Fixed: Rear Bounce, Pogo, Hop, Float

[Gangplank]

A quick search turned up this thread where our local suspension scientist fe1rx tested the shock parts and upper shock mounts. His conclusions are well stated, and (as always) worth the read.

OE Rear Shock Construction
http://www.1addicts.com/forums/showthread.php?t=1075240

How do you tag a user name in a thread?

[MightyMouseTech]

fe1rx

[Fume]

Originally Posted by Gangplank

A quick search turned up this thread where our local suspension scientist fe1rx tested the shock parts and upper shock mounts. His conclusions are well stated, and (as always) worth the read.

OE Rear Shock Construction
http://www.1addicts.com/forums/showthread.php?t=1075240

How do you tag a user name in a thread?

Not sure if I'm interpreting fe1rx's post correctly, but from what I'm seeing in his thread, the stock rear dampers, at normal ride height, is already resting on the OE bump stops. Is that common engineering practice for cars? If that's the case, I can definitely see why replacing the mount to something stiffer will have a big impact on the pogo effect when still using stock dampers/springs. Also could explain why bimmerbob felt no noticeable benefit since he already had PSS9 setup when he switched to Dinan RSM since maybe those Bilsteins doesn't have the car riding on the bump stops at ride height.

Edit: Also, I'm sure things aren't so black and white here either. Every component people mentioned here (e.g. shocks, springs, strut mount, bushings, etc) will likely be contributing to the pogo feeling, it's more of a matter of the magnitude.

[ShocknAwe]

Originally Posted by Fume

Not sure if I'm interpreting fe1rx's post correctly, but from what I'm seeing in his thread, the stock rear dampers, at normal ride height, is already resting on the OE bump stops. Is that common engineering practice for cars?

Maybe I'm missing something but resting on the bump stops by stock design makes no damn sense.

[Dackelone]

Originally Posted by Gangplank

A quick search turned up this thread where our local suspension scientist fe1rx tested the shock parts and upper shock mounts. His conclusions are well stated, and (as always) worth the read.

OE Rear Shock Construction
http://www.1addicts.com/forums/showthread.php?t=1075240

How do you tag a user name in a thread?

When your composing a post click "Advanced mode" or when you click reply tab in a thread simply use a "@" before the user's name.

like...

@ Gangplank (with no space between the "@" and user name). Some user names this won't work bc of special symbols or spaces in the name - fyi
Gangplank

Dackel

[Fume]

Originally Posted by ShocknAwe

Maybe I'm missing something but resting on the bump stops by stock design makes no damn sense.

Yeah that's what's throwing me off. Would be nice if Fe1rx can confirm or clarify.

This is the post I'm talking about: http://www.1addicts.com/forums/showp...7&postcount=14

That first image shows bump stop at "ride height". This is completely not how I imagined suspensions to be set up.

[Solo_M_Tech]

Originally Posted by thakid22

Several things here.. No doubt M3 RSFB are superior to the units the car receives at the factory. This post is not to diminish the value of any other part or system on the car. This post also is of no relevance to those who experience/notice no bounce from their rear suspension.

For those who DO notice/experience bounciness at the rear on stock suspension, this post proposes a solution. A solution tried by more than a few people. All suspension systems have some amount of vertical movement by nature. These strut mounts reduce that movement (and/or its sensation) at the rear. Additionally, they offer increased rear suspension travel.
In any event, the reduction in bounce was greatly appreciated.

I do find it interesting, though, that several of you guys say your vehicle never had any bounce back there. When I get in one of the E9x derived vehicles, I instantly feel it. It's always there in various degrees. I currently have a loaner X1 from the dealer with 5k miles on it. Sure enough, the bounce is there, though less than what I experienced in the 3/1er. Perhaps I'm just sensitive to those ride motions. But again, the mounts took care of it for me, and others as well, according to feedback in this very thread.

Im not saying they are not too soft, the problem isn't the bushing though. The problem is shitty dampening rates from the factory. You could effectively achieve the same effect by adding weight to the rear end. The bushings will make the factory shocks marginally more effective since more energy will be transmitted through the shock, and not the bushing. However the gains will be minimal, and in my opinion, any change is feel, is a placebo.

