A Slightly Fettled BMW Z4 35i
Discussion
So here's the offending article;
Aesthetically it's quite similar to a standard Z4 with the exception of a retrimmed steering wheel and the recent change to an M sport front bumper after I got hold of a free one locally, following a respray the front end looks far better less the stone chips of the old one.
Mechanically is where it gets a bit more interesting however. As journalists are very keen to point out with news of the upcoming Z4 in abundance, the E89 was a bit of a lard in the handling department. In comparison to my old E85 Z4 and VX220, it's hobbled by runflat tyres and nearly 1600kg's of heft not being terribly well controlled resulting in catastrophic understeer and considerable body roll when trying to press on down an A or B road. The upshot is that I found it to be a very capable cruiser, free from the rattly interior of old Z4's and able to cover huge distances in ample comfort.
What I wanted to do then was to retain as much of the long distance capability as possible whilst making it far sharper when faced with anything other than a straight line. Some research and I found that underneath these cars are a right old mash of their own parts in the middle, E90 3 series at the front end and the outgoing E85 Z4 at the back. To improve handling then the easiest thing to do would be to rob suspension components off of the E92 M3 and Z4M. These parts are lighter, stronger and most importantly replace the squishy rubber bushings with ball joints resulting in far less deflex under load, the difference can be seen below in the E92 M3 lower wishbone;
I had tried fitting an M3 anti roll bar however found a plug on the electronic power steering unit foul's it so an aftermarket roll bar from H&R or Eibach is the only way to go. This is unfortunate as the M3 bar is a lot lighter. The plug only just fouls the bar so I did try both and franky couldn't tell the difference, I may try to modify this in the future to get the M3 bar to fit.
The end result of the front end looks like this. Apologies for all the mud, I am in Cornwall afterall!
Not so much to photograph on the rear end I'm afraid, as per the E85 Z4 it's a trailing arm with upper and lower control arms, these three parts are slightly altered for the E89 Z4's and so are unique, the rubber bushes within the hub aren't however and can be swapped for the ball joints from the old Z4M.
BMW handily fitted ball joints to the upper control arm on the E89 and changed the troublesome trailing arm bushes (presumably for the better however may look into this) so these both stay. The only change is that one bushing on the lower control arm to that from the Z4M and a stiffer rear anti roll bar.
After this (and ditching the runflats for some proper tyres) I have to say it is completely transformed. I was hoping for a bit better turn in ability, less body roll and maybe even something resembling steering feel.
Well the end result was all of the above plus what I did not expect was the huge increase in mechanical grip from the front end! It now just darts into a corner and grips, It's been this way for roughly four months now and I can honestly say I still haven't been able to get it to understeer yet, maybe I'm just not brave enough.
Turn in is genuinely sharper than that of the VX220, if less linear. It still doesn't handle quick direction changes like the VX but at nearly twice the weight and somewhat taller I don't feel it's ever going to, outright grip is definitely beyond that which the Vauxhall can manage however and in combination with the extra power, the VX wouldn't see which way this thing went down most roads (let alone the standard Z4 whose stability control light would be incessant).
Speaking of extra power, a thorough engine service involving changing the usual oil/filters as well as coolant, spark plugs, ignition coils and the rocker cover complete with a new gasket led to a visit to the kind folks at Evolve Automotive for a custom ECU calibration and roughly 360hp which really brought it alive. I'm aware the engines in these are really quite solid so may look into getting closer to 400hp if I can maintain reliability.
Apologies for waffling on, this turned out somewhat longer than I thought and I've probably missed something somewhere. Nevertheless, onto some photos (I don't have many with the new bumper on);
Up in Wales for a weekend;
In it's natural state, pasted in mud and brake dust;
Shortly after fitting the new steering wheel, well worth doing as it was the only part of the interior showing any wear
And finally, looking far too clean on the BMW stand at this years Silverstone Classic
Plenty more to come from this yet I hope! I have a feeling the brake calipers from F series M3's will fit these, just a question of whether or not they'll get under 18'' wheels as I don't want to sacrifice the better ride of them over 19'' alloys.
