Newbie needs shocks/springs guidance
Newbie needs shocks/springs guidance
(OP)
Hi, guys. I'm an engineer, but not an automotive one. I'm researching suspension changes for my 2000 BMW 540. I've found good information on "feel" for many options. But one man will describe a suspension as "firm" while another will describe it as "harsh." It's very hard to do a normalized comparison without real data. I'd like quantitative data before thinking about qualitative data.
For example, a suspension thread on another board did a great job talking about an installation. Then we get into a debate about Bilstein dampers vs. Koni and Intrax springs vs. everything else. I see arguments for and against all options. Another post argues for soft springs and stiff shocks. A suspension engineer once told me that's a recipe for disaster. It'll handle well but will rattle your teeth. He said BMW typically uses stiff springs and soft shocks, which is the opposite of Audi. What should I believe?
The threads discuss lower stance and stiff ride but nothing about spring or damping rates. Honestly, suspensions confuse the heck out of me. I don't *really* know how to interpret such numbers. But still, numbers allow you to do a straight up comparison. Subjective interpretations based on personal preference are interesting, but non-actionable.
To the specifics. I have a 2000 540 wagon with OEM sport suspension. It's tighter than the non-sport suspension but not at all harsh. It's a sophsticated ride but the shocks are shot. Like many people, I'm trying to decide between Bilsteins, Koni Sports, Koni FSDs, and OEM. I also wonder if I should install the Eibach springs matched to the Koni FSDs. I live in Florida so I drive on decent quality roads with no snow. I'm an enthusiast but this isn't a track car - it's a wagon.
I don't care about lower stance. What are the definitive differences between my options?
Plus, I assume BMW spent a ton of time tuning the suspension. They made calculated decisions, and only then tuned on feel. Assume the OEM engineers really did target for the average driver. How would I know if I fall into the standard deviation for that average? Therefore, I want the engineering data *before* getting people's feel. I'm concerned about making things worse if I don't make a deliberate decision.
Any ideas? Thanks in advance.
For example, a suspension thread on another board did a great job talking about an installation. Then we get into a debate about Bilstein dampers vs. Koni and Intrax springs vs. everything else. I see arguments for and against all options. Another post argues for soft springs and stiff shocks. A suspension engineer once told me that's a recipe for disaster. It'll handle well but will rattle your teeth. He said BMW typically uses stiff springs and soft shocks, which is the opposite of Audi. What should I believe?
The threads discuss lower stance and stiff ride but nothing about spring or damping rates. Honestly, suspensions confuse the heck out of me. I don't *really* know how to interpret such numbers. But still, numbers allow you to do a straight up comparison. Subjective interpretations based on personal preference are interesting, but non-actionable.
To the specifics. I have a 2000 540 wagon with OEM sport suspension. It's tighter than the non-sport suspension but not at all harsh. It's a sophsticated ride but the shocks are shot. Like many people, I'm trying to decide between Bilsteins, Koni Sports, Koni FSDs, and OEM. I also wonder if I should install the Eibach springs matched to the Koni FSDs. I live in Florida so I drive on decent quality roads with no snow. I'm an enthusiast but this isn't a track car - it's a wagon.
Plus, I assume BMW spent a ton of time tuning the suspension. They made calculated decisions, and only then tuned on feel. Assume the OEM engineers really did target for the average driver. How would I know if I fall into the standard deviation for that average? Therefore, I want the engineering data *before* getting people's feel. I'm concerned about making things worse if I don't make a deliberate decision.
Any ideas? Thanks in advance.





RE: Newbie needs shocks/springs guidance
That is not the same thing at all.
If you like it the way it is then just replace the shocks with identical parts.
Cheers
Greg Locock
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Newbie needs shocks/springs guidance
Then you will be far ahead of most BMW owners...
RE: Newbie needs shocks/springs guidance
Another point: Consumer Reports doesn't seem to like Continental. The BMW community tends to prefer Michelins, although I think they're overpriced. Wikipedia says Bridgestone is the largest tire company, followed by Michelin and Goodyear. That implies (but doesn't prove) that those manufacturers have more to spend on R&D. What do you like about Continental?
RE: Newbie needs shocks/springs guidance
If you have a Control Engineering background, then this will have meaning to you, If not, then I can't help you.
