Thicker sway bars or leave OEM...?
 

Hey guys,

2014 BRZ on stock front and rear sway bars.
I have in my possession a 16mm Perrin adjustable rear sway bar and a Whiteline adjustable 22mm front sway bar and endlinks.

I am running Bilstein B14 coilovers, these are progressive springs that are a little soft, but perform very well at high speeds.
I am also running 265/35/18 Bridgestone Potenza Sports (similar to the Michelin PS4S)
As the car gets more power, wider stickier tire, does it make sense to stiffen the sway bars as well?
Thank you!

After further investigation I might have an interesting idea.
As long as the stiffness in front and back increases proportionally, the balance of the car should remain good. Regardless of size of bar etc.

I can set the 16mm rear sway to the hardest setting which is:
PERRIN 16mm Bar Hole #3 116% Stiffer than 14mm OEM bar

Then on the softest setting on the Whiteline 22mm front sway:
Soft Setting - 118.5% Stiffer than OEM

I think I'm going to put them on and see how it feels haha

If you're not tracking the car, I wouldn't bother with stiffer sways. They'll definitely affect the car's ride around town. I recently installed Eibach sways (similarly more than twice as stiff as stock front/rear) and was a little surprised at how much stiffer and jarring it feels on the street. This is with 4.4F/5.3R springs.

If you add power, and wider tires, doesn't mean you should add roll stiffness. If you were to do so, with more power you might want to add more stiffness to the front and leave the rear alone to maximize rear drive grip under cornering.

Not with those tires Imo, B14/16 spring rates are perfect for Potenza Sport

And even if one is tracking car, if one does on car with not overly wide & grippy tires & hasn't lot of extra aero installed, i also wouldn't bother with thicker swaybars. Even more so i wouldn't change just one (to not shift grip balance too much).
Thicker swaybars reduce roll .. but also make suspension less independent/decrease grip, as one overloads outer tire quicker.
I guess they are undeservedly popular aftermarket mod only for reasons of relatively cheap price & simple install for one thing, and other being that one may gain more confidence to push in corners more if one goes by feel of gut how much can be pushed from amount of roll .. even though grip is there even with less stiff antirollbars (actually even more of grip), just one might not have confidence to fully use it.
I get it if one has went far with track-moding and added lot of aero and drives on very grippy tires and wishes to reduce roll for increasing springrate just during cornering, reduce aero change and dynamic camber change from excessive roll on such car that sees due tires/aero much higher side-Gs. I get it, when one goes for different swaybars for sake of intentional grip balance change.
What i don't get, why one would wish to install stiffer swaybars on only street driven car, where one would see mostly drawbacks of that like eg. less compliant/comfortable ride, and where one corners not on limit and drives not on track slicks to see much side-Gs in roundabouts (unless one drives in soon to loose license manner that may endanger oneself and others on roads) to see any real gains from installing them.
Such mod might feel worthy on very wallowy with overly soft stock suspension car with very high CG like some SUV that sways like boat in turns. On twins for DD? Mostly cons, not pros.

Sorry if this wasn't clear, I'll be tracking it in a few weeks along with a hill climb. I have been overly cautious with swapping out sways based on everyone saying it's not really needed

SC with CSG tune in your sig .. so you have dealt with them in past - imho they would be right people to advise what would be beneficial or not for your use case if you describe all the details. One shouldn't blindly put suspension parts just by reasoning "many do this and it's cheap/simple", but in educated fashion if some specific handling change is wished/needed. And if you never been to track, no matter what the car setup is, weakest bit slowing down is driver. Investing in improving own skills & experience gives most return of getting faster then any car mods.

After posting pics of me autocrossing after doing a few track days a few years ago a good friend who is also an in demand race engineer\mechanic posted "You need sway bars" I took his word for it and never regretted it on track at least. I don't drive the car much on the street so it was a good decision. If I was more street focused I'd think twice.

For your tire setup, what you have now for sways should be adequate. Just having aftermarket sways similar to the setup you have now, served me fine until I went to adding aero.

I didn't really start needing more roll stiffness until recently. I was actually just PM'ing another member on here as I was having the same issue @ZDan was having with mid corner understeer.

They helped, particularly at Turn 4 at Palmer CW (a.k.a. remlaP). I'd estimate they've gained me ~0.2 to 0.5 seconds per lap, which is significant for me vs. time trials competitors!

That sounds promising. I was on aftermarket sways already but I think I am either undersprung, or need more roll stiff ness. I am moving my front sway to the stiffest setting and trying it this weekend. The understeer I am getting mid corner is driving me insane and the front tires have eaten up the fender liners. I am on a 7kg square spring setup now with roll center correction. I could easily see .2-.5 just getting rid of 70% of it.

What do you have for rear sway? I have the Eibach's (THANKS!) set to soft up front and stiff in back (2 settings each end). You thought about stiffer rear springs?

It is the Perrin 16mm in the soft position on the rear, same as OP. I may try upping that too, but I think the issue is mostly I am getting into the bump stops up front. It mostly occurs on longer flat corners that really put a lot of load on the outside tire. Everywhere else it feels fine and is even a bit loose. I will PM you a video link.

To be more clear I am still on OEM sways. I just have the Perrin/Whiteline sitting in my garage staring me down.

I think I'll get them both installed using my prior thought process of keeping the stiffness proportional front and back and give it a shot. Worst case, I switch back to OEM or find a less stiff front bar and run the Perrin a bit softer.
Especially on a lift, sways can be swapped extremely easily so there is no harm in trying them out.
Thanks everyone for the quick responses