Trail Braking and Rotation Questions

[rice_classic]

Originally Posted by Dezoris

I will attempt to disconnect it, if going with square pads don't do anything.

You don't have to remove it, just disconnect one side. Nice thing is you don't have to monkey with alignment with this one. I guess the same applies to pads.

[TrogDor the Burninator]

I'm just curious if you find the same issues when you are on a road track versus autoX ...

I haven't done any AutoX, only NASA road courses. I wonder if the lower speeds and sharper corners in AutoX magnify these issues.

[Dezoris]

Originally Posted by TrogDor the Burninator

I'm just curious if you find the same issues when you are on a road track versus autoX ...

I haven't done any AutoX, only NASA road courses. I wonder if the lower speeds and sharper corners in AutoX magnify these issues.

The car is more lively on a road course. Car tends to get more unstable in the rear under hard braking. And the rear of the car rotates without under-steer in most corners. But in higher speed sweepers you get understeer before oversteer.

In autox, only thing I can say is in the case of the S2000, your limit before snap oversteer is a fine line, that limit is hard to read and sometimes it comes on by a simple pavement change and not throttle.

The FRS you can be almost go flat and when the rear starts to go its does not just go, it starts almost bucking a bit so you can drive through it, or back off.

[TrogDor the Burninator]

Hearing this, I like the idea of removing the front sway bar on the FR-S ... Give the front a bit more ability to work dynamically versus being possibly too stiff ...

I'm not an expert by any means, but it seems like a good suggestion that was made.

[SubiePig]

I wouldn't worry about the fact that they were designed around the stock bars. Increasing stiffness in roll evenly front and rear leaving room for adjustment to dial in for personal preference is a better route in my opinion. Spring rates are set for the desired ride frequency they were looking for. With those rates I would guess is around 1.9-2.0 Hz, someone correct me if I am wrong. Not a terribly aggressive number. Proper bar size depends on a lot of things but you basically want to stiffen the car to give enough roll at maximum grip to give you a proper contact patch depending on the amount of initial camber you are running while keeping everything in balance. A production car is going to need roll stiffness increased to get it right as you would get to a point where your springs would cause you to skate over bumps if they were stiff enough to counter roll well enough.

Don't unhook the front bar. The roll in the front would be horrible.

Watching that video again, that course is horribly tight. I noticed at least one point where it looked like you had to much steering input. The car was pushing and bit as you exited and let out steering input. It is really hard to get a good feeling for setup on a course like that. We have local events where the courses are like that and I don't put any thought into setup from them.

[Wepeel]

Originally Posted by SubiePig

Don't unhook the front bar. The roll in the front would be horrible.

I agree with this. I mean, it's easy enough to give it a shot, but consider that you would be softer in roll in the front with the Ohlins without a front bar than you would be stock. The stock front bar contributes ~262 lb/in to wheel rate in roll, in a stock FRS that is 70% of the total front roll resistance. With your spring rates the majority of the front roll rate is still coming from the bar, ~57%. I would also imagine it would make the car quite tail happy.

Looking at the ratio of the natural frequencies of the front and rear during roll (bars and springs contributing) can give a reasonable indication of the under/oversteer balance of the car - a stock BRZ has a front/rear ratio of ~1.24, a stock FRS comes in about ~1.15 (looser), the most successful STX car last year was ~1.50 (tighter), the most successful CS RTR car was ~1.55 (tighter)... your 343 front rear with no front bar would be at ~0.92 - I would think that would be bordering on very difficult to drive but on a lot as small and tight as that video maybe it wouldn't be as difficult. But I also would think it would do bad things for putting power down.

[BlueBlazeRacer]

Your first line says first two autocross. If you are still new to autocross, trailbraking should be the last of the things you should be thinking about. Learn hard straight line braking first. Trailbraking is a skill you can learn later.

[F1point4]

From what I understand, having two different brake compounds front and rear , especially when the rear is stock makes the front brakes work super hard. Maybe explains why the lack of trail braking for you.

I ran HP+ on a dba slotted rotor in the front and stock pads/rotors on the rear and a drive on a road course turned my fronts blue.

