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Old 08-11-2011, 03:45 AM   #1
williaty
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Default Real Numbers on the GTSpec ALK




As part of Carpocalypse 2011: Frustration's Revenge, I had my control arms off the car, which means I had the opportunity to pull off my GTSpec ALK and compare it to a set of stock STi transverse link bushings I had laying in the shop. The picture above is the result. So I've got some answers now, but also several more questions.

The biggie: does the GTSpec ALK relocate the rear of transverse link pivot point to reduce or remove the anti-lift/anti-dive geometry? YES. Depending on from which flange you measure (more on this in a moment), the rear pivot is relocated either 14.6mm or 20mm downwards as compared to the stock bushing.

Does the GTSpec ALK relocate the rear of transverse link pivot outwards to increase caster? Either no or maybe. As far as I can tell, the GTSpec ALK does not move the pivot point relative to the centers of the holes for the two bolts that hold it to the chassis. However, the holes in the bushing body are MUCH larger than on the stock housing, allowing you to make a much bigger move with the "Free Caster Mod #2" technique. Given that flipping the pin on the aluminum arms is said to give you 0.5*, I would estimate that the designed-in-slop in the oversized holes are gaining you another 0.5-0.75*. This would require more effort than I'm willing to expend in order to prove, though.

Now, the big wtf... The GTSpec ALK is 5.4mm vertically taller between the mounting flanges than the stock bushing. That's why I listed two possible relocation figures in the second paragraph. If you look up at the picture, I aligned both bushings to a "baseline" that represents the mounting surface of the lower/outer ear of the bushing. Now, look at the tops. The top surface of the bushing housing is the other part that has to mount to the chassis. Yet somehow they both bolt up to the chassis without problem and sit flush against the sheet metal. It makes no sense to me that they should do that! Anyone have a clue what's going on with that?
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Old 08-11-2011, 04:19 AM   #2
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The GT Spec product is a copy of the stock Forester piece, just with a stiffer bushing.
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Old 08-11-2011, 04:24 AM   #3
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Quote:
Originally Posted by Back Road Runner View Post
The GT Spec product is a copy of the stock Forester piece, just with a stiffer bushing.
In theory, they all are.
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Old 08-11-2011, 05:09 AM   #4
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in theory, they all aren't?

just added some lines to an old picture of mine, not laid out quite so nicely though.



They also angle the bushing to align with the crossmember.

I'll stick with whiteline.

Last edited by jamal; 08-11-2011 at 05:15 AM.
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Old 08-11-2011, 05:28 AM   #5
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Well, Whiteline does change the hole position some. However, if you pull off a stock Forester rear bushing and stick it next to the GT Spec one, it's the same thing. The GT Spec one is just a whole lot stiffer.

Here's a pic of my stock Forester rear bushing. It looks mighty familiar, doesn't it?
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Old 08-11-2011, 05:32 AM   #6
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Quote:
Originally Posted by jamal View Post
just added some lines to an old picture of mine, not laid out quite so nicely though.
Yeah, I still don't get it. Both the stocker and the GTSpec fit flush against the chassis. There's no fitment problems with either. It makes no sense.

Quote:
I'll stick with whiteline.
Yet for many of us, the Whiteline unit has a fundamental flaw that's insurmountable: it's made of polyurethane.
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Old 08-11-2011, 05:34 AM   #7
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Quote:
Originally Posted by Back Road Runner View Post
Well, Whiteline does change the hole position some. However, if you pull off a stock Forester rear bushing and stick it next to the GT Spec one, it's the same thing. The GT Spec one is just a whole lot stiffer.

