Understeer Solutions? Sway Bars?
 

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 ?

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.

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.

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.

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.

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.

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

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

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.

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.

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

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.

http://www.modbargains.com/images/Pr...-9-11-13-1.jpg

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

Wouldn't running say -2.2 to -2.5 up front and -1.7 to -2.0 in back clean this up alot? Several guys locally doing Auto X are either -2 all around, or slightly more in front always seems with their BRZ & FR-S.

yup...

- Andy

Ok - Let me try to take in all of the above posts and respond as so that it makes sense:

I do not want to change my springs at all. I'm very happy with the level and being square.

I guess I was unaware that the rear camber was, not ideal.

I would be perfectly willing to go to something like -2.5 front, -2 or -1.5 rear.

What is the advantage of that, though?

The reason I like the rear sway idea, is because of the adjustability. Once i get the car figured out, i'd like to have something simple like that to adjust between the road course and AutoX.

(Keep in mind HPDE is not a fiercely competitive event for me, it's just the fun of it - I am not willing to drive the bleeding edge when there is no incentive except for a timed lap - Don't want to throw 30k into a wall - so i will be less interested in changing the car setup to cater to it)

So, if the three points on a rear sway make a big difference in oversteer/understeer (again, once the car is setup correctly) then that would be awesome.

Unfortunately I didn't bring out my GoPro this weekend - I never do anything with the footage after I get it :iono:

Also, if it helps - I plan on running Rivals next year instead of the ZII's

I am confused, you don't like the way the car handles but you are happy with the spring rates you are running?

Since the front of the car is a strut setup, you are not getting extra camber on compression. (not much at least) The rear of the car has the multi-link instead which gives you additional camber on compression.

I am happy with the firmness and the little amount of body roll in turns with the stiffer springs - that's what i'm referring to.

So having more negative camber in the front while cornering will ________? Keep it from understeering and provide better grip?

Fix your alignment issues first before attempting to add something to a setup that may make things more complicated. And difficult to dial in. If you drop your rear camber to 1.5 the car will rotate again. And be more neutral in autox. Go simple first. Rivals are a good tire but grip levels are close to ZII so its not going to change things all that much.

ohh how i wish to be in your shoes...


anyway, there is no "advantage", you are simply adjusting the car's behaviour to fit your desired goal.

Like i said at the very beginning, if you want less understeer you have to either add grip at the front or reduce grip
at the rear.

Increasing front camber from 1.5 to 2.5 in the will give you slightly more grip (in the front) during cornering while reducing the rear camber in the will reduce grip in the rear by a small amount during cornering.

You're increasing grip in the front under cornering, increasing the limit, and thus, giving you less oversteer.

However, the spring rates affect how your suspension loads; you're making the front work a LOT harder with square springs, so they give out faster than the rears, making you understeer. Aligning to give the front more grip is a band aid in this case. The real fix is to add a rear sway (or do both sways, but make the rear stiff in comparison to the front, relative to the stock sway balance), or change springs.

I'm not one to recommend parts that are not necessary. There are plenty of cases where an alignment helps, and this is one of those cases, but it will only "just help", not solve the issue.

Yes. It really is that simple.

There's more than one way to set-up a BRZ/FR-S, with advantages and disadvantages to all of them. For a driver like the OP that values stability on the track and is happy with the level of firmness and body roll he currently has, a proper alignment will do what he wants.

I do agree with the OP that the adjustability of a rear swaybar would be helpful (bump it up a notch for auto-x) but IMO the alignment needs to be taken care of first.

- Andy

I think I'll start with Camber, and then go from there. Still interested in getting a rear sway, but i'll change one thing at a time.

I'll be going into garage mode here pretty soon anyways (You know, North Dakota and all) so we'll see how things go next year!

Thanks all!

I'm curious why you were running so much rear camber in the first place?

Seemed like a good idea at the time... I went from Stock everything to wheels, tires, suspension, alignment in a few days before an event. Didn't have a ton of time to research.

