Stock height 325is dual-purpose shocks/springs + Koni questions

[Maybe Magpie]

Hi all,

I daily my 325is that was specced with sports suspension (Option 226/226A, not S704 as it's a post 9/87 car) and its primary usage is as a street car - my only thing with four wheels. While I mostly go easy on it aside from the occasional jaunt on a winding back road, in the future I'm hoping to try my hand at the occasional parking lot sanctioned autocross event or HPDE at my local-ish track to understand its limits (and my own!) better and have some fun. I live in an area with road quality that is extremely variable (glass smooth in some spots, surface of the moon in others has a lot of steep hills and potholes and speedbumps, etc). I have never scraped at stock IS ride height and personally I don't mind it as it's worth the tradeoff to me for extra ground clearance. I also don't want to rattle my teeth out or feel like driving it is a chore from NVH and keep it nice and livable, so given all that I've been hunting for options that aren't lowered further or harsh while still being a nice OEM+ upgrade when I do a suspension refresh in the future when the time comes - FCA balljoints, E30 M3 offset FCABs in OEM rubber, M3 endlink mount tab retrofit + endlinks, fresh front strut tower mount/bushings, fresh rear shock tower mounts/reinforcements are in my plans, maybe subframe reinforcement and front sway too.

With that in mind I wanted to have my ducks lined up ahead of time for springs and struts. I am currently on original 325is pink-dot sport springs so I'm a bit lower and stiffer than a regular stock 325i as it is by about an inch or so if I'm not mistaken. I believe the shocks in the strut housings right now were replaced at some point but are stock Boge sports option gas struts, if they're original they've held up well and still have life but if I do everything else I may as well do those too. I spoke to BMW group classic to confirm this and they confirmed I should have P/Ns #31301133438 and #33521091999 for the struts and P/Ns #31331130054 and #33539061134 for the springs, front and rear respectively.

All that said, from research it looks like that Koni yellow adjustables tuned to the mild end are quite pliant and pleasant for daily use when I'm dailying and are good for sportier uses when turned up in stiffness over the Bilstein + H&R combo I see a lot of people go for. I spoke to Koni and they say I should get 8641-1210Sport front struts and 802522Sport rears, and that the 1210s are shorter and stiffer damped so that it should be the one for with the IS springs. However, I found posts on here about how 1210s are for 4cyl late cars with the 51mm diameter struts and 1021s are for 6cyls and I'm not certain if 1210s would play nice with the heavier M20. Unfortunately that thread has no clear answers in the end and I've also seen other threads on here that say 1021s, other saying 1210s for M-technic sports suspension, and it seems 1210s are what the 318is use from another more recent thread, and the difference is about 20mm in housing length apparently which is not far off from how much lower a 325is with my options are below stock... Really I just want to ensure I don't blow anything out or have things batter on each other. Am I overthinking this?

From what I can tell there's other sport rear options aside from the 2522Sports, 80-2641Sport, and 80-2522SP1 as well as 8041-1186. I also asked Koni about the TC Kline 8041-1186TCK externally adjustable rears, as apparently the nonexternal rears are a bit of a pain in the ass to adjust. They said that those are for a mustang (apparently they share a rear strut spec and they fit those too) and for extremely lowered applications, I'm concerned about compatibility in terms of height and not sure if lowered mustang spec length is correct IS sport length or too short for that too. There were also some really old threads on here that said Bimmerworld sold a kit of top-adjustable Konis for all four corners (apparently during the 2005-2007 period?) but they don't appear to these days and I've had not much luck digging around with how Google's gotten so terrible lately.

Summarized: What strut/shock options am I best off with at stock 325is height, especially if I want external adjustments? Koni is preferable but I'm open to other options. Should I stick with my stock IS sports springs, or get fresh ones of the same P/N if I can find them for not stupid prices and do the same with the Boges? Is there an OEM equivalent of the same height or something very close in terms of height and rate that's a better pick when I don't really want to go any lower? Am I better off just saving up more money for a Ground Control kit? Does GC even make one that can be the same as stock 325is height/only a little lower than stock 325i? Bit stumped given all the conflicting information, especially given that most folks seem to lower their E30s while I don't intend to.

