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Premium Member
2008 Forester XT Sports
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1,705 Posts
Discussion Starter #1 (Edited)
Ok guys, I think I have come up with a plan for the suspension on my XT.

Here it goes:
OEM 04 STI struts and springs
OEM STI 20mm rear sway (STI mounts plus spacer)
SPT Rear Latteral Links
Group-N Trailing Arm Bushings
Rear Subframe Bushings
Steering Rack Bushings
Group-N Strut Mounts (maybe?)

All that above is pretty basic, the problem is that I want near stock ride height. So my plan is to use 2" Lifting Spacers in the front and about 2.5" Spacers in the rear. This should give me about a 1.5" drop with pretty even wheel well gaps. Maybe even add another half inch to each spacer to get closer to stock!

The spacers will be custom and I can do that.

What do you guys think about my plan for a daily driver?
Provided the spacers are structurally good (and indexed properly), do you think I will have alignment issues?
Are there any other easy parts I might as well do while I have it apart?
I have read the post about making your Forester on par with an STI and it seems these are the easiest but still reasonably good mods.


Post #13 has the front roll center calcs
Post #16 has the rear roll center calcs
 

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2008 FSXT M/T
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4,167 Posts
2" is way overkill, i think youll be happy w/ just 1" lift spacers and they are already on the market! thats what i ran and was really happy w/ the ride height.

basically youll do all those handling mods, then negate them w/ a higher COG and body roll caused by the lift kit... and as far as alignment goes, im sure the kit will throw a wrench in2 that mix as well.

if you want good handling, there is no way around it, stiffer springs and lower ride height are a must!
 

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8,844 Posts
Koni inserts in stock forester housings+ spt wagon pinks. Then you'll actually have a decent amount of suspension travel instead of having a car with no travel on stilts.
 

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2017 VW Golf SportWagen 5MT
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10,784 Posts
SPT Wagon pinks will have the same amount of travel as stock STi springs, won't they? They are same length and rates..

I wouldn't mix forester struts with Impreza springs, either do one or the other. I'm not saying it won't work, but I would use whatever is designed to work together.

Stan
 

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99 UK S-turbo
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higher COG and body roll caused by the lift kit...
I'd love to know why the body lift will create more roll.....

Raising it (effectively versus the STi 2" drop) raises the roll centre by more than the CoG so the roll couple is reduced and the car will roll slightly less won't it!

Simon
 

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2008 Forester XT Sports
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1,705 Posts
Discussion Starter #6
I'd love to know why the body lift will create more roll.....

Raising it (effectively versus the STi 2" drop) raises the roll centre by more than the CoG so the roll couple is reduced and the car will roll slightly less won't it!

Simon
Hmmmm, measuring out the roll center might be a good idea! That will give me a really good idea about how much body roll I am going to get at different heights.

I have not looked at how ride height effects the roll center on the Foresters. Simon, do you have any calcs or a thread showing that the roll center drops faster then the CoG on these cars?

For anybody that wants to learn about Roll Center and how to calculate it: Suspension Tech - Sport Compact Car Magazine
 

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2004 Forester XT
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109 Posts
Dang! That's sounds like alot of cool mods, just to be negated or greatly reduced by huge spacers that might complicate things and cause other issues.

If you're looking for improved handling with just a little drop, I'd hit up the wagon stuts & spring combo (with the other stuff too). Or maybe some swift springs (with the other mods too)

FYI - I just did the STI Strut/Spring swap. My wife drives the foz as her daily, and she hasn't had any clearence issues at all. And with the snow we get in Montana it had me worried. Her 68' Jaguar has those kinda issues, the foz still doesn't, even with the huge drop.

I'm no expert, but it sounds like you're trying to have the best of both worlds. Great handling, plus big ride height, plus comfort. And I just don't see that happening. Good luck though. As long as you don't break the bank you can always try something different. :shrug:
 

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2017 VW Golf SportWagen 5MT
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10,784 Posts
I haven't had clearance issues with STi springs and Impreza size struts either, but the car is alot lower than stock. I like it that way thought. Another member is running Koni inserts with Forester struts and Swifts with good results. I love my Konis.

Stan
 

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2008 Forester XT Sports
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1,705 Posts
Discussion Starter #9
Dang! That's sounds like alot of cool mods, just to be negated or greatly reduced by huge spacers that might complicate things and cause other issues.

I'm no expert, but it sounds like you're trying to have the best of both worlds. Great handling, plus big ride height, plus comfort. And I just don't see that happening. Good luck though. As long as you don't break the bank you can always try something different. :shrug:
I am trying to get the best of both worlds! What else would I want? Ha ha.

I really do need all the clearance I can get. I regularly have kayaks/canoes/bikes on my car and need to get down some trails that most cars cannot.

Like was posted above, I am going to take very careful measurements on my car and figure out where my roll center is now and where it will be when I lower it a little. If I do see a benefit to a certain ride height then that is probably what I am going to go with. I'll post up some CAD drawings and calculations on the roll center locations.

