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)

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.

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. :)

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

Is there any stock bar that will fit that is 16mm?

Yes, the current WRX rear I think is 16mm.

- andrew

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?

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.

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.

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

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.

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.