PSA: Finally, a fix for ride height that doesn't hurt the ride

[moroza]

For those who want a stiff sports-car feel, there've been some good options for springs. For the rest of us who value the well-tuned stock ride, we've been limited to spring choices that force a tradeoff of form with function, where the front either rides great but is comically high, or is a reasonable height but rides too firmly. In the 15 years I've had an E34, I've experienced at least nine different front springs in detail (and many more without paying as much attention):

• 535i stock - good ride, too tall
• 535i cut - awful ride, still too tall
• 530iT stock - good ride, way too tall
• M-Sport - good height, but significantly firmer
• Vogtland - too soft, too low, crashes over bumps
• H&R - Harsh & Rough
• E28 528e - slightly too tall, slightly firmer
• Bavauto - quite low and a bit too soft, not as bad as Vogtland
• Eibach - best of the group, comparable to M-Sport in ride and a bit lower
• More recently, I pulled the trigger on an experimental solution in which I now have enough confidence to declare a success.

There might be springs out there that are comparable to stock, even indistinguishable for some people's perception. Without an exact match of spring rate and its rate of change (and several parameters of damping), nothing will quite match the stock ride. This solution rides exactly stock, only lower, because it is stock, just modified in a way that affects height only, never rate. As far as I'm concerned, this is how they should've come from the factory.

The solution: The OE springs can be compressed to a lower free length, then heat-treated to temper them and make them last. This is a job for a specialist spring shop, not a DIY task.

The number one question is longevity. Talking to about 20 sources - some manufacturers, mostly shops - I gathered that 1. it can be done on some alloys and not others, 2. the alloy that can't be re-tempered started being used in the early 90's, so a 1994 car produced since 1987 is ambiguous, and 3. if they did fail, it would be extreme sag within a week or two, not snapping or far in the future. In any case, stock shocks bottom out ~15mm before the coils pack up, not including bumpstops. If they did fail, it'd be riding on the bumpstops - certainly a problem, but not an immobilizing one.

Well, it's been ten weeks and 2500 miles, 400 of which involved a highway drive at 4550lb GVW, and they're fine. Static ride height hasn't budged a millimeter, and was bang-on perfect to begin with*. Not a hint of bottoming out, with fairly soft shocks (Sachs). Evidently, our springs are the older alloy.

UPDATE: it's been over six months. Still doing fine.

UPDATE 2: it's been over a year, including weight gain, major cargo schlepping, SLS retrofit on the rear suspension, and now bigger tires. Still doing great.

UPDATE 3: it's been over a year and a half, plenty of use, and now I had my rears done as well.

The motorcycle spring shop that did mine were instructed to move only the middle coils, for a total free length reduction of 40mm. I specified this so that the end coils keep the same angle where they meet the spring pads. As the suspension compresses, the end coils progressively wind onto into the pads, reducing active coil count and raising the spring rate. This is a subtlety of spring design that is overlooked in most discussions. Failure to account for this is the reason cut springs ride so poorly. Getting it right is a multi-variable fine art, the kind of which is BMW's forte and some of what's behind the magic of their suspension tuning. The part of the spring that's responsible for that magic is unaffected by this modification, only the static height is changed.

I have my cake and I'm eating it too. And it comes with icing: total cost for the pair about $100 including shipping both ways.

*My cake did however go a little stale. I specified the height based on my car with an automatic, but installed them only during the manual swap, which lost a bit of weight. These photos are with 215/60R16 tires, SLS rear suspension, and after soundproofing, which has added at least ~55kg/120lb over the front axle. I'm using V3 strut mounts with E9x upper perches, which lower ~7mm, and E32 upper spring pads, which raise ~6mm. The front rides really well, still working on the rear.

[echo6sierra]

I've got the H&R springs in my 90 535i. I had to laugh at how accurate your description is. I'll be getting Eibach springs this year.

Sent from my SM-G892U using Tapatalk

[danespann]

Love this. Never thought about having the stock springs shortened without cutting. And your description of the lowering springs available is painfully accurate.

7k 6k on my coilovers here and I contemplate going softer very often. Stock 535 spring rates convert to something like 2K.

[eddycooper]

Looks like 'K' may be kg/mm?

https://coiloverdepot.com/pages/spri...suspension-102

[shogun]

Gentlemen, no fighting please. Be polite, even when having different opinions.