P = 1/(p2s^2+p1s+1)
Q = qn3s^3+qn2s^2+qn1s+1/(qd3s^3+qd2s^2+dqs1s+1)
The Beamer Conti's mind their P's and Q's the best, followed by Pirelli and Michelin.
If you have even a student version of Matlab or Excel, the student should try these Conti params at 3.0 bar:
p2=0.0684
p1=0.528
qn3=0.00792
qn2=0.211
qn1=0.4051
qd3=0.00258
qd2=0.0593
qd1=0.6473
If your BMW is used to shuffle stock quotes around, this is not important. If you want to be one with the road, this is a magic key.
My question is whether BMW specifies these tire characteristics or do they float up from their exceptional subjective evaluation techniques and a lot of tire rides?
RE: Newbie needs shocks/springs guidance
Sorry I'm slow to catch on but a long day of Matlab today has turned by brain into oatmeal.
RE: Newbie needs shocks/springs guidance
p1=0.528
qn3=0.00792
qn2=0.211
qn1=0.4051
qd3=0.00258
qd2=0.0593
qd1=0.6473
fyn=tf(1,[p2 p1 1])
mzn=tf([qn3 qn2 qn1 1],[qd3 qd2 qd1 1])
step(fyn)
xlabel('distance (m)')
hold on
step(mzn)
title('The 16 inch BMW Conti''s are "Fast" tires.')
RE: Newbie needs shocks/springs guidance
RE: Newbie needs shocks/springs guidance
Conti_250 = [0.080874 0.62856 0.0098625 0.22809 0.41877 0.0038361 0.074553 0.75643]
Mich_300 = [0.080713 0.5788 0.0074966 0.21517 0.38234 0.0022762 0.051449 0.52003]
Mich_250 = [0.11184 0.77321 0.011092 0.28379 0.29163 0.0039091 0.08319 0.65384]
Pir_300 = [0.084909 0.64914 0.007267 0.1611 0.24578 0.0033068 0.065196 0.66481]
Pir_250 = [0.057435 0.55253 0.0065171 0.15747 0.29006 0.0025284 0.05082 0.59305]
f1=tf(1,[Conti_300(1:2) 1])
f2=tf(1,[Conti_250(1:2) 1])
f3=tf(1,[Mich_300(1:2) 1])
f4=tf(1,[Mich_250(1:2) 1])
f5=tf(1,[Pir_300(1:2) 1])
f6=tf(1,[Pir_250(1:2) 1])
figure('Name','FY Rollout','Menubar','None','NumberTitle','Off')
step(f1,f2,f3,f4,f5,f6)
xlabel('Distance (m)')
legend('Conti 3.00','Conti 2.50','Mich 3.00','Mich 2.50','Pir 3.00','Pir 2.50')
mz1 = tf([Conti_300(3:5) 1],[Conti_300(6:end) 1])
mz2 = tf([Conti_250(3:5) 1],[Conti_250(6:end) 1])
mz3 = tf([Mich_300(3:5) 1],[Mich_300(6:end) 1])
mz4 = tf([Mich_250(3:5) 1],[Mich_250(6:end) 1])
mz5 = tf([Pir_300(3:5) 1],[Pir_300(6:end) 1])
mz6 = tf([Pir_250(3:5) 1],[Pir_250(6:end) 1])
figure('Name','Mz Rollout','Menubar','None','NumberTitle','Off')
step(mz1,mz2,mz3,mz4,mz5,mz6)
xlabel('Distance (m)')
legend('Conti 3.00','Conti 2.50','Mich 3.00','Mich 2.50','Pir 3.00','Pir 2.50')
Legend shows brand and pressure (bar). This is NOT cornering g's, but estimated 'relaxation'. Even a BMW driver probably can not put a pure step input into the tire, but a computer can easily give it a go. There is some speed dependence to it, but walk the track before you run it.
RE: Newbie needs shocks/springs guidance
RE: Newbie needs shocks/springs guidance
RE: Newbie needs shocks/springs guidance
Ully
RE: Newbie needs shocks/springs guidance
No need to name brands, I'm just wondering what your thoughts are with respect to what would work best with this configuration, and why. Also, why it might work better on a car with this configuration as opposed to something like, say, a double wishbone front / multi-link rear, rear drive car.
RE: Newbie needs shocks/springs guidance
RE: Newbie needs shocks/springs guidance