Proboner's Z4 build thread

[kaizzer]

I currently ride on BC Racing BR Series coilovers with custom swift springs. To be quite frank, the car rides amazing, with zero signs of being harsh/bouncy. I get compliments all the time from my passengers about ride quality and most find it hard to believe that they are "only BC's." I highly recommend giving them a try. With so many other areas to spend money on this platform, they are worth every penny and then some!

I am currently running on OEM style 37's with 235/40/18 tires up front and 275/35/18 in the rear - just for reference sake.

p.s

If you ever want to get rid of your current wheels, i'd gladly take them off your hands!

-Reef

[proboner]

Welp, Eibach springs have been purchased. Now I'm sure most of you by now are wondering if I'm just a glutton for punishment, and I think the obvious answer is a resounding YES!

Anyways, they came in yesterday and I had to do side by side comparisons since I now have stock (non-mtech), H&R, and Eibach springs. And away... we... go.

Front springs, from left to right, in order of shortest to tallest, we have H&R, Eibach, and stock.


As you can see from a height perspective, the Eibachs are right in the middle, but there are some other notable differences. The H&Rs have 6 total coils, while the Eibach/stock only have 5, and the H&Rs are much more tightly wound. Certainly a much higher spring rate for the H&Rs. This is important when you start looking at things like "flat ride". This is an idea I learned about from Fat Cat Motorosports, which I mentioned in my last post. In terms of front to rear suspension frequency, you want the rear frequency to be ~20% higher than the front, to allow the rear to settle faster and stay in concert with the front. With this much higher rate in front, I wouldn't be surprised if the frequency becomes higher in the front that rear, causing the rear to still be reacting to the previous bump, as a new bump hits the front. The end result is a non-cohesive suspension that feels much bumpier and less stable over imperfections.

Measuring spring thickness, the H&Rs come in at 13mm


Eibach right around 12.5mm


And stock at 12.5mm as well


Once again, the H&Rs seem to be much stiffer up front than the stock and even Eibach. Given this increased stiffness, it seems aftermarket struts are basically a requirement to keep up with the front spring rates. Moving on to the rear, the springs once again line up from shortest to tallest in the order of H&R, Eibach, and stock.


This time the H&R and Eibachs both have 6 coils, while I'd consider the stock to have 6.5. Once again measuring spring material thickness, the H&Rs are 15mm


Eibachs are the thickest by a significant margin this time, at 18mm


And stock sit right at 15mm as well


So taking these findings into consideration, it seems like the H&Rs stiffen up the front springs considerably, but only minimally increase rates in the rear. Whereas the Eibachs seem to have minimal rate increase in the front, and a potentially large increase in the rear. While the Eibach rates are probably better overall than the H&R, I'm wondering if a mix of Eibach front and H&R rear might be the best of both worlds? At least in terms of lowering the car with a ride only slightly stiffer than stock.

Well, I'll be installing the Eibachs this weekend, so we will soon know. And do believe that I'll be experimenting the H&Rs in the rear as well, if the Eibachs don't feel right.

[StLMO]

Following. The only car suspension that I wasn't fond of was my f30 and decided to install Dinan springs on factory edc. Didn't like it at all, bottoms out and it didn't get rid of the body roll. My z4 suspension is soft but not overly, so dealing with it waiting until I have to replace edc suspension. I saw the eibach springs offered, though mostly overseas. I'm interested in how they handle vs the h&r.

[proboner]

So I installed the Eibach springs and stock shocks. I've got a huge writeup for this but am getting burnt out writing it up so figured I'd just give the quick and dirty:

• Comfort- 8- Very close to stock comfort
• Height- 6- Front is pretty decent but rear is not great
• Handling- 6- Still a bit boaty, but well sorted

Comfort is great, I'm very happy with it. It does have some wallow to it, but not enough to really bother me. Surprisingly the rear springs arent harsh at all, despite them being much thicker.

Height in front is good with minimal gap, and will be perfect when I put on the 19s, which will have 1" taller tires. Rear gap is a bit too much and I'm getting a weird sound from springs. I'm going to give them a bit more time to settle, but may end up experimenting with the H&R springs in the rear.

Haven't had the chance to really test out handling, but feels fine so far.

On to the pictures:

[StLMO]

Looks great. So eibach are "softer" than the h&r and not quite as aggressive of a drop. What size tires are you running? Thought eibachs are supposed to level off the car more. Thanks for the review interested in what you find re noise in the rear springs but like you said maybe that the springs were settling.

[proboner]

Originally Posted by StLMO

Looks great. So eibach are "softer" than the h&r and not quite as aggressive of a drop. What size tires are you running? Thought eibachs are supposed to level off the car more. Thanks for the review interested in what you find re noise in the rear springs but like you said maybe that the springs were settling.

Instead of thinking of it as Eibachs being softer, I'd instead frame it as H&R being stiffer. Eibachs are still likely a bit stiffer than stock, but IMO the H&Rs are prohibitively stiff if continuing to use stock shocks/struts. The shock valving can't keep up with the frequency of the spring which causes it to ride like crap and prematurely wears the shock out.

