Experience with Toyobaru sway bar upgrades?

I've been thinking of upgrading the front sway bar on my 86 the same time I add front camber plates. With just a slight increase in front grip from front camber bolts alone, it already feels like the front suspension is easily capable of writing checks the rear can't cash and managing rear grip is the name of the game with this car, it only tends to understeer in tight low-speed corners now. I hear front grip ramps up rapidly with more front negative camber on these. I wouldn't mind moving the handling balance a bit toward understeer - when I had a rear-grip-biased tire setup and zero front camber on this car back when I first bought it, it wasn't as fast but the handling balance was closer to what I'd call ideal - you'd have to be pretty rowdy with the throttle to get the back end loose. If it had the same tires all-around the balance might've been perfect.

So front camber plates are usually paired with either a disconnected rear sway bar or a bigger front sway bar on Toyobarus to keep the car from becoming sidewaystastic, I'd like the car to feel more sharp and pointy and the lowering springs I'm running aren't much harder than stock so the sway bar upgrade looks like the better option to me.

Trying to decide between the Perrin 19mm or 22mm options, rate changes are listed here:

https://www.perrin.com/shop/suspension/frs-brz-front-swaybar

Anyone have any experience with sway bar upgrades on these? I'd prefer to stick to the stock rear bar for classing and cost reasons, so I'm thinking maybe the 19mm front bar with the stock rear bar?

I'd go bigger. In my experience, you can easily double the rate of stock bars. You can use camber to tune if you're not willing to change out the rear. 

If you're running soft lowering springs, you may get some unexpected handling changes by decreasing bumpstop time with a stiffer bar. 

Update: After getting a simulated version of the car with all the current mods set up in Assetto Corsa, I went about testing the stock sway bar setup vs. the two different rates on the 22mm sway bar around Mosport.

The 22mm bar's soft hole setting gave a more subtle difference than expected from more than doubling the front sway bar rate. The car was still mostly loose in the back, the harder front sway bar just reduced the car's hoontastic tendencies. I noticed that with stock sway bars, the front tires were running a lot cooler than the rears, while with this setup the fronts were running quite nearly as hot as the rears.

Next I tried the 22mm bar's hard hole setting, more than tripling the stock front anti-roll stiffness. This made a much bigger difference, taking the car from a fun and forgiving oversteer bias to serious-business super-neutral. The car felt like it had more grip everywhere but was a bit less forgiving - you couldn't just lift off the gas anywhere to tighten up the car's line anymore. At some points around the track the front tire temperatures were actually exceeding the rear temperatures.

So I'll be getting the 22mm bar, probably around the middle of the year, and I'll try the soft setting first.

Update: The real part has been installed on the real car now, with the soft setting. Will get to try it out at an autocross this weekend.

Oh forgot to update, the autocross got postponed to June 5th. Will get to test them out then, or maybe some time around the end of this month.

Update: Tried it out in an autocross yesterday, running about -2.0~-2.3deg front camber. Results were consistent with what I found in the simulator, the car still has a healthy oversteer bias but it's much more manageable now. A big difference I noticed in autocross is the ability to control a small amount of slip on the rear to improve rotation without getting so sideways that countersteer is needed. This run was similar to the times from Cayman GT4s and a GR Supra:

This was also my first time trying out my under-$100 tire temperature probe setup and it shows that I need more negative camber on the front. Right now I have the camber bolts in the maximum negative position and the plates about 3/4 way to maximum negative. There's another autocross coming up this weekend, for this one I'll try the camber plates at the maximum negative position as well.

Nice run! I'm recovering from shoulder surgery or I would have been out there too. Maybe in another month or so I'll be good to go again.

Did some sim testing with bigger rear bar options combined with moving the 22mm front bar to the hard setting on the car's "digital twin"

First I tried the Perrin 19mm rear bar on the soft setting (about double the current rear bar), this was definitely faster than the current setup but it didn't feel good. The car started to get a bit snappy on corner exit and it didn't like any combinations of braking and turning anymore.

