By on March 1, 2010

James writes:

I have a 1995 BMW E34 530i, and I’m looking into getting it lowered. At first I thought this was a simple affair, that I just needed lowering springs. But some people are telling me that I can’t just put new lowered springs without buying new shocks that are designed to handle these lowered springs, for fear that I’ll wear my tyres out and possibly other components. I thought this might be true for going super-super-low, but these springs will only lower my car 1.5″ at most (Bavauto springs 1.0″-1.5″), if I’m lucky. Is this just my mechanic trying to sell some extra parts, or do I really need new lowering shockers, even for going just a little lower?

Sajeev answers:

Indeed, your mechanic might have a valid reason. Or he might be misinformed. Very few people aside from suspension engineers and super geeks on message boards know the real deal. So I recommend doing two things: ask the manufacturer of said lowering springs (Bavarian Autosport) and jump on a popular BMW forum and solicit help from some of the senior members who tune, tweak and share their knowledge on a regular basis. Both will help you decide if new dampers are in your future.

But shock technology isn’t a black art, it’s common sense: suspension dampers (shocks or struts) operate in a range of motion, just like your arms or legs.  They work far more precisely/efficiently in a narrower window of motion: it’s the sweet spot of the shock.  It’s like a sandwich: sometimes a bite has with far more bread than anything else. Yuck. But sometimes you get a good taste of everything smack dab in the middle. You always want the sweet spot in dampers, it’s what lowers impact harshness on small bumps and controls float on undulating roads.

Back to lowering your BMW: lowering springs can force the damper to operate out of its factory-authorized sweet spot, and do it enough times to annoy you.  But it’s more likely when you go over 1 inch worth of drop. On a BMW, I still suspect a 1.5 inch drop won’t make a difference for many years to come if–and it’s a BIG if–your dampeners are relatively new and you live somewhere with smooth roads.  If you don’t know the dampers’ age, replace them now. No excuses!

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26 Comments on “Piston Slap: Finding The Sweet Spot...”


  • avatar
    criminalenterprise

    You go lower properly as a natural result of a properly sporty suspension. Suspensions don’t get properly sportier unless you replace the dampers.

    You save so much money by hanging onto a fantastic 15 year-old car, why cut corners on the (relatively) minor extravagances?

  • avatar
    crash sled

    The problem is, if you bite into a BMW sandwich, it’ll taste like knackwurst. Yech. Go find yourself a ’63 Chevy, and lower that bad boy. Grilled steak and roasted potatoes, baby.

  • avatar
    BMWfan

    Are you really sure you want to lower your car? If it used primarily for track time, then I say go for it. If use use it only on the street, You might want to consider the implications. Scraping your underside on every speed bump, and firming up an already firm suspension are recipes for unhappiness. Plus, you will never get your money back for the mod, and you will severely limit your resale pool. Modded BMW’s are usually unsellable BMW’s. If you really still want to do it, go to the the 5 series forum at Bimmerfest.com, and learn how to do it right. Good luck!

  • avatar
    Arkay

    I had the exact car: a ’95 530i with a 5-speed manual transmission no less, and I had the car ‘massaged’.

    The suspension used a matched kit (can’t remember who sold it) of Bilstein dampers and lowering springs by Eibach, about 1-1 1/4″ only I think, but it made a world of difference on my day to day drive in terms of steering response and feel without sacrificing the ride comfort…much. I also installed a set of beefier sway bars, again a kit that was matched to the dampers and springs.

    The E34 to me remains one of the quintessential BMWs, I wish back then when I was much younger I could have afforded the 540i M Sport that came with the manual gearbox – that was when I lived in Toronto and BMW Canada made a limited run of those cars basically with the bits from the 3.8 litre E34 M5s from Europe matched to the 540i running gear. Great car…

    • 0 avatar
      Bimmer

      BMW made only 32 ///M540i in 1995. Basically an ///M5 with a motor from 540i made specially for Canada. All had a numbered plaque on the central console. Car had ‘floating’ front brake discs with 18-inch M parallel spoke wheels – 8J x 18 at the front and 9J x 18
      at the rear, with 245/40ZR 18 tyres. LSD (limited slip differential) was standard and ASC+T traction control was an option. Interior featured M Sport seats in M cloth with Amaretta suede bolsters (leather was an option) and had carbon fiber dash trim. Also rear head rests were standard. Like all of Canadian E34s, ///M540i had headlight washers and heated front seats. Unlike the US-model 540i Sport that come only in standard 540i colors (also available for ///M540i), the Canadian ///M540i could be ordered in ///M5 only colors of Daytona Violet and Avus Blue. I’ve seen two or three of this cars in person. Last siting about 1.5 years ago in Oakville, also saw there an Alpina B7 in Alpina Blue.

