What causes bounce? Shocks, Springs or both.

[Lambobimmer]

I have the BMW PS and it always has had a lot of bounce. I am a novice at suspensions but I want to find out what needs to be replaced to get rid of it.

[IGoFast1589]

Originally Posted by lamboworld

I have the BMW PS and it always has had a lot of bounce. I am a novice at suspensions but I want to find out what needs to be replaced to get rid of it.

"Bounce" is most likely the feeling of the spring moving freely without proper control from the shock. Is your suspension old? Has it been on the car for a lot of miles? If your dampers are old and need to be replaced you can get the "bounce" feeling that you are describing because the damper isn't holding pressure like it used to and cannot control the spring as well as it once did. Can you please give us more background of your suspension setup? What type of driving do you do, is there a specific scenario where you particularly notice it and so on? Anything that you think may be useful to know.

[GaryS]

M3 rear subframe bushings will fix most of the bouncing over bumps.

[IGoFast1589]

Originally Posted by GaryS

M3 rear subframe bushings will fix most of the bouncing over bumps.

Bushing deflection, good call.

[Lambobimmer]

Originally Posted by IGoFast1589

"Bounce" is most likely the feeling of the spring moving freely without proper control from the shock. Is your suspension old? Has it been on the car for a lot of miles? If your dampers are old and need to be replaced you can get the "bounce" feeling that you are describing because the damper isn't holding pressure like it used to and cannot control the spring as well as it once did. Can you please give us more background of your suspension setup? What type of driving do you do, is there a specific scenario where you particularly notice it and so on? Anything that you think may be useful to know.

The BMW PS was new when I bought it and it has been installed for about 6 months. IMO it has always felt very "bouncy". It is not noticable at normal speeds unless you hit a dip in the road and then you can feel it. However, at high speeds it is very noticable and it tends to bounce around more than I would like it to.

I believe that the shocks are just too soft for my taste. The spring rate is probably fine so maybe I need to pair them with some Koni Yellows for a stiffer ride.

[xerox445]

The rebound is too low on the shocks.

[cvc 22349a]

Originally Posted by IGoFast1589

Bushing deflection, good call.

+2. That's it, especially if the PS suspension is only 6 mos. old.

[GaryS]

Here is a quote from TC Kline:

Originally Posted by ///M1

Picked up the latest Roundel, there is a small section on the TC Kline 135i....

Per Kline's own words: "One of the first things you need to do with the 135i if you upgrade the suspension is put the M3 subframe bushings in it. The bushings are way too soft in the 1- and 3- series cars. If you do any kind of suspension upgrade and keep the stock bushings, the back end will bounce... Even if you put the stock M3 rear springs in a 135 or 335, the car would be really bouncy over bumps, because the subframe bushings are going to deflect 1-1 1/2 inches... For the M3, BMW used better bushings instead of the mushy stuff used in the other cars... Replacing the bushings is key."

[Harlequin]

How hard are the Bushings to install? Do you need to drop the whole rear subframe out?

[crex]

+3 on bushings! I did my rear subframe and much better.

[MPBK]

the bump on the road.

seriously, could also be this
http://www.1addicts.com/forums/showthread.php?t=524864

[Dackelone]

Originally Posted by lamboworld

The BMW PS was new when I bought it and it has been installed for about 6 months. IMO it has always felt very "bouncy". It is not noticable at normal speeds unless you hit a dip in the road and then you can feel it. However, at high speeds it is very noticable and it tends to bounce around more than I would like it to.

I believe that the shocks are just too soft for my taste. The spring rate is probably fine so maybe I need to pair them with some Koni Yellows for a stiffer ride.

Are your springs YELLOW ??? The Performance springs are yellow.

Perhaps whoever has installed the PS did not use the PS springs with the kit. You have to roder them seperately.

Next thing you should do is check the shocks for leaking oil. Perhaps you hit a pothole and blew a shock out. You can jack teh car up and pull up the shock rubber dust caps/bellows and look for leaking oil. IF you can see any oil... your shocks are shot. You could always puch down on each corner of the car and see if any corner is weaker than the rest.


Dackel

[fboutlaw]

It depends on the bounce you are experiencing.

If it's up and down bounce, it's the shocks, but if it's a bit of side to side wobble, it could be the bushings.

I want to give this thread some credibility so here goes.

