stiff rear suspension

[bdriven]

Hi folks,

I have a 2000 , X5, 4.4i. I now have 156,000 miles on it. Can't afford a new one, so I have replaced pretty much everything on this baby.

Recently, I feel that rear suspension is way too stiff, even for the sports version, I feel it so stiff, that it does not feel safe at higher speeds.

I do have a gt1 system at home, but I am not getting any error messages.
a while back I elevated the rear axle just a bit, but now, thinking that maybe that was the problem, lowered the rear axle level with the front. ( i do this via gt1).

Hopefully you guys can help me sort a few things out.
Could it be bad struts? when they go bad, they dont stiffen up, right?

THANKS!!!

[Ricky Bobby]

Well if you raised the rear air bags that does increase the pressure in the system on the rear, that's the only reason I can see it being "excessively stiff".

When I bought my X5 (I have 2-axle air suspension) the ride height was calibrated 1.5" HIGHER than stock height. Needless to say, I was used to it, but I also was ecstatic at the improved ride quality when I calibrated it to be stock height.

Lower that axle to the proper height my friend in the rear and it should be better, and measure from lower wheel edge to fender, I know for 20s with sports package is 709mm in rear, not sure on your wheel size, but here is a chart:


_______________ 17"____18"____19"____20"___these are wheel sizes
front axle_______685____697____710____722
rear axle________687____699____712____724
sport fr_________670____682____695____707
sport rr_________672____684____697____709

[bdriven]

Thank You RB, will get to it tonight. will let you know how it goes.

[Ricky Bobby]

No problem!

[bcredliner]

As I understand your initial post you were OK with the ride at the increased rear height until recently? And you lowered it back down to what it was initially and it is still as stiff as it was at the higher height?

[bdriven]

I did lower it back, but cant tell if it was the initial setting, I didn't take measurements, will get back with the actual numbers. the gt1 has one option to lower the rear axle on equal increments. so it may not be the original height. will confirm soon!

[Gregory891]

Did you also perhaps change from 17" to 19" tires (or bigger diameter) as well, that will also contribute to stiffness.

[bcredliner]

Originally Posted by Gregory891

Did you also perhaps change from 17" to 19" tires (or bigger diameter) as well, that will also contribute to stiffness.

A larger rim diameter won't impact ride unless tire used on the larger rim is shorter from the rim to the ground.

[Gregory891]

Actually no, ride is a function of many factors that influence shell, chassis and suspension harmonics.

Tire height (profile or aspect ration) actually dampens the ride, so if you upgrade (I'm using the E53 as I own one) from the basic 17" tires (65 aspect ratio) to the 19" option (50 aspect front and 45 aspect rear) or the iS spec 20" (40 aspect ratio), your ride WILL become rougher. Aspect ratio is the issue as well as the tire width (more sensitive to road imperfections due to the wider footprint).

Similarly a larger diameter sway bar will also cause a firmer ride as it will constrain the suspension (to a degree).

Lowering the car might cause the same for several reasons. The main one is that lowering is frequently done with shorter springs which usually have a firmer rate vs. relocating the spring perch lower (threaded coil-overs allow you to do this in theory with stock springs although few do this). You can find other reasons as well.

The height differences (VERY helpful) in rickybobby's chart are useful and you'll note that when you go the big / WIDE wheels, they add some height - to improve comfort lost due to the lower aspect ratio AND since inner wheel clearance is reduced.

Back to bdriven's issues: I'd suggest you set your car to the height settings for your suspension (sport or stock) and check your tire pressures as well. Both are likely your issues. Example: raise your pressure from 32 to 40 psi and you WILL notice a change.

[bcredliner]

Originally Posted by Gregory891

Actually no, ride is a function of many factors that influence shell, chassis and suspension harmonics.

Tire height (profile or aspect ration) actually dampens the ride, so if you upgrade (I'm using the E53 as I own one) from the basic 17" tires (65 aspect ratio) to the 19" option (50 aspect front and 45 aspect rear) or the iS spec 20" (40 aspect ratio), your ride WILL become rougher. Aspect ratio is the issue as well as the tire width (more sensitive to road imperfections due to the wider footprint).

Similarly a larger diameter sway bar will also cause a firmer ride as it will constrain the suspension (to a degree).

Lowering the car might cause the same for several reasons. The main one is that lowering is frequently done with shorter springs which usually have a firmer rate vs. relocating the spring perch lower (threaded coil-overs allow you to do this in theory with stock springs although few do this). You can find other reasons as well.

The height differences (VERY helpful) in rickybobby's chart are useful and you'll note that when you go the big / WIDE wheels, they add some height - to improve comfort lost due to the lower aspect ratio AND since inner wheel clearance is reduced.

Back to bdriven's issues: I'd suggest you set your car to the height settings for your suspension (sport or stock) and check your tire pressures as well. Both are likely your issues. Example: raise your pressure from 32 to 40 psi and you WILL notice a change.

Who are you addressing with actually no?