Aesthetically it's quite similar to a standard Z4 with the exception of a retrimmed steering wheel and the recent change to an M sport front bumper after I got hold of a free one locally, following a respray the front end looks far better less the stone chips of the old one.
Mechanically is where it gets a bit more interesting however. As journalists are very keen to point out with news of the upcoming Z4 in abundance, the E89 was a bit of a lard in the handling department. In comparison to my old E85 Z4 and VX220, it's hobbled by runflat tyres and nearly 1600kg's of heft not being terribly well controlled resulting in catastrophic understeer and considerable body roll when trying to press on down an A or B road. The upshot is that I found it to be a very capable cruiser, free from the rattly interior of old Z4's and able to cover huge distances in ample comfort.
What I wanted to do then was to retain as much of the long distance capability as possible whilst making it far sharper when faced with anything other than a straight line. Some research and I found that underneath these cars are a right old mash of their own parts in the middle, E90 3 series at the front end and the outgoing E85 Z4 at the back. To improve handling then the easiest thing to do would be to rob suspension components off of the E92 M3 and Z4M. These parts are lighter, stronger and most importantly replace the squishy rubber bushings with ball joints resulting in far less deflex under load, the difference can be seen below in the E92 M3 lower wishbone;
I had tried fitting an M3 anti roll bar however found a plug on the electronic power steering unit foul's it so an aftermarket roll bar from H&R or Eibach is the only way to go. This is unfortunate as the M3 bar is a lot lighter. The plug only just fouls the bar so I did try both and franky couldn't tell the difference, I may try to modify this in the future to get the M3 bar to fit.
The end result of the front end looks like this. Apologies for all the mud, I am in Cornwall afterall!
Not so much to photograph on the rear end I'm afraid, as per the E85 Z4 it's a trailing arm with upper and lower control arms, these three parts are slightly altered for the E89 Z4's and so are unique, the rubber bushes within the hub aren't however and can be swapped for the ball joints from the old Z4M.
BMW handily fitted ball joints to the upper control arm on the E89 and changed the troublesome trailing arm bushes (presumably for the better however may look into this) so these both stay. The only change is that one bushing on the lower control arm to that from the Z4M and a stiffer rear anti roll bar.
After this (and ditching the runflats for some proper tyres) I have to say it is completely transformed. I was hoping for a bit better turn in ability, less body roll and maybe even something resembling steering feel.
Well the end result was all of the above plus what I did not expect was the huge increase in mechanical grip from the front end! It now just darts into a corner and grips, It's been this way for roughly four months now and I can honestly say I still haven't been able to get it to understeer yet, maybe I'm just not brave enough.
Turn in is genuinely sharper than that of the VX220, if less linear. It still doesn't handle quick direction changes like the VX but at nearly twice the weight and somewhat taller I don't feel it's ever going to, outright grip is definitely beyond that which the Vauxhall can manage however and in combination with the extra power, the VX wouldn't see which way this thing went down most roads (let alone the standard Z4 whose stability control light would be incessant).
Speaking of extra power, a thorough engine service involving changing the usual oil/filters as well as coolant, spark plugs, ignition coils and the rocker cover complete with a new gasket led to a visit to the kind folks at Evolve Automotive for a custom ECU calibration and roughly 360hp which really brought it alive. I'm aware the engines in these are really quite solid so may look into getting closer to 400hp if I can maintain reliability.
Apologies for waffling on, this turned out somewhat longer than I thought and I've probably missed something somewhere. Nevertheless, onto some photos (I don't have many with the new bumper on);
Up in Wales for a weekend;
In it's natural state, pasted in mud and brake dust;
Shortly after fitting the new steering wheel, well worth doing as it was the only part of the interior showing any wear
And finally, looking far too clean on the BMW stand at this years Silverstone Classic
Plenty more to come from this yet I hope! I have a feeling the brake calipers from F series M3's will fit these, just a question of whether or not they'll get under 18'' wheels as I don't want to sacrifice the better ride of them over 19'' alloys.
mato said:
The F series calipers will fit the front of it is e90 based, you could go for the smaller disc, still retaining the 4 pot calipers.
