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      03-11-2019, 08:16 PM   #1
harperium
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Bouncing over speed bumps

Curious to what is normal and what indicates new dampers are needed. My car has 33K miles.

In my 340, I had the Eibach Pro Kit springs installed about 3 months ago. When going over speed bumps, I get a good 3 or 4 bounces on both the front and the rear.

I drove a loaner 330 GT recently and I recall that going over speed bumps at a normal speed (maybe 5 mph, not slow, not fast), both the front and rear seemed well damped and didn’t really bounce. It was a pronouced difference to my lowered 340i.

Anyway, just thought I’d ask to see what is considered normal.

If I have to get new dampers I would probably get Bilstein B8 as they are designed for lowering springs.
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      03-12-2019, 09:54 AM   #2
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Has it done this since install or progressively gotten worse?
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      03-12-2019, 12:18 PM   #3
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Does your car still have OEM shocks? Stock xDrive shocks are too soft to effectively control the spring oscillations. This is typical behavior of stiffer springs combined with softer shocks.
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      03-12-2019, 02:10 PM   #4
harperium
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The car does have OEM/stock dampers

it seems like the bouncing has gotten worse, but i don't have any hard data to back up the claim.

it was noticeable when driving the 330xi GT. over the same bumps, the GT bounced just once and was done, vs my car which does 3 or 4 bounces (each diminishing). But only over speed bumps at slow speed.
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      03-12-2019, 02:40 PM   #5
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Quote:
Originally Posted by cfm56d7b View Post
Does your car still have OEM shocks? Stock xDrive shocks are too soft to effectively control the spring oscillations. This is typical behavior of stiffer springs combined with softer shocks.
maybe the heavy weight of the GT helped it stop bouncing but i think it's more so the above reason
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      03-12-2019, 04:56 PM   #6
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Quote:
Originally Posted by harperium View Post
The car does have OEM/stock dampers

it seems like the bouncing has gotten worse, but i don't have any hard data to back up the claim.

it was noticeable when driving the 330xi GT. over the same bumps, the GT bounced just once and was done, vs my car which does 3 or 4 bounces (each diminishing). But only over speed bumps at slow speed.
Your impressions are well founded.

That's why stiffer springs and OEM shocks do not usually lead to desired suspension behavior other than a lowered stance.

Coilovers would be a much better choice with additional tuning options: height, rebound and compression controls. Some coilovers offer independent rebound and compression controls for even more precise suspension tuning behavior.
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      03-12-2019, 05:51 PM   #7
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I want to say the struts are maybe blown? it can happen rather quickly with lowering springs + factory struts
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      03-13-2019, 07:46 AM   #8
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Even without lowering springs my OE 704 dampers would let the car bounce to the point of inducing nausea after 50k. Some people pretend that springs don't wear out the shock faster... :

Your inclination on them being spent is spot on.
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      03-13-2019, 08:43 AM   #9
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I don't think the dampers are completely worn out - obviously there's a spectrum. But it does feel like the dampers are half spent.

Time to start saving for Bilsteins...
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      03-14-2019, 07:33 AM   #10
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After I lowered mine with h&r sport springs the bounciness was embarrassing, to say the least. Installed b8's (inexpensive) in rear only and it transformed the ride. Eventually doing fronts, but very happy for now.
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      03-14-2019, 01:48 PM   #11
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Bilstein B6 shocks work well with OEM springs. With a shorter body, Bilstein B8 shocks are designed for lowering springs and feature stiffer dampening to compensate for shorter distance the shock has to travel.

B8 shocks and HR Sport Springs are a popular combination, although coilovers offer more suspension tuning options.
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      03-15-2019, 09:40 AM   #12
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Lowering springs will usually kill stock dampers at an increased rate. No surprise there.
B8s are a good choice
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      03-15-2019, 10:21 AM   #13
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Springs don't kill shocks in 3 months. And blown shocks are usually stiff and bottom out. If it's still oscillating, it's just underdamped.
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      03-15-2019, 01:54 PM   #14
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This is kind of what I'm thinking - that I am now realizing that while the lowering springs do give better handling and cornering in general, the overall suspension is a bit under-damped.
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      03-15-2019, 02:48 PM   #15
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Quote:
Originally Posted by harperium View Post
This is kind of what I'm thinking - that I am now realizing that while the lowering springs do give better handling and cornering in general, the overall suspension is a bit under-damped.
The most practical way to under appreciate the combination of soft shocks and stiffer springs:

- Find a stretch of road with frequent bumps and imperfections
- Drive between 40 and 60 mph
- The bounce symptoms will magnify as the shock will fail to rebound in time
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      03-15-2019, 09:43 PM   #16
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Quote:
Originally Posted by kern417 View Post
Springs don't kill shocks in 3 months. And blown shocks are usually stiff and bottom out. If it's still oscillating, it's just underdamped.
Dont agree. I've had it happen in 3 months or less. Also have a friend were it happened as well in about 2-3 months.
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      03-15-2019, 10:38 PM   #17
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Quote:
Originally Posted by cfm56d7b View Post
The most practical way to under appreciate the combination of soft shocks and stiffer springs:

- Find a stretch of road with frequent bumps and imperfections
- Drive between 40 and 60 mph
- The bounce symptoms will magnify as the shock will fail to rebound in time
Yeah! I’ve noticed certain stretches of road that seem to magnify the bumps

I have the B8 dampers on order. Looking forward to have a “complete” sport suspension (I have the Eibach Pro Kit springs with OEM dampers now).

Edit: Bilstein B8's are still unavailable. Switching to Dinan springs + bumpstops and Koni Sport yellow dampers.

Last edited by harperium; 03-19-2019 at 08:20 AM.
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