Forester STI – Whiteline Rear Anti Roll / Sway Bar

If you’re not already aware, A Subaru Forester is basically a jacked up Impreza with a slightly larger, boxy body. Those are the things that attracted me to one, the performance and tuning potential of an Impreza but with more space in the back for stuff.

Being ‘jacked up’ and the ‘larger, boxy body’ both result in a fair bit of body roll. Even though the STI is lowered a fair bit compared to a normal Forester, has stiffer springs and inverted STI dampers as any other Impreza STI has, it still suffers with a bit of body roll. My particular Forester STI is an earlier model so the OEM rear anti roll bar (ARB) was thicker than ones fitted to later face lifted models but it still had a bit more roll than I’d like.

The relatively soft rear ARB also results in cornering characteristics that tend towards understeer which is pretty much the normal, safe option for a production car setup. A more balanced setup is what you want if you’re looking for a more enjoyable, sharper feeling drive.

So going by others experiences of both Foresters and Imprezas, plus what I know of suspension setup already, the remedy to both problems is a thicker / stiffer rear ARB. This will resist more of the chassis tendency to roll, particularly with the high sided rear end of the Forester, and adjust the front / rear balance of grip to reduce that tendency to understeer through corners.

I also read that the standard ARB mounts tend to break if a stiffer ARB is fitted with them. This can be a problem with Impreza’s too but is worse with the Forester as the ARB mounts are longer so the leverage on the failure point, where they mount to the body, is greater.

So I decided to get a few Whiteline parts.

Whiteline Rear Sway Bar 22mm – BSR37Z
Whiteline Rear Sway Bar Mounts Heavy Duty – KBR21-22
Whiteline Sway Bar Link Assembly – KLC32

None of the above are Forester specific parts though Whiteline do sell Forester specific Heavy Duty Sway Bar Mounts (KBR18-22).

I chose to go with Impreza items and here’s why. The normal Forester range has a much higher ride height than the Impreza on which it’s based so the OEM rear ARB mounts are longer to bring the ARB down with the rest of the suspension. This keeps the ARB arm at the correct angle. Here’s the Impreza and Forester mounts to compare.


The Forester STI though, has a lower ride height than the normal Forester range, closer to that of the Impreza. That means the ideal ARB mount length is probably somewhere between the Impreza and Forester lengths. I also had in mind that it’s quite possible I would decide to lower mine even more with springs or coilovers in the future which would bring the geometry of the rear suspension even more towards or even just the same as that of an Impreza.

So rather than fit the longer Forester specific ARB mounts then find that the ARB ended up sitting at an extreme angle I went for the shorter Impreza ones thinking if I found they were’t quite long enough I could space them out a little from the body with the option of removing the spacers later on if/when I lowered the car more. The other thing to consider was the fact I have a tow bar fitted and the mounting brackets for that were likely to clash with the larger heavy duty ARB mounts. Which could be dealt with by cutting stuff or, probably the simplest and neatest option, spacing the heavy duty mounts away from the body a little to clear the tow bar brackets. So the last thing I’d want to do is have to space out the longer brackets, making them even longer. Lastly the Impreza brackets are anodised gold aluminium things and look way cooler than the Forester specific steel ones!


I should also mention why I chose the KLC32 drop links which are usually sold as upgrades for the front. This is because the Forester STI has STI lower suspension arms just as the Impreza STI does so these drop links fit nicely. Non STI foresters have lower arms like the WRX and require the C shape drop links.

So my parts order arrived.



Before I could get to fitting any of it though I made some measurements of the mating faces of the ARB mounts so I could make some spacers.





Some 10mm aluminium spacers. 10mm is the thickness of the tow bar bracket so these are the minimum spacer thickness required to prevent the ARB mounts clashing with the tow bar brackets.


Bit of primer.


Bit of black.


Getting the holes in the spacers right.




Now up with the Forester.


Eyeing up the mounts to see how they would fit and if there might be any other clashes with stuff.




Well there were going to be a few issues with things wanting to occupy the same bit of space so I had to make some adjustments to the spacers but that was fine as that was the point of them. I could make the spacers whatever shape I needed and that’s preferable to cutting the ARB mounts or tow bar brackets.

My usual approach of some CAD (cardboard aided design) was just the thing for getting a template for the spacer shape required to clear the towbar bracket.



Left side spacer modified for tow bar bracket clearance.


The other side was a bit more of a pain because of other brackets.


I ended up trimming the other brackets a little and making a fair bit of adjustment to the spacers to end up with this.


I also had to cut the corner off the ARB mount. This was completely unavoidable as the fuel filler neck was in the way and I certainly wasn’t going to cut a hole in that.


With the spacer finally sorted I could now actually fit the new ARB setup. So I did and this is how it sat with the car on the ground still at normal FSTI ride height.


Looks pretty good to me with the ARB arms close to horizontal and with plenty of clearance around them. I also sprayed all the new parts with the Mil Spec Wax I used previously on the whole car.



The potential problem with the shorter ARB mounts was the possibility of the them being too short meaning the ARB could ‘invert’ if/when the suspension got to full droop. The rear wheels being at full droop is fairly unlikely as there’s a lot of travel on the standard shocks so the car would have to leave the road a fair bit before that happened but the possibility of it would not be ideal. So I was pleased to see when I lifted the car back up again there was still a decent amount of angle left so there was no chance of the pivots between the drop link and ARB inverting.



Some more pictures of everything fitted.




The spacers in place.



A closer look at why I had to cut the corner of the ARB mount to give clearance for the fuel filler neck. It’s worth pointing out there would be no issue with clearance here if I had fitted these without the spacers.




Well I’ve had the 22mm ARB on the car for a good while now and I can say it was time and money very well spent. It made a very noticeable reduction to body roll and has certainly improved the balance of front / rear grip such that the the car feels much more neutral. It will still understeer before anything else when you get to the limit of grip but it’s not leaning on the outer front corner quite as badly and the rear feels a more ‘lively’. So I’d recommend anyone out there with a Forester STI to do this or something similar especially if you have the face lifted FSTI with the softest OEM ARB.