Can confirm everything
@xXDavidCXx tracks with what I've found.
I did the rear sway bar and ran it alone for a few autocross/track events and while it "feels" good on initial turn in... all it does is throw away grip out back while not adding anything up front. I initially threw the 26mm RSB on first just out of sheer laziness/because it's easy... and was honestly really underwhelmed. It feels better when you first turn the wheel, and then it plows like a pig as you overload the outside front corner onto the bump stop.
Your biggest enemy in a street class is your lack of camber. Preserve as much as possible and it will be able to corner faster.
The above was on stock springs and shocks FWIW. At subsequent events I found setting the front bar to stiff made it better yet.
People who go straight to the rear bar and think it's the best solution for every case don't understand the entire car. There's not enough weight out back to actually allow it to limit roll so the body rolls the same-ish amount of front, but the rear now hikes the inside tire sooner and is throwing away rear grip.
On a street class car I'd throw a big-ish FSB on (I'm pretty happy with the H&R 26mm, I've taken measurements on it and the soft setting while stiffer than stock isn't ridiculously so), and play with camber, toe-out, and tire pressures to sort out the balance. With the bigger FSB you'll want to be a bit more aggressive in trail braking to help turn-in and it will be faster. Most of the people who have claimed adding a front bar period is always a bad idea are... slow. There are exceptions like when the spring rates and stuff are so far from stock etc so I'm not getting into that... but on a near-stock suspension car there's a lot to be gained by limiting dynamic camber loss.
I imagine without a rear bar to "help" in street class, if it rains or you're on a really low grip surface, that setting the front bar on soft might be beneficial in those instances. With a big front bar and little grip up front (cold tires or wet surface) the car will be "edgier" to drive... though since I'm not in street class and have -3.2ish deg camber that might be a differentiator. My main point: play around with the settings in various conditions.
https://www.datadrivenmqb.com/suspension/swaybartheory
Time for a thought exercise:
The above comparison also illustrates something that few people seem to understand. If you lessen overall body roll up front, you’re also going to lessen body roll in the rear.
Adding roll stiffness to the rear (in an attempt to limit overall roll) is only effective up until the inside rear tire comes off the ground. This happens because these cars have a ~60/40 weight distribution. Once the inside rear comes up, any additional stiffness is not doing anything to actually help body roll, just hike the inside rear tire higher (while raising the overall center of gravity in the process). To be fair, it will add comparably more roll stiffness on initial turn in, but it’s not doing anything for overall grip in a steady state fully-loaded turn.
When you add roll stiffness to the front, the entire body of course doesn’t roll as much, and the outside rear tire does not go as far into the positive (camber-wise).
After adding a front bar, it may be ideal to remove some camber from the rear to maintain balance. For what it’s worth I did not do that, the plan is to eventually add even more camber up front.
Let’s also consider something else: Even if the car now “pushes”… if the overall grip limit is higher is it not faster?
Setup 1: Stock front sway bar and 26mm rear bar, and the rear comes around at 53mph on corner entry
Setup 2: Bigger front sway bar and 26mm rear bar, now the front starts pushing but not until 55mph
Which one is faster around the track?
Some people also like to point to wheelspin: “Wheelspin on corner exit was worse with a big front bar”.
What if you have more wheelspin because you are pulling more Gs, unloading the inside tire more?
Taking a step back and considering things like this is exactly why capturing good data (at least to the best of your abilities) is paramount to actually making the car faster. Having measurable things to assess in an attempt to take the driver’s feel or bias or consistency out of the equation.
Suspension is a fun and highly debated topic. There are a thousand different ways to set up a car (more of them are closer to wrong than not), and every person will like each one a bit differently even if it’s not necessarily the fastest.
You have to be able to adapt to the setup and potentially change some inputs to get the most out of any change because you're adjusting the shape of the friction circle. There will be more on this in the next article (linked below)… with a more in-depth look at the testing data to show why I came to the above conclusions.
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All that said, I totally get not wanting to do the work to undo a mod and install a front bar. But it depends on if you want to be competitive (or chase a lap time, etc) or not. I've installed and removed multiple parts on my car because it turns out most of the aftermarket is full of bullshit parts and the manufacturers don't even understand how they work or how to properly design stuff, and a large percentage of people who have these cars speak out of their ass and only recommend the parts they've put on their own car.
I'm going to guess you don't care about being competitive since you're not on a 200TW tire. In that case you shouldn't even be looking at wheel spacers as a tuning option. In my experience if there's a difference it's negligible.
IMO if you're not serious about being competitive then just do what you want to the car within the confines of STH or XA if there's something silly you want to do that will actually make the car not-miserable to drive. I run in XA due to some track-related mods and because fuck the SCCA camber rules.
However with regards to wheel spacers and their effects:
Running the numbers through load transfer calcs on a spreadsheet of mine... confirms that you'd probably never ever notice a difference. But if you do it... placebo is a hell of a drug so if it makes you think you're faster then go for it. I played with wheel spacers on a prior track/autocross car (a 2200lb Mazda2 built for STF originally), and it was very subtle/effectively negligible.
Stock stock:
Adding 0.4in to track width front and rear (5mm per side):
Adding 0.4in to track width rear only (5mm per side):