Advice needed: E36 Convertible & Hardtop Spring Rates (KW v2, sagging rear)

[tranced]

Hi all,
Currently have a 325i Convertible with hard top installed. Car sits on square 17x8.5 DS2's, Toyo Proxes A/S, w/KW v2 coilovers front & rear. Turner thick sway bars front & rear.
The problem is the rear springs are sagging and have been rubbing the outside of the fender arches on and off, and less often if at all without passengers. I will typically not have passengers.
The rear perch adjusters are beyond the maximum height, so I cannot raise further. I found that KW sells coil spacers which I could use to raise the rear a bit, but this may result in coil bind so I'm looking to replace the rear springs altogether.

The car is street only. Has less than a pinky finger of wheel gap (if that) at the front, and tucking in the rear.
I like the handling as is and don't find it too jarring or stiff. The only comparison I have is to a stock suspension.

So far I have found that the front KW v2 spring rate is 400lb/in, and that common accepted front/rear rate split is 150lb. This would have me purchasing 550lb rear.

My goal is to raise the overall ride height to equal or less than stock so that I have a decent wheel gap and suspension travel, which may mean maxing out the KW front ride height, however less than stock that may be.

I have been looking at swift rear springs, tc kline rear spring perches, and vorshlag rear spring platforms to complete the replacement.
Considering the car has the added weight of being a convertible w/hard top, would a 550lb/in 6" long rear spring allow the ride height I am looking for while not disturbing the handling balance from the KW v2 base?

Appreciate any advice. If you have alternate suggestions to the direction I'm in I'd like to hear as well.

Picture of rear for posterity:
IMG_8442_web.jpg

[E36M3LX]

do you know how tall your rear springs are now?

i would call or email feal suspension. they may have the answers you need and they definitely have the parts you need.

[circuit.heart]

Get the specs from KW about what the rear spring rate is. KW V2's sometimes slam the rear ride height low even brand new, it might not actually be a sagging problem. Whatever your original rear rate is, you can bump that up to about 50-100lbs/in over and usually the damper won't care too much (you can adjust the rebound damping up a bit to balance the stiffer spring). *Normally* I would say that a 6" 550lb spring should be about right for stock height goals.

Inserting a spacer between the spring and the lower perch (on the arm) is also an option, you'll just raise ride height without changing spring rate. I agree that in-coil spacers are not the play here. But if the spring is actually collapsing, this won't work long term - you do need to know if the spring is working as intended (intention is wrong) or if the spring is dead.

[RBNetEngr]

Other than the KW Clubsport set, all KW and ST coilover systems for the E36 use the same spring rates, which are 400 lb/in linear spring in front (70nm/mm) and 479 lb/in progressive rate barrel shaped spring in the rear. The rear spring is identified as #2003.

https://www.kwsuspensions.com/extras...31_1222-17.pdf

The Clubsport uses a rear spring that I believe is labeled #2018 and is a 525 lb/in progressive spring.

Could the rear springs be installed incorrectly? I have an ST coilover kit on my E36 M3 and was able to set the rear ride height to stock ride height, and the perch adjuster was not at its limit.

I know it’s tight, but can you post some photos of the springs? And what process did you use to set the rear ride height?

[tranced]

Other than the KW Clubsport set, all KW and ST coilover systems for the E36 use the same spring rates, which are 400 lb/in linear spring in front (70nm/mm) and 479 lb/in progressive rate barrel shaped spring in the rear. The rear spring is identified as #2003.

https://www.kwsuspensions.com/extras...31_1222-17.pdf

The Clubsport uses a rear spring that I believe is labeled #2018 and is a 525 lb/in progressive spring.

Could the rear springs be installed incorrectly? I have an ST coilover kit on my E36 M3 and was able to set the rear ride height to stock ride height, and the perch adjuster was not at its limit.

I know it’s tight, but can you post some photos of the springs? And what process did you use to set the rear ride height?

Thanks RBNetEngr, I found that same doc, but couldn't find any info about the rear spring rate. That helps a lot!
I had the rear wheels off two weeks ago during a tire rotation, and didn't see anything out of the ordinary. There was a line of rust on each spring, however, on the horizontal faces along the coils.
I'll take pictures next time I have the car up.
I purchased the car with this set up, and the rear height was as described. PO had a shop do the adjustment & alignment. From pictures of the car earlier in its life (w/KWs installed), the rear looked slightly higher, which indicates the springs are wearing. Note again that the perch is beyond its max adjustment.

@circuit.heart's observation about KW slamming the rear height seems to follow experiences from Audi users: (https://www.audizine.com/forum/showt...ag-in-the-rear)
And thanks, circuit.heart. I am still aiming in the direction of 550lb/in 6" springs.

[RBNetEngr]

This is with the ST XTA Plus 3 coilovers, which use the same springs that your KW V2 has

[tranced]

This is with the ST XTA Plus 3 coilovers, which use the same springs that your KW V2 has

I wonder what's causing the perceived difference in height between that and mine? Seems like that has a taller tire sidewall, and less wheel spacer (if any)?
My rears have 5" of clearance from the ground to the side skirts. Could it be my rear shocks are going, or is it just the weight difference?

[RBNetEngr]

Right now it has 225/45R17 tires, so the sidewalls are a little taller than the 235/40R17s that the car came with.

