Springs from Eurocarparts... Are they OEM?

[Siftah]

THAT is the problem.
They make one spring irrespective of things like engine size and all sorts, differential size/ratio, auto or manual, leccy roof lock or manuals etc.
They will all impact the springs used because the weight will be different.

I agree to an extent - it's crap that they (ECP) don't make different spec springs as the original cars had a couple (ie: 2?) different spring's fitted.

However - the weight of a full tank of fuel probably makes more difference to the weight of the vehicle than most of the optional extras do. BMW themselves only have 2 (?) part numbers for the springs, so it's not *that* sensitive to the weight any way...

I bought OEM spec Bilstein dampers for my last car, and it rode about 10-15mm higher at the front, which still looked ok, but it wasn't right. The reason why, the lower hub seat notch was positioned about 10-15mm further down the strut.
They basically made one front strut for most of the 'heavier' engined cars, but ignored variables such as air-con models and 3/5dr variants which all impacted the actual weight.

That does sound pretty shoddy

Personally I think anything after market is usually crap unless it's expensive (ie, £1000+ adjustable damping coilovers)
Suspension is a black art and to just go throwing in things of an unknown quantity that you only bought because they were cheap is just like buying Goodday tyres or something similar and pretending they must be just as good as Goodyears!
Dave

I do agree with a lot of what you're saying there - OEM stuff is generally of a great quality, no manufacturer is going to seriously compromise the vehicle by skimping too much on parts like the suspension. Having said that, the OEM springs do have a rather shoddy lifespan...

I happen to think it's quite an interesting area, I'm in two minds about swapping to Eibachs myself and in two minds about swapping from runflats to non-runflats, for much the same reasons.

Basically I think changing from runflats to none and going from OEM springs to Eibachs is going to quite drastically change the suspension dynamics. I'm hoping the softer non-runflat tyres will counteract the slightly stiffer and lower springs. Less-stiffness in the sidewalls is going to surely make the turn-in a little softer (though I know those who've fitted them disagree!) and likewise, dropping the car a little and running non-OEM springs is also going to make a difference, but I'm not quite sure how it'll all fit together yet.

It could be an expensive and irritating mistake to make

Sorry for the slight thread-hijack, but I think suspension+tyres are the same topic anyway really, they all work together, so hopefully nobody will mind too much

 

[Tweed]

*snip*...Eibachs...*snippety snip*...I'm hoping the softer non-runflat tyres will counteract the slightly stiffer and lower springs...*snip*

Actually, the ride on Eibach's is supposedly better than OEM (can't remember who said it first, I think Easty's running them?)... Personally, I'm going to go down the Eibach's route when my springs go again. I can't see the tiny 15mm extra drop outweighing the better look, better ride & better reliability

 

[peddy]

OK - quick test. shows mine as just under 3 fingers, but since that is such a random measurement I'll also quote 11cm from wheel rim to arch.

(Yeah - I know the official measurement is to wheel centre but I don't have the figure to hand)

OEM replacment springs about 6 to 9 months old 3.0i sport so should be the same

BMW springs also don't have any settlement.

Mine is around 12.8cm!! So even higher than standard!! :x :thumbsdown:

My suspisions first started when I noticed the part numbers were the same across all Z4 models on ECP.

THAT is the problem.

They make one spring irrespective of things like engine size and all sorts, differential size/ratio, auto or manual, leccy roof lock or manuals etc.

They will all impact the springs used because the weight will be different.

I bought OEM spec Bilstein dampers for my last car, and it rode about 10-15mm higher at the front, which still looked ok, but it wasn't right. The reason why, the lower hub seat notch was positioned about 10-15mm further down the strut.
They basically made one front strut for most of the 'heavier' engined cars, but ignored variables such as air-con models and 3/5dr variants which all impacted the actual weight.


Personally I think anything after market is usually crap unless it's expensive (ie, £1000+ adjustable damping coilovers)

Suspension is a black art and to just go throwing in things of an unknown quantity that you only bought because they were cheap is just like buying Goodday tyres or something similar and pretending they must be just as good as Goodyears!

