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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 5 Series > E39 (1997 - 2003)

E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 12-23-2012, 11:02 AM
samboychips samboychips is offline
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Bilstein Sport (B8) with stock springs

Hi all, I've been spending alot of time searching on the net about this question but no luck. AnywayI have a 97 523i and I'm getting a set of Bilstein B8 next week and I'm just wondering is it possible to keep using the original (stock) springs along with them. Will the ride be really crap? What outcome would I be expecting? Thanks in advance.

Last edited by samboychips; 12-23-2012 at 09:36 PM. Reason: Typo on title
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  #2  
Old 12-23-2012, 12:22 PM
4given 4given is offline
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Are they sport springs? If so, they should be fine.
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  #3  
Old 12-23-2012, 01:27 PM
samboychips samboychips is offline
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No I don't think so. Lets assume they are not cos I got the car fully stock with no mods at all. Even with original 15" bmw rims. So right now I' on the quest of replacing The consumables, already done MAF, both camshaft and crankshaft sensors, o2 sensors, spark plugs and coil housing, all oil changes and stuff. So now I could put my effort on the wheels. Just got a set of 17" m5 multi-spoke rims and orderd a set of b8 ready after Christmas.
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  #4  
Old 01-22-2013, 10:47 PM
samboychips samboychips is offline
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Hi all, after a month since installation and waited for the suspension to be settle, I would like to post my findings.
Firstly, the riding comfort did not compromise too much but cornering is definitely sharper. Alot less body roll, more obvious during roundabouts. Now I could do more than 40km/h without worrying the car is going to flip.
The ride height is about the same as stock. I think its alright but let you guys be the judge of it. I could always fit lowering springs to them, but I'm having second thoughts since I live near the country side the roads are rough and there are always rocks and stuff on the ground so I'm now very comfortable with the clearance. Anyway I am posting few pics to give you guys some references. Hope they will help someone. Cheers.
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  #5  
Old 01-22-2013, 10:49 PM
samboychips samboychips is offline
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Hi all, after a month since installation and waited for the suspension to be settle, I would like to post my findings.
Firstly, the riding comfort did not compromise too much(passengers on the back didn't notice) but cornering is definitely sharper. Alot less body roll, more obvious during roundabouts. Now I could do more than 40km/h without worrying the car is going to flip.
The ride height is about the same as stock. I think its alright but let you guys be the judge of it. I could always fit lowering springs to them, but I'm having second thoughts since I live near the country side the roads are rough and there are always rocks and stuff on the ground so I'm now very comfortable with the clearance. Anyway I am posting few pics to give you guys some references. Hope they will help someone. Cheers.
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  #6  
Old 01-23-2013, 09:03 AM
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DHoang DHoang is offline
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WHen you installed the shorter length Sport dampers onto your stock full length springs, two things occurred.

1) the spring is now "pre-loaded" to remain captive within the shorter overall extension dimension of the sport damper & shock. This peload dim is approx. 1" or 2.5cm on each corner, which means the stock springs just got recallibrated to have a higher potential energy stored into the coil winding.

2) the overall distance between the wheels being able to fully extend away from the wheel arches will be reduced by ~ 1" or 2.5cm. This is what some call the "top out" or "max extension" distance.

In both per above, the reduction produces less body lean when turning at high g-force and better tire contact when going over uneven surfaces. This is what's providing you with a different driving feel.

Regarding a loss in comfort when going over rough roads, your current setup will only rear its ugly head if you drive over rough roads like an old granny.
The increase in downward force (per #1 above )can be too overbearing if you don't match the speed of the vehicle with the increase speed of the rebound action from your new spring preload. Drive more quickly through rough roads and you may find the suspension being smoother. Hard to believe, but that's a byproduct from a change in spring preload.
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  #7  
Old 01-23-2013, 09:08 AM
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DHoang DHoang is offline
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YOur first picture showing the overall decrease in height between the Bilsten (Left) and stock strut (right) is what I'm referrring to as spring preload. By compressing the spring down w/ the bilstein strut, the spring has been preloaded further than the stock preload. This has increased the potential energy of the spring.
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  #8  
Old 01-24-2013, 08:54 AM
samboychips samboychips is offline
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Thank you very much for your input DHoang. On the above is exactly what my mechanic told(warned) me before installation (almost word by word). Anyway he too wants to know what happens when stock springs are used. He had tested the car afterwards with proper wheel alignment and amazed the "rebound" wasn't as much as he would anticipated. I took his advice on trying the car for a period, if I wanted I could always install the springs later.
But you have brought my attention to the "Top Out" issue. To my understanding there is more potential energy stored in the springs. Hence the Bilsteins are "stretch/push" up more than they are suppose to be, and after compression the "kick backs" would be more aggressive. Will this be shortening the life span of the shocks? Or even compromise the overall safety?