Attached is the blueprint for the front sports springs I have that BMW Group Classic helpfully sent me, both as tribute and in case it'd help anybody else in the future. If I'm reading it correctly (I'm not 100% sure) the overall length/OAL is 150.1 + 126.5 +12 + 12 mm, i.e. 300.6mm, i.e. 11.834 inches. 313mm if you count the bits at the end, 12.322 inches. Unfortunately they didn't seem to be able to find the blueprints for the rear sports spring, so that's all I've got in terms of hard numbers.

Thanks in advance.

[Maybe Magpie]

Oop, sorry for the double-post but the forums upload shrank the blueprint image beyond legibility for the front spring. Here it is in full resolution if anyone needs it (#31331130054).

[Panici]

Definitely stay away from Bilstein if you're looking for comfort. I have set of B8s on my E36 328i and have ordered a set of Koni Orange to replace them.

I have the H&R Sports and Bilstein Sports on my E30, and again the valving is way too harsh.
Have toyed with the idea of Koni Yellow Adjustable for it, as I frequent rough back roads with my E30 and value comfort.

My understanding was that the Koni Yellows were intended for a lowered ride height, and I would be concerned that they're too short for stock height.
A set of H&R Sport springs do not significantly lower the ride height, and I've never bottomed out my lower-then-stock 24v oil pan even on rough roads.


You mentioned bushings, but I just wanted to confirm your thoughts that even the softest Poly bushings will add NVH compared to rubber.

[moatilliatta]

Jstock rides better than H&R Oe's to sports W/ B8's. You have to go to a spec E30 GC setup till the start complementing each other.

Package deal is what you want. GC is a package deal, and should be able to set you up for what ride heights you want. You could probably go up +100 on spring rates and still be comfortable.

Set of IE bars will help, 16mm rear if your looking to build more power and want to put it down.

With your list of events your would like to accomplish, I would go up on the spring rates to make it enjoyable.

Id go with Sachs if you don't want to think about it, and want to keep it was close to stock as possible with a good ride.

[Maybe Magpie]

Definitely stay away from Bilstein if you're looking for comfort. I have set of B8s on my E36 328i and have ordered a set of Koni Orange to replace them.

I have the H&R Sports and Bilstein Sports on my E30, and again the valving is way too harsh.
Have toyed with the idea of Koni Yellow Adjustable for it, as I frequent rough back roads with my E30 and value comfort.

My understanding was that the Koni Yellows were intended for a lowered ride height, and I would be concerned that they're too short for stock height.
A set of H&R Sport springs do not significantly lower the ride height, and I've never bottomed out my lower-then-stock 24v oil pan even on rough roads.


You mentioned bushings, but I just wanted to confirm your thoughts that even the softest Poly bushings will add NVH compared to rubber.

Yup, I was considering the HD rubber OEM ones for stuff like motor mounts and transmission mounts next time those get done for a bit of extra stability for that stuff without introducing poly squeak/NVH, and thus my pick of of M3 OEM FCABs for the lollipops as they give additional caster and are slightly stiffer without being poly. I don't have a build thread or anything but the tl;dr for my approach to this car is very much OEM+, reinforce and improve where it makes sense to and is possible while not overdoing it and messing up what makes the car special. Aside from ground clearance another reason I want to stay stock height is that way I don't have to mess with additional suspension shit to deal with camber and toe (especially in the rear subframe). Saves some $ and effort.

Jstock rides better than H&R Oe's to sports W/ B8's. You have to go to a spec E30 GC setup till the start complementing each other.

Package deal is what you want. GC is a package deal, and should be able to set you up for what ride heights you want. You could probably go up +100 on spring rates and still be comfortable.

Set of IE bars will help, 16mm rear if your looking to build more power and want to put it down.

With your list of events your would like to accomplish, I would go up on the spring rates to make it enjoyable.

Id go with Sachs if you don't want to think about it, and want to keep it was close to stock as possible with a good ride.