      America got totally different car – 540i Sport with a choice of 6-speed Getrag unit or 5-speed auto by ZF. It had Adaptive M suspension with the Nurburgring package, Servotronic M steering and M system II wheels with 235/45 ZR17 tyres. Car had M Technic bodykit, but was same color as a car, rather then contrasting color as Euro ///M5 had.

  • avatar
    cdotson

    Sweet spot on a shock? Not exactly. They do have a range of motion, and by lowering your static ride height you offset the range of motion in the lowered direction. You need to determine if the static offset of lowering allows the shock position at full jounce to crash.

    Lowered dampers have a shorter rod inside the shock to prevent the rod from crashing into the end of the tube at full suspension jounce. Some may even have internal jounce and/or rebound bumpers to soften the blow of maximum compression/extension.

    Viscous dampers are position independent. They respond to inputs by varying damping force depending on the relative speed/acceleration between the rod and the cylinder. Range of motion is the positions of the valve body on the end of the rod between the top and bottom of the cylinder without catastrophic contact, through which it will respond with the same force for the same input velocities.

    Lowering causes a shift of the suspension mounting points that change the effective ratio of the spring and damper. A change in damper valving may be desired if the motion ratio changes dramatically due to the lowering (i.e. if stock your damper moved 5mm for a 10mm wheel input and lowered your damper moves only 4mm for the same 10mm wheel input, you may want “stiffer” damping to compensate for the proportional reduction in input velocity due to motion ratios). That is all dependent on initial suspension geometry and how much that changes via lowering.

  • avatar

    I’ve looked at a few stock images of that 530, and yes it does look like it could go a hair lower. -About ~1.3″ front, ~.75-1″ rear

    The rule of thumb I’ve heard is that no matter what the looks are for your front wheel-arch, the control arms should be parallel to the road surface. ie: not slammed so low that the ball-joint end actually pitches Up with respect to the ca’s inside mounting point on the unibody.

    You usually replace your dampers at the same time. Proper kits will come with dampers that have appropriately shortened piston rods. Every time I’ve researched this, the rule was to get the right new dampers and don’t use the old ones.

    So your friends are correct as far as my info goes.

    +And you might consider getting a whole Suspension Kit, as opposed to going budget basement for just springs.

    Footnote: If you’re worrying about the cost of dampers though, are you sure you want to be driving a BMW?

    -You could spend at least that amount having a $tealership repair tech move a floor mat.

  • avatar
    twotone

    I’d keep it stock and enjoy it for what it is. Loved all my 5-Series cars — 1991 535i manual, 1999 540i Sport manual. Suspension upgrades are a lot of time, effort and $$ for marginal performance IMO.

    Twotone

  • avatar
    dingram01

    Go ahead, waste money and ruin your ride simultaneously if you must. If you have complaints about your steering, get it fixed. Something is wrong.

    I had a bone-stock 540i6 until I CFC’d it last summer. Great car, great handling (EXCELLENT steering). And replacement parts are not very expensive IF you stick with the stock setup. Why would anyone have a complaint about the factory setup in these cars, honestly?

    Consider the other areas you’re going to need to spend on: valve cover gaskets, intake manifold gaskets, water pump, radiator, so forth. Save your cash for these necessities when they arise and leave the dang suspension alone. Or, if you must spend on the suspension, at least do the routine things like the control arms which have a finite lifespan.

    All this obsession with lowering, “sport exhausts”, K&N air filters, crossdrilled and/or slotted rotors, makes me a very sad human being. All for cars that never see a track.

    • 0 avatar
      ponchoman49

      Agree!

    • 0 avatar
      Bimmer

      I’ve to disagree regarding brakes. OEM rotors are prone to warping, if you drive BMW as it was designed to be driven. A friend of mine has E34 525iA and he always had warped rotors, until I recommended him to try Ate slotted rotors. Lasted long time and he was very pleased with them. Ate also makes OEM rotors for BMW and Merc.

  • avatar
    guyincognito

    You can definitely lower the car that much without major issues. The ride will likely suffer but otherwise it should be fine. I would echo what others have said and suggest replacing the dampers (how many miles on the stock ones? The should be replaced around 60K miles anyway), the sway bars (these will have a more noticeable effect on handling), and having a look at the suspension bushings (front lower control arms, rear trailing arm bushings).

    • 0 avatar

      Good call on also doing Bushings!!!
      Way overlooked part.

    • 0 avatar
      dingram01

      Ordinarily there’s no hard and fast rule about when to replace shocks in E34s. I had to replace my fronts after an unhappy incident with a badly-constructed transition area in a highway construction zone. Ouch.