[E91WAG3N]

Interesting... Does anyone know off-hand if the BMW Performance Suspension comes with new RSMs and if so, do they differ from the stock units?

I'm planning replace my stock suspension with BMWPS in a year or two, but will be addressing the RSFB in the immediate future, replacing with 1M/M3 bushings. I may do the Dinan RSMs in the interim as well.

EDIT: Found a complete listing of the kit and found that BMWPS does not include RSMs.

[Gangplank]

Is the rear strut mount parts 4-5-6-7 in this diagram?
http://www.realoem.com/bmw/enUS/show...33#33536783101

Anyone else noticed that the "additional shock absorber" is a different part for the M-sport suspension? Is that the bump stop?

Part 3 on the rear on that one...

and part 10 on the front here:
http://www.realoem.com/bmw/enUS/show...95#31336783090

[Bimmer-Bob]

Originally Posted by thakid22

I do find it interesting, though, that several of you guys say your vehicle never had any bounce back there. When I get in one of the E9x derived vehicles, I instantly feel it. It's always there in various degrees. I currently have a loaner X1 from the dealer with 5k miles on it. Sure enough, the bounce is there, though less than what I experienced in the 3/1er. Perhaps I'm just sensitive to those ride motions. But again, the mounts took care of it for me, and others as well, according to feedback in this very thread.

Although I disagree with your assessment that Dinan's rear shock mounts sufficiently addressed the rear end oscillating "pogo" movement, I too am completely perplexed by anyone who doesn't notice that deficiency in the stock suspension. It was downright scary at speed, IMO, the way the car would bounce and hop after hitting expansion joints and other road irregularities.

[Gangplank]

Originally Posted by Bimmer-Bob

Although I disagree with your assessment that Dinan's rear shock mounts sufficiently addressed the rear end oscillating "pogo" movement, I too am completely perplexed by anyone who doesn't notice that deficiency in the stock suspension. It was downright scary at speed, IMO, the way the car would bounce and hop after hitting expansion joints and other road irregularities.

With or without the M3 RSFB's or inserts? Before I installed the inserts is was pretty unsettled and loose.

[Bimmer-Bob]

Originally Posted by Gangplank

With or without the M3 RSFB's or inserts? Before I installed the inserts is was pretty unsettled and loose.

I'm talking about without the inserts. The inserts do a world of good, although I just switched to full bushings and think they're a little better (although, I still maintain that for most people, the inserts are the best choice considering the price, ease of installation, and overall improvement in handling).

[gap]

Originally Posted by Bimmer-Bob

Although I disagree with your assessment that Dinan's rear shock mounts sufficiently addressed the rear end oscillating "pogo" movement, I too am completely perplexed by anyone who doesn't notice that deficiency in the stock suspension. It was downright scary at speed, IMO, the way the car would bounce and hop after hitting expansion joints and other road irregularities.

There is a road twisty road I drive and in one of the long sweeping corners there is a dip. Going around the curve with the suspension loaded and going
over the dip would cause the stock rear to wiggle a good bit, think it is probably bump steer. Definitely didn't inspire confidence.

[MightyMouseTech]

There is a long right hand, medium speed sweeper with a bump in the middle just outside of work. I go around it every day.

Installing the M3 RSFB completely got rid of the side to side sway when hitting that bump, but the back end of the car will still jump a bit sideways every single time. I am running stock dampers/springs. At least it is a controlled jump now. Just feels like the back end jumps a foot sideways, but is now composed about it. Hopefully installing the Dinan rear upper bushings will increase the rear shock travel and get rid of that jump.

Will be doing the rear upper bushings in the spring when I do Koni at all four corners and Swift springs.

[Gangplank]

@MightMouseTech You mean the Dinan upper shock mounts correct? Your description matches my experience. The RSFB inserts quelled the rear end wiggle or loose feeling. It was mostly side-to-side but not exactly on axis over bumps. After its much more solid. There is a controlled buck or hop.

