Advice please... small/med/large shims on Phat LCA bushes?

[Mickyboy]

Hi all. I'm hoping to tap into vast knowledge base on the forum please!

About 2 months ago I replaced my stock LCA bushes with the highly recommended Jspeed ones from Garage 88 (Phat), clearly they are a quality product. I got a local suspension place (I won't mention their name) to install them with specific instructions on having the LARGE shim below and SMALL shim above the bushes (which the installer wrote down at the time) as recommended by the manufacturer and the supplier.

Yesterday, whilst having a roll centre adjustment kit installed at the same place, I asked if the installer (same guy) would check the shims he installed 2 months earlier and tell me what size they were. Well it turns out he has put the same size shims top and bottom, ie the medium sized ones, despite my earlier request. Of course he justified his decision by saying there is no reason or benefit for installing a large shim bottom and a small one on top. Whether he is right or wrong, this is information I should have been told at the time he originally installed them. Of course the large and small shims that came with the bushes have since been thrown out by the installer so I don't even have them anymore. (may have to start looking for some).

He is an experienced installer so I trust him to know his stuff, but I don't think I'll be using him again. Unfortunately I'm far from an expert on the science of suspension so I am unable to intelligently argue with him on the subject. In all honesty I'm REASONABLY happy with how the car feels, but if there is a further improvement in turn in and feel to be made simply by moving some shims then I'd be mad not to give it a try. All I'm after is the best possible handling/steering feel with minimal compromise to the ride quality.

Which leads me to these questions...

What exactly does the large shim bottom/small shim top achieve? Obviously it would raise the rear of the LCA somewhat, but why? Is it an increase in castor or something else?

Does doing that have any detrimental effect on ride quality or NVH as compared to having the medium shims top/bottom?

I know that the dedicated thread on the Garage 88 LCA bushes touches on this subject, but I'm really hoping to get some more clarity on the subject.
Any input greatly appreciated,

Mick.

[alessandro132]

Hi Mick,

Found this as a good starting point: viewtopic.php?f=38&t=5481&start=135

Trying to distill my thoughts here so might be very rough around the edges but bear with me!

It appears that stock set up/geometry would be akin to big shim on top, small shim on the bottom, so I'd say by reversing this (raising the control arm) you're increasing your castor angle (+ve) as much as possible from the supplied shims, which would in turn improve directional stability resultant from the increase in positive castor.

I think because it's only increasing castor by a small amount (matter of mm) you're not overdoing the castor so you can notice sharper, more defined turn in (directional stability) as a result and not over-heavy/less responsive steering feeling from too much positive castor.

I can personally attest to this on the road when I swapped over from my OEM bushes to the J Speeds which have the small shim on top and big shim on the bottom.

[Mickyboy]

Thanks Al,

Yeah I remember reading that post (a few times) but was still a little confused as to how exactly it works. I think I'm gonna have to try the small/large shim set-up and see how it compares. Now i need to find some more shims. I guess I'm gonna need another wheel alignment after doing that too, right? I just got one done! This is getting expensive.

[alessandro132]

It all adds up

And if it makes you feel better, I rashed my brand new Work XT7s on my way home late last night - looking at around $400 to reweld and respray

[shav]

Thanks Al,

Yeah I remember reading that post (a few times) but was still a little confused as to how exactly it works. I think I'm gonna have to try the small/large shim set-up and see how it compares. Now i need to find some more shims. I guess I'm gonna need another wheel alignment after doing that too, right? I just got one done! This is getting expensive.

Hey Mick, why dont you wait till your ready for your next tire rotation rather than spend up getting the shims changed and new wheel align? If the car is still handling ok for now, I'd just leave it till you need to do your tire rotation. Just sayin

[Mickyboy]

Far too logical for my liking Shav!

[shav]

Far too logical for my liking Shav!

oh of course,....what was I thinking.

[Robbks]

Just for a little perspective here.
The gen4 liberty Chassis and it's front end geometry is far superior as far as caster (and thus dynamic camber) is concerned
as compared with the 1988 design geometry of everything that came before it, where the LCA mods made a vast difference, but there were also large changes in geometry.
i.e flipping LCA mounts to move the pivot point 6-7mm and then adding 12mm spacers.

is anyone actually experimenting with different (to factory) wheel alignment settings?
I know i am.
When i first bought my gen4 i had a fresh alignment to factory specs to see how it handled.
not bad, just typical Subaru, understeery, but stable and predicatble.

I then went to the old settings i'd used with good success (after refinement) on previous rides (Gen2 Legacy, MY99 Forester)
which were 0* toe all around the car, and -1.5* camber on the front. But the gen4 geometry wouldn;t even allow 1.5*, 1.2* was the max.
With these settings the car got much better, it wanted to turn in better, change directions better but it did have two downsides
1) it did lose a little straight line stability on bumpy roads, but nothing drastic or worrying
2) During reasonable cornering where the dynamic camber (due to larger caster angle) would really hook up and when the weight transferred over the outside wheel, the car would turn more sharply than the steering input would suggest. great for the track as it just pulls you round the corner, but not for the road if you're not expecting it

I've now had a new alignment, still with zero toe, but we've backed off the camber to 0.75* (standard is 0.33*)
I suspect it will be the improvement over stock that I want, but without that extra whip which is not needed on a road car.