      I am convinced, by the look of them, that these were the original shocks. 180K on the clock at that time, and no discernable difference in feel with brand new ones.

      Unless you know they’re bad, don’t just replace parts at 60K intervals.

      Also, it is generally the front upper control arms, AKA “thrust arms,” whose bushing usually need replacing first. But a look at the ball joints in all the control arms should be a regular practice for sure.

    • 0 avatar
      guyincognito

      @ dingram01,

      There aren’t any front upper control arms on the E34, it has a Macpherson Strut design.

      I can tell you that after 100K miles on my 1999 M3 the FLCA, RTAB, RUCA, RLCA, & Frame mount bushings were shot (granted they probably take much more abuse than those on an E34).

    • 0 avatar
      dingram01

      There aren’t any front upper control arms on the E34, it has a Macpherson Strut design.

      Your 3-series suspension does use one control arm, but not the 5-series. There are two control arms per side on a 5-series. Both are mounted to the bottom of the car and connect via ball joints to the steering spindle, into which the strut is pinched.

      The so-called “upper control arms” are mounted low, and cross up and over the “lower” ones. I prefer the term “thrust arms.” Their job is to control fore-and-aft movement of the wheel, whereas the lower control arm keeps the wheel positioned side-to-side.

      The same front setup, essentially unchanged, remains in the current 5-series as far as I know. Needless to say there are several other differences between your 99 M3 and a 95 530. But your point about bushings is a good one and another argument in favor of saving the suspension bux for repairs on the stock setup.

  • avatar
    blue adidas

    You should be able to insert between two and three fingers between the wheel and the wheel arch. Any lower, and it’s going to look ghetto and drive badly. Lower this only about a half inch and that’ll be about the equivalent of a M5. Modifying a car is like plastic surgery… you want it to look good, but most people go overboard.

  • avatar
    SunnyvaleCA

    I know some German cars are jacked up for the USA market to be more crash-friendly with all the “light” trucks we have on our roads. Is this BMW one of those? In that case, just go with the European suspension setup.

    Another option is to use a tire with a slightly smaller diameter. You could get 0.5 inches right there. Plus, you would effectively lower the gearing of the car at the same time.

    • 0 avatar
      dingram01

      I know some German cars are jacked up for the USA market to be more crash-friendly with all the “light” trucks we have on our roads. Is this BMW one of those?

      That’s a new one. I’ve heard that tuning is often softened for US “tastes” but never that cars are jacked up. I do believe E34s got a somewhat more compliant tuning stateside, but I repeat my assertion it’s still perfectly adequate for any driving us roadgoing mortals undertake here.

      Smaller diameter tires (i.e., lower profile) will make for a harsher ride and will also throw off the already-imperfect speedometer even farther.

  • avatar
    Darth Lefty

    BMW’s use struts. This means that lowering the car results in a significant move in the location of the roll center away from the car’s CG. This makes it want to roll more. In order to compensate for this, lowering springs are often very hard, harder than you might want.

    Another related issue is that your original struts may no longer offer sufficient camber adjustment once the car is lowered.

    Here’s an educational diagram…
    http://images.sportcompactcarweb.com/tech/0508_sccp_02_z_+suspension+roll_center.jpg

    Note how the same lowering has more of an effect on the strut car than on the wishbone car.

  • avatar
    lilpoindexter

    Like Sajeev said, If you don’t know how old the dampers are replace them. If you think it looks better lowered, you will like the firmer ride. Who cares if you never take it on a race track, you will enjoy it on every freeway onramp…DO IT UP!!!!

  • avatar
    BostonDuce

    A 1.5″ drop w/o the corresponding firmer shocks is going to mean you’ll hit the suspension stops with a BANG on a regular basis.

    Make sure that your oil pan or radiator support clearance will not disappear with 1.5″ less height.

    If you decide to do it, you will need a 4 wheel alignment.

    Expect altered wear on your wheel bearings and suspension bushings as they will now be operating with different positions and loads.

    The coil-over kits that are sold assembled with springs & shocks are matched for the stock piston height, but are huge $$ in comparison to replacement struts.

    BD

  • avatar

    Lowering springs will most likely also have an increased spring rate – the stock shocks weren’t designed to work with this spring rate, which will quickly blow them out.

    This is why you should upgrade to at least a Bilstein – something more aggressive than stock, otherwise you’ll keep blowing them out.

  • avatar

    One thing to remember: going to an aftermarket coil over shock setup pretty much negates anything said here.

    And I agree with those who’ve mentioned the usefulness of going to any aftermarket lowering setup for a street car, but that’s not exactly answering the question. So I didn’t mention it at the time. But kudos, anyway.

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