Did some research on the bar setups other people were running and that seemed to make sense, you rarely find anyone running more than a 16mm rear bar on a Toyobaru - lots of pretty serious setups are using the 14mm or 15mm factory rear bars.

So next I tried the Perrin 16mm rear bar on the medium setting, which is around 25% harder than the current 15mm rear bar. Surprisingly this combination felt way closer to the current setup than simply moving the front bar to the hard setting and leaving the stock rear, it still felt very sharp and "pointy" while retaining some oversteer bias rather than having the aggressively neutral balance from the stock rear bar.

Next I tried the hard setting which is about 60% harder than current, this was a pretty subtle difference from medium, it felt like the car might rotate a little better with this setting. Both setups felt good and could deliver times just as good as any of the other setups I tried but with much more consistency.

So now I'm thinking about trying the 22mm front bar on the hard setting with a Perrin 16mm rear bar set to medium or hard...

Keith Tanner said:

I'd go bigger. In my experience, you can easily double the rate of stock bars. You can use camber to tune if you're not willing to change out the rear. 

If you're running soft lowering springs, you may get some unexpected handling changes by decreasing bumpstop time with a stiffer bar. 

all of this.  It is interesting how in some applications adding front bar will reduce understeer/increase what I think of as controllability because the outside front rate isn't going infinite on the bump stop, AND the inside rear is bringing more to the party so the handling becomes more progressive instead of getting to a point where you snap spin.

Plus, personal prejudice, I like a stiff front because you can really bomb into the corner entry and shove all of the weight of the car on the outside front.

This is a first gen, right? 22mm stiff is 100% the way to go on a second gen, I'm not sure how similar the older cars are though.

I'm impressed that your assetto corsa correlation is that good, someone must have put a bunch of effort into that mod. I've been messing around with the GT4 (actual game car, not a mod) and it's basically an oversteering mess compared to real life.

Yeah it's a 2017 2.0L, the 2.4L models are very similar in terms of suspension and handling.

My AC model is based on a 2015 GT86 included with the sim, from there I brought it up to 2017 spec and then applied my IRL mods. The only clear inaccuracy the original car had was too much diff coast action.

One issue I thought of is that if I get the 16mm Perrin rear bar, the soft setting would be useless to me since I don't have any use for a rear bar softer than the factory 15mm. A bar that ranged from slightly harder than the 15mm bar to nearly 2x as hard would be more useful. ST Suspension and Blox make 17mm rear bars but don't list any rates, think I'll send them some emails...

Would you be able to make any recommendations for a dead stock 2015 FR-S, 100% street driven? Maybe with a mild oversteer bias?

Even a stock model could use lots more front antiroll bias, for that you might want to try a 19mm front bar on a hard setting, a 20mm front bar which would probably have the widest range of useful options for an otherwise stock suspension, or maybe a 22mm front bar on a soft setting like what I'm running now at most. Anything harder and the car will become very neutral.

So I messaged 4 companies that make 17mm or 18mm sway bars, the last one I messaged, first to get back to me, and the only one with a useful answer was Whiteline. They have a conversion chart for aftermarket sway bars that does seem to work:

So it looks like 17mm is the ticket to maximize the availability of potentially useful new sway bar rates for this setup. 17mm soft should be similar to 16mm medium, 17mm medium should be similar to 16mm hard, and 17mm hard should be similar to 19mm soft - which seems to be too much but it would be a newly available stiffness that could be worth a try. Unfortunately Whiteline only makes an 18mm model, so I'll have to go with a 17mm from ST or Blox, whichever I can get cheaper.

Blox 17mm rear sway bar ordered, with the way this winter's looking I can probably start work on it earlier around late February/early March, first order of business will be to try removing the stock rear sway bar links so that there's time to order replacements if they need to be removed destructively like the front ones did...looks like the first IRL testing may be at the 2024 Challenge. I'm thinking the medium setting (~+65% stiffness) is the safest to start with.