Your experiences of aftermarket suspension on the Z4 MC

[Stuart Truman]

Reading this thread with interest. Great to see a passionate debate not descend into a squabble

The only thing I think Alpina do to the cars suspension is at the front end. Shocks and possibly springs. The rear is stock.

I've just had a 4 wheel alignment done and they reduced the toe in to closer to neutral as per the stock M roadster alignment. The car is now much more direct with steering. I'm quite happy with it.

 

[bertman]

Yeah a bit of ozzy humour there gents. Don't worry I'm an acquired taste even here!

Just got back from some track time and I wasn't impressed with the suspension at all. I've never driven anything that's felt so floaty through high speed corners. Inspired very little confidence! but of course the car made of for it when I opened the taps down the straight OH WOW! Anyway suspension upgrades have now hit the top of my shopping list so I'll be sure to let you know what I end up using

 

[exdos]

UPDATE

When I fitted an H&R 30mm front ARB (E46 M3 pattern) I didn't bother fitting a larger rear ARB at the same time because I'd read that this would do nothing for a Z4MC. However, whether this only applies to a Z4MC with OEM suspension, or not, I wouldn't know until I'd driven the car. After driving the car with the suspension modifications I've recorded in this thread, including the bigger front ARB, I decided to fit the larger H&R rear ARB (e46 M3 pattern) because the handling was still not as good as that of my Z3MC (with uprated front and rear ARBs) and the steering wasn't as "light-touch" as I felt it could be.

Because the ACS Racing suspension shifts the ratio of F:R spring rates from the OEM ratio, where the front suspension becomes relatively much stiffer, it follows that the rear suspension becomes relatively much softer. Since much of the lateral bodyroll of an OEM Z4MC is contained by very stiff rear springs, so with much softer rear springs with ACS suspension, there is less control of bodyroll by the rear suspension, consequently, it appears to me that a stiffer rear ARB is required to compensate for the softer rear springs with my ACS Racing suspension.

The Z4MC shares the same OEM rear ARB as the M3 CSL, so the H&R rear ARB should be a direct swap, which it proved to be. Removing and fitting the rear ARB off the floor is a bit of a pain to do because you need to remove the silencers and fiddle about under the car to remove the OEM ARB with the drop links attached (one of which need to be twisted in a certain way to enable the ARB to be removed). I'd recommend fitting new drop links when fitting the H&R ARB, because removing the old ones might bend the shafts of the old drop links. The points of attachment of the rear ARB are onto brackets attached to the rear subframe and they look pretty strong, so I don't expect the uprated ARB will over-stress them.

From test driving the car with the uprated rear ARB, I noticed more "push" from the rear end, but I have managed to correct this by increasing the stiffness of the front dampers and with a slight increase to front toe in (from zero). The car now feels very well balanced with the very light-touch steering that I like. The only thing that I might now consider fitting would be caster/camber plates, but they'd have to have sufficient compliance and not be track-only types.

 

[daz05]

Reading the US forums can be dangerous, they seem to go that stage further than we do here which can create all kinds of ideas....

Anyway, Exdos, I was reading the Dinan article about E92 M3 bump stops the other day, the article suggested they were a key component of the suspension design in that they contributed to the softer ride of the car in mundane driving situations. The article said they were soft on inital compression and then got much stiffer as they compressed further meaning the car could still perform on track and the like.

I also read that some owners, not necessarily M3 owners, when changing to shorter springs and were actually using Z4MR rear bump stops when lowering their cars because they were shorter, the theory was that by lowering the car was riding on the bump stop more than it should and by switching they actually increased travel which had been shortened after the spring changout.

I'm not sure I fully follow the logic but it got me thinking, if our bump stops are so short surely that must be a contributing factor to the stiff ride over bumps and holes in city driving, could we introduce a thicker or same size but more compliant bump stop to soften the ride in the same way as per the M3?

I'm not sure I fully understand the logic here but interested in gaining more information. I also noticed the bump stop part numbers are different for Coupe and Roadster.

