dmitrik4

iTrader: (5)

One thing I've noticed is that my car still has some steady-state understeer. Alignment and tire pressures help, but haven't dialed it out completely. Rather than looking for ways to loosen up the rear end, I'm wondering about ways to increase front grip.

Has anyone tried running a softer front sway bar? The stock bar is 26.5mm. The old auto-tranny bar is 25.4; the stock MX-5 bar is 21.1. I know that going to a softer front bar would give up some crispness in transition, but should provide benefits in sweepers.

TeamRX8

iTrader: (25)

lol, not again ....

Spin9k

Under what conditions and speed ie, doing race track, street, or autocross driving are you getting "steady state understeer"? Any time anti-sway bars are under deflection, by defintion, you are in a transient condition.

I've seen cars that appear to lack anti-sway bars on a race track. They are quite comical in appearance from behind.

tpdrx8

He says CS so I am assuming autocross, but spins on the right track, what is your setup now? tires? alignment? pressures?

I run the baghead bar on it's softest setting which I have been told is a tad stiffer than the stock bar.

The ONLY time I have had my car push is when the dial bewteen my ears is set wrong.

EricMeyer

Not sure if your looking for alternative approaches to problem solving but I'll throw in my .02 You have what appears to be a pretty good notion of other swaybar sizes and this makes me think your alignment and pressure changes are educated and correct. If this is the case I would share that SOME people think reducing grip in the rear end to allow for more grip in the front is a bad thing. Some people think that there is a fixed amount of grip in the rear and reducing it will make the rear loose, have less grip and work less than optimal. In reality you may have TOO much rear grip and you NEED to get that too the front. Sharing some setup info (as others have hinted at) would help us to help you.

My gut says (and I'm probably wrong) it's either a ride height issue in the rear, too low of spring in the rear or too high spring in the front. I'm going with either of the first two. Final answer. Don't need to phone a friend.

Share more. There are a strong handful of smart people on this forum that enjoy helping people and are experienced enough to do so.

dmitrik4

iTrader: (5)

Thanks Eric. I'm autoXing in C Stock, so my changes are limited to shocks, tires, front bar and alignment. no spring rate or ride height changes. no rear bar changes. I've been doing this on and off for about 10 years, but seriously for ~3 years. I'm a mechanical engineer with a decent understanding of car setup, but i'm by no means an expert.

shocks: OTS Koni Sports. Almost (i.e., 1/4 turn off) full stiff in the rear; ~2/3 stiff in front, depending on the course (we use both a transition-heavy runway course and a sweeper-heavy parking lot). Tires: 285/30/18 A6s on required stock-size wheels. Pressures are typically ~34f/36r, but might change depending on how the car is working. Front bar is stock.

Alignment:

Front
Camber: max negative, which on my car is ~-1.2*
Caster: +6.5*
Toe: 1/16" out per side

Rear
Camber: -1*
Toe: 1/16" out per side

Spin - i'm not sure i follow. "Transition" in the sense I would use it is moving from one state (e.g., straight-line driving or constant speed) to another (e.g., turning or accelerating). Steady-state would be maintaining whatever attitude the car is in (e.g., in the middle of a sweeper). A good example of steady-state cornering is a skidpad; while the bar is in torsion at that point, the car is in a steady state (i.e., constant cornering load, constant speed - rare as that might be during an autoX run).

wow, thanks Mark.

TeamRX8

iTrader: (25)

Application is autocross and he is only allowed to change the front swaybar, shocks, and alignment with any size DOT-R tire on the factory width/diameter wheel. You simply need to optimize the alignment and shocks to get the car neutral. You can even use these same changes to get it loose enough to justify a stiffer front bar. Making the setup softer is going in the wrong direction. It's been tried and nobody has been successful with it. OE or stiffer has always been the ticket. Don't thank me, thank the people who already tried to pioneer it. Rear toe out is not necessary either.

40w8

My 07 GT had that heavy understeer from day one. My goals are to always fix or tune with what I already bought. The alignment specs show that the front wheels should have about 1 more deg of camber than the front, so if you just send it to the shop, the rears will look splayed (some ricers like that look). Get that rear camber turned down to about -1.65 (the minimum I could get), and you can thank me later.

dmitrik4

iTrader: (5)

the minimum i could get in the rear was ~-1*, which is what i have. the max i could get in the front was ~-1.2*, which is also what i have. the shop i use is run by guys who have been autoXing and club racing for a long time.

and that was my question...have other people tried it, and what were their experiences? you know, you could have written this post first.