I'd often heard people claiming that the Eibachs provided a bit more of a raked stance, which I would definitely confirm. H&R definitely provide a better all around lowering, but like I said, I couldn't stand how they rode.

In terms of the noise, I'm really not 100% sure what it is at this point. There's lots of reference to hearing the rear coil bind with KWs, maybe this is similar, but it doesn't sound like that to me. When I initially installed the rear springs I neglected to put the lower rubber spring mount in, which I thought was allowing the springs to move around a bit which was making the noise. However I installed the rubber mounts and the noise persists, albiet to a slightly lesser degree. Maybe they still need a bit more time to situate themselves? I'll certainly have updates in the coming weeks, as I think it's become obvious that I'm a genuine psycho about this.

[StLMO]

I actually like the stance of your car with the Eibachs. Looking forward to your update and whether the rears get sorted out. My new wheels should be here in June, I'm just afraid of tires rubbing going over bumps and dips.

[proboner]

Originally Posted by StLMO

I actually like the stance of your car with the Eibachs. Looking forward to your update and whether the rears get sorted out. My new wheels should be here in June, I'm just afraid of tires rubbing going over bumps and dips.

Found the culprit of the rattle, which was the rear shocks slightly touching the exhaust on bumps. Turned the shocks 180* and problem is fixed.

There is absolutely no worry of your tires rubbing with the Eibachs or any other aftermarket lowering spring. Even with the H&Rs that were surprisingly low, I would only rarely rub the fender liner (which is plastic, so the tires win) and that was with taller/wider than stock diameter tires.

Edit: I would also like to add that since switching to the Eibachs the GF is enjoying the Z4 again, which was really the impetus for this all in the first place. When I first got the car and it was on stock suspension we'd go for rides at night and she would LOVE the 2nd-3rd gear WOT runs and scream with delight. After switching suspension she got very quiet and simply no longer enjoyed the car... everything about it made her nauseous, even and especially WOT acceleration. I took her for a ride soon after swapping to the Eibachs to show her how much better it rode and she once again had very little to say about it. I figured that maybe she'd been in so many different versions by now that it all felt pretty much the same to her, but I knew that for myself the difference was night and day.

Well yesterday we went to pick up lunch that required a drive into an area which was comprised of relatively deserted and twisty roads. I took the top down and drove to our lunch spot. On our way home I opened it up a bit in 2nd gear when leaving the parking lot and the joyful scream came out again. She commented on how it felt like a rollercoaster and gave her a similar tingle in the pit of her stomach and demanded that I do it again! I lined us up on a nice clear straight away and gave her a full 2nd gear pull from 4k through redline and she threw her hands up and screamed in delight. If that's not a win I don't know what is.

[StLMO]

That’s awesome to hear. The N54 on a custom MHD tune and supported add ons is way fun. My wife recently drove it for the first time since modifying and she took it up to 140mph. At first I thought she was joking but she was serious. We have a lot of great newly built open highway between us and her mother’s house. Unfortunately I decided to sell mine. Pulled everything off this past weekend and meticulously returned everything back to stock for the next owner to enjoy. Hope you continue to enjoy the car. For me, it was also really satisfying to know that another Z won’t be pulling up next to me everywhere I go.

[proboner]

Upgraded from halogen to LED headlight bulbs, as I'm sure many have done. Super simple upgrade and pretty surprised with the difference it made!

New LEDs


Compared to stock halogen- make sure you're getting something sized similarly


Daytime stock


Daytime LED


Daytime compared


Nighttime stock


Nighttime LED


Night compared


Tough to capture on camera, but the stock stuff is so dim and yellow by comparison. Would definitely suggest the upgrade, as it's cheap and super easy to do. And boy do I need to get my headlight lenses corrected!

[KennyP]

Do they compensate for dimming? Like when turning off lights gradually dim off. With some LED kits that dimming causes flickering before going off.

[proboner]

Originally Posted by KennyP

Do they compensate for dimming? Like when turning off lights gradually dim off. With some LED kits that dimming causes flickering before going off.

I have no idea, haven't even driven her at night since they were installed. Either way I can't imagine that bothering me.

[proboner]

Gave Mazikeen a wash today and then took her out for a quick round of disc golf. I don't know why, but cars always look amazing at the curb at Hellyer disc golf course. My old E85 did and so does the e89.


Oh and then I snagged a pic of the cat yawning in a beam of light so...


And then just a picture in the driveway with her stablemates


I'm just sitting here waiting for parts and it's driving me nuts! Ge here already!

[proboner]

Well some good news on a few fronts this week. Although Vivid Racing has been leading me on for MONTHS now about when these wheels would come in, they finally had an update on Friday that sounds like more than BS.

