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dmitrik4 05-13-2011 10:47 PM

CS: softer front sway bar?
 
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 05-14-2011 01:26 AM

lol, not again ....

Spin9k 05-14-2011 08:37 AM

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 05-14-2011 10:49 AM

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 05-14-2011 08:07 PM


Originally Posted by dmitrik4 (Post 3976828)
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.

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 05-14-2011 10:05 PM

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).


Originally Posted by TeamRX8 (Post 3976886)
lol, not again ....

wow, thanks Mark. :rolleyes:

TeamRX8 05-14-2011 10:05 PM

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 05-14-2011 10:13 PM


Originally Posted by dmitrik4 (Post 3976828)
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.

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 05-14-2011 10:13 PM

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.


Originally Posted by TeamRX8 (Post 3977465)
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.

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 05-14-2011 10:41 PM

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 05-14-2011 10:57 PM

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 05-14-2011 11:05 PM

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. ;)


Originally Posted by TeamRX8 (Post 3977485)
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

:dunno: 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.... :dunno:

40w8 05-15-2011 12:26 AM

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 05-15-2011 05:15 AM

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 05-15-2011 06:09 AM


Originally Posted by TeamRX8 (Post 3976886)
lol, not again ....


yeah, here we go ....

Spin9k 05-15-2011 07:46 AM


Originally Posted by dmitrik4 (Post 3977464)
Spin - i'm not sure i follow. ... A good example of steady-state cornering is a skidpad;

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 05-15-2011 09:41 AM

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 05-15-2011 10:26 AM

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 05-15-2011 01:19 PM

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.


Originally Posted by tpdrx8 (Post 3977684)
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.

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 05-15-2011 01:38 PM

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 05-15-2011 01:46 PM

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 05-15-2011 01:50 PM

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 05-15-2011 02:42 PM


Originally Posted by TeamRX8 (Post 3977818)
You are easily short at least 1/2 deg camber on the front, it is there legally for the taking ...

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.


Originally Posted by bse50 (Post 3977815)
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.

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 05-15-2011 02:51 PM

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

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

dmitrik4 05-15-2011 03:24 PM

:lol: my guy suggested just that, but i think i'll try staying legal. ;)

tpdrx8 05-15-2011 07:16 PM

I realize I should just let this go but this is such a great shot by Karen I just had to share. This is me at the Atlanta tour, not understeering to the point that the inside right is off the ground. :D:


http://www.flickr.com/photos/11760021@N02/5706172758/http://www.flickr.com/photos/11760021@N02/5706172758/ by http://www.flickr.com/people/11760021@N02/, on Flickr

EricMeyer 05-15-2011 08:03 PM

I know NOTHING about AutoX. I think I just saw rear toe OUT in the setup. Is that a common practice in AutoX? Pretty much everyone I know in the road racing market runs 1mm rear toe in total

fastmike 05-15-2011 08:31 PM

I was one of the early people to try out RX8's.
I fussed with alignment and bars. Only sorta liked the car when I had rear toe out.
I am not big on lots of rebound to "loosen" one end of a car.

I am big on lots of slow speed compression but without going $all out$, it wasn't going to happen.
Basically build a set of front shocks with almost no bleed on the compression side of the piston but blow off quickly to a middle of the road setting for bumps.
It will "act" like a big FSB in transitions.
I use whether of not I am lifting the inside rear at corner exit to size the FSB along with some rear rebound settings and rear droop allowances that exist in stock class. You don't want to lift an inside rear with the Torsen which everyone knows.
I like LOTS of front grip.
Big FSB's don't always allow that to happen on many cars.

As a side note: I think(never proved) that the RX8 and MX5 toe in in the rear under power or when leaning over.
When you toe in with a Torsen, it can cause understeer when on the throttle.
Has anyone modeled the rear? That doesn't take into effect bushing toe changes which Mazda loves to do.

Anyhoo. The 8 was a little bit of a disappointment compared to my RX7TTR1. I was hoping for a 4 seat FD.:dunno:

dmitrik4 05-15-2011 08:51 PM


Originally Posted by EricMeyer (Post 3978031)
I know NOTHING about AutoX. I think I just saw rear toe OUT in the setup. Is that a common practice in AutoX? Pretty much everyone I know in the road racing market runs 1mm rear toe in total

totally different world. autoX cars are usually set up really loose in the rear; some of the Civics I know of are so loose they would likely be almost undriveable at road course speeds.

TeamRX8 05-16-2011 07:51 PM

the RX-8 does not have a Torsen, that said if the front bar is too soft it will spin the inside tire like mad and do more crazy sh1t than a 1-legged wh0re with an unlimited life time supply of blow and booze

fastmike 05-16-2011 09:31 PM


Originally Posted by TeamRX8 (Post 3979209)
the RX-8 does not have a Torsen, that said if the front bar is too soft it will spin the inside tire like mad and do more crazy sh1t than a 1-legged wh0re with an unlimited life time supply of blow and booze

Where do I meet up with her?!?!?
I stand corrected. It isn't a torsen but I use that term loosely.
Can I say "torque sensing?"

