Understeer on '22 BRZ

[Icecreamtruk]

Originally Posted by Fletch

Thanks for the answers. I really messed up by not checking the RR's wear straight after the last session. I ended up having to drive 100 miles home (super sketchy) on them as I found my street tires were badly corded when i took them off. So im limited what I can read from the RRs. The inside is predictably worn from the ride home. The outside is pretty good. A tiny bit excessive on the edge of the sidewall but not really enough to indicate im rolling over them badly IMO - but I could be wrong.

Yes the springs and shocks are stock. I'd really prefer to keep them that way. I think they're pretty damn good for what it is and i use the car on the street a lot.

On my race car we'd soften the front sway bar to dial out this kind of understeer (or stiffen the rear), but I had an alignment guy trying to tell me its the opposite with 'this type of suspension'. I'm an idiot mechanically so im not sure what's correct or not. If this is something that can easily be fixed with a sway bar that would be a good option for me.

I guess my big question though is do others experience this with comparable camber numbers??? From the answers it seems no, which maybe points to something being wrong somewhere with my setup.

Regarding the "advice" from the alignment guy, its generally wrong. Softer front or stiffen rear = more rotation (oversteer). There are some edge cases, where the car is rolling so much (because of grippy tires and soft springs) where a stiffer roll bar might help get more traction because of less loss of camber to do body roll. Thats what he's hinting at (I hope at least) and it might apply in your case but its not due to the "type of suspension", all cars loose camber as a consequence of body roll and soft springs and grippy tires will always result in lots of body roll, regardless of suspension type.

You can get stiffer bars if you plan on using similar tires, but its not needed. If you do, I would suggest you get adjustable bars (front and rear). The whole point of sway bars is to adjust your car's balance, its a shame to change it just to be stuck with another static balance that you cant adjust (which might or might not be right).

[strat61caster]

This cars front sway bar is too soft from the factory for oe tires and good alignment. More grip just exacerbates it. Nobody makes a softer front bar for a reason.

[Racecomp Engineering]

Originally Posted by strat61caster

This cars front sway bar is too soft from the factory for oe tires and good alignment. More grip just exacerbates it. Nobody makes a softer front bar for a reason.

Cusco does, but that's for rally (with lower grip).

- Andrew

[ZDan]

No way I'd put in a stiffer front bar without also a stiffer rear one. Oh yeah, what I did...

Honestly if I don't get coilovers for next season I'll likely put the stock front swaybar back in and keep the Eibach rear, see what that does to reduce understeer...

[TommyW]

Originally Posted by Fletch

Yes im trailing the nuts off the thing. Even with comedy levels of brake+steering angle the rear wont come around like it should. The fronts just overload and push forward way past the apex.

you're going in too hot mid corner and overloading the fronts. Try a stiffer rear bar and less trail braking mid corner

[Fletch]

Originally Posted by Racecomp Engineering

How much toe do you have?



With semi-slicks, the stock suspension is far from ideal even with -3 degrees camber. And right, I certainly wouldn't recommend softening the front bar.

- Andrew

Toe is F: -0.9mm, -1.0mm R: +0.6mm, +0.3mm
Caster 5.8, 6.0

And slight correction to my original post, my track tires are actually Victra RC-1s not RRs. I have a lot of cars and an aging brain

[SCFD]

Originally Posted by Fletch

Toe is F: -0.9mm, -1.0mm R: +0.6mm, +0.3mm
Caster 5.8, 6.0

And slight correction to my original post, my track tires are actually Victra RC-1s not RRs. I have a lot of cars and an aging brain

What hot pressures are you running? I believe the RC-1s typically need a couple psi or more than other tires to extract the most performance out of them.

However, based on what you've described so far, I'm leaning more towards a driving issue as your car shouldn't have "loads" of mid-corner push.

[ZDan]

IMO you tune the car to suit the driver. If the driver says there's too much push, my instinct is to address that issue and serve the driver. No driver is perfect, every driver has their own specific idiosyncrasies. It's a bit ridiculous to just say "sounds like a driver problem..." Also, with a few years of development, my street/track car *still* has understeer issues.

Anyway, to OP, if you won't get lower/stiffer springs, stiffer rear sway bar would be my #1 recommendation.

[glhs386]

Originally Posted by Icecreamtruk

Thats what he's hinting at (I hope at least) and it might apply in your case but its not due to the "type of suspension", all cars loose camber as a consequence of body roll and soft springs and grippy tires will always result in lots of body roll, regardless of suspension type

By "type of suspension" I'm sure he was referring to MacPherson struts. Compared to double wishbones the lack of camber gain is a much bigger issue, so I would agree with his assessment.