Dave

Yep, I kinda got what you mean by "general" when I noticed the same part numbers mentioned on their site.

 

[Mr Whippy]

15mm drop is a fair old bit.

My car scrapes on car park curbs at the front with my wife in the car, it doesn't on my own. 15mm drop would take the car into proper damage territory at the front, and probably starting to make the rear exhausts/back box move in to harms way at the back.

Why do people think low is good?

Quicker to hit the bump stops and ruins the ride, not matched to dampers any more because they are firmer.


This is yet another legacy from the old days like K&N's. Todays cars are very low by design in the first place (it's vogue these days and manufacturers make low riding cars as standard and do specific things to achieve it), and the bump stop rate/length and variable winding of the spring are designed together to offer the ability to ride low (the Z4 IS low standard in sport spec), and yet not bottom out, and also offer good ride etc.

As soon as you change springs you have to ask how the geometry kinematics, static alignments work now (anyone seen the change before/after lowering the front/rear)... and then also the general ride, damping rates vs spring rates at different spring lengths. Ie, is it now over-damped for low-shaft speeds and under-damped for high shaft speeds... it's just all unknowns and not ONE provider of these kits will tell you the changes or compromises or anything. In my view it's just all made up crap. Lower sells, they make low springs, if it still works then they sell it. You have no idea if it's actually going to be totally awful or not.

I've driven maybe 70 different examples of my last car on the road fairly hard, and out of all of them, the ones on original suspension are the best by a country mile. The modded ones range from not nice to really ruined.


Personally unless you know what you want to achieve from a car from suspension upgrades, then leave well alone, or at least realise it will be expensive to experiment and you have to be brutal towards your mods. If it's not right, don't keep it because it cost you £400 to buy/fit the kit!

OR, buy bits from a reputable tuner who has tuned these specific cars a great deal, raced them, and so on. The only ones in the UK I can see who have done this are Simpson, and their kit is a top-end coilover one... I wouldn't go for anything less... especially on a 200bhp+ sports car!


All imo


Dave

 

[Siftah]

Why do people think low is good?

I don't, personally - but I think the Eibach springs are probably better quality than the OEM ones. Mostly because nobody has reported them breaking and the OEM ones do. However; That's probably flawed logic as there are clearly less people running Eibachs for it to be representative.

Quicker to hit the bump stops and ruins the ride, not matched to dampers any more because they are firmer.

I thought dampers are usually constant rate across their travel - is this not the case with the Z4?

Spring rate should have been developed to take in to account the reduced ride height, especially by a company like Eibach who have considerable experience with aftermarket springs, it shouldn't really hit the bump stops any more often... certainly, that's not the sort of performance I tend to worry about anyway. If I'm driving too fast over hump backed bridges or trying to take speed bumps at 40mph then that's not something that concerns me.

The car being lower *does* make a tangible difference to the dynamics, weight is better when it's lower down, ok, 15mm isn't going to totally transform it, but it should make the handling better and lessen the effect of weight transferance. Whether the stock suspension is capable of being adjusted enough to allow for it is a fair point though - I would suspect it probably can be.

This is yet another legacy from the old days like K&N's. Todays cars are very low by design in the first place (it's vogue these days and manufacturers make low riding cars as standard and do specific things to achieve it), and the bump stop rate/length and variable winding of the spring are designed together to offer the ability to ride low (the Z4 IS low standard in sport spec), and yet not bottom out, and also offer good ride etc.

I'd disagree with "good", it handles well but it's not the smoothest on UK roads

As soon as you change springs you have to ask how the geometry kinematics, static alignments work now (anyone seen the change before/after lowering the front/rear)... and then also the general ride, damping rates vs spring rates at different spring lengths. Ie, is it now over-damped for low-shaft speeds and under-damped for high shaft speeds... it's just all unknowns and not ONE provider of these kits will tell you the changes or compromises or anything. In my view it's just all made up crap. Lower sells, they make low springs, if it still works then they sell it. You have no idea if it's actually going to be totally awful or not.

