Question for suspension experts

Hey guys,
First off, thanks to all for contributing such great info to this forum. It's been extremely helpful over the past few months as I've been making plans for my 2017 LB GT Premium PP. On to my question...

I just finished installing BMR's SP080 springs, BK055 LCA bearing kit, and the CB005 cradle bushing lockout kit, and on the ~1 mi test drive I noticed the car is extremely bouncy coming from the rear. I expected a certain amount of twitchiness since I certainly need an alignment, but it feels seriously underdamped: the rear seems to experience a somewhat high frequency oscillation that takes a few cycles to dampen.

Can anyone think of anything I may have missed that I should check?

For some additional background:
-I stuck with my stock PP shocks/struts given the spring rates of the SP080's.
-No other suspension mods
-I made sure to cut the bump stops per the BMR installation instructions
-I seem to be getting the expected F/R ride height after installation and the short test drive, and driver/passenger sides are pretty consistent.
-I made sure to properly seat the springs during installation.
-I made sure to tighten all front/rear bushings with the car up on ramps to account for any clocking issues


Unfortunately I haven't been able to find any alignment shops that have a multi-alignment option like I've seen some reference on the forum, and I'd really like to sort out any potential issues before the alignment if I can. Otherwise I'd just go get the alignment and hope for the best.

Thanks again!

It could be at least partially the LCA bearing. That causes all the vehicle's reactions to occur much quicker and will make the car feel different than it did previously. Vehicle reaction time is real quick- Up. Down. It can also make the spring rate more effective because it reduces bind in the suspension's travel.

My guess is the high compression of the PP shocks cause a bounce up and the reduced bind and effectiveness of the vehicle's reaction down is more noticeable now because the LCA stiffened everything up. Perhaps the lack of control of the PP shocks are more apparent now than it was prior.

I've seen a bunch of posts here of people complaining about the PP shocks and their excessive compression / lack of control. Idk whether that's true bc I don't have a PP car. But that could be affecting the ride quality.

Apart from that I'm not sure - maybe someone else can chime in.
[MENTION=10281]BmacIL[/MENTION], [MENTION=26233]Rebellion[/MENTION], what are your thoughts?

Well, the rear does suffer from a lack of rebound control. With SP080's though, you shouldn't see much difference, and should actually improve on the PP stock ride.

First thing I would do is check bumpstops. I know you said you cut to install instructions, but it's worth another check. Please post the rear bumpstop height if you can get a chance. I would consider trying to cut off more or replace with the Steeda ones. They're shorter but of a stiffer material, so they'll still protect you when you hit a big one, but will allow for more free travel. The car uses its stops a lot.

It's definitely not an alignment issue. One other item that is unfortunately a little pricey that supposedly helped with bouncy feeling after LCA bearing installs is the billet upper mounts that Steeda makes also. It has a spherical bearing instead of a bushing. The LCA bearing by itself should not cause the car to be more bouncy (in an uncontrolled, resonant fashion at least), though will make the suspension react quicker overall to inputs.

Bluemustang said:

It could be at least partially the LCA bearing. That causes all the vehicle's reactions to occur much quicker and will make the car feel different than it did previously. Vehicle reaction time is real quick- Up. Down. It can also make the spring rate more effective because it reduces bind in the suspension's travel.

My guess is the high compression of the PP shocks cause a bounce up and the reduced bind and effectiveness of the vehicle's reaction down is more noticeable now because the LCA stiffened everything up. Perhaps the lack of control of the PP shocks are more apparent now than it was prior.

I've seen a bunch of posts here of people complaining about the PP shocks and their excessive compression / lack of control. Idk whether that's true bc I don't have a PP car. But that could be affecting the ride quality.

Apart from that I'm not sure - maybe someone else can chime in.
[MENTION=10281]BmacIL[/MENTION], [MENTION=26233]Rebellion[/MENTION], what are your thoughts?

Click to expand...

The LCA shouldn't have a huge effect on underdamping...I am actually noticing a better ride at speed, most likely due to the damper/spring combination working more effectively "as it should". On the other side, I also think that whatever phenomena you had previously, the LCA will make it more apparent due to the lack of the "vague zone" (suspension turned off at low speeds and at transition points) that previously was there and the hysteresis (weird inflexion on the response that I can't explain why). With the stock LCA bushing, your senses becomes "dulled" so to speak.

The stock damper also has this hysteresis zone, which a stiffer springs and theoretically, the LCA, will help to minimize. [MENTION=10281]BmacIL[/MENTION] can explain this better than me, the behavior of these dampers are not as linear as expected.