Here's a pic of my stock Forester rear bushing. It looks mighty familiar, doesn't it?
Yet compare it to the housing of the Whiteline one as well. They all appear to be clones of each other in terms of the alumnium housing.
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Old 08-11-2011, 05:59 AM   #8
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looks like a difference in caster between all three. forester - none, gtspec - some, wl - more.

and what's the problem with polyurethane? I've had that ALK for 5-6 years now. gives a decent thunk through the floorboard but no sqeaks and no degradation of the materal.
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Old 08-11-2011, 06:22 AM   #9
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Poly has different vibration transmission characteristics than rubber and requires a different maintenance schedule.
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Old 08-11-2011, 06:38 AM   #10
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Quote:
Originally Posted by williaty View Post
Yet compare it to the housing of the Whiteline one as well. They all appear to be clones of each other in terms of the alumnium housing.
Of course they are. They're all just the Forester part with a new bushing pressed in. Whiteline did however go to some effort to play with the hole location though. I know the location and angle in part are there to compensate for the angle change due to the change in position, but it also adds a little more caster too or so they say. I just can't say if you'd actually see a difference measuring it tossing on a Whiteline one or GT Spec one or if it is simply marketing at work.

Although I don't really know the specifics of the vibration variation between poly and rubber products, I did mostly opt for rubber where possible. I just kind of see rubber as having less potential for failure. Now Whiteline has made a habit of making excellent poly products, but I do know that some attempts at poly bushings suck and literally just falls apart.
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Old 08-11-2011, 12:59 PM   #11
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Quote:
Originally Posted by williaty View Post
Poly has different vibration transmission characteristics than rubber and requires a different maintenance schedule.



and YOU seem to be the only one that has issue with this


jesus...wake UP

all my 'poly' bushings have got greased ONCE with the right grease and DONE....ZERO maintenance


are you still running 205 tires on your 3300 pound car and wondering why it does not handle well???
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Old 08-11-2011, 02:59 PM   #12
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I went from the Whiteline "comfort" ALK to the GTSpec ALK. No noticeable change in handling, but a definite improvement in NVH.
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Old 08-11-2011, 03:47 PM   #13
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What's the difference between these two comparative pictures?





Willaty's picture versus jamal's, GT Spec to Whiteline? They're set in the same direction: longer mounting tab is pointing up.

Willaty's picture versus jamal's picture, OEM to OEM? They're set in opposing directions: 'curved notch' in Willaty's is effectively pointing down while in jamal's, it's pointing up.

Willaty: rotate the OEM piece in your picture and recompare.
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Old 08-11-2011, 04:05 PM   #14
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Quote:
Originally Posted by Big-E View Post
Willaty: rotate the OEM piece in your picture and recompare.
The way mine is shot is the way they go onto the car. They're both "right-side-up". If they're not, then the arms came from Subaru with the bushings installed upside-down on them.


No reshooting, they're back on the car.
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Old 08-11-2011, 04:19 PM   #15
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Quote:
Originally Posted by williaty View Post
The way mine is shot is the way they go onto the car. They're both "right-side-up". If they're not, then the arms came from Subaru with the bushings installed upside-down on them.

No reshooting, they're back on the car.
Ok. Thanks.

Then to your original wtf and yes I agree then that how can they effectively measure differently, but still mount w/o problems?
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Old 08-11-2011, 04:47 PM   #16
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williaty are you sure you're comparing the same sides on those links? If you had L/R paired in the picture, one would be "flipped" with respect to the other and thus be off. I believe jamal's photos are properly aligned. Since the mounting points are fixed on the frame the mounting tabs on the ALK have to be at the same height. The body of the aftermarket ALK's drops the through hole for the pin and provides the geometry change. Statement of the obvious I know but there's no other way.
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Old 08-11-2011, 04:49 PM   #17
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They are both right-side bushings, both orientated the same way.
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Old 08-11-2011, 07:26 PM   #18
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You can also add spacers underneath a group n bushing or between the black pin and control arm to change anti-lift/anti-dive geometry or caster respectively.
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Old 08-20-2011, 10:26 AM   #19
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I've been curious about the durometer rating on the GT Spec ALK but couldn't find it published. I called Calvin @ GT Spec and he had to call the home co. to find out but he stated the GT Spec bushing was 70 (Shore A) and added a "stock" bushing was 50. I didn't ask which "stock" bushing this was, Forester, WRX or STI, but my curiosity has gotten the best of me and I've ordered a Rex Gauge durometer for further testing. I realize this data would've been nice to have 6 years ago but nonetheless if any of you want to send me any bushings for testing I'll be glad to do it.

