E39 suspension [Archive] - bimmerfest

chonch

07-07-2003, 10:29 PM

I have an important question regarding the suspension on my 1998 540i (E39). After reading around and searching the board, I could see that everyone has mixed emotions about this topic, so I am looking for more insight......please help me out. (Mods, I sent you a PM regarding this topic) :thumbup:

My neighbor sold me the suspension from a 2000 M5 with less than 5000 miles on it (front shocks, rear struts, all springs, and the rear sway bar). He never drives the car and basically just uses it for fun on the weekends. Well, I figured that I could not let that deal go for $300 and told him that I would take it....I also kept in mind that my 540i has over 60,000 miles on the stock springs, struts, and shocks, so it was time to change them.

Well, I talked to a few shops and a few people on the boards and they said that it was a bad idea to use the setup because it would not deliver the appearance and handling that I was looking for.

I am looking to decrease the wheel gap between the fenders and the 18" rims I just purchased, while at the same time make the car handle better. But since the M5 is heavier, I was told that the suspension package from my neighbor would not lower the car enough.....so I am looking for other options.

Now my question is this.....would the M5 shocks and struts work with some aftermarket springs like Eibach pro-kits or H&R sport springs? And would the ride be bearable for an everyday driver?

Or am I better off putting the M5 suspension on ebay and buying some koni adjustables to use with either eibach or H&R springs?

My 540i is my daily driver and I am not interested in using it on the track, but do like to drive fast on the highways or around town for the thrill.

So what do all of you ? Thank you again for your time and wisdom...

BillP

07-08-2003, 08:25 AM

A few folks have done what you are talking about and the car ends up being higher than the 540 sport package. I've seen photos.

However, it is a bit lower than the non-sport suspension.

The above is with the M5 shocks/struts/springs.

I have been told (not sure how accurate this is, though) that the M5 spring perches are different from those on the 540, so even if you were to add an additional 200lbs to your 540, bringing it to the same weight as the M5, the car would still be higher.

So, it isn't the springs or shocks that really are the problem, it is the spring perches and aftermarket springs won't make it any better. I guess you could try it, but the labor cost will eat you up if you have to do it over again.

Personally, I would dump the gear (sans sway) on ebay and get the right stuff. In fact, I passed up a similar deal as you found and went with Koni/H&R and am extremely happy I did.

Install the rear sway, though. 10 minute install and, for most folks, worth the time/energy.

Bill

chonch

07-08-2003, 09:13 AM

Thank you for the input.......

So you are saying to dump the gear......therefore I have 2000 M5 suspenion for sale....... :D :D :D

.....and install the rear sway bar?

I was also told that installing an unmatched sway bar is worse than installing unmatched shocks. Therefore, I was told that the rear sway should never be installed, especially since the front one would remain stock......

I have come to the conclusion.....I love this board because I am getting much more feedback then I did with the three mechanics I visited.

BillP

07-08-2003, 09:23 AM

I am not a suspension guru [DaveZ, chime in please], but "matching" front and rear sways affects the tendency of the car to understeer or oversteer at its limits. Our cars come from the factory with lots of understeer dialed in (it is safer for inexperienced drivers) and fattening up the rear sway will lower this understeer a bit, but definitely won't push it into an oversteer situation. As proof (somewhat), there are dozens of E39 drivers who have done exactly what I recommended or gone with an even bigger rear sway while leaving the front sway alone. As luck would have it, replacing the rear sway takes 10 minutes and replacing the front sway takes four hours.

BTW, the reason you have the M5 rear sway, but not the front, is because your M5 friend only replaced his rear sway, right?

Bill

mottati

07-08-2003, 09:25 AM

If you change the rear bar only, you will change the ballance of the car, in that you will decrease understeer. this is a good thing on the e39 540.

Many people do the rear bar only because it's quite cost effective, and easy to do. Plus the car will be a little more neutral in it's handling.

It sounds like you mostly are going for the look of being a little lower, so i'd suggest you sell the M5 stuff and get either an eibach kit or H&R's (which will probably be firmer than the eibach)

I personally have the dinan stage 3 setup, which I love. Great on the street and very good on the track, but it doesn't really lower the car a noticable amount.
Mike

chonch

07-08-2003, 09:42 AM

Thank you all for your help.......

Well, now I feel like an idiot....but it is good to get a nice butt-whippin in order to learn.

With regard to the rear sway...I am keeping it. Unfortunately, my neighbor did not go into detail about why he only had the rear sway other than the fact that the Dinan kit he received did not come with it....I dont know for sure...

DZeckhausen

07-08-2003, 04:57 PM

With regard to the rear sway...I am keeping it. Unfortunately, my neighbor did not go into detail about why he only had the rear sway other than the fact that the Dinan kit he received did not come with it....I dont know for sure...The Dinan Stage 3 suspension for the 540i comes with a front swaybar. The Dinan 540i front swaybar is the same diameter as the M5 stock front bar, but costs more than three times as much. The Stage 3 kit for the M5 does not come with a front swaybar, telling me the Dinan 540i bar and the M5 front bar are approximately the same.