However, from the PP car I had test driven, the setup is underdamped to begin with...putting stiffer springs will definitely result in more underdamped feel. Could be bumpstops also, as said by [MENTION=10281]BmacIL[/MENTION], apart from causing the bounciness it does adds to the effective spring rate when they are used.

Rebellion said:

The LCA shouldn't have a huge effect on underdamping...I am actually noticing a better ride at speed, most likely due to the damper/spring combination working more effectively "as it should". On the other side, I also think that whatever phenomena you had previously, the LCA will make it more apparent due to the lack of the "vague zone" (suspension turned off at low speeds and at transition points) that previously was there and the hysteresis (weird inflexion on the response that I can't explain why). With the stock LCA bushing, your senses becomes "dulled" so to speak.

The stock damper also has this hysteresis zone, which a stiffer springs and theoretically, the LCA, will help to minimize. [MENTION=10281]BmacIL[/MENTION] can explain this better than me, the behavior of these dampers are not as linear as expected.

However, from the PP car I had test driven, the setup is underdamped to begin with...putting stiffer springs will definitely result in more underdamped feel. Could be bumpstops also, as said by [MENTION=10281]BmacIL[/MENTION], apart from causing the bounciness it does adds to the effective spring rate when they are used.

Click to expand...

It's not so much hysteresis as just the tuning. The low speed bleed settings on the PP dampers are very tight, so with very low displacement but consistent frequency inputs like concrete expansion joints, the fluid won't pass by easily, causing a significant portion of the bounce. Higher rate rear springs would make a classically underdamped system worse, but this is a bit more nuanced. The higher rate will force a sharper/faster response and break through more of the bleed.

Thanks guys! Sounds like the consensus is that the bumpstops may need to be cut further. I'll give Kelly a call tomorrow to get his opinion. I'll also snap a couple photos when I have time to get the car back in the air.

I wonder if others have had to cut their bumpstops beyond the written instructions?

Now I'm contemplating going with Konis or possibly Steeda's shock/strut offering. The bounciness has to go.

That makes perfect sense, apparently I need to do some more research to compare PP dampers to the leading aftermarket options. Did I miss shock dyno curves? I'll dig into this some more before pulling the trigger on anything else.

This behavior is extreme enough that I'm thinking something isn't right with my setup though. There are plenty of positive reviews with this spring/damper combo and I can't believe any of them would find my ride quality to be acceptable.

BmacIL said:

It's not so much hysteresis as just the tuning. The low speed bleed settings on the PP dampers are very tight, so with very low displacement but consistent frequency inputs like concrete expansion joints, the fluid won't pass by easily, causing a significant portion of the bounce. Higher rate rear springs would make a classically underdamped system worse, but this is a bit more nuanced. The higher rate will force a sharper/faster response and break through more of the bleed.

Click to expand...

Jmart said:

Thanks guys! Sounds like the consensus is that the bumpstops may need to be cut further. I'll give Kelly a call tomorrow to get his opinion. I'll also snap a couple photos when I have time to get the car back in the air.

I wonder if others have had to cut their bumpstops beyond the written instructions?

Now I'm contemplating going with Konis or possibly Steeda's shock/strut offering. The bounciness has to go.

Click to expand...

Koni's will be a bit much for SP080's, as they're quite firm on compression even at the softest rebound settings. The Steeda ones will work very well though.

I would call Kelly first and then maybe try cutting another 1/4"-3/8" off.

If you are not interested in chasing the perfect damping rates the Steeda fixed valve Pro-Actions are very very good. Might be slightly over-damped for the SP-080's but not as much as the Koni's for sure. I really like mine though I'm running Steeda Linear Sport springs (20% higher rate than the PP). The price is right.

Jmart said:

Thanks guys! Sounds like the consensus is that the bumpstops may need to be cut further. I'll give Kelly a call tomorrow to get his opinion. I'll also snap a couple photos when I have time to get the car back in the air.

I wonder if others have had to cut their bumpstops beyond the written instructions?

Now I'm contemplating going with Konis or possibly Steeda's shock/strut offering. The bounciness has to go.

Click to expand...

I am on the same rear springs with PP shocks. Its steady and pretty well planted for me. I'm not getting any bounce. I cut the bump stops down as recommended.

I was on Konis for a while with these springs but even on full soft, I found them to be too harsh.

