Impreza struts vs. Forester struts: The Difference

Porter · 08-22-2006, 02:00 PM

There is a lot of speculation that floats around about Impreza struts and Forester struts and mixing and matching and what works and what doesn't.

I got the hard data from KYB directly, they manufacture the OEM struts themselves in all the variations, and they produce the most common OE replacement and OE fitment sport shocks currently available for the Subaru platform.

All measurements are in Millimeters.

The Differences:

Code:

FRONT
  Lower Hole To Spring Seat
     Impreza   252
     Forester  253
  Total Strut Body Length
      Impreza   356
      Forester  377
  Extended Length (Body + Shaft)
       Impreza   525
       Forester  560 [514]
  Compressed Length (Body + Shaft)
       Forester  391

REAR
  Lower Hole To Spring Seat
     Impreza   315
     Forester  330
  Total Strut Body Length
      Impreza   367
      Forester  407
  Extended Length (Body + Shaft)
       Impreza   605
       Forester  643 [632]
  Compressed Length (Body + Shaft)
       Forester  455

Hopefully this will help some of you with the differences in strut geometry.

The second figure on the Forester extended length measurements is due to the internal droop limiting spring that is in the Forester struts. The figure in brackets is the free extension before the spring becomes involved. The total extension is the length when the limiting spring is fully compressed (shaft fully extended under load).

I have not touched on the differences in spring length or preload, those are equally important figures... but this chart should illustrate why there are different spring designs between the Impreza and Forester.

Enjoy,

Porter

pleiad7 · 08-22-2006, 02:03 PM

This deserves a sticky.

Porter · 08-22-2006, 02:07 PM

Thanks!

mo_boost · 08-27-2006, 06:17 PM

Did you by chance get the difference in total stroke w/o the spring (fully compressed to fully extended)? That would be tremendously helpful. I am working on trying to make some sort of adapter to fit the AGX shocks/struts onto Foresters.

Porter · 08-27-2006, 07:53 PM

I believe both struts retract almost fully into the housing, with about an inch of shaft exposed. The "fully extended" measurement is to the top of the chrome shaft surface, not including the threaded area.

Subtracting the strut body length from the total extended measurement should give you a rough idea of the length of total travel.

I will call KYB back tomorrow and get a real answer on the total stroke.

BTW... I don't think it's going to be easy to "adapt" AGXs to the Forester and keep Forester geometry... the spring perch height and total travel are quite different.

My personal solution would be to use a set of Koni inserts sized for the Forester, or a Forester-specific coilover.

Peaty · 08-28-2006, 06:55 PM

Just a little pic to add since I happen to have one, notice the top of the Foresters strut, it appears the top can be screwed off but I have not tired myself. I'm not sure if it's threaded or not.

Porter · 08-29-2006, 02:18 PM

Peaty,

It's not threaded. That is a standard KYB/Showa strut top cap. It is press-fit into place and holds the inner strut cartridge assembly in place. There is a seal system underneath the cap.

Peaty · 08-29-2006, 03:05 PM

Is there a way to remove the cap, change the insert and put a new cap on?

Porter · 08-29-2006, 07:00 PM

Quote:

Originally Posted by Peaty

Is there a way to remove the cap, change the insert and put a new cap on?

If you remove the cap the strut is essentially "ruined" for KYB-valving purposes.

It is however quite ideal for Koni-insert use... though the housing will need to be trimmed down somewhat (slightly) depending on the exact length of the Koni insert.

Hmm... lots of Koni interest here. I'll be on the phone with Koni tomorrow.

Porter · 08-31-2006, 04:40 AM

EDIT

Added compressed length to the figures. Note that this is total body and strut shaft to the end of the chrome rod area, not including the threaded end.

teiva-boy · 09-12-2006, 04:57 PM

Whats the word from Koni?

I'm about to work with Tom@kartboy and seeing if it's possible to make our own spacer (ala whiteline's kit) for the stockers.

Porter · 09-13-2006, 05:28 AM

I have not gotten a chance to speak with the folks at Koni, work has been crazy. I know the right individual there though, we worked together somewhat on the SVX fitment inserts a few years ago.

teiva-boy · 10-05-2006, 11:37 AM

Any word on speaking to your contacts at Koni?

Evil XT · 11-28-2006, 09:11 AM

Anywork from koni?
Can we usethe Koni incerts?

marooned RS · 12-21-2006, 02:22 PM

Quote:

Originally Posted by Evil XT

Anywork from koni?
Can we usethe Koni incerts?

..........Don't know if this will help,but you can try contacting Dave or Barrett at www.allwheelsdriven.com, he might be able to help you out or at least answer your questions.They have been been fabbing up Subaru strut bodies to take Bilstein HD strut inserts(same as Koni I believe) for Impreza rally cars,they have the screw top which you need anyway,H&R springs,Group N top hats

08-22-2006, 02:00 PM	#1 (permalink)
Porter Asphalt Surfers Unlimited Contributing Member Join Date: Feb 2006 Location: Roanoke, Virginia Posts: 751 Gallery: 0 Feedback Score: 0 reviews	Impreza struts vs. Forester struts: The Difference There is a lot of speculation that floats around about Impreza struts and Forester struts and mixing and matching and what works and what doesn't. I got the hard data from KYB directly, they manufacture the OEM struts themselves in all the variations, and they produce the most common OE replacement and OE fitment sport shocks currently available for the Subaru platform. All measurements are in Millimeters. The Differences: Code: FRONT Lower Hole To Spring Seat Impreza 252 Forester 253 Total Strut Body Length Impreza 356 Forester 377 Extended Length (Body + Shaft) Impreza 525 Forester 560 [514] Compressed Length (Body + Shaft) Forester 391 REAR Lower Hole To Spring Seat Impreza 315 Forester 330 Total Strut Body Length Impreza 367 Forester 407 Extended Length (Body + Shaft) Impreza 605 Forester 643 [632] Compressed Length (Body + Shaft) Forester 455 Hopefully this will help some of you with the differences in strut geometry. The second figure on the Forester extended length measurements is due to the internal droop limiting spring that is in the Forester struts. The figure in brackets is the free extension before the spring becomes involved. The total extension is the length when the limiting spring is fully compressed (shaft fully extended under load). I have not touched on the differences in spring length or preload, those are equally important figures... but this chart should illustrate why there are different spring designs between the Impreza and Forester. Enjoy, Porter __________________ -Porter- '04 F-XT Silver I love the smell of brake pads in the morning. Smells like... victory.

