Cornering Question
 

I got a rookie question that I THINK might be related to suspension?

Trying to gain a little knowledge here. When I'm cornering pretty hard around a bend, no traction loss, my car feels like it's lightly bouncing on the side with the majority of the car load. In other words, if I'm cornering hard right, the left side feels like it's wobbling/bouncing a bit.

This gives a bit of an unpredictable feel that I don't like as I can't tell if the car is about to lose grip or not. But I don't know if that's supposed to be a normal feeling or something is off. Though I know I've powered through corners harder than that before to the point where I hear light tire slip. So my question is, what's happening here? Is this normal? Is this part of what people consider body roll? Is this related to the springs/dampers? Other suspension parts?

2018 BRZ with PP. Camber bolts up front. Whiteline KCA326 bushings on rear. Racecomp Yellow lowering springs. Stock PP struts.
Alignment: -1.5F L&R, -1.7R L&R, 0 toe front, 1/8 toe rear.
General G-Max AS-05 in 235/40R18 all around on 18x8.5 Konig Hypergram wheels.

That's not a rookie question at all. Do you feel it equally in both directions? Did it come on suddenly?

I'm going to guess you're engaging the bumpstops.

Is your traction control kicking in?

No traction control kicking in, I never reach a point of slipping and wouldn't want to test that theory on public roads. I wouldn't say I feel this suddenly, in fact it's hard to describe whether I always feel it or not. I tried a quick one today just for the sake of trying to replicate it and the car felt pretty solid. This was a tighter ramp so I'm sure I didn't go as quick and it was slightly uphill. To be a little more specific, yesterday, the ramp was a slight down slope and decently wide. Not sure what speed I held on it, maybe 40-50 mph.

I have only recently decided to think about this so I may need to actually do a few tests of right and left turns like this to get a better feel for when it happens.

But as far back as I can remember, this has happened many times in the past and has always felt normal. Normal in the sense that it seemed like that's just what happens when you begin to push the car a bit hard on a turn. Maybe the best way to describe it is it feels like the car is solid as I begin, and then there's a small wobble in suspension (as if the tire sidewalls are heavily flexing or I'm about to lose grip) that is quickly regained as the car feels like it plants back down. But this wobble continues to happen up and down several times over the course of several seconds. It feels pretty gradual and smooth.

I definitely don't think it's a malfunction of any sort. The car isn't old, I'm at 55K miles and take great care of it. It just doesn't feel solid as I would have imagined a great handling car such as this would. And I'm only curious as I want to understand - does this mean I'm at my tires limits and I should back off? Is it just a natural stock suspension feel when pushing a turn?

Ok, makes a little sense. I don't know suspension in depth yet, but reading on it gives a simple generalization. If this is related to what I am experiencing, it seems that since I am on lowering springs, I am more likely to hit the bump stops. I am reading that people discuss cutting their bump stops when lowering their car. What are the benefits and negatives to this? Is it a proper approach to improving the handling in the example I describe or could it lead to a more dangerous situation? Are there any better OEM+ solutions to this? Would aftermarket shocks like KONI reduce the travel and help prevent hitting the bump stops?

EDIT: I just realized, the Racecomp Engineering Yellow springs I have came with their updated bump stops, which I do have installed.
Another thing to mention is, if I'm hitting the bump stops, would it not be kind of harsh? Again, I will have to give this a few more tests to really focus on the feel, but it feels like a fairly smooth rocking/wobbling motion.

I seem to remember people complaining about the damping of the PP struts, perhaps they contribute to this?

It's hard to tell exactly when you hit the bumpstops, the first part of engagement is smooth-ish.

This issue is likely damping related. The PP dampers do this a little bit, but more so when they start to wear.

- Andrew

PP dampers on my '17 were *hard* onto the bumpstops just parked, but with lower springs than yours. Swift BRZ Sport, nearly -1.5" That was definitely way more than the Sachs struts could deal with, even after cutting bumpstops first in half, and then down to 1/3 (~20mm). You're not as low, but during cornering I'm sure you are finding the outside front bumpstop pretty early on, and of course ride quality at that point is not very smooove! Could be part of what you're feeling here. Recommend Bilstein B6 or B8, they have a ton more bump travel up front, they worked like a charm in my case.

I believe stock 2017+ (non PP) also pairs well with mild lowering springs like the RCE Yellows. I'm running that ('18 non PP with Yellows) and haven't noticed any issues on street or track.

Of course. Would need time on a skid pad to really get a feel for what's happening. You have Andrew's attention so I defer completely to his experience. My initial thought was underdamping either from age, or too high of a spring rate.

I know the feeling you describe. I've experienced it many times but never on my 2013, at least not yet. All stock. It lays into the bump stops and rides them without complaining.

I do a lot of highway miles, so I would hop they're not too worn at 55K miles yet. But that's good to know. So to expand on that, does that create any sort of danger on top of the feel? In other words, could the bouncing (likely from poor damping as you describe) increase the chances of traction loss? Or is it more just an unpredictable feeling?

Agreed on the Bilstein's. The plan was to burn through the PP dampers first before moving on as I figured I'd get my money's worth from the package. Maybe that time is coming! :D

Replacing PP/Sachs with Bilsteins was the best thing I ever did to that car...