[SportInjected]

I'm pretty sure he means the first 2 autocross sessions of the season, not ever.

[wparsons]

Just a couple thoughts/guesses...

1) You might need more front camber relative to the rear, have you been monitoring temps across the tires, or checking for wear onto the shoulders?

2) Maybe try playing with pressures?

3) Are you just entering too hot? If you're still carrying too much speed the car will just plow instead of rotating, the fronts need grip for the car to rotate.

[raul]

@Dezoris

More front negative camber. Most autocross setups I see on the twins, including mine, and cars at nationals target -3.0F / -1.5R as a good all-around setup for the twins. From there you fine-tune to your driving style and tire, and add the desired toe out in the front and toe in in the rear. The added camber in the front will make the car more willing to rotate by increasing lateral grip in the front during corner entry and mid corner.

Also, have you checked how close your tires are wearing to the traction markers? It might give you a clue as to what camber adjustments you need. Also, I think you mentioned running 235 wide tires, what are they mounted on? Mounting too big a tire on a skinny wheel may not be letting the tire use enough of it's shoulder to maximize your grip.

Also, have you played with pressures? If the car feels like it's got too much rear grip when compared to the front, increase pressure in the rear or decrease in the front, depending on what your particular tires like.

[TrqlessWonder]

May also want to look into the possibility of having lowered the car a bit too far/not enough spring rate/some combination thereof. Whacking the bumptstops does a pretty good job of turning the nose of the car into a plowing mess.

[Dezoris]

Originally Posted by BlueBlazeRacer

Your first line says first two autocross. If you are still new to autocross, trailbraking should be the last of the things you should be thinking about. Learn hard straight line braking first. Trailbraking is a skill you can learn later.

First two autos this season. Done it and track days countless times.

Originally Posted by F1point4

From what I understand, having two different brake compounds front and rear , especially when the rear is stock makes the front brakes work super hard. Maybe explains why the lack of trail braking for you.

I ran HP+ on a dba slotted rotor in the front and stock pads/rotors on the rear and a drive on a road course turned my fronts blue.

Going to swap pads Friday to test this weekend see if that's the issue.

[Dezoris]

Originally Posted by wparsons

Just a couple thoughts/guesses...

1) You might need more front camber relative to the rear, have you been monitoring temps across the tires, or checking for wear onto the shoulders?

2) Maybe try playing with pressures?

3) Are you just entering too hot? If you're still carrying too much speed the car will just plow instead of rotating, the fronts need grip for the car to rotate.

Wear markers on front are perfect, however maybe could run 1psi more front. The rear I had to lower not enough roll. But something I will play with this weekend. Car does not plow really feels neutral even under heavy braking. It maybe that I am wanting a less balanced car and its too neutral but still fast.

Originally Posted by raul

@Dezoris

More front negative camber. Most autocross setups I see on the twins, including mine, and cars at nationals target -3.0F / -1.5R as a good all-around setup for the twins. From there you fine-tune to your driving style and tire, and add the desired toe out in the front and toe in in the rear. The added camber in the front will make the car more willing to rotate by increasing lateral grip in the front during corner entry and mid corner.

Also, have you checked how close your tires are wearing to the traction markers? It might give you a clue as to what camber adjustments you need. Also, I think you mentioned running 235 wide tires, what are they mounted on? Mounting too big a tire on a skinny wheel may not be letting the tire use enough of it's shoulder to maximize your grip.

Also, have you played with pressures? If the car feels like it's got too much rear grip when compared to the front, increase pressure in the rear or decrease in the front, depending on what your particular tires like.

I have hesitated going overboard with front camber but it seems like I am fighting against the truth of front struts on this car.

Running 17x8 wheels 45 offset. 235 should be good. My front traction marks are almost perfect. Rears not rolling enough because I raised pressures to see if it would help.

Originally Posted by TrqlessWonder

May also want to look into the possibility of having lowered the car a bit too far/not enough spring rate/some combination thereof. Whacking the bumptstops does a pretty good job of turning the nose of the car into a plowing mess.

Car is only lowered 10mm, Ohlins suggested 25mm which is way too much for a street car in my area.