[MightyMouseTech]

Originally Posted by Gangplank

@MightMouseTech You mean the Dinan upper shock mounts correct? Your description matches my experience. The RSFB inserts quelled the rear end wiggle or loose feeling. It was mostly side-to-side but not exactly on axis over bumps. After its much more solid. There is a controlled buck or hop.

Yes, the Dinan rear upper shock mounts.

[chris82]

Originally Posted by Fume

Yeah that's what's throwing me off. Would be nice if Fe1rx can confirm or clarify.

This is the post I'm talking about: http://www.1addicts.com/forums/showp...7&postcount=14

That first image shows bump stop at "ride height". This is completely not how I imagined suspensions to be set up.

That's piss poor. You can compress the stock dampers with one finger fyi. No wonder the whole suspension back there bounces around, they can't control SHIT.

In all honesty, I thought the stock suspension was okay once I put non-RFT tires on. For a stock car it was still pretty harsh over bumps, especially compared with older model BMWs, which are some of the most comfortable cars I've ever been in (think E36, E46, E39, etc.). However, I always though the stock suspension was fine at highway speeds.

[thakid22]

Originally Posted by ApexResistance

Im not saying they are not too soft, the problem isn't the bushing though. The problem is shitty dampening rates from the factory. You could effectively achieve the same effect by adding weight to the rear end. The bushings will make the factory shocks marginally more effective since more energy will be transmitted through the shock, and not the bushing. However the gains will be minimal, and in my opinion, any change is feel, is a placebo.

I agree, the stock damping is dismal. What happened to the days when BMW spring/shock calibrations seemed to be almost witchcraft. Supple, but endlessly capable.
Today though, not so much.

I also agree that the bushings make the shock more effective by reducing undamped motion. The shock cannot dampen bushing movement. Take (some of) that energy out of the bushing and transfer it to the shock and now the shock can dampen that additional energy in both compression and rebound. The result is reduced, more controlled movement of the body.
No placebo effect here. Again, the difference is night and day, and is easily quantified.

[thakid22]

Originally Posted by Bimmer-Bob

Although I disagree with your assessment that Dinan's rear shock mounts sufficiently addressed the rear end oscillating "pogo" movement, I too am completely perplexed by anyone who doesn't notice that deficiency in the stock suspension. It was downright scary at speed, IMO, the way the car would bounce and hop after hitting expansion joints and other road irregularities.

Having that you have not tried the Dinan mounts, I can accept your reluctance or inability too see their merit. I was not convinced until I had them installed and tried them for myself.
Glad I had an open mind though, as I was thoroughly pleased by the results. So pleased, in fact, that I started this thread for others who may not like the rear bounce.

[Bimmer-Bob]

Originally Posted by thakid22

Having that you have not tried the Dinan mounts, I can accept your reluctance or inability too see their merit. I was not convinced until I had them installed and tried them for myself.
Glad I had an open mind though, as I was thoroughly pleased by the results. So pleased, in fact, that I started this thread for others who may not like the rear bounce.

I've been running the Dinan mounts for years. But I changed the dampers and springs at the same time, so it's impossible for me to quantify the effect of the mounts themselves. But I do know that I continued to experience the confidence-sapping rear-end pogo until I changed the RSFBs.

The slop is in the subframe. No amount of additional damping in the rear shocks is going to change that.

[thakid22]

Originally Posted by Bimmer-Bob

I've been running the Dinan mounts for years. But I changed the dampers and springs at the same time, so it's impossible for me to quantify the effect of the mounts themselves. But I do know that I continued to experience the confidence-sapping rear-end pogo until I changed the RSFBs.

The slop is in the subframe. No amount of additional damping in the rear shocks is going to change that.

You stated several facts here...
The stock subframe bushings are very soft and induce sloppiness. #FACT
You changed Dampers and Springs. #FACT
You continued to experience pogo/bounce. I'll take your experience with that combo as #FACT.