 

[exdos]

Daz,

I agree with you about some of the information on US forums. A lot of the information relates to their competitive Auto-X "scene", but I'm unsure of what this exactly entails. I have it in mind that this involves driving around some sort of short course in a large car-park marked out with cones, where manoeuvrability is key to fast times. If this is correct, then their requirements from suspension are at total variance to mine, and probably yours too?

The weight of a car should be supported by the springs at each corner and there should be sufficient play in the springs to allow for compression under maximum load without complete coil-binding. The only reason why suspension also has dampers as well as springs is to prevent the springs from oscillating (i.e boing, boing, boing) after the springs have been compressed during vehicle movement. If the dampers are matched to the springs which are used with them, then the "stroke length" of the dampers should be such that the pistons have the same range of length change as do the springs under all loads. This works well with linear springs with higher spring rates, as used on coilovers, where the range of compression is probably no more than, say, 4 inches. However, with softer springs used on the typical McPherson strut (i.e. Z4MC OEM front dampers) the compression range of the spring is probably greater than the stroke length of the damper, so when the spring compresses near to the fully compressed length of the damper's piston, a rubber bump stop on the end of the piston makes contact with the damper case, which makes it more difficult for the piston to be compressed further. In this way, the bump stop works in conjunction with the spring at the highest levels of suspension loading, to resist further compression.

So if you fit lowering springs of the same spring rate to OEM on the same damper by, say 1", you effectively shorten the stroke length of the piston by 1", so for a given loading, the bump stop will come into play sooner and with less loading than it would with OEM springs. Therefore, fitting a shorter bump stop makes sense. This fits perfectly with what you say about using Z4MR bump stops on other cars.

With the OEM suspension of the Z4MC, the stroke length of the dampers has been matched to the OEM springs and the bump stops should only ever come into play under near-maximum loading, and so should never really come into play in city driving because the loads should not cause sufficient spring compression to permit the bump stops to meet the damper casing. Therefore, if you were to put thicker bump stops on the dampers, as you suggest, then you would make the bump stops come into play sooner, and since they work in conjunction with the springs to resist compression, you would be STIFFENING the suspension and making the ride worse, not better. This is opposite to what you suggest.

 

[daz05]

Thanks for taking the time to explain all that, it was worth asking anyway.

 

[Beedub]

will be giving abit more of a detailed review on my clubsport setup this week, ive got a track day booked for tuesday so really looking forward to giving these things a real beating, the car is sat back on it its cup sport rubber, a quick run out today with the R compound tyres blew my mind.... the car feels insane, With the tyres warm i can use every last drop of performance and only get a slight squealing tyre instead of wheel spin, Cant wait to get out to the track and give these things a real test, i need to change the settings however as ive adjusted them wrong, after re-reading the Kw instructions ive added to much compression(bump) front and rear... I need to reset these and dial them in, the rebound is set at kws recommended 6clicks front and 12 clicks Rear, compression/ bump should be set @ 0.75 from full stiff Front and rear, i hadnt got the grasp of how that "works" with the adjustment wheel and added to much.

The bad news??? i stuck my go pro to the side of the car to record the action, when i got home, it was gone!!!! ! now the sticky pad of those things feels enough to pull the bumper off so i guessing i didnt fix it on properly!! so while today was good on one side, it was bad on this side... ive only used it 3 times!!

im going to buy another one tomorrow and hope it gets here in time!!

All in all the car looks really cool sat on the super chunky Cups, lowered down alittle, wheels cambered heavily and blower whistling away on idle.... i walked up to it today on my drive and im pretty certain their isnt many cars that i could afford that would make me smile like this thing, all the really evocative things are out of my current price range. Can't wait to take anthony out in it when he gets older.

very sad the lack of use its had this summer season, i alway knew it was going to be a dead year with work and anthony so im extra excited to have a good time this week bring. it. on.

Will update later in the week.

hows your jon??