I agree with the other folks about the need to enlarge the rear bar on our E39s because the factory dialed in too much understeer in order to keep the lawyers happy. I started out by installing the M5 rear bar. A couple weeks ago, I installed the M5 front bar on my 540i and then did it on my neighbor's. Fresh with the knowledge gained from that work, I wrote up some detailed instructions: http://www.zeckhausen.com/howto/bmwe39/swaybar_replacement.htm

With two people, we got the time down to just over two hours, using ordinary tools and jackstands.

Now that I have the M5 front bar installed, my 540i's body roll is greatly reduced. It feels fantastic. But at the limit, I'm back to square one in terms of understeer. So I'm installing a Dinan rear swaybar and setting it to the middle setting.

BimBob

07-08-2003, 07:44 PM

So... What the most cost effective larger rear bar solution for an E39?

JEM

07-08-2003, 07:49 PM

Just remember: lowering is done for looks, not for performance, particularly on a Macpherson-strut-equipped car.

And, as for the 'heavier' M5 - one of these days I'll get the M5 and the 540iA on scales, but so far as I can tell most of the weight difference is unsprung - bigger brake rotors and calipers, heavier wheels and tires - and won't impact ride height. The engine and related hardware is probably 25-35lb heavier than a 6-speed 540i, but no heavier than a slushbox 540iA. The exhaust system is a lot heavier, but that's countered by the lack of a spare tire. Otherwise, comparably-equipped M5s and 540is are the same car.

Stock-to-stock, the M5 is not noticeably lower than a sport-package 540i. IMO there's good reasons for that, it's a real car that has to live on real roads with real driveways and real speedbumps.

I've got a used Dinan Stage 3 package sitting in the garage here, once we move back into our house that goes on the M5 and the M5's stuff plus a new M5 front bar goes on the 540, and we'll see how it all works out. Personally, I think the M5's suspension settings make almost a perfect daily-driver setup, it's nicely snug but doesn't beat you up at all.

DZeckhausen

07-08-2003, 08:17 PM

Personally, I think the M5's suspension settings make almost a perfect daily-driver setup, it's nicely snug but doesn't beat you up at all.I agree. I like the 540i settings and may add camber plates if I start to autocross her more, but with the M5 front bar and a Dinan rear bar, I've found a suspension that I really love and for a price that can't be beat.

DKSF

07-08-2003, 08:19 PM

Just remember: lowering is done for looks, not for performance, particularly on a Macpherson-strut-equipped car.

Not sure that I completely agree with that statement. There are performance benefits to be had from lowering a car, primarily lower center of gravity. I find it hard to believe that BMW engineers would make the sport package suspensions ~1" lower than non-sport ones only for looks.

There are other benefits to be gained from aftermarket suspension components, but they are not directly related to ride height, but with spring rates and strut stiffness.

Having said that, I will say that the benefits of lowering a car diminish pretty rapidly the more it is lowered. In fact, performance is degraded pretty significantly and could become dangerous if the car is lowered too much.

In the case of our BMW's, there is no easy solution to improving the handling. Obviously, our cars are some of the best handling cars out of the box. There is nothing out there that will out-engineer BMW in the aftermarket. Yes you can improve the performance and appearance of your car but everything is a tradeoff. Lowering the car will always reduce suspension travel, which will result in a degradation in ride quality and perhaps overall cornering ability depending on how much it is lowered.

I have an aftermarket suspension (and BTW, I don't drive it this low) and I found that I experienced an a good amount of benefit (improved turn in, less body roll) at the expense of some ride quality.

JEM

07-08-2003, 09:34 PM

Not sure that I completely agree with that statement. There are performance benefits to be had from lowering a car, primarily lower center of gravity. I find it hard to believe that BMW engineers would make the sport package suspensions ~1" lower than non-sport ones only for looks.

Two critical points:

First, as much as BMW seems to love them and has made them work very well, Macpherson struts' main advantage is in being cheap to build and easy to install on the production line. They're not very good from a geometry standpoint, and when you lower one much you move the roll center dramatically - you end up with a roll center that moves around a whole bunch with suspension travel, even below ground level, and the end result is squirrelly as all hell.

Yes, the sport-package suspensions are 20mm or so lower than the non-sport, and IMO that's not far short of the limit of how far you can lower a Macstrut suspension without moving the lower-arm pivots up too.

Second, in the real world (as opposed to a smooth track) suspension travel is everything. A car that bottoms is a miserable creature to live with - not only is it uncomfortable in everyday driving, you can't drive it really hard because you'll always have that little doubt in the back of your head as to what the thing is going to do the next time you hit a bump in the middle of that 80mph corner.

BMWs do better on suspension travel than most cars, and I wouldn't sacrifice much if any of that for someone else's notion of style.

chonch

07-08-2003, 10:18 PM

Ågent99

07-09-2003, 03:05 PM

... Now that I have the M5 front bar installed, my 540i's body roll is greatly reduced. It feels fantastic. But at the limit, I'm back to square one in terms of understeer. So I'm installing a Dinan rear swaybar and setting it to the middle setting.