I will add one more #FACT though...
Adding Dinan rear mounts to my E90 Sport Package (with stock-ish struts and factory springs) IMMEDIATELY quelled the rear hop/bounce/pogo on my vehrear. #FACT
Several others with stock suspension components gained similar results. #FACT

I do have a question form you though...
You said no amount of stiffer rear damping will exorcise the pogo/bounce from the rear.
It seems you have actual experience with stiffer struts, so I'm interested in your take on the following scenario:
I had bounce back there on stock sport suspension. I bought Koni FSD shocks and it improved (I assumed because they were new). There was still bounce so I bought Bilstein HD shocks hoping to cure it, and here is where my question comes in. When I intially installed the HD's dive/squat/roll/pitch/hop/pogo/bounce ALL were reduced to negligible levels. The body of the car was super flat and composed under all normal and most sporty conditions. But, this did NOT come at no expense. The ride was EXTRA firm. No not firm, but hard/harsh/bumpy. The car was expertly tied to the road, but the ride was wayyyy too rough. Nevertheless, the rear bounce was gone, with a bonus of superb body control and resistance to dive/roll/squat.
I liked the added body control (and lack of rear bounce too) so much that I decided to keep the HDs even though the bump harshness was much too high. Mind you, at this time I was still using factory (albeit they new) rear mounts that were installed with the prior FSD shocks.
Figuring that no one could actually be satisfied with this level of harshness though, I googled the HDs and found that they tend to ride super stiff out of the box until they break-in. Sure enough, over the next several hundred miles, the ride got smoother and smoother each day as the shocks broke in. BUT, as the ride got smoother, quieter, and more forgiving, the body control was diminishing at a proportionate rate. 500 miles later, with the Bilsteins break-in process well underway (if not completed), the ride was smooth, quiet, firm. Dive, squat and body control, and roll, were on par with FSD's (slightly better in some dynamic situations). Very nice indeed. However, the rear bounce/pogo was there again, just like before. It left me with the impression that in their stiff, new, pre break-in state, the additional HD damping had solved the bounce. And they had. But the final damping rate after break-in was low enough to allow the bounce to easily be seen and felt again. I share this experience to say, that stiffer shocks DID cure my bounce as well. But again, I was on stock springs. Secondarily, it didn't stay cured because the HD damping artificially high, when new out of the box at initial installation. When the HD monotube shocks broke in to their "normal" state, the bounce was back. I had planned to buy M3RSFB or even stiffer shocks than the Bilsteins, because the bounce had to go. I'm glad I ran into Dinans before incurring those expenses because they were exactly what I needed.

Again, I'll be the first to admit that the stock BMW suspension calibration is severely compromised for a number of reasons, depending on your actual use and needs. I suspect trying to design around the runflats is part of the problem.

There are multiple solutions to any problem. My problem was strictly the rear pogo effect. Dinans fixed that, for me. Could M3 subframe bushings do the same and more? Of course.
Are there also other ways of quelling the bounce. Again, of course. Might your results be different than mine on if tried on a different suspension? Once more, of course.

At the risk of sounding repetitive, all those who have tried the dinans on STOCK suspension have been pleased. I have no experience with this situation in regards to coilovers, air bags, lowering springs or any other non stock(ish) configuration. Accordingly, I won't comment on those setups. But on stock suspension the Dinans were EXCELLENT at removing bounce.

[Gangplank]

I'm sure someone else will chime in on the differences the dampers and springs make, but my real issue with the soft suspension was a side-to-side and roll on corner exit. Its especially noticeable on off camber corners. The back end rolls and then moves laterally again. For me the RSFB inserts settled the rear end s-to-s and up-down axis.

I do have the M-sport suspension which comes with different bump stops than the stock 128 or 328 so not sure if that helps. After reading more in the above linked thread it sound like the Dinan RSMs do give some improvement. I don't think anyone is debating whether they make an improvement, but whether they do as much as the RSFB inserts or M3 RSFBs is the question.

Of course one thing that I've seen repeated here and there is that members did the RSFB inserts and then eventually wanted more and did the full M3 RSFBs. I'm wondering if they inserts by themselves by being stiffer put more wear into the rear shock mounts so over time some of the looseness comes back. In that case it may be worth while to do both.