And that's why forums like this are great, such a good opportunity to get feedback from other users!

Personally unless you know what you want to achieve from a car from suspension upgrades, then leave well alone, or at least realise it will be expensive to experiment and you have to be brutal towards your mods. If it's not right, don't keep it because it cost you £400 to buy/fit the kit!

OR, buy bits from a reputable tuner who has tuned these specific cars a great deal, raced them, and so on. The only ones in the UK I can see who have done this are Simpson, and their kit is a top-end coilover one... I wouldn't go for anything less... especially on a 200bhp+ sports car!
All imo
Dave

Sounds like good advice to me, though, personally, I think 15mm of ride height and sticking with reputable aftermarket suppliers shouldn't be *too* risky... though I'd still like to hear from someone running non-runflats and Eibachs before I drop my hard earned on them!

 

[Mr Whippy]

I'd be happy to buy Eibach springs if they just made their own but at OEM rates, with specific replacements part number for part number...

Problem is they are 15mm drop, and as said that gets the front bumper into easy damage range, and the back-end might start to be a problem too.

My biggest worry is kinematic. The camber gain is pretty high front and rear, but higher at the rear (nearly double from some rough checks). The result is that lowering the car adds more neg camber at the back than the front, so more understeer tendancy. That might be tweaked with a firmer rear spring rate, but I have no idea. Eibach simply don't tell us ANY of this. Do they even consider it?

Then the second issue is that the gain won't be linear. It may well be designed to err positive change at the front after a given deflection (say as the bump stop is hit) to give a safe transition in to front-end understeer at the front at really high limits. The back end might well do the same... just too many questions.


That is why I won't buy anything from Eibach, because they just don't TELL us anything. Such companies often use the excuse that we won't understand, but it stinks of them not having done their homework or analysis... they might just think a 15mm drop and 10% rate change is within tolerance, so it's 'ok' to just do a quick road test and say it's ok!?
Again, they don't even tell us what testing they did, what compromises they had to make, nothing. Silence is usually an admission of not having the info to hand in the first place in my experience.
Their products are often sold by dealers who don't know the most simple info like original spring rate or wheel rate vs new spring/wheel rate. If they can't reassure me on even simple considerations, never mind the more complex ones, then how can I trust them that when I take a bend a bit wrong, and there is a bump half way around it, that it's not going to send me understeering through a hedge because of weird kinematic changes?

The spring, damper, static alignment, are all things we can change, BUT, mostly, the kinematics are a function of the pickup points. They can't be changed, so the spring, damper and static alignment are set with the kinematics in mind. When you change the things you can change (just springs) it doesn't take a rocket scientist to realise the other variables need to be re-visited to make sure they work optimally.
No suggested new alignment settings from Eibach? No recommended dampers?


Eibach have some good people no doubt, but BMW have even better ones with budgets that Eibach could only dream of, simulators they could only dream of, and road-test gurus they could only dream of... until Eibach tell/show us more, and specific to OUR car, and our needs, with consideration for our needs, then I won't be buying their stuff
I trust BMW a bit more

If I make a change it'll be little ones at a time and being very critical of those changes. If they make things worse, then they get binned!



Sorry to sound so negative and boring

Just I hate these companies that suggest they are fantastic, but offer no evidence to prove they are.

That is why the only people I'd trust with any Z4 type mods etc if I were buying them in, is Dinan. They are the only ones who talk to you, and talk specifically about each product! You just know they are in to the stuff they do. They have demo cars that they build up to spec, they offer really in-depth detail changes to specific single models.

Thumbs up to Dinan! (no I don't work for Dinan )

Dave

 

[cj10jeeper]

Dave - spot on with these comments.