TeamRX8

iTrader: (25)

You could search first too as I only know what other people have posted here and seen their results. Hence my orinal post so go stand in front of the mirror and roll your eyes there instead

40w8

I just saw your tire size and pressures, and while I track not AutoX, isn't that a killer large tire for the stock wheel/

I'd think 265/35r18 would be plenty overkill, and I'd run 3 or 4 more psi hot in the front over the back.

dmitrik4

iTrader: (5)

a 265/35 is significantly taller than the 285, which works fine on the wheel but does not endear me to my tire guy. plus Hoosier doesn't make a 265/35/18 A6.

i did search; the hugely powerful vBulletin search tool showed me one post from 2008 where someone liked a smaller bar. otherwise everything i found discussed using either the stock bar or a larger bar.

if you can point me to some other discussion, i'd appreciate it. otherwise....

40w8

Yeah, I like to gear down, too, especially since I have a geared up 6spd auto.

I run 225/40r18 Hankooks v12's which are significantly stickier and 2#'s lighter than the original 225/45r18 kumho SPT's.

Just for giggles and even lighter, I'm gonna run 215/40r18 Hankook v12's next, and I'll have 40# wheel-tire combo.

bse50

Tyres are the culprit. They're just too wide and mounted on narrow rims that's even worse.
With the limited amount of modifications that you're allowed to perform grip shouldn't be a problem. You will probably decrease your "lap"times by working on faster transitioning times and steering response.

TeamRX8

iTrader: (25)

yeah, here we go ....

Spin9k

That is a good example, and perhaps many corners in autoX simulate that, at least in the short term, where continuous understeer slows you considerably when your setup isn't right. Wasn't sure what you did with the car... anyway nothing I can tell you as I'm not an autoXer. Others have the experience to help and advise as to setup ... except I can assure you the fun is in eventually getting it 'just right' and enjoying the results

tpdrx8

Tyres are not the culprit.

I have been running the 285's on 8" wheels for over a year. Based on the success that we are having with them - first and second place at the Atlanta Tour for example - I would look elsewhere.

I can tell you that you have your pressures backwards to what I have been running - I run 39F and 36R. Fossum/Ruggles do something more like you have so that's not all of it, but it would be a simple place to start and see if it makes a difference for you and your car.

bse50

There's who's winning with 255 wide tyres so stating results is not the way to determine the setup. His "problems" are.
Heavy understeer means too much rear grip 99% of the times. With 285 tyres that's what your getting with such an underpowered car. Pressures may help but the best way to take understeer off, given that the alignment and suspension setup are spot-on, is to work with tyre sizes.

The benefits of narrower tyres go beyond that but this is not the place to discuss such matters. Sure running around cones in parking lots is different than tracking the car but the point is still sound imho.

dmitrik4

iTrader: (5)

i've been thinking of bumping down to 245s or 255s, but don't expect it to change the balance of the car...after all, if moving down in tire width reduces rear grip, it should reduce front grip as well. and i don't believe i said anything about "heavy" understeer; it's a little pushy mid-corner and i'm thinking about how to improve that.

in Stock classes, wider tires almost always prove to be faster, even if they are "too wide" for the wheels.

i'm going to start trying a much wider range of pressures to see if i can start to zero in on something that works for my car.

bse50

With an RWD car the problem is that the front wheels just act as a "resistance" when turning, if you have too much rear grip you will just keep "pushing" the front out of the desired turn radius.
It surely is worth a try, just find somebody with a set of stockers and you're good to go.

TeamRX8

iTrader: (25)

Come to the USA and show us how to do it then because we obviously don't know how even though that concept has also been shown not to prove out for the intended application

You are easily short at least 1/2 deg camber on the front, it is there legally for the taking ...

bse50

i wish i could, i had to do something pretty similar because of a couple of tight chicanes where my previous setup was prone to understeering.

dmitrik4

iTrader: (5)

that's one thing that has been bugging me. time to start loosening bolts and pulling on things, i guess. that and pressures might get 'er done.

no need to go that far; i do drive the car on the street every day.

FWIW, it seems to push a bit more on my stock-size street tires.

kbrewmr2

pull a "hoppe" and start bending things in favorable directions

if you're short on what camber vs what other people can get that seems like spot #1 to work on to me...

dmitrik4

iTrader: (5)

my guy suggested just that, but i think i'll try staying legal.