Your governing equation on the suspension is: f''(x) b*f'(x) m*x=0. I may have messed that up on my phone, but it's the second order spring damper equation.

The time it takes the car to settle is primarily influenced by the damping force (shocks). The magnitude of oscillation is controlled by the springs.

This is over simplified, but the same equation applies to all three axis of your car. Z is springs/dampers while x and y are the rigidity of your bushings and other suspension joints.

Fix your shocks.

[GaryS]

Originally Posted by fboutlaw

If it's up and down bounce, it's the shocks, but if it's a bit of side to side wobble, it could be the bushings.

Stock rear subframe bushings with Performance springs bounces up and down too, about 1-1.5" as TC Kline says in the quote I posted. I didn't want to install the M3 rear subframe bushings, but I had to after I installed my suspension, because the bouncing was driving me crazy.

[Lambobimmer]

Originally Posted by Dackelone

Are your springs YELLOW ??? The Performance springs are yellow.

Perhaps whoever has installed the PS did not use the PS springs with the kit. You have to roder them seperately.

Next thing you should do is check the shocks for leaking oil. Perhaps you hit a pothole and blew a shock out. You can jack teh car up and pull up the shock rubber dust caps/bellows and look for leaking oil. IF you can see any oil... your shocks are shot. You could always puch down on each corner of the car and see if any corner is weaker than the rest.


Dackel

Yes they are yellow. I bought the entire kit new after I bought my car from Tischer, so I know that the springs and shocks are correct. I will check to see if any of my shocks are leaking but I ultimately believe that the shocks are too soft for my taste.

[dicker]

My car does the same thing with the BMW kit with Eibachs, especially in slower turns on the throttle. I leased mine so I'm not about to spend close to $1k including labor to change them out for the next owner lol.

[Dackelone]

Originally Posted by lamboworld

Yes they are yellow. I bought the entire kit new after I bought my car from Tischer, so I know that the springs and shocks are correct. I will check to see if any of my shocks are leaking but I ultimately believe that the shocks are too soft for my taste.

Humm... maybe something like Bilstein or Koni's would be better. Or even KW's coil overs. ?

[bogart]

tires cause bounce too... especially if you are still on run flats. is it an oscillating bounce or just bouncy over bumps?

[cpt97m3]

Originally Posted by Harlequin

How hard are the Bushings to install? Do you need to drop the whole rear subframe out?

I did it at home, and you can search for my how to post. You need to drop the subframe down 5-6 inches or so, but you can leave the diff and driveshaft attached. It took me 6 or 7 hours or so. You do need some kind of bushing removal tool, but other than that it's basic labor, just tedious. I really like the improvement in feel. It was worth it for me since I didn't have to pay for labor.

[HP Autosport]

Many components can cause bounce. Not enough rebond damping on the dameprs? Sure. Dampers don't generate enough damping force quick enough? Sure. Subframe bushings? Sure. Upper damper compression and rebound cushions? Sure. Lower damper mount? Sure.

You will need to pinpoint which component(s) causes the bounce and address it.

[MZWIE]

I installed the PS and there is no bounce (BTW the PS comes with Z8 bushings).

I define bounce as the lack of proper dampening when the suspension expands or contracts.

In other words. We have all seen some old car going along on the road and it looks like it's mounted on "jello". That to me that is bounce.

Perhaps the OP is experiencing the ondulations of the road. Of course the stiffer the suspension the more you feel. Personally I like a real stiff ride so this does not bother me at all.

In my opinion the PS does a great job of quickly controlling any bounce. Even over the most severe bumps.

[3liter1]

Originally Posted by e34m5

I installed the PS and there is no bounce (BTW the PS comes with Z8 bushings).

I define bounce as the lack of proper dampening when the suspension expands or contracts.

In other words. We have all seen some old car going along on the road and it looks like it's mounted on "jello". That to me that is bounce.

Perhaps the OP is experiencing the ondulations of the road. Of course the stiffer the suspension the more you feel. Personally I like a real stiff ride so this does not bother me at all.

In my opinion the PS does a great job of quickly controlling any bounce. Even over the most severe bumps.

+1
I have the TC Kline SA setup, and began to wonder if I needed to upgrade the subframe bushings after reading this thread. But if you define bounce as the rapid reaction of the suspension to the undulations in the road , I would think stiffer bushings would just increase that dynamic.