New 2009 2010 BMW Z4 - ZPOST - View Single Post

proboner · 11-09-2020, 10:22 AM

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.

11-09-2020, 10:22 AM	#3
proboner Private First Class 67 Rep 198 Posts Drives: 2003 Z4 3.0 6-speed Join Date: Feb 2017 Location: Mountain View, CA iTrader: (0)	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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