You're right however the problem there is that I'd be effectively taking the existing brakes and fitting smaller, less effective ones in their place. Unless I'm mistaken, I don't think it's legal to do that either.Larger or the same size discs would be fine however smaller is a no go. It'd have to be the 370mm disc and caliper if I did do anything, for 18'' wheels it seems to be down to their design as to whether the caliper will fit or not.
CarAbuser said:
I'm interested in the changes you made to the suspension, what hardware did you purchase?
How much of the improvement came from ditching the runflats and how much from the suspension changes?
I've put the BMW part numbers below, I hope that helps. You can get these directly from BMW if you really want the little M logo's on or TRW are the supplier for BMW so you can get the exact same part just with the M logo shaved off from any motor factor.How much of the improvement came from ditching the runflats and how much from the suspension changes?
Front suspension:
Left Tension Strut With Rubber Mounting - 31102283575
Right Tension Strut With Rubber Mounting - 31102283576
Wishbone Left - 31102283577
Wishbone Right - 31102283578
Rear suspension:
Ball Joint (X2) - 33306852895
The order I did things went tyres > roll bars > suspension components.
In my opinion the tyres mainly improved comfort and road noise, there was a noticeable increase in traction under acceleration and braking but still a lot of understeer through corners.
The roll bars made much more of a difference by pretty much doing what they say on the tin and reducing roll, I don't think there was so much of a difference in outright grip as there was in your confidence to go that bit quicker due to the much improved control in the way the car reacts. Definitely a big improvement though as it made the car much more enjoyable. After fitting these 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.
The M3 parts bring the bigger differences in outright grip, I don't know how the car would react with these parts and the standard roll bars but I'm sure it can only be an improvement. The steering response is much sharper and faster to tun in along with almost eradicating understeer. Initial turn in actually feels lighter through the steering wheel before it weights up and gives little nibbles of information through the wheel of what the front tyres are doing, nowhere near the sort of feedback that comes with the VX220 but much, much improved on standard.
There are a few things to be aware of if you do want to do something similar, in order to change the rear bar you'll need to drop the entire exhaust, not too much trouble but the studs may be rusted to death making them a right pain to get apart, the levelling sensor for the xenon lights is on the other side on 3 series' so you'll need to make a small bracket to connect to the lower wishbone then check the lights are aligned correctly and after fitting the suspension components an alignment will be required too, the lower wishbones on the M3 are slightly longer than standard so you'll have a huge amount of toe in to get rid of as well, there's plenty of adjustment in the Z4's suspension but BMW track rods are extremely good at seizing up so some heat may be required.
shalmaneser said:
A brief look at ECP seems to suggest that the 35i has 330 or 348mm front brake discs.
I'm running CSL discs @ 345mm on my e46 M3 using porsche calipers with the standard 18" wheels and there is sufficient clearance if you use a 12mm spacer on the front.
This would suggest you might be OK with four pot calipers - certainly worth looking into I'd have thought.
I was worried about the handling implications of running spacers but I can confidently say that 12mm spacers have had no discernible effect on the handling whatsoever. And they make the car look much better with the wheels filling the arches somewhat better.
Lovely looking car, and some very tasteful mods.
348mm discs on the European 35i, in America it's only the 35is that has 348mm discs and the 35i has 330mm for some reason.I'm running CSL discs @ 345mm on my e46 M3 using porsche calipers with the standard 18" wheels and there is sufficient clearance if you use a 12mm spacer on the front.
This would suggest you might be OK with four pot calipers - certainly worth looking into I'd have thought.
I was worried about the handling implications of running spacers but I can confidently say that 12mm spacers have had no discernible effect on the handling whatsoever. And they make the car look much better with the wheels filling the arches somewhat better.
Lovely looking car, and some very tasteful mods.
Porsche calipers with the existing discs was another option I was looking at actually, is there a marked improvement with those fitted?
It should be said that the standard 35i brakes aren't bad at all, a little better never hurts though?
Not a problem guys! If anyone else wants some help with doing similar, just drop me a message. Currently helping a friend do this with their 335d so should be familiar with the rear suspension on the E9x's soon too.
In regards to geometry, I just stuck moreorless to the standard settings. There could be more to have in getting a fast road setup done, I sent my old Z4 to a local Lotus specialist who did a marvellous job so may do that again in the future.