Trouble is the majority of the market for them (and I don't mean members here at all) is people who read mags, visit Halfords, etc. and equate known brand name to better. Drop the car 15mm to 30mm or more = good and improved performance. There's also the placebo effect of I put 'good' springs on so it is better in every aspect of performance, comfort, etc.

 

[mmm-five]

This is the same problem I had with the M5.

We ended up getting a damper & spring set made up specifically for the e34 M5 that didn't lower it and was just to be used as a replacement for the electronic suspension. If it wasn't for my friend's contacts in the industry I don't think we'd have gotten anyway as the springs we ended up using were not for designed for an e34 M5 and we had to use some creative thinking to get it to fit without issue, and so that it could be replicated easily once the prototyping was done.

We ended up with a car that was as pliant on country roads as the EDC equipped ones, but hunkered down in fast corners due to the progressive & variably wound springs we used.

It is possible to get something done like that, but you need someone who know's what they're doing, with the right industry contacts and with a willingness to invest a lot of their own time into getting the rates right.

In my case it helped that my contact also had an e34 M5 and used my car (with H&R lowering springs and no-name dampers) as a prototype. Before the car was done it would easily scrape the sump on speed cushions, and the tyres would foul the arches on hard cornering, so it had to be replaced.

 

[Siftah]

Sorry to sound so negative and boring

No, thanks for taking the time to write a detailed and thought provoking post

Puts me right back at square one though, considering just sticking with the BMW springs.

What are peoples thoughts with regards to the run flats though, given this context, ie: the suspension just wasn't designed for non-runflats, so how are they *really* going to affect the ride...

 

[PawnSacrifice]

What are peoples thoughts with regards to the run flats though, given this context, ie: the suspension just wasn't designed for non-runflats, so how are they *really* going to affect the ride...

Personally, I found it made the car a lot softer, by that I mean the ride is improved (allowing me to push on more) but the feel is not as sharp. Turn-in feels a lot less sporty, but that's misleading in many ways because I'm sure the improved ride allows me to turn-in and corner faster. It's just a feel thing. My strut brace has cured that to a large degree. I was going to run Eibachs as well, to firm it back up... M wheels prohibit this (and Dave's explanation above make me feel less sorry), so I may fit the H&R stiffened anti-roll bars instead - the one thing I did enjoy with the run flats was that harder edge feel (ignoring the fact that the setup probably slowed me up - placebo anyone?).

That's my personal opinion, I know some people will think that's utter toss.

In the trade off between the two, I think the change is worth it. Also, for the same price as a couple rear OEM RFTs I got a full set of Eagle F1s

 

[Siftah]

Personally, I found it made the car a lot softer, by that I mean the ride is improved (allowing me to push on more) but the feel is not as sharp. Turn-in feels a lot less sporty, but that's misleading in many ways because I'm sure the improved ride allows me to turn-in and corner faster. It's just a feel thing. My strut brace has cured that to a large degree. I was going to run Eibachs as well, to firm it back up... M wheels prohibit this (and Dave's explanation above make me feel less sorry), so I may fit the H&R stiffened anti-roll bars instead - the one thing I did enjoy with the run flats was that harder edge feel (ignoring the fact that the setup probably slowed me up - placebo anyone?).

That's what I'd imagined would happen - stiffer sidewalls usually change the handling, they tend to give you more turn in and they also tend to make the car snap into oversteer quicker as the tyre transitions from having grip, to not having grip, much quicker. With a softer sidewall the tyre distorts more and loses grip more gradually. That tends to make people feel safer and corner harder as the effect of losing grip is more gradual, it gives you more warning.

This is all my own very humble non-expert opinion from having driven for a while and what I've read and heard from people, not to be taken as 'knowledge'

I love the sharp turn-in on the Z and I don't mind the snappy handling (that's the fun for me). The bumpy ride doesn't really bother me either, it's a sports car after all and dodging potholes on the way to work is offset quite easily by the sheer joy of a foot down b-road blast of a Sunday.