 

[Beedub]

ok all day track session complete.

heres my findings..... well after realising my damper settings were all wrong, i lifted the car and went to setting things to KW's recommended settings.... ok...things started to feel much more stiffer.. it feels like i could run over a coin and tell you which side i'd hit..... theirs no getting away from it, the ride is very firm, but.... but.... very well controlled, everything is solid and making no noise or clicking often associated with these track suspension sets..... so a definitely large leap back in ride comfort, but a huge huge step forward in handling, cornering speed, my local roads are pretty good but i still find myself avoiding drain covers and road imperfections..... the ride height ive set it too is near perfect, no contact ANYwhere and also easily high enough to ride even the biggest speed humps.... might not look as good but for me, id rather have function over form.

one thing of note, the set screws are a pain on the arse.. tighten to the recommended 1-2nm and these will back ut and allow the perches to move as i found out the hard way. so i had to grit my teeth and add more Tq to the set screws , i painfully bear my teeth as i tighten this alittle more to hold the perch but NOT strip the perch threads.... i seem to have gotten away with it and the perches are solid now, i will keep an eye on these as i feel they will need a regular "nip"

now onto the track.... right down to the first corner..... the car feels exactly what i wanted from what its telling me.... the car is now much further away from my driving limit so i really look forward to the challenge of reining it all in again, with road slicks, cornering speed, grip, and lack of body roll are all massively improved and high speed braking is now a joy to undertake, lean on those brakes and and squat is GONE. Of note traction in 1st/2nd seems to be alittle worse?? i guess that squat was helping me put that power down, maybe it was the heat on the day.... interesting i was only a few seconds behind the catherham times, which was great.

now.... the only thing i did feel was alittle of the fun had gone, im travelling that much faster, the smiles were gone and im concentrating super hard.... everything is happening at a much higher speed which i found rather uncomfortable, great but not for the faint hearted... for what i wanted they are perfect, i think ill give the road slicks a miss and stick to a high performance road tyre and i think i'll have the perfect balance.

to summerize.. huge step forward in dynamics, cornering and grip.... braking is improved now with non of the squat, lots of adjustment to get things right, no noise, perfect oem like fitment, large increase in lap times.

large step back in ride comfort, definitely need to run reinforcements with this setup, bump adjustments can be confusing. most definitely a track biased setup with just enough le-way for road use.

aso pleased to report the car is continuing to be very reliable, not one hiccup all day, cooling was bang on, oil temps bang on... and even in high heat power remained constant..... if anyone is considering the clubsport setup.. i promise you wont be disappointed. Sadly no pics were taken on the day or video, i used to take along my partner who did all that bit for me.. i was way to busy driving

Edit.... of note when i just check my ARB brackets they were all loose, so take the time to check these!! 21nm is your Tq figure.

now who's next with a nice review for us??

 

[daz05]

Sounds good, glad you got there with it.

 

[exdos]

Byron,

Good review I'm glad you've eventually managed to get your car on track and find that the suspension has been a very worthwhile mod.

It's interesting that you say that a little of the fun had gone, but that's because you were having to concentrate harder because of the increase in speed you were able to maintain. I found exactly the same thing too when I fitted KWV3 and uprated ARBs to my Z3MC. I had previously been so used to doing the usual: brake with pitching, slow in with bodyroll, and fast out with squatting. Then after upgrading the suspension the car stops pitching, squatting and there's virtually no bodyroll, it's a real eye-opener to experience a car that has had its handling completely transformed. You then need to relearn what the car can do and try to discover the little signals which tell you that you might be near the limits of grip. Once you've got the experience under your belt, you realise that the car is far more stable than in OEM state and you can trust it and relax and just enjoy it and be amazed at its capabilities. I've found that setting the geometry so that the steering will self-centre and go straight ahead without steering input is the key to the best handling: I'd far rather have to use a bit of effort to change direction than having the steering wanting to dart in all directions (i.e. toe-out). I found that getting the castor setting with zero toe was key to this, which allows me to run with not as much negative camber as some do. I've yet to put trackday tyres on any of my cars, and it amazes me what you can do on road tyres with upprated suspension and the geometry properly set up. I run Falken 452s on my Z3MC and from my datalogging they are good for well over 1g of lateral loading in the dry.