At the time I did the alignment myself with BMW's target data from Bosch.
There was nothing to adjust at the rear, that was all exactly the same having only changed one ball joint each side, the front had a whopping 3.37 degrees of toe in initially however we soon dialled that back to the target 0.14. Front camber was the only other thing that changed, before doing anything it was -0.40 degrees both sides and afterwards -0.50 degrees, these are the upper reaches of BMW's targets but within tolerance so left it as is. Hope that helps!
scz4 said:
Great info above, I've taken note 
Looks all of the above can be had for no more than £250 from here (front end) - https://www.onlinecarparts.co.uk/trw-2201926.html
What geometry settings have you gone with for "fast road"?
No lowering springs planned?
Precisely, the M3 parts aren't particularly expensive. Due to the, err 'mixed' surfaces the car covers down here, lowering the suspension isn't something I want to do at the moment. I'd recommend trying this before changing out springs/dampers as it compromises the ride far less.Looks all of the above can be had for no more than £250 from here (front end) - https://www.onlinecarparts.co.uk/trw-2201926.html
What geometry settings have you gone with for "fast road"?
No lowering springs planned?
In regards to geometry, I just stuck moreorless to the standard settings. There could be more to have in getting a fast road setup done, I sent my old Z4 to a local Lotus specialist who did a marvellous job so may do that again in the future.
At the time I did the alignment myself with BMW's target data from Bosch.
There was nothing to adjust at the rear, that was all exactly the same having only changed one ball joint each side, the front had a whopping 3.37 degrees of toe in initially however we soon dialled that back to the target 0.14. Front camber was the only other thing that changed, before doing anything it was -0.40 degrees both sides and afterwards -0.50 degrees, these are the upper reaches of BMW's targets but within tolerance so left it as is. Hope that helps!
Mr Tidy said:
Really informative thread OP. 
If I move on from my E86 3.0Si to an E89 then a manual 35i would be what I would want - maybe with a sneaky remap!
And I love your red interior!
Thanks! I'd really recommend Evolve Automotive for remapping, they were one of the first to start playing with these engines so have a lot of experience, will also give you before and after dyno runs so you can see how healthy the car is beforehand and how much you've gained afterwards.If I move on from my E86 3.0Si to an E89 then a manual 35i would be what I would want - maybe with a sneaky remap!
And I love your red interior!
I'm really liking the read leather as well, it's a much softer shade of red than some of the more in you're face shades around (Looking at you Audi)
Julian Thompson said:
Some great info here. I was looking closely at upgrading my z4 brakes and made some notes which might be of some use if you don’t have part numbers. Some will be nonsense so just ignore.
I still can’t find a way to upgrade the rears particularly as they have the electric handbrake. Any ideas?
Unfortunately it seems that the rear end is pretty much unique to the Z4 so upgrading the rear brakes is going to be quite an involved process! Audi brakes might be one way to go with this which would then just mean getting hold of discs of a larger size.I still can’t find a way to upgrade the rears particularly as they have the electric handbrake. Any ideas?
The rear brakes are already a fairly generous size on the six cylinder cars (I think my old Z4 only had 325mm on the front!) so shall do something with the fronts first as they do the vast majority of the work then think about the rears if necessary.
Julian Thompson said:
BMW Performance 4 pot:
yellow: 34106855475 + ...6
red: 34106855477 + ...8
orange: 34106855479 + ...80
discs 370x30 mm (drilled): 34106797603
dust cover: 34116792237 + ...8
brake pads: 34116859066
This is exactly the route I'm going, I've gotten hold of calipers from an M4 and the discs will be the 370mm ones you've mentioned (TRW's number for these is DF6600S).yellow: 34106855475 + ...6
red: 34106855477 + ...8
orange: 34106855479 + ...80
discs 370x30 mm (drilled): 34106797603
dust cover: 34116792237 + ...8
brake pads: 34116859066
The calipers I'll reseal, sand down and repaint silver. In keeping with the theme, some M4/M3 wheels are also on the way as the 18's aren't going to clear the new calipers!
Hopefully I'll have this sorted within the next few weeks so shall keep things updated here.