All of this is with standard geometry and specB suspension (22mm adjustable rear bar)

[Rome_BRZ]

Why don't you give Garage 88 and speak to Michael about it since he's the one who supplied them?

[Mickyboy]

Yep I've contacted him via email. Thought I'd get some more opinions whilst awaiting his reply.

[alessandro132]

Just for a little perspective here.
The gen4 liberty Chassis and it's front end geometry is far superior as far as caster (and thus dynamic camber) is concerned
as compared with the 1988 design geometry of everything that came before it, where the LCA mods made a vast difference, but there were also large changes in geometry.
i.e flipping LCA mounts to move the pivot point 6-7mm and then adding 12mm spacers.

is anyone actually experimenting with different (to factory) wheel alignment settings?
I know i am.
When i first bought my gen4 i had a fresh alignment to factory specs to see how it handled.
not bad, just typical Subaru, understeery, but stable and predicatble.

I then went to the old settings i'd used with good success (after refinement) on previous rides (Gen2 Legacy, MY99 Forester)
which were 0* toe all around the car, and -1.5* camber on the front. But the gen4 geometry wouldn;t even allow 1.5*, 1.2* was the max.
With these settings the car got much better, it wanted to turn in better, change directions better but it did have two downsides
1) it did lose a little straight line stability on bumpy roads, but nothing drastic or worrying
2) During reasonable cornering where the dynamic camber (due to larger caster angle) would really hook up and when the weight transferred over the outside wheel, the car would turn more sharply than the steering input would suggest. great for the track as it just pulls you round the corner, but not for the road if you're not expecting it

I've now had a new alignment, still with zero toe, but we've backed off the camber to 0.75* (standard is 0.33*)
I suspect it will be the improvement over stock that I want, but without that extra whip which is not needed on a road car.

All of this is with standard geometry and specB suspension (22mm adjustable rear bar)

Good post. Not too sure how much I want to fiddle with toe settings, but will be looking to run more negative camber at the front (new wheel/tyre package is just poking so want it sitting flush).

I think a little bit more negative camber with existing toe settings and increased castor from the LCA bushes will give me very nice turn in and front end grip through corners.

[Robbks]

Good post. Not too sure how much I want to fiddle with toe settings, but will be looking to run more negative camber at the front (new wheel/tyre package is just poking so want it sitting flush).

I think a little bit more negative camber with existing toe settings and increased castor from the LCA bushes will give me very nice turn in and front end grip through corners.

problem is, it's the toe that makes a lot of difference
toe out on the front makes initial turn in really good as it's like putting the breaks on the inside wheel only.
toe out on the rear also makes the car turn much better, but unsettles it.

Adding too much camber and leaving the toe stock can increase camber wear on the insides. and not provide any better initial turn-in, but should help mid-corner.
i went with zero toe and liked the feel it gave the car, it's now effortless to drive (with camber not maxxed out)

[shav]

Great posts Robbks. I too am looking for better turn in and wouldnt mind improving the stock setup to suit. Im not running the Spec B suspension like you. But if I could run perhaps even 0.5-1mm of toe in to help with the turn in, I reckon it will be worth it. At the moment I am getting understeer. Possible causes are due to poor tire quality and lack of camber/ toe in. However, I think it may not be to any advantage with standard springs/shocks. I reckon the weight transfer and body roll will be too much for the front corner to handle. Any thoughts with the setup of stock GT suspension?

[alessandro132]

Good post. Not too sure how much I want to fiddle with toe settings, but will be looking to run more negative camber at the front (new wheel/tyre package is just poking so want it sitting flush).

I think a little bit more negative camber with existing toe settings and increased castor from the LCA bushes will give me very nice turn in and front end grip through corners.

problem is, it's the toe that makes a lot of difference
toe out on the front makes initial turn in really good as it's like putting the breaks on the inside wheel only.
toe out on the rear also makes the car turn much better, but unsettles it.

Adding too much camber and leaving the toe stock can increase camber wear on the insides. and not provide any better initial turn-in, but should help mid-corner.
i went with zero toe and liked the feel it gave the car, it's now effortless to drive (with camber not maxxed out)

If my understanding is correct, then toe out (to a conservative extent) ought to minimise camber wear by negative camber (say -2 degrees)?

I have a feeling I won't be able to get away with anything less than that amount of camber to get the front wheels/tyres sitting nice and flush with the guards.

Will do some experimenting though

[bigBADbenny]

I'll be finding out very soon at any rate.
Jspeed LCA bushes, WL RCA kit and BC V1 coilovers going on asap!
Thus needing to dig up Phat's LCA instructions!

I was under the impression that the shims are meant to help "level" the lower control arms according to:

A: the amount by which the car is lowered on either springs or coilovers.
B: to match the geometry rectification provided by a Roll Center Adjustment kit.

Since Mickyboy is lowered by an inch at the front on Eibach springs and is planning a WL RCA kit, I'd guess that he'd use more shims on top of the rear bush, in order to get the front lower control arms more level.

Am I on the right track?