Last edited by samboychips; 01-24-2013 at 08:59 AM.
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  #9  
Old 01-24-2013, 11:02 AM
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DHoang DHoang is offline
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Quote:
Originally Posted by samboychips View Post
But you have brought my attention to the "Top Out" issue. To my understanding there is more potential energy stored in the springs. Hence the Bilsteins are "stretch/push" up more than they are suppose to be, and after compression the "kick backs" would be more aggressive. Will this be shortening the life span of the shocks? Or even compromise the overall safety?
YES! Too much preload will shorten the lifespan of damper.
But you do have one distinct advantage on your side. Your Bilstein damper, which is unique because it is designed to be heavy duty for amateur track racing as well as street, can withstand the increased spring preload FAR Better than a twin tube damper (BIlstein is aka a monotube designed damper). The higher nitrogen gas that's pressurized inside a Bilstein as well as the larger diameter flow valve and fatter shimstacks makes for a stiffer damping curve, so they can accomodate the extra preload force.

As far as overall safety being compromised, here's what you have to consider:

Before installing your BIlsteins, your suspension setup was something like this:
Let's say the baseline ground clearance (distance from the ground to the bottom of your oil pan) is 10" in the vertical.
Stock suspension's total available suspension travel= 4" (from fully compressed to fully extended)
static sag (how much distance is used up w/ weight of car and passenger(2x) sitting over the suspension = 1"
So when the car is parked w/ you and another in the car, we have:
3" = available suspension travel for compression.
1" = available travel in the rebound direction.


NOW, your setup w/ stock springs and Bilstein sport should have produced something like this:
total available suspension travel=3" (w/ Bilstein sport damper having a 1" travel limited)
static sag should be (not the same 1" as before, but less, maybe ~5/8" (due to increasing your spring preload by 1"). IT can't sag to 1" as before b/c now w/ the springs preloaded, it carries more force to hold up more weight.
So, let's say it's 5/8"; therefore (3"-5/8"=2.375")= available suspension travel for compression.
5/8" = Available rebound travel.
For the ground clearance, if we had 10" clearance w/ a 3" avail. suspension travel per before, now, w/ a 2.375" avail. suspension travel, ground clearancee should be reduced from 10" to 9.375" theoretically speaking.

So basically, you would have seen your car's ride height lowered, you should feel your car handling more responsively because of the shortened overall suspension travel in both directions, plus the change the static sag ratio from 25% to 21% would have increased the rebound force which would therefore increase tire traction.

Id' say you have increased your safety factor if anything, but at the expense of comfort.

WHat's weird is that you're showing NO CHANGE in ride height from before & after. All I can think of is perhaps the preloading of the spring has a far greater impact than I think it is. THe way I see it, if you lost 1" of overall suspension travel (as per the 1st picture provided proves), yet after the install, your sag dimension didn't change any whatsoever, then your new available suspension travel for compression obviously remained the same as before, (let's say 3" cushion before bottoming out) but what is there left over in the other direction for your available rebound suspension travel? That has to be factored into account to reflect a 1" reduction in overall suspension travel when going w/ a sport damper. Could this suggest that you are already "TOPPED OUT" or about to hit the travel limiter in the rebound direction? Surely that can't be, but if it is, then uh-oh...something's not right. ANd if THAT'S THE CASE, then YES, you're compromising safety.
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Last edited by DHoang; 01-24-2013 at 12:01 PM.
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  #10  
Old 01-25-2013, 02:40 AM
Joelgk Joelgk is offline
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It is also just likely that after 15 years, the OE springs and the struts have been weak anyway and the ride height was low to begin with than stock height. So when the B8's were installed the length though shorter did not show much difference than stock?
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