My personal experience is that a big rear sway bar on this car absolutely sucks, especially with the stock Torsen on uneven surfaces. I yanked out a 19mm Hotchkis and replaced it with a 16mm Whiteline. For anyone trying to make this car rotate, my advice is to exhaust all your other options (camber, spring rates, etc.) first.

[SCFD]

Originally Posted by ZDan

IMO you tune the car to suit the driver. If the driver says there's too much push, my instinct is to address that issue and serve the driver. No driver is perfect, every driver has their own specific idiosyncrasies. It's a bit ridiculous to just say "sounds like a driver problem..." Also, with a few years of development, my street/track car *still* has understeer issues.

Anyway, to OP, if you won't get lower/stiffer springs, stiffer rear sway bar would be my #1 recommendation.

That's fair, my last car was highly tuned to suit my driving and not necessarily because it was the "best setup".

But before trying to change sway bars, it'll be worthwhile playing around with tire pressures first.

[Fletch]

Originally Posted by glhs386

By "type of suspension" I'm sure he was referring to MacPherson struts. Compared to double wishbones the lack of camber gain is a much bigger issue, so I would agree with his assessment.

My personal experience is that a big rear sway bar on this car absolutely sucks, especially with the stock Torsen on uneven surfaces. I yanked out a 19mm Hotchkis and replaced it with a 16mm Whiteline. For anyone trying to make this car rotate, my advice is to exhaust all your other options (camber, spring rates, etc.) first.

Thanks. My understanding is that -3 fronts is about max on the stock setup and i already have a slight bit of rubbing so the only real option other than sway bars would be to reduce the rear camber?

My race car has Macpherson struts too and operates under the usual philosophy (softer front, stiffer rear = more rotation) so im not sure what he was talking about. Im pretty sure he was inferring that I should go the opposite in this car... I wouldn't have really given it much weight if he was just a regular alignment guy but he races Spec Miata and those guys REALLY know setup. Maybe I just heard him wrong. As I mentioned before im not great mechanically.

[glhs386]

My theory is that you don't have enough roll stiffness for the grip level of the tires which is causing you to ride down hard on the front bumpstops under cornering. This is where counterintuitive tuning such as running a larger front swaybar and harder springs can potentially reduce understeer as well as reduce the amount of camber required. You haven't shared much info about your other race car, but if it's well sorted with appropriate spring rates and sufficient bump travel then I imagine it would respond better to conventional tuning ideas. I think you need to forget about trying to make the stock suspension work, if I were you I'd try a rear spring rate biased coilover like the B14/B16 (those might be too soft, even) combined with a larger front swaybar and stock-ish rear swaybar. That's more or less my current setup, although admittedly I haven't had a chance to track test it yet.

[TommyW]

Originally Posted by glhs386

My theory is that you don't have enough roll stiffness for the grip level of the tires which is causing you to ride down hard on the front bumpstops under cornering. This is where counterintuitive tuning such as running a larger front swaybar and harder springs can potentially reduce understeer well as reduce the amount of camber required. You haven't shared much info about your other race car, but if it's well sorted with appropriate spring rates and sufficient bump travel then I imagine it would respond better to conventional tuning ideas. I think you need to forget about trying to make the stock suspension work, if I were you I'd try a rear spring rate biased coilover like the B14/B16 (those might be too soft, even) combined with a larger front swaybar and stock-ish rear swaybar. That's more or less my current setup, although admittedly I haven't had a chance to track test it yet.

Correct.
Sticky tires need a stiffer overall setup via springs and bars. That was my experience in allowing good tires to do their job.

[Fletch]

Originally Posted by glhs386

My theory is that you don't have enough roll stiffness for the grip level of the tires which is causing you to ride down hard on the front bumpstops under cornering. This is where counterintuitive tuning such as running a larger front swaybar and harder springs can potentially reduce understeer as well as reduce the amount of camber required. You haven't shared much info about your other race car, but if it's well sorted with appropriate spring rates and sufficient bump travel then I imagine it would respond better to conventional tuning ideas. I think you need to forget about trying to make the stock suspension work, if I were you I'd try a rear spring rate biased coilover like the B14/B16 (those might be too soft, even) combined with a larger front swaybar and stock-ish rear swaybar. That's more or less my current setup, although admittedly I haven't had a chance to track test it yet.

Ah thanks, if the travel/bumpstops are the issue that would explain it perfectly. High speed stuff is actually pretty neutral-to-loose, its just when need the nose down...

My race car is a vintage 944. I have a race shop look after it for me and do all the setup work when i need it. This BRZ was intended to be a cheap way of doing basic track reconnaissance but ive ended up using it as a kind of daily because it's such a great little car. That's why im a little reluctant to make it too track focused...

Guess i'll have to take a step back and figure out what to do.. Thanks for your help!