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Old 06-01-2012, 12:45 AM   #1
NYC BRZ
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Sway Bar Upgrades

Does anyone know the part number for the stock rear sway bar for a 2010 Forester XT? It's 17mm and apparently is a direct swap. Not a crazy upgrade but cheap! I want to give it a shot before I go crazy for aftermarket bars (which I know I will)
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Old 06-01-2012, 09:38 AM   #2
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Does anyone know the part number for the stock rear sway bar for a 2010 Forester XT? It's 17mm and apparently is a direct swap. Not a crazy upgrade but cheap! I want to give it a shot before I go crazy for aftermarket bars (which I know I will)
The rear bar in the BRZ/FR-S is 14mm. Going to 17mm is a big bump in roll stiffness. The Cusco aftermarket bar is only 16mm. You'll end up pretty tail happy.
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Old 06-01-2012, 09:52 AM   #3
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that stuff can be tuned out. for low speed autocross, I'd want a looser rear and then tune it out with toe settings...

but someone needs to try to see if it works.
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Old 06-01-2012, 09:59 AM   #4
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We're planning on testing 16, 17, 18, and 19mm rears. And then again when we have a front to test as well. Also need to do some math when I have more time.

- drew
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Old 06-01-2012, 12:28 PM   #5
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Is there any stock bar that will fit that is 16mm?
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Old 06-01-2012, 12:48 PM   #6
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Yes, the current WRX rear I think is 16mm.

- andrew
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Old 06-01-2012, 02:25 PM   #7
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Am I doing this right? If lever arm length, attachment point, bar total length and hollow/solid remain the same, and only the diameter increases, will the stiffness increase be (NewDiameter^4)/(OldDiameter^4), so ~ 70% more roll stiffness for a 16mm bar?
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Old 06-01-2012, 02:36 PM   #8
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Am I doing this right?... so ~ 70% more roll stiffness for a 16mm bar?
For a solid bar, yes. For hollow it would be (od2^4-id2^4)/(od1^4-id1^4). But it's not 70% more roll stiffness, just 70% more bar stiffness.

Actually it will probably end up being a tiny bit more than that, due to reduced deflection in the lever arms.
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Old 06-01-2012, 06:43 PM   #9
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For a solid bar, yes. For hollow it would be (od2^4-id2^4)/(od1^4-id1^4). But it's not 70% more roll stiffness, just 70% more bar stiffness.

Actually it will probably end up being a tiny bit more than that, due to reduced deflection in the lever arms.
Ok. Then would roll stiffness gain be (springs + new bar) / (springs + old bar) ?

This weekend I'm going to try to see if I can understand David Gould's roll/weight transfer stuff.
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Old 06-01-2012, 08:22 PM   #10
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Ok. Then would roll stiffness gain be (springs + new bar) / (springs + old bar) ?
More or less. Don't forget the motion ratios.
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Old 06-01-2012, 08:32 PM   #11
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More or less. Don't forget the motion ratios.
I'm going to try and figure out the front first. 1:1 for both... I was using .8 in the back before, but RCE says ~ .75. So my eyeball wasn't too far off. Will have to see about the rear bar's motion ratio next.
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Old 06-04-2012, 11:38 AM   #12
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Those looking for A VERY CHEAP 16mm rear swaybar upgrade. Check out the 10+ Legacy GT rear sway bars. They are the same as the STi which shares the BRZ platform. Guy on my forum selling them for $25

http://legacygt.com/forums/showthrea...la-179658.html
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Old 06-04-2012, 11:46 AM   #13
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Does anyone think that maybe the stock rear sway bar should be left as is, and only the front should be stiffened up? I ask because i would think a stiffer rear sway bar would increase an already present oversteer.
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Old 06-04-2012, 11:53 AM   #14
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You would think so, but its drivers preference. I have always driven nothing but subarus. EVERY subaru understeers like a pig. So the rule of thumb was always bigger rear bar, but thats my preference. I think a bigger bar upfront as well as a 17mm adjustable rear bar to dial in preferance would be good.
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Old 06-04-2012, 11:58 AM   #15
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You would think so, but its drivers preference. I have always driven nothing but subarus. EVERY subaru understeers like a pig. So the rule of thumb was always bigger rear bar, but thats my preference. I think a bigger bar upfront as well as a 17mm adjustable rear bar to dial in preferance would be good.

Ooh, i forgot about adjustable sway bars. Good call. And i suppose i would rather oversteer than understeer.
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Old 06-04-2012, 12:14 PM   #16
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I would be wary of just jumping into a big rear bar for the FRS with no other changes but with the BRZ, I think you can safely go a little bigger in the rear. We're doing some testing to find a sweet spot both with the OEM front bar and later with an upgraded front.

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Last edited by Racecomp Engineering; 06-04-2012 at 12:40 PM.
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Old 06-04-2012, 12:25 PM   #17
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If this were a usual Subaru, I'd say do the sways first. But in this case, I'm going to do RCE's springs first and then decide if I want to change the bars.
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Old 06-04-2012, 01:09 PM   #18
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Agreed. As I do no have a BRZ/FRS...it looks like a drop is in order first, then maybe some bracing, strut bars, bushings, then some sways. If this car is even half as good stock as my Autox 2.5rs with full suspension mods was. I can not wait to own one.
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Old 06-04-2012, 01:10 PM   #19
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Did anyone find out if the front bar is similar to any other subaru setups?
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Old 06-04-2012, 01:11 PM   #20
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Quote:
Originally Posted by Racecomp Engineering View Post
I would be wary of just jumping into a big rear bar for the FRS with no other changes but with the BRZ, I think you can safely go a little bigger in the rear. We're doing some testing to find a sweet spot both with the OEM front bar and later with an upgraded front.

- Andrew
I am on the same page, after a spirited test drive I think I would not mind some more front roll stiffness. Especially with my desire to run a wider stickier tire all around. I will not be touching the rear bar for a while if at all on my FR-S.
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Old 06-04-2012, 01:32 PM   #21
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Quote:
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Did anyone find out if the front bar is similar to any other subaru setups?
It is unique for the BRZ/FRS.

I'm not convinced bracing and strut bars are all that necessary for most applications, but we'll see. Bushings in a few key areas will be good to have.

Changing the swaybars will for sure be helpful for auto-x, and an adjustable rear can be very nice. I do tend to stay away from very large swaybars though.

A good alignment is first.

- Andrew
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Old 06-04-2012, 02:01 PM   #22
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Here are my list of desired suspension changes in order (it's a short list)

1. More negative camber up front
2. Slightly stiffer spring rates all-around with good dampers.

Ummm that's it for now!
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