In the trade off between the two, I think the change is worth it. Also, for the same price as a couple rear OEM RFTs I got a full set of Eagle F1s

That's a good point too, there's a considerable cost saving over the life of the car

I think I need to speak to someone with coil-overs... This is going to get expensive.

 

[cj10jeeper]

I think a change of tyres is far less critical in the way that changing springs is. So long as you go like for like in width and profile then non of the issues of changing the steering geometry take place.

I'd also offer that for the most part people compare £200 bridgestones with £80 Falkens. Reckon if I spent £200 a corner on decent non runflat rubber it would work a hell of a lot better than any RFT set up. (al la ///M)

As for the suspension being designed for RFT's my understanding is it wasn't but BMW made an early attempt (and poor) to tune it to RFT's and got it wrong.

 

[nickoneone]

The only reason you are going to europarts is because the oem springs are so crap. why would anybody insist on oem springs when we al know thwy break like dry twigs at the slightest pothole. Insisting on BMW springs is the triumph of snobbery over experience.

 

[Leon_in_uk]

We provide finance for their customers, I'll ask one of the reps if you need any info?

 

[Siftah]

We provide finance for their customers, I'll ask one of the reps if you need any info?

Ask them if there's a technical contact we could email to ask some in-depth questions, ie: spring rates in comparison to the OEM parts etc. That sort of thing could be really interesting...

 

[Leon_in_uk]

Ok it will be Tuesday now though, I'll get all info and perhaps a group buy?

 

[Leon_in_uk]

Do you know if unipart/partco offer the same springs? I can contact them also

 

[RichardG]

Just how many different springs come as OEM?

From what I remember when I bought my car you had the standard suspension as fitted to the 2.2 and the 2.5 the 3.0 came with sport suspension 15mm lower as standard.
So by my reckoning that's s huge different OEM range of 2 springs.

I specced my car with the sport suspension when I bought it and when the rear springs broke I searched for aftermarket spring at the correct height rather than OEM, I just didn't want to put something on I knew would fail again and failed. I chose to go down the Eibach route due to a couple of factors;

Eibach at least are a recognised name within the industry and are likely to have carried out some research, as has been stated in this thread BMW tried to match the suspension to the RFT's and failed, a pattern part maker who would more than likely just blindly copy something as best they could.
The warranty was significantly better than that offered by BMW.
They couldn't make the ride any worse, I was already on 17" Non-RFT's at that point
and finally price - all 4 springs for the cost of 2 from BMW. The only extra cost coming from the 4 wheel alignment carried out afterwards, which would have been done away after fitting the OEM springs.

I have since changed the wheels to 19's and the ride is no worse than it was as standard, if anything I find the initial part of the ride is more compliant than before, but I guess more importantly I have found that despite lowering it a further 15mm it doesn't bottom out anymore than it did when I first got the car.

The biggest improvment to steering feel came when I fitted the M steering wheel, physolocical I know, but it definately feels more reassuring.

As someone else stated there is a lot of unjustified snobbery about fitting aftermarket parts, BMW can and do get it wrong (most of there boring current designs for one, but that's a different thread), and for the most part there components have to be a compromise, how many people on this forum have changed there brake pads because the OEM are not up to the job.

I might be missing the point here, but I think there is difference between parts made by companies such as Eibach and parts supplied by the likes of ECP, It would be interesting to hear the views of anyone else who has fitted Eibach's or other aftermarket equipment.

 

[Mr Whippy]

Wrt tyres and springs.

1/ride rate = 1/tyre rate + 1/wheel rate

Since wheel rates are in the order of 20,000N/m and tyre rates 200,000-250,000N/m, the impact of tyres has much less effect than the change in springs on the ride rate you feel and the rate of change of weight transfer etc.

Dave

 

[peddy]

Well I had the springs changed back on Friday and the ride is as it should be, but bow do OEM springs look crap! They're so think comapared to the ECP ones. If they did the M-Sport springs I would stick with that!

IMO if you have one of the 2.XLtr models then go for something like the ECP ones.