Yes, who's next?

 

[Beedub]

thanks jon/daz..... really pleased with it.....

john you described that perfectly.... the fun goes and it becomes a very serious prospect..

now...... come on then..... next???

still think someone should try the bilstein HDs with oem or eibach springs.... that could be a hidden gem or a setup right their for seriously good money.

 

[ChawenHalo]

thanks jon/daz..... really pleased with it.....

john you described that perfectly.... the fun goes and it becomes a very serious prospect..

now...... come on then..... next???

still think someone should try the bilstein HDs with oem or eibach springs.... that could be a hidden gem or a setup right their for seriously good money.

Beedub, this KW Clubsport is it Uniball joints, sililar you'd find in a GT3?

Has steering feel improved?

 

[Beedub]

thanks jon/daz..... really pleased with it.....

john you described that perfectly.... the fun goes and it becomes a very serious prospect..

now...... come on then..... next???

still think someone should try the bilstein HDs with oem or eibach springs.... that could be a hidden gem or a setup right their for seriously good money.

Beedub, this KW Clubsport is it Uniball joints, sililar you'd find in a GT3?

Has steering feel improved?

yes.... uniball top mounts with all rubber removed, part of the reason i run the reinforcement plates on top of the top mounts!! They are silent as well which is pretty unusual by all accounts.



steering feel.. hmm difficult one.... im definitely getting more feedback, but also im getting lots more nvh transmitted two... the steering feel feels pretty god damn good, these type of solid top mounts do have draw backs as well, but for me, they offer many more cons than pro's... our firewall brace seems to transmit the NVH even more. Still cant fault the kw build quality, they really are top notch.... lovely design as well!!

but in answer to your question, yes they are uniball solid topmounts, and in the rear i have the Rear billet race spec (poly bushed) reinforced top mounts.... these were special order from the usa as they usually come with neoprene rubbers, they are totally rebuildable but again further add to NVH.... all in all it transmits to a pretty serious feel to the car, and a directness my z4m has NEVER known.

 

[ChawenHalo]

thanks jon/daz..... really pleased with it.....

john you described that perfectly.... the fun goes and it becomes a very serious prospect..

now...... come on then..... next???

still think someone should try the bilstein HDs with oem or eibach springs.... that could be a hidden gem or a setup right their for seriously good money.

Beedub, this KW Clubsport is it Uniball joints, sililar you'd find in a GT3?

Has steering feel improved?

yes.... uniball top mounts with all rubber removed, part of the reason i run the reinforcement plates on top of the top mounts!! They are silent as well which is pretty unusual by all accounts.



steering feel.. hmm difficult one.... im definitely getting more feedback, but also im getting lots more nvh transmitted two... the steering feel feels pretty god damn good, these type of solid top mounts do have draw backs as well, but for me, they offer many more cons than pro's... our firewall brace seems to transmit the NVH even more. Still cant fault the kw build quality, they really are top notch.... lovely design as well!!

but in answer to your question, yes they are uniball solid topmounts, and in the rear i have the Rear billet race spec (poly bushed) reinforced top mounts.... these were special order from the usa as they usually come with neoprene rubbers, they are totally rebuildable but again further add to NVH.... all in all it transmits to a pretty serious feel to the car, and a directness my z4m has NEVER known.

Great stuff! After the GT3 experience its exactly what I wanted to do with the Z4MC. TBH I did not mind the noise of the 911, it just felt sop much more intemate and tied down. I thought it was well worth it.

Presumably with the extra weight you have in the front (SC etc)you have to compensate in the fro,nt suspension settings?

 

[ChawenHalo]

To be fair to the Z4MC its such a crap small tourismo car over any thing less than perfectly smooth roads, you might as well orientate it closer a clubsports car or the other way with 19" wheels ACS suspension etc for more comfort.

 

[exdos]

Byron,

Would you mind telling me what settings you've been running and/or the KW recommended settings of the Clubsports on track? What is the range of settings available?