It might actually be a little more than 360, the dyno run was done straight after remapping and warming the engine up. They said it'd feel stronger still as the car adapted to it and on the drive back that was definitely noticeable.
The torque really gets bumped up though, that went from roughly 330lbft at 2400prm to holding 400lbft in almost a perfect flat line from 3000 to 4250rpm, if you're within that range in any gear it'll get a move on pretty well.
I think I'll have to take some more interior photos too!
The torque really gets bumped up though, that went from roughly 330lbft at 2400prm to holding 400lbft in almost a perfect flat line from 3000 to 4250rpm, if you're within that range in any gear it'll get a move on pretty well.
I think I'll have to take some more interior photos too!
Looks like you've got 18's on yours, have you tried switching from the run flats to a regular tyre?
Having just fitted the 19 inch wheels tonight I'm pleased and slightly relieved to report that so far there's no discernable difference between the 18's and 19's!
I suspect this is largely down to the tyres as they are now 235/35 R19 on the front and 275/30 R19 on the rear, up from 225/40 R18 and 255/35 R18. The extra width means I've only lost roughly 6mm out of the side wall so the ride is pretty much the same.
I'm also a big fan of Goodyear's Eagle F1 tyres, I find they've got 99% of the grip of Michelin tyres but are much quieter and have noticeably more give over bumps, well worth a go unless you really want the grippiest thing out there in which case Michelin all the way.
Having just fitted the 19 inch wheels tonight I'm pleased and slightly relieved to report that so far there's no discernable difference between the 18's and 19's!
I suspect this is largely down to the tyres as they are now 235/35 R19 on the front and 275/30 R19 on the rear, up from 225/40 R18 and 255/35 R18. The extra width means I've only lost roughly 6mm out of the side wall so the ride is pretty much the same.
I'm also a big fan of Goodyear's Eagle F1 tyres, I find they've got 99% of the grip of Michelin tyres but are much quieter and have noticeably more give over bumps, well worth a go unless you really want the grippiest thing out there in which case Michelin all the way.
I made up some droplinks very similar to those in your second link. Though the primary reason for doing so was because the standard item doesn't have any metal bushing for a bolt to go through on the lower part of the link.
This means that if you push a bolt through the rubber and put a nut on the roll bar side, there's nothing solid for it all to tighten up against so it all pushes around within the drop link bushing when the car leans.
Without solidifying it somewhere, there's absolutely no point in an aftermarket rear bar because your mountings aren't fixed!
Availability was the main reason at the time. I don't know what it's like now but when I was doing this, there weren't any Eibach rear bars I could find within a reasonable lead time.
As previously mentioned, I'd rather have used bmw bits but they certainly do a good job and at the front at least there was no discernable difference between the M3 roll bar and H&R's one (apart from weight).
This means that if you push a bolt through the rubber and put a nut on the roll bar side, there's nothing solid for it all to tighten up against so it all pushes around within the drop link bushing when the car leans.
Without solidifying it somewhere, there's absolutely no point in an aftermarket rear bar because your mountings aren't fixed!
Availability was the main reason at the time. I don't know what it's like now but when I was doing this, there weren't any Eibach rear bars I could find within a reasonable lead time.
As previously mentioned, I'd rather have used bmw bits but they certainly do a good job and at the front at least there was no discernable difference between the M3 roll bar and H&R's one (apart from weight).
Any motorsport parts place will sell bits for making up droplinks, I took some adjustable Porsche ones apart and used some rod ends just because that's what I had available. I plan to replace them every two years going forward.
If you make them the same length as the existing ones with adjustment for +/- 25mm in the same style as that second thread linked then you can't go far wrong.
If you make them the same length as the existing ones with adjustment for +/- 25mm in the same style as that second thread linked then you can't go far wrong.
It's not too tricky, just need to be careful of getting the lengths right.
Overall though the rear bar is a bit of a pain to get working!
You'd absolutely get a good result just by doing the front end, I'd suggest doing the front M3 bits and front roll bar first. Then decide if springs or coilovers are needed.
Just waiting on the M4 brake calipers to get here then I'll be repainting them and changing discs/pads all round as they're due.
It does look like I've gotten hold of a reasonably priced supply of bmw's 370/380 four piston calipers so could put kits together to bolt onto Z4's and presumably E9x's too if there's interest?