Anybody know what the Vertical Center of Gravity measurements are for the Forester?
 

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99 UK S-turbo
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I have not looked at how ride height effects the roll center on the Foresters. Simon, do you have any calcs or a thread showing that the roll center drops faster then the CoG on these cars?
Well following this link from that page Suspension Roll Center Photo shows how to work out the roll centre on a mac strut.

I'm sure you could put the info into an excel spreadsheet so that once you've crunched it once you lower and raise the 2 mounting points by the same amaount to get the incremental change in RC.

Simon
 

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2007 Forester XT Sport
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403 Posts
I'd love to know why the body lift will create more roll.....

Raising it (effectively versus the STi 2" drop) raises the roll centre by more than the CoG so the roll couple is reduced and the car will roll slightly less won't it!

Simon
Dick Shine, a pretty well established VW performance guy had a whole web page explaining how lowering a car can INCREASE body roll, by raising the roll center over the CoG (I think that was it, he had diagrams and such :lol: )

IN GENERAL, raising it will increase roll, and lowering will decrease roll.

IN GENERAL that is. But as you and the VW guy have shown, it can have the opposite affect as well.
 

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99 UK S-turbo
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Actaully no, most cars have Mac struts, so as the lower arm is 'never' (I'm sure here will be the odd exception) half a cars width long, Lowering it (for the same spring rate) nearly always increases roll and rasiing it decreases roll......

As the arm is less than half a cars width long, lowering a car by say 2" typically lowers the roll centre by about 2.5" as the roll couple between CoG and roll centre has therefore increased by 1/2" the roll moment increases and the car rolls more.

Simon
 

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Premium Member
2008 Forester XT Sports
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1,705 Posts
Discussion Starter #13 (Edited)
Ok guys, I have done some roll center calculations for a few different setups and here are the results:

Lowered CoG: This refers to how much the CoG lowers compared to stock.
Roll Center: This is the calculated height of the roll center off of the ground.
Lowered RC: This is how much the roll center is lower compared to stock.
Roll Moment Change: This is [Lowered RC]-[Lowered CoG] which gives us the net effect of the CoG and roll center changes on the roll moment.


Stock Ride Height
Lowered CoG:0"
Roll Center: 11.957"
Lowered RC: 0"
Roll Moment Change: 0"

Dropped 3.5" with 04 STI take offs
Lowered CoG:3.5"
Roll Center: 2.328"
Lowered RC: 9.629"
Roll Moment Change: 6.129"

Dropped 3.5" then 2" Strut Top Spacers added
Lowered CoG:1.5"
Roll Center: 8.010"
Lowered RC: 3.847"
Roll Moment Change: 2.347"

(Rear values in post #16)

The key number here is the Roll Moment Change. Now since I do not have real CoG measurements at this point I can't calculate what % roll increase there will be by lowering your car "x" amount. These calculations do show that the more the car is lowered the worse the suspension geometry gets in regards to chassis roll. So with struts/springs/sways being equal, the more you lower your car the more it will roll!

I have attached the CAD drawings I made to calculate the roll centers.

Any of you guys know where I can find any information on the height of the Center of Gravity on these cars?
 

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05 FXT
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Ditch the subframe spacers and fix the roll center :)

Off Topic relative to your desires, but relevant to a lot of the discussion here.
 

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2008 Forester XT Sports
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1,705 Posts
Discussion Starter #15
Ditch the subframe spacers and fix the roll center :)

Off Topic relative to your desires, but relevant to a lot of the discussion here.
I completely agree! I forgot to measure the spacer height while I was under the car. Does anybody know the measurement on them? I will model that as well to see what it does!
 

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2008 Forester XT Sports
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1,705 Posts
Discussion Starter #16
The above calcs (post #13) were for the Front Suspension, here are the ones for the back:

Stock Ride Height
Lowered CoG:0"
Roll Center: 7.336"
Lowered RC: 0"
Roll Moment Change: 0"

Dropped 3.5" with 04 STI take offs
Lowered CoG:3.5"
Roll Center: -0.547"
Lowered RC: 7.883"
Roll Moment Change: 4.383"

Dropped 3.5" then 2" Strut Top Spacers added
Lowered CoG:1.5"
Roll Center: 4.248"
Lowered RC: 3.088"
Roll Moment Change: 1.588"
 

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Premium Member
2008 Forester XT Sports
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1,705 Posts
Discussion Starter #17 (Edited)
Well it seems nobody has any comments on the roll center calculations.....odd.

But anyway, I got my 2" Strut spacers done. Here are some pics:





 

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Premium Member
2008 Forester XT Sports
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1,705 Posts
Discussion Starter #19 (Edited)
Looks like Google Picasa is having issues right now, once that is resolved the pictures will show up.

Google having issues? Does this mean the end of the world is coming? :icon_confused:

Edit: I guess not it seems like its functioning again
Edit again: Might be back down!
 
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