Yeah, I'm not planning on B8s or B6s, from what I picked up the high pressure type of shocks are a lot gnarlier on anything but exemplary roads. I've been talking to Koni, TCK,and others to try and work out what's best here. I might just save up for GCs run high, but I doubt I'll be making much power - all I have tentatively in mind there after a manual swap someday is a 272 cam, injectors, a SSSquid chip, beefier rocker arms just for longevity's sake and so on. I considered turbo but decided against it and my M20 is in good enough shape it'd feel like a shame to junk it and 24-valve swap even if a nonvanos M50 with spicier cams calls to me. The odds of me making north of 200 crank aren't high, I'm into E30s due to personal ties and enjoying slow car fast analog giggle-induction so I probably won't need beefier sways.

If I can sort out a clear answer w/Koni and TCK about this I'll report back. Thanks, fellas.

[Maybe Magpie]

Good news and an update just for anyone in the future who might run into similar annoyances, and those who may still lack answers to similar questions previously asked in other threads!

BLUF summary: 1210s are more optimal for lowered cars due to droop (even just slightly, like stock IS) according to Koni, but TCK attests that both 1210s and 1021s work in with 51mm front strut diameter cars at stock height and can give good results, take your pick. Lowered go 1210 or shorter, 325i unlowered definitely go 1021, IS/M cars regardless of cylinder count either works at stock height.

To get more in-depth, I did a bunch of confirming with Koni and TC Kline, they sent me the following info:

We have confirmed that the 8641 1210Sport is the correct front strut for the factory OE Sport suspension (with 51mm OD strut housing) with one of our larger BMW specialty dealers, BimmerWorld. So you may want to just double check the OD of your factory housings. The shorter droop length of the 1210Sport does a better job of keeping a sport spring in place when the car is raised and the suspension droops. The 1021 has a longer extended length that works better with taller stock base suspension springs. The 1210 is the preferred choice for a stock E30 M3 and 318is/325es/325is due to the shorter factory spring.

Front
8641 1210Sport (OE Sport suspension)
Min L – 19.21”
Max L – 23.03”

8641 1021Sport (OE base suspension)
Min L – 19.09
Max L – 24.17”

Rear
80 2522Sport (OE base suspension) off car compress to adjust.
Min L – 15.39”
Max L – 23.98”

80 2641Sport (OE Sport suspension) off car compress to adjust.
Min L –15.51”
Max L – 22.83”

8041 1186Sport (Externally adjustable options (Mustang) TC Kline).
Min L – 15.08”
Max L – 22.24”

The Mustang [ed. note: 1186TCKs] rear shocks will work just fine.
On the front use the Koni sport inserts

[when asked if this still applies to stock height IS]

We have seen this application many times with good success.
You will like the results.

[when asked about 1021 vs 1210s]

We like the 1021 inserts from our experience, but Lee at Koni knows his stuff, so it’s your call.

So looks like the move (assuming you're not lowered) is front 1021s rear 2522s for 325i, 318i, etc, front 1210s and rear 2641s for 325is/318is/M3, or rear 1186TCKs if you want external adjustment on the back two as well (but those in specific require rear shock mounts that have a 12mm diameter hole for the shaft instead of stock 10mm, lots of companies sell them from a quick search, including TCK). When my suspension stuff is next up on the docket I'll probably be going with 1201s and 1186TCKs myself, I might keep my original sports springs or get fresh (or at least fresher used) ones of the same part number, or maybe GC coil conversion kits run at IS height if I've got extra money burning a hole in my pocket. That said, TC Kline also said that they've had good results with 1021s on M and IS cars that worked just fine and that it's a personal call, so I'd welcome anyone who has 1021s or 1210s at stock-ish ride heights chiming in with their own opinions and experience.

Hopefully anyone as puzzled and bewildered as I was at first finds this thread helpful in the future. I'll post another followup if and when my suspension refresh is completed, ideally later this year or early in the next! Sometimes it's worth playing email tag and car detective.

[Panici]

Excellent, thank you for the followup.
Gives me a path forward for my mildly lowered E30.