As far as discs/pads go, at the moment I'm assuming I can't go too far wrong with TRW or Brembo?
Overall though the rear bar is a bit of a pain to get working!
You'd absolutely get a good result just by doing the front end, I'd suggest doing the front M3 bits and front roll bar first. Then decide if springs or coilovers are needed.
Just waiting on the M4 brake calipers to get here then I'll be repainting them and changing discs/pads all round as they're due.
It does look like I've gotten hold of a reasonably priced supply of bmw's 370/380 four piston calipers so could put kits together to bolt onto Z4's and presumably E9x's too if there's interest?
As far as discs/pads go, at the moment I'm assuming I can't go too far wrong with TRW or Brembo?
Julian Thompson said:
Yes thanks I checked it today and they are 18. Not tried anything yet so that sounds like a good plan. Do you have pics of it now on the 19s?
I didn't give it a clean because the weather's been rubbish all weekend but did grab a picture or two, nothing too pretty I'm afraid but the last one gives a good show of where they sit in the wheelarch. 
They're actually replica's, the genuine ones are wider again so don't quite fit as well.
You can find out more about them here; https://f30.bimmerpost.com/forums/showthread.php?p...
I was a little sceptical of replica's however these have loads of people running around on them without issue and since there isn't a set of original 19'' Z4 wheels for sale that aren't either cracked or been repaired, they can't be much worse surely?
You can find out more about them here; https://f30.bimmerpost.com/forums/showthread.php?p...
I was a little sceptical of replica's however these have loads of people running around on them without issue and since there isn't a set of original 19'' Z4 wheels for sale that aren't either cracked or been repaired, they can't be much worse surely?
Time for an update and the brakes are on!
As I think has been previously mentioned, the calipers are off of an M4 and discs are the 370mm performance discs from a 340i/440i etc.
It's still in the process of bedding in somewhat but the pedal does feel a little more solid, certainly feels as though there's a lot of potential there as they bed in properly.
The calipers themselves aren't that much larger then the old ones and so don't feel any different in terms of weight, if anything they are a bit lighter perhaps? Anything gained there is likely offset by the larger discs however picking them up side by side, I'd say there isn't that much between them.
The biggest difference is in the pads themselves as the contact patch on the M4 calipers is a lot larger than the original pads.
Very pleased with them so far, shall update when they're properly bedded in.
As I think has been previously mentioned, the calipers are off of an M4 and discs are the 370mm performance discs from a 340i/440i etc.
It's still in the process of bedding in somewhat but the pedal does feel a little more solid, certainly feels as though there's a lot of potential there as they bed in properly.
The calipers themselves aren't that much larger then the old ones and so don't feel any different in terms of weight, if anything they are a bit lighter perhaps? Anything gained there is likely offset by the larger discs however picking them up side by side, I'd say there isn't that much between them.
The biggest difference is in the pads themselves as the contact patch on the M4 calipers is a lot larger than the original pads.
Very pleased with them so far, shall update when they're properly bedded in.
Not too much to report on as spare time has been going to the VX220 in this thread:
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Over New Year it did hit the 100K mark however! I have to say BMW put together a really solid car with this one, not looking too shabby for just over four laps of the planet XD
A quick oil and filter service will be coming up, otherwise business as usual.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Over New Year it did hit the 100K mark however! I have to say BMW put together a really solid car with this one, not looking too shabby for just over four laps of the planet XD
A quick oil and filter service will be coming up, otherwise business as usual.
Simon182 said:
Were those brakes ever available as an option on the Z4?
On the F30 there are a number of coding options available for the brakes, particularly if the car has the optional m-sport brakes fitted. I'm not sure what the coding does in regards to pedal feel etc.
Nope, never an option. They were robbed off of an M4 and are the same caliper fitted to 440i, 340i, M3's etc. I'm not too sure about the coding either, bias isn't electrically controlled surely? Pedal feel is excellent (in my opinion) regardless, very similar to Boxster/Cayman/911's.On the F30 there are a number of coding options available for the brakes, particularly if the car has the optional m-sport brakes fitted. I'm not sure what the coding does in regards to pedal feel etc.
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