• Usual answer: "3 more weeks" over and over and over again
• This answer: "Wheels will land late in the first week of May, then shipped to us in AZ, then to you in CA"

So that's nice. The CF front lip and sideskirt extensions I ordered a few weeks ago sound like they'll be getting here sooner than anticipated as well. The original estimate was delivery on May 7th, but it now looks like the next couple days. They had quite a great tracking itinerary with Fedex:

• Wu Ku District- Taiwan
• Ta Yuan District- Taiwan
• Anchorage- Alaska
• Memphis- Tennessee
• San Francisco- Caifornia

Not sure how it makes sense to go from Alaska to Tennessee, but you do you, Fedex!

So anyway yeah! I'm stoked that some of these big pieces will be here soon! Now to accomplish some smaller tasks in preparation. Decided to cut the valve cover plastics to fit the PR ignition coils and reinstall. Super straight forward, although I wish I'd cut it a tiny bit smaller length wise.






And then I decided to experiment with the rear springs, since the Eibachs sit a good amount higher in the rear than the front. For the first time since owning this car, actually decided to measure the fender heights. Keep in mind I'm running slightly taller than stock tires, so your results will vary.
Eibach all around:

• Driver Front- 26.25"
• Driver Rear- 26.5"
• Passenger Front- 26"
• Passenger Rear- 26.75"

This is measured in my driveway which probably isn't totally level and is comprised of many bricks, that surely have slight height variances between them. A picture of the ride height for reference:


Then I installed the H&R springs in the rear...
Eibach front, H&R rear

• Driver Front- 26"
• Driver Rear- 25.5"
• Passenger Front- 26"
• Passenger Rear- 25.75"

As can be seen from the measurements and in the pictures below, the H&Rs sit about an inch lower than the Eibachs in back, and about 0.5" lower compared to the Eibach's currently installed in front. I've got to admit, I'm really surprised what a huge visible difference 0.5" of ride height makes. It's very apparent!






I also took it for a quick drive to let the springs settle a bit, and it already feels noticeably stiffer in the rear. I think keeping the front soft will make it manageable though, but only time will tell. The plan now is to 3D print some 0.5" risers to raise the rear ride height equal to the front and see how I like it. At first blush though, I think this is going to be the optimal choice.

And of course, how do you not take a picture of the e30 while you're doing work on the z4?

[StLMO]

Great news on the wheels. Excited to see how they look on the z. 👍

[KennyP]

What intake do you have on your car?... is it custom made?
And did you do coolant tank and vacuum canister relocation yourself? How complicated is that? Parts needed? Any drilling to fit coolant tank to driver side?

[proboner]

Originally Posted by KennyP

What intake do you have on your car?... is it custom made?
And did you do coolant tank and vacuum canister relocation yourself? How complicated is that? Parts needed? Any drilling to fit coolant tank to driver side?

Intake is custom, fabricated by the previous owner, as is the coolant tank and vacuum canister relocation. Unfortunately I have no insight into how any of that was done.

[KennyP]

Originally Posted by proboner

Intake is custom, fabricated by the previous owner, as is the coolant tank and vacuum canister relocation. Unfortunately I have no insight into how any of that was done.

Ok. looks like they went rather in depth... everything has been moved to make room for the air intakes. Even boost solenoids are now located on the bulkehead/firewall.

Anyway love this thread. Not many people take time to do such extensive writeups. Wish there were more threads like this.

[proboner]

Well the CF lip and sideskirt extensions came in this week. I ordered them from a company out of Taiwan on ebay for $700 total. They were wrapped up pretty well and received no damage during shipping.


After unwrapping and under further inspection, they appear to be fiberglass with a layer of cf epoxied into place. In the end I don't really care, but figured people would be interested.








Install of the sideskirt extensions was super easy and straight forward. There's a mounting hole on the rear of the skirt that aligns to a stock bolt and locates the rear of the extension. Then you simple need to select your location on the front and drill the rest of the mounting points.


The front was... not so easy. The center bar fits way too tight I ended up actually cracking one corner when installing.


I found using a heat gun did help, but it was still a pretty large pain in the ass, and it's only just mocked up.


Washed her up today to take a few pictures while I wait for the hardware to come in to complete the install. I'm going to take a couple weeks to decide how I like it, but as of now I'm pretty iffy on them. The Volks should be arriving in the middle of May, so once those go on I'll make the final decision. For now, here are a few shots in the current stage.

[proboner]

Got em fully installed and took a few more pics with the top down and not in direct sunlight. It's okay I guess... we'll see

[spyfish007]

I think it looks good. CF on a black car is always a challenge because you dont have the contrast to make it pop. The added lines provide extra detail and the CF is nice for those that notice.

[proboner]

Was looking at the to-do list in the garage yesterday and decided to tackle the "whats making that rattling noise?" line item. Jacked Mazikeen up on the passenger side and laid under there to try to find the source and think I've got it.

Appears the cats are starting to come apart, or something was accidentally dropped down into the piping where it connects to the downpipe. Either way, seems like this will need to come off for further inspection, in which case might as well get the LSD out of the way as well!