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      10-15-2020, 12:57 AM   #1
Ichiro
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ST XA Coilover review

Hi Zpost peeps,

I've finally lowered my Z after 7 years of ownership. I'm documenting my experience in this thread and maybe it can be of help to others considering the same.

Disclaimer: I'm no auto journalist, and I lack motorsport experience (bar a few track events that I went to for fun). So take my personal review with a large dose of salt!!!

My Car: 2013 E89 28i Auto (w MSport pack but not adaptive)
Wheels and tires:
Front - 20x8.5 +32ET | 245/30 R20
Rear - 20x10 +45ET | 285/25 R20

When deciding to lower the car I was researching the following products: KW V1, Vogtland, Bilstein B12, ST X and ST XA. I wanted to lower the car ever so slightly, and improve the handling as I wasn't a fan of the harsh and floaty M Sport suspension. The MSport suspension was fine when I was getting used to the car in the early days of ownership and didn't really know any better. But as the years progressed, I found it overly harsh and unsettled on bumpy corners of any type. I ditched the run flats and still had complaints with the suspension, so next up was to replace the springs and shocks to make it better.

On a side-note, my wife has a 3rd gen Mini Cooper S and I love the way it handles. So in my head, I wanted a smoother ride but also reduce body roll and float to make the Z a bit more like the Mini.

I settled on the ST XA set as they're manufactured by KW and similar to the V2 set except the ST XA are galvanised steel shock bodies as compared to stainless steel from KW. I'm ok with that as I live in Sydney where we don't have snowy winters (best city ever ). The ST XA reviews that I found on the net seemed to hint towards a more composed ride and that's what really sealed the deal in my mind. I think this is in part due its progressive springs vs linear springs used by other brands. The other bonus for me being the XA coilovers have rebound adjustment so I can at least fine tune it to be softer if needed.

Installation:
I tried to install these suckers myself (3 times). I started with the rear and removed the shocks easily but then I really struggled to even remove one spring. My thanks to jeebus87 for his guidance but I just couldn't do it myself. So off to an indy went the Z and now she's back.

Ride:
During the first ride it felt very stiff and almost bouncy on the rebound setting of 12 clicks from the left for all shocks (front and back). This is the ST factory setting. I wasn't too impressed with this but knew that I'd have to adjust it according to my preferences. So I played around with it for the past week and I've found a happy medium as follows:

Settings:
Front: 7 clicks from the left (from softest)
Rear: 8 clicks from the left (from softest)

With this setting, there isn't much body roll (that I can perceive), there's hardly any body pitch (the back and forth motion on take off). The ride is firm, but absorbing and not floaty. It handles bumps and irregularities on corners very well now and the car is more fun to steer in to tight corners. I have more confidence in the car now and it feels more athletic. I've put about 700kms (430 miles) on the new setup and it really shines on twisty back roads where I can feel the car come alive and respond much better to my inputs and really stick to the ground. On normal roads its slightly firmer than before but more compliant. I tried 1 click from the softest setting all around and this was very comfortable - more than the stock M Sport suspension.

Fitment and quality:
These struts are larger in size than Megan Racing, HSD, KSport, BC Racing and some others. It's one of the reasons I chose them thinking the longer shock would equate to more travel and hence a comfortable ride. The product looks well built and seems to be heavier than the OEM units they're replacing. Fitment is perfect and adjustability is easy except for adjusting the rear coil sleeves. This is more due to the E89 rear subframe/body area being tight to work with.

There have been no metal on metal noises so far except for a very slight shunting noise from the rear. I had the shop investigate this noise and its not coming from the coilovers but rather the rear drivetrain area (passenger side). It happens when I accelerate and decelerate suddenly (with force). Time will tell if it worsens and may require replacement of any bushings.

Alignment settings:
Front Left
Toe +0.9
Camber -0.4

Front Right
Toe +0.9
Camber -0.4

Rear Left
Toe 0.0
Camber -1.5

Rear Right
Toe -0.3
Camber -2.4

With all that said, I'm still getting used to it and will post an update after I've had a chance to live with it for a while and take it on some more spirited runs where it really shines. Thanks for reading so far and here are some phone pics to go along with my review.