Update: I just got off the phone with Kelly, who recommended I get my alignment and give the new LCA bearings a chance to break in a bit before worrying.

One thing I neglected to mention previously is that I'm currently running my CB005 kit without the front upper bushing cups in place due to a minor mixup with what I was shipped. Kelly is on the ball and is rushing me the taller cups so I can get those swapped in as well; for now I'm going to hold off on my alignment until I can swap in the upper cups. Once they're installed and I'm aligned, I'll drive the car some more and report back. It's possible that the BK055/CB005 combo has stiffened everything up to a point that the upper bushing deflection is causing the strange resonance that I'm experiencing.

TL/DR: I could be experiencing a perfect storm of inputs between the missing CB005 upper cups, the guaranteed need for a realignment, and overly stiff LCA bearings that need a chance to break in.

As a side note, thanks again to Kelly for the outstanding support! It's refreshing to work with a company that stands behind their products 110%.

Jmart said:

Update: I just got off the phone with Kelly, who recommended I get my alignment and give the new LCA bearings a chance to break in a bit before worrying.

One thing I neglected to mention previously is that I'm currently running my CB005 kit without the front upper bushing cups in place due to a minor mixup with what I was shipped. Kelly is on the ball and is rushing me the taller cups so I can get those swapped in as well; for now I'm going to hold off on my alignment until I can swap in the upper cups. Once they're installed and I'm aligned, I'll drive the car some more and report back. It's possible that the BK055/CB005 combo has stiffened everything up to a point that the upper bushing deflection is causing the strange resonance that I'm experiencing.

TL/DR: I could be experiencing a perfect storm of inputs between the missing CB005 upper cups, the guaranteed need for a realignment, and overly stiff LCA bearings that need a chance to break in.

As a side note, thanks again to Kelly for the outstanding support! It's refreshing to work with a company that stands behind their products 110%.

Click to expand...

Knowing that, I bet that could be the reason.

Jmart said:

Update: I just got off the phone with Kelly, who recommended I get my alignment and give the new LCA bearings a chance to break in a bit before worrying.

One thing I neglected to mention previously is that I'm currently running my CB005 kit without the front upper bushing cups in place due to a minor mixup with what I was shipped. Kelly is on the ball and is rushing me the taller cups so I can get those swapped in as well; for now I'm going to hold off on my alignment until I can swap in the upper cups. Once they're installed and I'm aligned, I'll drive the car some more and report back. It's possible that the BK055/CB005 combo has stiffened everything up to a point that the upper bushing deflection is causing the strange resonance that I'm experiencing.

TL/DR: I could be experiencing a perfect storm of inputs between the missing CB005 upper cups, the guaranteed need for a realignment, and overly stiff LCA bearings that need a chance to break in.

As a side note, thanks again to Kelly for the outstanding support! It's refreshing to work with a company that stands behind their products 110%.

Click to expand...

That makes more sense now. Willing to bet that is the cause. Not surprising - Kelly is on the ball. Give us an update to see if that sets you right. No need for an alignment until you get everything situated.

Update: the CB005 upper bushing cups arrived right on time and they went in without a fuss. CB005 is now 100% installed, along with the LCA bearing and SP080 springs. Car still isn't aligned.

Went out and drove ~20 miles in various conditions to really assess my situation. Although a portion of the strange resonance I was feeling definitely went away, the rear still feels very unsettled and excessively bouncy - instead of a firm up/down, I get a firm 3-5 up/down oscillations over any imperfections in the road.

At this point I'm at a bit of a loss. I'm planning to get an alignment Monday and drive the car for a couple of weeks in the hope that the LCA bearings loosen up, this is something Kelly suggested I try. If that doesn't work, though, I'm not sure what my next step will be. Part of me wants to just jump into new shocks/struts, but the reason I selected the SP080s was to retain my stock PP units and I'd probably want a different spring to pair with whatever dampers I select. This isn't an ideal road to be traveling so soon.

Jmart said:

Part of me wants to just jump into new shocks/struts, but the reason I selected the SP080s was to retain my stock PP units and I'd probably want a different spring to pair with whatever dampers I select. This isn't an ideal road to be traveling so soon.

Click to expand...

If you want to go with a simple, non-adjustable solution for your car that is affordable the Steeda fixed valve Pro-Action shocks are really really good. They are what the PP shocks should have been. And affordable too. Properly damped for our cars - much better rebound. Between that and either properly trimmed bump stops or the Steeda adjustable bump stops and you should be in much better shape.