[wannaBMthree]

Awesome! Think this would work with Bilstein HD's?

[moroza]

It would work, but same spring rate with increased damping rate might not ride quite right. Bilstein Touring would be a better (closer to stock, anyway) match.

[TiagE39]

Strongly considering this...can finally have the front not look like a Lada without the rear too low like it does with lwring springs.

[Bob Duato]

Ugh, thanks for making rethink my whole life, at least as it pertains to the suspension setups I've been considering for weeks.

A couple questions for you:

How did you determine that your springs were an appropriate alloy, or did the shop have to do that?

Did you measure the compressed spring difference on the car? I'm not up on my spring physics, so maybe it's equal, but how did the 44mm reduction in free length translate once on the car?

Having realized the omission of weight difference in manual vs auto, would you have instead opted for something other than 44mm?

Thanks, and props for the ingenuity

[moroza]

How did you determine that your springs were an appropriate alloy, or did the shop have to do that?

The determination was made solely on the basis that if they were the wrong alloy, they'd've certainly failed by now. Could've taken a sample to a metallurgical lab for about $150 instead, but I decided to prepare for failure and take the risk.

Did you measure the compressed spring difference on the car? I'm not up on my spring physics, so maybe it's equal, but how did the 44mm reduction in free length translate once on the car?

It's equal. Other factors held constant, and assuming there's sufficient coil stack height remaining, a 44mm reduction in free length means a 44mm reduction in loaded length, given the same load. The 44mm reduction is relative to 530iT springs on a 525iT, which sit ~20mm higher than 525iT springs. My ride is therefore ~24mm lower than stock.

Some numbers...
Factory-specified ride height is 588mm between the bottom of a 15" stock rim and the front wheel opening directly above. I call this distance "rim gap". Stock 530iT coils on my 525iTA sat at 605mm. Now a 525iTM, with modified 530iT coils it sits at 565mm. I'd like a bit lower, 560mm. For reference, Vogtlands on a 525iM (close enough to a 525iTM) sit at 551mm, and on a 530iTA at 529mm. These numbers can vary by ~3-4mm depending on what exactly is in the car and where. For example, a full tank of fuel raises the front by about 3mm.

These springs appear to be made by wrapping layers of steel into a sort of rope, then the rope shaped into coils. I surmise this allows for fine control of wire diameter, which is the only difference between springs of a particular series. All E34 Touring front springs appear to be a single series; all have 6.5 coils, 385mm free length, and coil diameter ~144mm at the base and ~153 in the middle coils. 525iT wire diameter measures 13.2mm, 530iT 13.5mm. E34 sedan non-sport front springs seem to be in two other series, one with 7 coils and one with 6.5, otherwise similar dimensions. Rears follow a similar pattern with different dimensions.

Having realized the omission of weight difference in manual vs auto, would you have instead opted for something other than 44mm?

Thanks, and props for the ingenuity

Yes, I'd've had them compress the softer 525iT coils (by 33mm) instead, otherwise these by 49mm.

[Bob Duato]

Ah, I see. I was thinking 44mm is a helluva drop, but that makes sense now. Thanks for that breadth of information.

So basically it comes down to paying for a test or going for broke. Then just measuring the desired difference in ride height and having the middle coils "compress tempered" by that difference.

[prash]

TL;DR. Which H&R springs too harsh. They have OE Sport springs which don't lower the car enough, then Sport springs and then Super Sport and race.

http://www.hrsprings.com/products/detail/springs

I have the Sport springs and they are great. I had to replace all four corners and my Koni's recently after one spring cracked but after 25 years and amount of driving I do that's fine.

[tymhm]

Great list and insights, as it comes at a time I'm shopping for lowering suspension for my 530i Touring. I'm leaning towards Eibach, however I came across some mentions of Lowtec springs and struts but haven't seen to much mention of them. The price point works nicely for my budget, however I don't want to sacrifice quality for price, as I'd rather buy once.

[moroza]

Bumping with an update. Front springs doing fine, and now I had the rears compressed as well. The rears have tighter coil spacing and can't be compressed as far. I chose 735iL SLS springs partly because they're already the softest/lowest available, and partly because they have one of the lowest coil counts of compatible springs, with the most room for further squishing. Even so, the shop was only able to reduce free length by 25mm. For most cars, that would be more than enough, but SLS complicates matters. I'd still like the rear about 15mm lower, but at this point I'm going to say "good enough". The ride, in any case, is much better than good enough, and with SLS, I don't have to worry about cargo.