STXA coilover set


Installed on the car




Installed on the car under load


Before


After



Last edited by Ichiro; 10-22-2020 at 09:29 AM..
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      10-15-2020, 11:10 AM   #2
proboner
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Thanks for the writeup, excited to receive mine soon!
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      11-09-2020, 11:22 AM   #3
proboner
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Just to add onto this thread, to provide more feedback to the community.

Car:
  • 2011 35i
  • stock adaptive (but not m-sport) suspension
  • 18's with 245/40/18 front and 275/35/18 rear

Goals (in order of importance)
  • Lowering- stock height was an eye sore
  • Comfort- had to be GF approved and not make me feel like I was destroying the car on large cracks in the highway
  • Handling- stock stuff rode swells like a boat

Started off buying H&R springs to run with stock adaptive suspension. It accomplished point 1 on my list, but definitely not 2 and 3. In fact my gf refused to ride in the Z4 due to getting car sick. This caused me to quickly look for a more thoughtful solution to my suspension woes.

Reading threads in the community, KW v3's seemed to be the only setup that had been run extensively. They have relatively good reviews overall, but a $2k+ pricetag and the fact that they were overkill for my goals made me resistant. After a bit more research I happened across ST. As Ichiro pointed out above, they're manufactured by KW and are basically the same setup, just made with different material. The ST XA is equivalent to the KW v2, which for some reason isn't made for the Z4, but in my mind would be the perfect fit for my usage.

I received and installed the ST XAs on my 35i last week. In terms of the goals I was trying to achieve, I'd say I'm pretty close to where I was with the H&R springs, at least with the very few miles I've logged since install. I started off with the rebound set right in the middle at 8 clicks both front and rear. To explain, there are 16 clicks of total adjustment, full left is softest and full right is stiffest. At eight clicks I was actually surprised with how stiff it felt, so I moved down to 2 clicks from softest and just now took it out for a drive. It is still very stiff.

I believe this has to do with poor front strut design. Generally in coil over design, the strut body is shortened to move the shock and spring perch down compared to the stock setup. This allows you to lower the car several inches while continuing to use the same length spring and shock and keep the same range of motion in the suspension. This is optimal.

Instead, ST (and assumingly KW) basically kept the stock strut body and shock length (maybe 1/2" lower), but allowed the spring perch to be adjusted well below the stock location.




This gives you the ability to lower the car, but it reduces available shock travel and forces the shock out of it's optimal operating range. I'm not sure what they were thinking with this one. I mean I'm no engineer, but this seems like a pretty obvious oversight.

I've realistically only logged about 20 miles on the setup, but I'm thus far not impressed with comfort, which is supposed to be one of KW's big selling points... handling well while remaining comfortable. Perhaps I'll have to play with the rebound a bit more and see if I can find something I like, but as of now I'm pretty sure the GF is going to be pissed.

In terms of lowering, the front at the lowest setting is a bit lower than useful, so it's nice to have a full range of adjustability. The rear however, sits higher than stock suspension with H&R lowering springs, when at it's lowest position in the rear. This could certainly be fixed by removing the adjustment sleeve, or the rubber gaskets, or both, but that kind of defeats the purpose doesnt it? Think removing a coil from the rear spring would be beneficial for height adjustability


The middle coils just bind anyway. I dunno, it really doesn't seem like a super well thought out kit.

I've yet to do any type of driving to comment on handling, so I'll leave that alone for now.
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      11-11-2020, 05:38 AM   #4
KennyP
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KW V3 on stock settings was bit too stiff for me aswell. I have set my rebound 2 clicks softer from stock both front and rear if i remember correctly. At first i played around with bump, ended up softening that both front and rear and then went on to softening rebound.
On stock settings my car was way too bouncy, especially the front, dash started to make noises etc. on softer settings its much better. Ride height doesnt really seem to matter... mine is pretty low and still ok to drive.
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      11-11-2020, 12:41 PM   #5
proboner
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Quote:
Originally Posted by KennyP View Post
KW V3 on stock settings was bit too stiff for me aswell. I have set my rebound 2 clicks softer from stock both front and rear if i remember correctly. At first i played around with bump, ended up softening that both front and rear and then went on to softening rebound.
On stock settings my car was way too bouncy, especially the front, dash started to make noises etc. on softer settings its much better. Ride height doesnt really seem to matter... mine is pretty low and still ok to drive.
Hmm thats an interesting thought. Maybe I'll increase my ride height (just for experimentation sake) and see if it improves ride quality at all.
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