 

[Beedub]

now...... come on then..... next???

still think someone should try the bilstein HDs with oem or eibach springs.... that could be a hidden gem or a setup right their for seriously good money.[/quote]

Beedub, this KW Clubsport is it Uniball joints, sililar you'd find in a GT3?

Has steering feel improved?[/quote]

yes.... uniball top mounts with all rubber removed, part of the reason i run the reinforcement plates on top of the top mounts!! They are silent as well which is pretty unusual by all accounts.



steering feel.. hmm difficult one.... im definitely getting more feedback, but also im getting lots more nvh transmitted two... the steering feel feels pretty god damn good, these type of solid top mounts do have draw backs as well, but for me, they offer many more cons than pro's... our firewall brace seems to transmit the NVH even more. Still cant fault the kw build quality, they really are top notch.... lovely design as well!!

but in answer to your question, yes they are uniball solid topmounts, and in the rear i have the Rear billet race spec (poly bushed) reinforced top mounts.... these were special order from the usa as they usually come with neoprene rubbers, they are totally rebuildable but again further add to NVH.... all in all it transmits to a pretty serious feel to the car, and a directness my z4m has NEVER known.[/quote]

Great stuff! After the GT3 experience its exactly what I wanted to do with the Z4MC. TBH I did not mind the noise of the 911, it just felt sop much more intemate and tied down. I thought it was well worth it.

Presumably with the extra weight you have in the front (SC etc)you have to compensate in the fro,nt suspension settings?[/quote]

yes that one side needed some tweaking in terms of set height, other than that good to go, after we removed all the stock bits it didnt add a huge amount of weight... the only really heavy piece is the actual supercharger which is huge.

 

[Beedub]

Byron,

Would you mind telling me what settings you've been running and/or the KW recommended settings of the Clubsports on track? What is the range of settings available?

hi john.... im using ....all from full hard.

front 6 clicks rebound (has 18 clicks)
Front 0.75 bump (4 clicks) (has 4 Full revolutions 20 clicks)

Rear 12 clicks rebound (has 18 clicks)
rear 0.75 bump (20 Clicks of adjustment)

the recommended settings from kw translate to a super repsonsive car but it feels rock hard!!

 

[exdos]

hi john.... im using ....all from full hard.

front 6 clicks rebound (has 18 clicks)
Front 0.75 bump (4 clicks) (has 4 Full revolutions 20 clicks)

Rear 12 clicks rebound (has 18 clicks)
rear 0.75 bump (20 Clicks of adjustment)

the recommended settings from kw translate to a super repsonsive car but it feels rock hard!!

Byron,

Thanks for that info. The reason why I asked is because I'm wondering if you've also tried finding the best settings for road use? For me, one of the great advantages of adjustable suspension is that you can have the best of both worlds: a great track car AND a great road car. Those settings sound pretty similar to my track settings of KWV3 (with genuine front coilovers) on my Z3MC, but for the road I considerably soften them and the handling is still superb on much rougher surfaces, but with the added advantage of a much better ride.

Bearing in mind that your Clubsports have those nice adjusters, which makes the task of adjusting between different settings, a very simple job, I'd recommend that you also try to set up your car for road use. Bearing in mind the settings that you've given me I'd like to suggest that you try the following on the road:

ALL from Full Hard
Front Rebound = 10 clicks
Front Bump = 10 clicks

Rear Rebound = 14 clicks
Rear Bump = 15 clicks

From what I've read, the spring rates of the Clubsports for the Z4MC are not dissimilar to those on my Z3MC and the both cars are of similar weights and my Z3MC with track settings is far too hard on public roads. So, I would expect that settings in the order of those that I've suggested would be a good starting point for making your suspension great for road use. IMO well worth a try.

 

[Beedub]

yes will definitely give it a try jon!!! next time the car is out i'll dial back the settings and see what its like!! ive never tried it on the really soft settings, so it will be interesting....

im a huge fan of the Re Rear mounts however.. fantastic items.