E32 springs require E32 upper mounts and lower perches. They otherwise fit and work just fine in an E34.

Some numbers: OE specification is 525mm between the bottom of a 15" rim and the lip of the rear wheel well above it. Most E34 that I've measured sit ~530mm empty. SLS unloads the rear suspension even at minimum pressure, raising it by roughly 30mm. 510mm looks and works well, and was my target. I have ~5mm of rubber spacers between the strut mount and the body. With the 735 springs, the spacers, about 100kg in the rear, and SLS depressurized, ride height was about 493mm. SLS filled and bled, I got 523mm. At minimum pressure, damping is too low, so I raised it another 5mm for 528mm ride height, perfect damping, and an excellent ride.

Total cost of this modification: about $280 including four rounds of shipping.

[circuit.heart]

How close do you get to bottoming out? Are your roads just that much better than ours? The factory BMW springs really are soft, when I tried to lower my old E34T without increasing rate it would blow right through the bump stops a few times per trip.

[moroza]

Nowhere near it; the car has never bottomed out with this suspension. Our roads are a bit better than CA on average, but I've driven it to the Bay Area a few times (with as much as 900lb of cargo) and my home road is 2+ miles of steep and iffily-maintained forest service road. Note that I have SLS, which makes the spring rate highly progressive on two scales of time delta: greater than ~10 seconds (more cargo -> regulating valve increases hydraulic pressure) and less than a second (hit a bump -> half a liter of nitrogen per side being compressed increases hydraulic pressure, and the force/displacement curve is a lot, er, curvier than with coils alone).

[m60power]

Excellent update, and the ride height looks really good to me! Glad to hear you found a nice balance between ride height and SLS fluid pressure at the struts / overall spring rate. That is a good point you make about the highly progressive spring rate in the dynamic situation of small time delta displacements of the rear strut / spring.

[peanukeeyes]

Hi, I’ve been lurking this thread lately as it’s finally given me some hope of resolving that lifted front end on my 525iT. I started calling around for a shop that would do this compress and temper method but so far no dice —Nobody wants the liability. Is there a way I could get in touch with the shop you had this done and send them a set of front OE springs to shorten?

[moroza]

Cannon Racecraft. Talk to Tony. They'll also make custom coils on request (~$360/pair last I checked).

I'll take this opportunity to picwhore, and update on the stuff you can't see. I've since revised the SLS modules for increased damping at baseline pressure, and also lengthened my lower spring perches by 20mm to drop the rear by that amount. I've since gone back to the 16" rims, but don't have clean photos (I live two miles from pavement; keeping the car clean all the time is a fool's errand).

[peanukeeyes]

Cannon Racecraft. Talk to Tony. They'll also make custom coils on request (~$360/pair last I checked).

Thank you so much! Car looks great. I’m currently getting mine sorted out in more necessary ways than stance but this mod is high on my list as soon as I get all the leaks,etc fixed. Thanks again! I’ll PM you before I call Tony and update this thread once I’ve got the springs in.
DCDCB8AC-54A4-4D01-88F5-D1CAF0656093.jpg16EA56CF-57A3-410F-8F16-7C41FDD02319.jpgF45C6FCE-3E30-4895-B292-0D935C26CE5D.jpg

[moroza]

Yep, front suspension by Lada on these. Yours makes it look like the front offset is too low. Is that just an illusion?

[peanukeeyes]

Yep, front suspension by Lada on these. Yours makes it look like the front offset is too low. Is that just an illusion?

I think it’s just an illusion? They seem to sit more flush to the fenders in front and tucked in the rear though. I’m thinking of getting some 10mm spacers for the rear to help make it look less of a reverse stagger. 9A952A72-E858-4B12-9487-2C355904AB64.jpg

[moroza]

Or, for a lot more work and a cleaner result, you could switch the trailing arm assemblies for E32, as I did, gaining 7mm per rear corner and more brake heat capacity

Looking for a ZF 5-speed? How about a six-speed? See here and here.

[BleedsBlue]

moroza, that Touring is sitting so proper. Love it.