As you enter a turn and transfer weight to the outside tires, the body rolls to the outside as well. Because our cars have a Machpherson Strut design for the front suspension, every degree the body rolls translates into a degree of positive camber added to the outside tire PLUS a fraction due to suspension compression. In the rear, you have a similar result, but the rear suspension design gains negative camber under compression, so it isn't a full 1:1.

What's happening in your situation is that you're quickly going positive up front while the rear is staying closer to square with the road. So to counteract this, you need more negative camber up front so you can afford to lose some to body roll. Reducing the rear camber will nudge it further into positive and reduce rear grip slightly, to assist with rotation.

Oh, and as a side note:

Sway bars will reduce body roll which, in turn reduces camber loss. However, by linking the two sides of the suspension more firmly, you're essentially shifting more weight to the outside tire, off of the inside. This can actually reduce the overall available grip. Often this loss of total grip is balanced by a more controlled suspension. But a well set up and more independant suspension will have a greater ultimate grip level and be better behaved over rough surfaces.

This is why I'm not convinced that sways are the answer for this car as opposed to say, a Subaru impreza (rear sway first thing!). Our cars are so well set up from the factory that body roll isn't as big of an issue. So we can take advantage of that fact with smaller sways.

(Granted, I have had some moments of doubt on this stance. There's a set of RCE sways sitting in my garage, still in the box, in case I change my stance on them again..)

As you enter a turn and transfer weight to the outside tires, the body rolls to the outside as well. Because our cars have a Machpherson Strut design for the front suspension, every degree the body rolls translates into a degree of positive camber added to the outside tire PLUS a fraction due to suspension compression. In the rear, you have a similar result, but the rear suspension design gains negative camber under compression, so it isn't a full 1:1.

What's happening in your situation is that you're quickly going positive up front while the rear is staying closer to square with the road. So to counteract this, you need more negative camber up front so you can afford to lose some to body roll. Reducing the rear camber will nudge it further into positive and reduce rear grip slightly, to assist with rotation.

:popcorn:

Now we just need @Sam Strano saying he needs more front spring rate, and @ZDan to chime in about struts and camber gain.

http://www.gifsforum.com/images/gif/...e_good_gif.gif

:)

I'll add my opinion to, not because it matters but because I have one...

I, also, don't think a rear sway bar is the right way to go, not until you get the alignment sorted at least. If you find you're still understeering then I'd look at the softest adjustable bar available. This car really doesn't conform to the norms when it comes to suspension tuning.

If any bar, I would look at an adjustable 16mm rear one.

I forgot, I don't think I saw any mention of toe settings. What are you running?

0.

This is the sheet:

http://i4.photobucket.com/albums/y14...ps7b1b513f.jpg

To my understanding, a touch of toe in up frontmight help, and would be more stable at highway speed. It should make the front tires wear better to consider the amount of deflection in the stock bushings. But your present settings seem to be in the generally accepted sweet spot.

This.

More independent rear suspension on a RWD car is faster...

I'm a big fan of 0 toe all around.

A little bit of toe OUT up front will improve turn-in feel. Toe IN is good gor high speed stability, but hurts feel.

In the rear, tow IN will help reduce "snap" oversteer. This is good for track use. Toe OUT in the rear will lead to oversteer. Only good for AutoCross on tight courses and Gymkhana, not considered safe for street use or track use.

So I just like 0 all around. It's also much nicer to the tires too, especially when running aggressive camber settings.

I'm also one of those heathens that thinks SAI isn't a big deal. But that's for another discussion. :D

The problem with adjustable bars is it effects the drop link angle which skews the curve of the bar.

For the price of a bar, and the 10 minute installation, just go get one and try it out. It's a no-brainer.

when looking in to rear sway bar you have to think that our torsen type Lsd really don't have to have that rear inside wheel spinning in the air. big loss of power their. then you have to upgrade to clutch type lsd so more money again. I would go for stiffer back spring's