weight literally nothing... i cant get my scale to even register a reading.... i running aggressive offsets so i can run aggressive camber/alignment settings.... of course i understand your goal is very different to mine but i shall use some of your feedback in fine tuning my car.

btw i also swapped to magnesium wheel nuts and shot peened ARP studs to A) allow easer swapping of the wheels. b) have a stronger setup c) allow upto 12mm spacer fitment on each corner (75mm studs) hope this info helps.... the stud and nut conversion was again significantly lighter than the stock bolts, every little helps right?? ;-)

 

[Beedub]

before you ask... you dont want to know how much the spacers were.... or the wheels studs and nuts
insanely expensive, BUT imo worth while.

 

[aerobod]

I find that slight toe-out puts quite a bit of feel back into the steering. Currently I'm running 0.03° toe out (still within BMW spec that allows up to 0°02', or 0.033° toe out), car feels very responsive to turn-in and has lost the slight straightahead dead feeling I had from the front 245/40-18 Michelin PSS tyres when running 0.06° toe-in. This works well with the 1.55° front camber I'm running, with absolutely even tyre wear, throwing in monthly auto-x sessions in the summer to scrub the tyre shoulders a bit.

I doubt that you have the kind of public road "twisties" in Canada that we have here in the UK, particular the sort in my part of the UK. They can be very tight and narrow with very undulating surfaces with lots of bends. I found that when I was running any toe-out on public roads, the turn-in could be too sharp to account for some of the bump-steer inputs you get from the poor road surfaces, particularly with negative camber in the order of -1.5 degs or above. I find it's just too tiring to drive like that all the time. Toe -in can make the steering feel "dead", as you say, and I've found that 0 toe gives a best compromise setting where you can have sufficiently quick steering for relatively slow speed cornering but also sufficient self-centreing and straight line stability at high speed (i.e. over 140mph at The Ring). If you've ever played around with caster, you'll also find that increasing caster can give quick turn-in without the need for toe-out or much negative camber and gives good self-centreing. I'd fit caster/camber plates on the Z4MC if someone made "streetable" ones, but all those I've seen are of race spec with no damping bushes in them.

Took the car to 200km/h in Montana on highway 89 last week. The Babb to Browning section of this road is very reminiscent of fast UK B-roads or tight Welsh A-roads (such as the A4212 west of Bala). It is quite narrow in places and particularly challenging on the brakes with plenty of corners marked at 25mph and lots of elevation change, but has some very fast and straight sections along valley bottoms between mountain ranges. This road also has significant changes in camber and some "oh crap" blind crests that are followed by corners: http://maps.google.ca/maps?ll=48.58873,-113.274751&spn=0.014676,0.042272&sll=52.935811,-3.715782&sspn=0.106152,0.338173&oq=babb,+mt&hnear=Babb,+Glacier,+Montana,+United+States&t=p&z=15

With my current suspension settings, the car was both composed and eager. It depends on what you feel comfortable with in suspension settings, but I'm sticking with slight toe-out matched to the front camber set to the inner limits of the slots for the current tyre setup (I'm using (Michelin PSS 245/40-18 front, 275/35-18 rear, 33f/31r pressure for the road, 36-38f/34-36r for auto-x and the track).

 

[exdos]

before you ask... you dont want to know how much the spacers were.... or the wheels studs and nuts
insanely expensive, BUT imo worth while.

That's an open invitation. I do want to know how much?

Whilst I can see that a pentagon is the minimal design for weight saving purposes, what support is there for the circular contact section of the inside of the wheel against the hub between the bolt positions from lateral forces in particular?

 

[JaEdBa]

before you ask... you dont want to know how much the spacers were.... or the wheels studs and nuts
insanely expensive, BUT imo worth while.

That's an open invitation. I do want to know how much?

Whilst I can see that a pentagon is the minimal design for weight saving purposes, what support is there for the circular contact section of the inside of the wheel against the hub between the bolt positions from lateral forces in particular?

the opposite mounting studs or bolts and the lateral rigidity of the wheel surely? I may be wrong, but the deflection would be minimal and certainly wouldn't be the limiting factor in the set up..

 

[exdos]

this road is very reminiscent of fast UK B-roads or tight Welsh A-roads (such as the A4212 west of Bala).

Most of the roads that I drive on are not up to the standard of those roads. In fact the roads in Wales are some of the best in the UK, they get a lot of money thrown at them and are used by very few lorries so they stay in very good condition. My favourite drive of all is this route : http://www.youtube.com/watch?v=krh7-qxnMAA&feature=related (not my video); the surface of this road is mostly excellent smooth tarmac with few undulations. This video, shows part of the route from a better camera position but without sound: http://www.youtube.com/watch?v=RxSNWOIAx-g (not my video)

I'm sticking with slight toe-out matched to the front camber set to the inner limits of the slots for the current tyre setup (I'm using (Michelin PSS 245/40-18 front, 275/35-18 rear, 33f/31r pressure for the road, 36-38f/34-36r for auto-x and the track).

I'm not knocking your settings at all because I know they work. I've driven that road in the video with -2.5 degs front camber with a tad of toe out with firm settings on adjustable suspension in my Z3MC (i.e track set-up) and it was brilliant, but I just don't want those kinds of settings permanently on my car.

 

[exdos]

the opposite mounting studs or bolts and the lateral rigidity of the wheel surely? I may be wrong, but the deflection would be minimal and certainly wouldn't be the limiting factor in the set up..

if you draw a line from each bolt to the opposite side-edge of the pentagon then it is at least 1cm shorter than it is with a circular spacer. As I see it, this means that the wheel has less contact/support from the hub. Therefore, leverage exerted by lateral forces must be greater than with the OEM situation or with a circular spacer. This may well be well-within the safe limits of the materials and the engineering, and just a point I'm making which maybe worthy of no further consideration.

 

[Beedub]

before you ask... you dont want to know how much the spacers were.... or the wheels studs and nuts
insanely expensive, BUT imo worth while.

That's an open invitation. I do want to know how much?

Whilst I can see that a pentagon is the minimal design for weight saving purposes, what support is there for the circular contact section of the inside of the wheel against the hub between the bolt positions from lateral forces in particular?

this is a bmw motorsport part these things are run with proper slick tyres are are putting way more stress than my road tyres/slicks can ever muster.... its a non issue ;-) the contact patch is more than adequate, to see them installed with them wheel on, you'd understand what i mean!...

also due to the added stress im placing on my car with much more power and cornering ability in terms of outright grip in run alittle more Tq on the wheel nuts, studs, this setup has huge advantages but like i said, is very very expensive.