08-22-2006, 02:03 PM	#2 (permalink)
pleiad7 The Seventh Sister Administrator Join Date: Jan 2006 Location: North of the Bay Posts: 17,146 Gallery: 21 Feedback Score: 29 reviews	This deserves a sticky. __________________ -Silke 04 FXT PP PSM ~ "Subed" 98 Forester S ~ "Slynki"

08-22-2006, 02:07 PM	#3 (permalink)
Porter Asphalt Surfers Unlimited Contributing Member Join Date: Feb 2006 Location: Roanoke, Virginia Posts: 751 Gallery: 0 Feedback Score: 0 reviews	Thanks! __________________ -Porter- '04 F-XT Silver I love the smell of brake pads in the morning. Smells like... victory.

08-27-2006, 06:17 PM	#4 (permalink)
mo_boost Developer Contributing Member Join Date: Jan 2006 Location: Houston, TX Posts: 129 Gallery: 0 Feedback Score: 3 reviews	Did you by chance get the difference in total stroke w/o the spring (fully compressed to fully extended)? That would be tremendously helpful. I am working on trying to make some sort of adapter to fit the AGX shocks/struts onto Foresters. __________________ Got Boost?

08-27-2006, 07:53 PM	#5 (permalink)
Porter Asphalt Surfers Unlimited Contributing Member Join Date: Feb 2006 Location: Roanoke, Virginia Posts: 751 Gallery: 0 Feedback Score: 0 reviews	I believe both struts retract almost fully into the housing, with about an inch of shaft exposed. The "fully extended" measurement is to the top of the chrome shaft surface, not including the threaded area. Subtracting the strut body length from the total extended measurement should give you a rough idea of the length of total travel. I will call KYB back tomorrow and get a real answer on the total stroke. BTW... I don't think it's going to be easy to "adapt" AGXs to the Forester and keep Forester geometry... the spring perch height and total travel are quite different. My personal solution would be to use a set of Koni inserts sized for the Forester, or a Forester-specific coilover. __________________ -Porter- '04 F-XT Silver I love the smell of brake pads in the morning. Smells like... victory.

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08-29-2006, 02:18 PM	#7 (permalink)
Porter Asphalt Surfers Unlimited Contributing Member Join Date: Feb 2006 Location: Roanoke, Virginia Posts: 751 Gallery: 0 Feedback Score: 0 reviews	Peaty, It's not threaded. That is a standard KYB/Showa strut top cap. It is press-fit into place and holds the inner strut cartridge assembly in place. There is a seal system underneath the cap. __________________ -Porter- '04 F-XT Silver I love the smell of brake pads in the morning. Smells like... victory.

08-29-2006, 03:05 PM	#8 (permalink)
Peaty The Modfather Join Date: Jan 2006 Location: Lawrence, KS - Rock Chalk Posts: 6,860 Gallery: 0 Feedback Score: 8 reviews	Is there a way to remove the cap, change the insert and put a new cap on? __________________ Peaty 2010 Legacy 3.6 R - Limited 2006 B9 Tribeca - Limited 1999 Miata - MX5

08-31-2006, 04:40 AM	#10 (permalink)
Porter Asphalt Surfers Unlimited Contributing Member Join Date: Feb 2006 Location: Roanoke, Virginia Posts: 751 Gallery: 0 Feedback Score: 0 reviews	EDIT Added compressed length to the figures. Note that this is total body and strut shaft to the end of the chrome rod area, not including the threaded end. __________________ -Porter- '04 F-XT Silver I love the smell of brake pads in the morning. Smells like... victory.

09-12-2006, 04:57 PM	#11 (permalink)
teiva-boy Join Date: Apr 2006 Location: San Diego Posts: 706 Gallery: 0 Feedback Score: 3 reviews	Whats the word from Koni? I'm about to work with Tom@kartboy and seeing if it's possible to make our own spacer (ala whiteline's kit) for the stockers. __________________ This information is provided "as-is".

09-13-2006, 05:28 AM	#12 (permalink)
Porter Asphalt Surfers Unlimited Contributing Member Join Date: Feb 2006 Location: Roanoke, Virginia Posts: 751 Gallery: 0 Feedback Score: 0 reviews	I have not gotten a chance to speak with the folks at Koni, work has been crazy. I know the right individual there though, we worked together somewhat on the SVX fitment inserts a few years ago. __________________ -Porter- '04 F-XT Silver I love the smell of brake pads in the morning. Smells like... victory.

10-05-2006, 11:37 AM	#13 (permalink)
teiva-boy Join Date: Apr 2006 Location: San Diego Posts: 706 Gallery: 0 Feedback Score: 3 reviews	Any word on speaking to your contacts at Koni? __________________ This information is provided "as-is".

11-28-2006, 09:11 AM	#14 (permalink)
Evil XT Join Date: Jan 2006 Location: NJ Posts: 596 Gallery: 0 Feedback Score: 3 reviews	Anywork from koni? Can we usethe Koni incerts? __________________ Positive Pressure Research and Development & Peculiar Mollusks

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