Dave, what might installing a rear STRUT bar accomplish? I have a feeling it isn't much...it is pretty high up on the suspension and you probably won't notice it until you hit tight corners at appreciable speeds...on a track most likely.

So you have an M5 sway bar for sale soon, Dave??? :D

Chris

DZeckhausen

07-09-2003, 05:02 PM

Dave, what might installing a rear STRUT bar accomplish? I have a feeling it isn't much...it is pretty high up on the suspension and you probably won't notice it until you hit tight corners at appreciable speeds...on a track most likely.

So you have an M5 sway bar for sale soon, Dave??? :DI will indeed have an M5 rear bar for sale. But I've already got a list of local vultures who want to get their hands on it! :)

I put a rear strut brace on my 1991 Taurus SHO and it made a very noticable difference in reducing rear door rattles and creaks. The E39 chassis is much stiffer, so I would think the benefit is far less. Especially if you do NOT have the fold-down rear seats, which is the case with my 2001 540i/6.

JEM

07-09-2003, 05:42 PM

If I understand you correctly, JEM, you would not lower a BMW car because it generally has little to no significance?

And in your opinion, the best aftermarket suspension package is a Dinan kit, for both daily driving and track?
Thanks

I can't think of many road cars I'd lower very far without a clear functional reason for doing so, because it's been my experience that you usually lose more than you gain.

This is not an absolute - in some cases the engineering of the aftermarket bits is clever enough to maintain good geometry and jounce travel - but you don't get this by just swapping springs.

As for Dinan's stuff - I certainly haven't experienced everything that's out there, but my experience has been that Dinan's stuff is a very good compromise. They don't lower the car much, most of their bits maintain OEM levels of NVH isolation, and the balance between ride comfort and stiffness is good.

The one significant downside to the E39 package that they do not have the one bit of adjustability that really makes sense in a Macstrut car, particularly one that sees track use - the front camber plates are not adjustable.

DKSF

07-09-2003, 05:45 PM

I will indeed have an M5 rear bar for sale. But I've already got a list of local vultures who want to get their hands on it! :)

I put a rear strut brace on my 1991 Taurus SHO and it made a very noticable difference in reducing rear door rattles and creaks. The E39 chassis is much stiffer, so I would think the benefit is far less. Especially if you do NOT have the fold-down rear seats, which is the case with my 2001 540i/6.

Chris: Not THE Dave, but just some other schmoe named Dave....yeah, the rear strut bar is theoretically supposed to add to the rigidity of the chasis and reduce body flex. I would, as Dave Z. mentions, think that the benefit is negligible. DK.

JEM

07-09-2003, 06:35 PM

Chris: Not THE Dave, but just some other schmoe named Dave....yeah, the rear strut bar is theoretically supposed to add to the rigidity of the chasis and reduce body flex. I would, as Dave Z. mentions, think that the benefit is negligible. DK.

I'd tend to agree.

A strut-tower brace assumes (a) you have struts and (b) there's some structural flex you're trying to eliminate.

E39s do not have rear struts. The spring loading goes up into the shock-tower, but all the wheel-location loads go into the rear subframe. Since the loads are spread around quite a bit, I'd expect the benefit to be very small.

It all comes down to being able to determine that there's a problem. There are front strut-tower braces out there for E39s, but do we know how much E39 front structures flex under load?

I recall someone once looking for a front strut-tower brace for a Saab 9000. Okay, maybe he found one somewhere...but the back of the 9000's front strut towers is the top of the firewall. It's a perfectly boxed design. I dare you to make that one flex.

DZeckhausen

07-09-2003, 06:50 PM

I recall someone once looking for a front strut-tower brace for a Saab 9000. Okay, maybe he found one somewhere...but the back of the 9000's front strut towers is the top of the firewall. It's a perfectly boxed design. I dare you to make that one flex.Even better are my fellow members of the Impala SS club who buy the Hotchkis strut tower brace or, more accurately, "engine bay" brace. Since the body of the Impala SS is completely isolated from the frame by rubber bushings (body-on-frame construction, like a pickup truck) there is no way that brace does anything other than add weight and get in the way of service items. I can't stand even looking at those things, it's so silly!
:tsk:

BillP

07-10-2003, 09:52 AM

Even better are my fellow members of the Impala SS club who buy the Hotchkis strut tower brace or, more accurately, "engine bay" brace. Since the body of the Impala SS is completely isolated from the frame by rubber bushings (body-on-frame construction, like a pickup truck) there is no way that brace does anything other than add weight and get in the way of service items. I can't stand even looking at those things, it's so silly!
:tsk:

Uh, I have one Impala SS Hotchkis strut tower brace for sale - cheap. Apparently it is barely used. Call me, fast! :cry:

Embarrassed,
Bill :)