Understeer Solutions? Sway Bars?

[Gopherboy6956]

I am looking at Sway bars and some advice…

Let me explain my situation - i'm curious as to what others are thinking.



I have a BRZ with:

RCE Tarmac 0’s – setup with 350 rate springs instead of 225/250 (lowered about an inch)
17x8 wheels with Dunlop 245 ZII’s
-1.5 Front , -2.5 Rear Camber
Front Strut Tower Brace

I’ve been doing some HPDE and AutoX events, and on the HPDE events, the car is amazing as is. Very confident and safe. Borderline understeer in some situations, but at higher speeds it’s just fine.


However, in AutoX – I understeer like Mad. Probably due to the tower brace, but it like the other characteristics is gives the car, so I want to keep it.

So my question is – what size / type of sway bar should I be looking at? Should I do front and rear, or just do a slightly larger than stock rear (16mm or so)?



Any input from you guys below would be great! (Since I've done business with all of you )


@Racecomp Engineering ?
@PERRIN ?
@GrimmSpeed ?

[7thgear]

how long have you been autocrossing?

sounds like a driver error, you're plowing through corners because you are not braking early enough (1# autocross driver error), so you cook your tires trying to stop and carry too much speed into the corner, overheating them even more as you turn.

this is a very balanced car. Considering your mods, you should not be understeering if you are driving correctly.

The good news is that driver training is free!

[Gopherboy6956]

Originally Posted by 7thgear

how long have you been autocrossing?

sounds like a driver error, you're plowing through corners because you are not braking early enough (1# autocross driver error), so you cook your tires trying to stop and carry too much speed into the corner, overheating them even more as you turn.

this is a very balanced car. Considering your mods, you should not be understeering if you are driving correctly.

The good news is that driver training is free!

I've been Autoxing for 3 or 4 years now, 4-5 events a year. I still placed 3 in raw times, so I can't really complain...

But, there were two major turns yesterday that I should have been able to carry more speed through - I was getting beat through it by M3's and Miata's... I even had my race pads on, so stopping was going quite well throughout the day.

I got in about 9 runs yesterday on the track, and I tried is so many different ways - I'm sure I didn't have the lines 100% nailed or that I was executing correctly everywhere, but after my first two runs, all my times were within .5 seconds of each other so It was very consistent.

[7thgear]

well, when you say things like "understeer like mad" one can only assume one thing...

you have two options, increase grip in the front or decrease grip in the rear

so either soften the front or stiffen the rear, you can do this via spring changes or swaybar changes. You can also adjust tire pressures for autocross specific days.

You can also adjust alignment for autocross specific days.

[CSG David]

Originally Posted by Gopherboy6956

I am looking at Sway bars and some advice…

Let me explain my situation - i'm curious as to what others are thinking.



I have a BRZ with:

RCE Tarmac 0’s – setup with 350 rate springs instead of 225/250 (lowered about an inch)
17x8 wheels with Dunlop 245 ZII’s
-1.5 Front , -2.5 Rear Camber
Front Strut Tower Brace

I’ve been doing some HPDE and AutoX events, and on the HPDE events, the car is amazing as is. Very confident and safe. Borderline understeer in some situations, but at higher speeds it’s just fine.


However, in AutoX – I understeer like Mad. Probably due to the tower brace, but it like the other characteristics is gives the car, so I want to keep it.

So my question is – what size / type of sway bar should I be looking at? Should I do front and rear, or just do a slightly larger than stock rear (16mm or so)?



Any input from you guys below would be great! (Since I've done business with all of you )


@Racecomp Engineering ?
@PERRIN ?
@GrimmSpeed ?

Are you running square spring rates? That alone will induce some understeer. Your alignment should also fix some of the issues as well. Most setups dial in understeer for safety purposes.

[autobrz]

I would say before changing springs, try to add caster and camber up front. Caster helps with lower speed corners when the wheels are turned at a larger angle.

[Dezoris]

I personally think that is way too much rear camber for the ZII let alone any street tire for autox.

Either you are just over driving the front in Autox or more than likely your setup has too much rear grip. I don't think a square spring rate is going to turn your car into a FWD setup like you are describing. I am running square rates at 350/350 and car is still very eager to rotate.

[GTB/ZR-1]

All that rear-biased camber probably isn't helping you, either...

[ft_sjo]

I personally found adding a 16mm rear bar made a world of difference. Much better turn-in without creating too much of a difference front to rear. For a track car though, perhaps an 18mm rear bar with the next size up on the front would be better, and not run super stiff springs on the shock absorbers.

This may be of use: http://www.ft86club.com/forums/showthread.php?t=37006

[Draco-REX]

Too little front camber, get another degree on there and maybe dial some of the rear camber out.

If this were a heavier sedan, I'd say use sways to tune the car. But I'm not sold on sways for this car.

[CSG Mike]

Originally Posted by Gopherboy6956

I am looking at Sway bars and some advice…

Let me explain my situation - i'm curious as to what others are thinking.



I have a BRZ with:

RCE Tarmac 0’s – setup with 350 rate springs instead of 225/250 (lowered about an inch)
17x8 wheels with Dunlop 245 ZII’s
-1.5 Front , -2.5 Rear Camber
Front Strut Tower Brace

I’ve been doing some HPDE and AutoX events, and on the HPDE events, the car is amazing as is. Very confident and safe. Borderline understeer in some situations, but at higher speeds it’s just fine.


However, in AutoX – I understeer like Mad. Probably due to the tower brace, but it like the other characteristics is gives the car, so I want to keep it.

So my question is – what size / type of sway bar should I be looking at? Should I do front and rear, or just do a slightly larger than stock rear (16mm or so)?



Any input from you guys below would be great! (Since I've done business with all of you )


@Racecomp Engineering ?
@PERRIN ?
@GrimmSpeed ?

You want to do just a rear sway bar. Your square spring rates are making you understeer.

Alternatively, you can increase your rear spring rate, or decrease your front spring rate.

[Racecomp Engineering]

IMO start with a new alignment. Before adding parts or changing rates. Just do it. Even if you add bars or change rates, you should need more front camber for sure. And a hair less in the rear. It will still be stable and confidence-inspiring at the track.

I think the alignment is the number 1 cause here...

- Andy

[ModBargains.com]

Had a really sick deal on Whiteline sway bars a few weeks ago. Might be tempted to do you for the deal again if you want 'em.

[DylanFRS]

Any video of your runs? That would definitely help diagnose the problem.