Front and rear have 3mm spacers. Front needed them to provide sufficient clearance between the tires and front springs. The rears have them to just widen the track a little.

So, when you said you have the rear height adjuster maxed out, does that mean the ’A’ Measurement shown in this diagram is 42mm? For mine, I started at 43mm (the ST installation instructions list 43mm as maximum) and it ended up being higher than I wanted, so I lowered it to get the ride height I have now. I don’t have that measurement recorded.

[tranced]

Right now it has 225/45R17 tires, so the sidewalls are a little taller than the 235/40R17s that the car came with.

Front and rear have 3mm spacers. Front needed them to provide sufficient clearance between the tires and front springs. The rears have them to just widen the track a little.

So, when you said you have the rear height adjuster maxed out, does that mean the ’A’ Measurement shown in this diagram is 42mm? For mine, I started at 43mm (the ST installation instructions list 43mm as maximum) and it ended up being higher than I wanted, so I lowered it to get the ride height I have now. I don’t have that measurement recorded.

For me, PO installed 15mm hub-centric spacers on all sides. Since I don't seem to be bottoming out, I'm wondering if I can go to a narrow spacer so they would tuck rather than rub the fender flares, while still clearing the wheels from rubbing the coils. Rear camber is currently at -2.0 and I don't want to go further.

Yes, dimension A is beyond 42mm (half of the threads of the collar are not engaged on the perch).
If KW v2 come from factory as defaulting toward the low side of ride height, and assuming they're engineered for coupe/sedan (and not convertible specific), then I'm left to think they are just too low of a spring rate for my application. I would think any harder on the rear and the KW would not be balanced (handling or NVH-wise) per their preferences for the majority (sedan/coupe) of their audience.

[RBNetEngr]

For me, PO installed 15mm hub-centric spacers on all sides. Since I don't seem to be bottoming out, I'm wondering if I can go to a narrow spacer so they would tuck rather than rub the fender flares, while still clearing the wheels from rubbing the coils. Rear camber is currently at -2.0 and I don't want to go further.

Yes, dimension A is beyond 42mm (half of the threads of the collar are not engaged on the perch).
If KW v2 come from factory as defaulting toward the low side of ride height, and assuming they're engineered for coupe/sedan (and not convertible specific), then I'm left to think they are just too low of a spring rate for my application. I would think any harder on the rear and the KW would not be balanced (handling or NVH-wise) per their preferences for the majority (sedan/coupe) of their audience.

If you have stock size wheels/tires on it, there is no need for 15mm spacers in the rear. That was probably done purely for a cosmetic reason, or because the PO wanted the rear track width to match the front. I only put 3mm spacers on the rear because I wanted to move the rear wheels out a little for appearance. I didn’t need rear spacers for any clearance reasons.

In the front, put the car on a jack, remove a front wheel, remove the spacer and then reinstall the wheel. How much clearance is there between the tire sidewall and the coilover spring? KW recommends a minimum of 4mm. Mine had about 2mm, so I added a 3mm spacer and now have 5mm of clearance.

For track driving I have wider wheels and tires (245/40R17 at all four corners, mounted to IFG 17x8” wheels) so a 5mm front spacer will add the clearance I need. The 17x8” wheels I use with the track tires have 40mm offset.

With stock wheels/tires, or with stock sized wheels having the same offset as stock (41mm) there should be no need for 15mm spacers at any wheel.

[tranced]

Update: RBNetEngr, I didn't have a chance to test the clearance without spacers, but I had the rear tires replaced and took some pictures of the spring situation. You can see how far the perch is (beyond the threads).
With new tires/full tread depth, the rear rubbed when going over road-to-sidewalk ramps typical of new york city. I will consider purchasing thinner spacers as it seems tucking in the rear is normal for coilover setups, but I still would rather have more ride height.

IMG_8497.jpg
IMG_8501.jpg

[RBNetEngr]

The next time you have it raised, and with a wheel off, see if you can find the number on the spring. I’m wondering if you have something other than the ‘2003’ spring.

[Mless5]

It seems to me that you are missing upper spring pad.

[RBNetEngr]

It seems to me that you are missing upper spring pad.

No, KW instructions say to eliminate the upper spring pad. The height adjuster goes directly against the chassis.

[tranced]

@rbnetengr the springs were part number 2003.

Since my last post I did some research and found 62mm swift springs from springrates.com in 5.5" (140mm) and 9kg (~500 lb/in).
This would allow me to re-use the KW adjustable perch. I also ordered Rogue Engineering 2.5" spring alignment cones/plates to serve as the new lower spring mount. They were an exact fit for the 62mm ID springs. Although they are stated for installation on the spring top, I found they would fit on the control arm hole, without the factory rubber pad. It's a tight fit, but with the weight of the car over it, the cone pressed into place. With the shock attached and perch adjusted, droop was not enough for the spring to fall out. It all went in fairly simply.

In my rush to finish the installation, I mistakenly thought the adjustable rear sway bar links had to be longer to maintain zero preload. In hindsight, the links should be shorter with a taller ride height. as the ride height increases, the control arm droops downward, bringing it closer to the sway bar mounting point on the frame.

The caveat to all this: when using the KW perch and rogue cone, 5.5" springs are not long enough on my setup. I basically ended up with the same ride height in the rear.