In 2-3 weeks I'll personally have for testing a WL "standard" ALK for GD, a stock GD (07) STI transverse link, and a Group N transverse link (the one available through Subaru). I'd like to confirm the GT Spec numbers and even tried to order one but none of the standard vendors nor GT Spec will have any in stock until end of September. Would also like to test some stockers you guys might have lying around such as from a Forester (BRR?) a GD wagon and a WRX. Full report in a few weeks.
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Old 08-20-2011, 11:54 AM   #20
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Quote:
Originally Posted by A-man07 View Post
Would also like to test some stockers
I can send you a stock one from an 02 ts wagon, probably 30k on them. I suspect it's pretty soft and gooey. send me a pm if you want it.

Last edited by chadr111; 08-23-2011 at 09:36 AM.
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Old 08-20-2011, 02:06 PM   #21
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There should be a small note when testing relating to age of the tested product. I don't know the rate of variation over time for these things, but I would think there would be some importance associated with this.

Yes, the stock one I have here is available. It's not like I'm doing anything with it short of tossing it in the dumpster at some eventual point.
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Old 08-20-2011, 02:19 PM   #22
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Quote:
Originally Posted by chadr111 View Post
Would also like to test some stockers
I can send you a stock one from an 02 ts wagon, probably 30k on them. I suspect it's pretty soft and gooey. send me a pm if you want it.[/quote]

Sure. PM sent. As noted above, please write the model and year this came off.

Quote:
Originally Posted by Back Road Runner View Post
There should be a small note when testing relating to age of the tested product. I don't know the rate of variation over time for these things, but I would think there would be some importance associated with this.

Yes, the stock one I have here is available. It's not like I'm doing anything with it short of tossing it in the dumpster at some eventual point.
Yes, the age would be good to know, so please write down the year and model of your Forester when you send it. PM's you with the address.

Thanks.
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Old 08-20-2011, 03:08 PM   #23
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i've got stock 04 and 05 sti alks sitting around if you're interested.
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Old 08-20-2011, 05:41 PM   #24
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Quote:
Originally Posted by williaty View Post



As part of Carpocalypse 2011: Frustration's Revenge, I had my control arms off the car, which means I had the opportunity to pull off my GTSpec ALK and compare it to a set of stock STi transverse link bushings I had laying in the shop. The picture above is the result. So I've got some answers now, but also several more questions.

The biggie: does the GTSpec ALK relocate the rear of transverse link pivot point to reduce or remove the anti-lift/anti-dive geometry? YES. Depending on from which flange you measure (more on this in a moment), the rear pivot is relocated either 14.6mm or 20mm downwards as compared to the stock bushing.

Does the GTSpec ALK relocate the rear of transverse link pivot outwards to increase caster? Either no or maybe. As far as I can tell, the GTSpec ALK does not move the pivot point relative to the centers of the holes for the two bolts that hold it to the chassis. However, the holes in the bushing body are MUCH larger than on the stock housing, allowing you to make a much bigger move with the "Free Caster Mod #2" technique. Given that flipping the pin on the aluminum arms is said to give you 0.5*, I would estimate that the designed-in-slop in the oversized holes are gaining you another 0.5-0.75*. This would require more effort than I'm willing to expend in order to prove, though.

Now, the big wtf... The GTSpec ALK is 5.4mm vertically taller between the mounting flanges than the stock bushing. That's why I listed two possible relocation figures in the second paragraph. If you look up at the picture, I aligned both bushings to a "baseline" that represents the mounting surface of the lower/outer ear of the bushing. Now, look at the tops. The top surface of the bushing housing is the other part that has to mount to the chassis. Yet somehow they both bolt up to the chassis without problem and sit flush against the sheet metal. It makes no sense to me that they should do that! Anyone have a clue what's going on with that?
sorry to be dumb, but which is which? OE on LEft & GTSpec on right?

Rob
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Old 08-20-2011, 05:45 PM   #25
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GT Spec on left. Sort of a blue color.

Stock on right, bare aluminum.
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