I still base FSB size wheelspin not lean. Don't even ask what I do in the wet with FSB's.

FM

TeamRX8 05-16-2011 10:55 PM

It's called "theory" for a reason .....

40w8 05-17-2011 12:01 AM

Your pic is golden to help your condition.

I can see that you have enough lean in the front so softer won't help.

Also, your inside rear should be up more (losing grip).

I'd start by running 40 psi hot in front 36 psi rear.

Then, I'd get more neg camber on the fronts(-.5 more like someone said), and zero to slight toe in in back.

If still understeering figure out how to stiffen rear with some shock that pushes with air like Bilstein.

J/K (maybe), but put a smaller tire on rears to get more pull and less traction.

tpdrx8 05-17-2011 06:40 PM

Mark, stop me, please!

TeamRX8 05-17-2011 08:32 PM

I vote for more body roll :D:

not

fossumja 05-18-2011 07:52 PM

A few comments, then I'll stay out of this and let the uninformed opinions fly.

Every nationaly competetive CS RX-8 is running 285 Hoosiers with basically the same setup you describe (including stock or slightly stiffer front bar).

Your camber settings sound low (i.e. should be more negative), but there is a lot of variation in alignment rack calibrations.

When we went from 245 Hoosiers to 285 Hoosiers we had to increase rear pressures more than front to maintain the balance. To me this means the rear gained more traction than the front increasing US, but the overall traction is greater with the 285s.

What you describe as SS push might be down to driving style and/or preference. If you want to change the balance, IMHO the best thing to do within CS rules is increase rear tire pressures.

Jim

ULLLOSE 05-18-2011 08:27 PM


Originally Posted by dmitrik4 (Post 3977464)

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


wow, thanks Mark. :rolleyes:

You planning on doing a little drifting? Can't see any other reason to run all that caster. Then there is the reduction in -camber that goes along with it.


Rear toe out, bet that is stable in a slalom. :SHOCKED:

olddragger 05-19-2011 12:07 PM

is this understeer balanced? Same for right and left turns?
Yes-- i do mean if your corner weights are as good as you can get them?
Probably are, but since everything else has been covered i thought I would mention it.

TopGear8 05-19-2011 12:14 PM

^You can't corner weight a car if he's not on coilovers...

TeamRX8 05-19-2011 12:29 PM

Sure you can, but swapping spring spacers in/out is a major pita ....

olddragger 05-19-2011 01:38 PM

and you can stratigically shift weight in and on car. Staying within the rules of course.
OD

dmitrik4 05-25-2011 06:31 PM


Originally Posted by ULLLOSE (Post 3981392)
You planning on doing a little drifting? Can't see any other reason to run all that caster. Then there is the reduction in -camber that goes along with it.


Rear toe out, bet that is stable in a slalom. :SHOCKED:

:dunno: slaloms just fine.

i tried running that caster and much lower caster (~+2); didn't affect static camber i could achieve at all. that was the first thing i tried when i was disappointed in my static camber range. i figured in that case i could at least take advantage of the negative camber gain while the wheel is turned.

ULLLOSE 05-26-2011 04:51 PM


Originally Posted by dmitrik4 (Post 3987472)
:dunno: slaloms just fine.

i tried running that caster and much lower caster (~+2); didn't affect static camber i could achieve at all. that was the first thing i tried when i was disappointed in my static camber range. i figured in that case i could at least take advantage of the negative camber gain while the wheel is turned.

Your doing it wrong. :dunno: I have not seen an RX-8, or MX-5, that did not gain -camber when reducing caster. I have also never seen an RX-8 achieve +2 caster, typical minimum is around +4, I think your equipment/tech is suspect. ;)

TeamRX8 05-26-2011 09:16 PM

in this case I'd say "everything" is suspect :suspect:

dmitrik4 05-26-2011 11:23 PM

:eyetwitch yeah, i'm a real shady character.


Originally Posted by ULLLOSE (Post 3988450)
Your doing it wrong. :dunno: I have not seen an RX-8, or MX-5, that did not gain -camber when reducing caster. I have also never seen an RX-8 achieve +2 caster, typical minimum is around +4, I think your equipment/tech is suspect. ;)

it could have been +4; it was almost two years ago that i tried it and i didn't have my notes around. i could have that number in my head from my previous car.

but in any event, available -camber didn't seem to change significantly whether caster was set at minimum or maximum; IIRC, the difference was ~.1*. i figured the negative gain while the wheel was turned would likely outweigh that tenth of a degree. i could be wrong. anyway, thanks for the input.

TeamRX8 05-27-2011 10:55 AM

I only meant to question everything, probably the most valuable tool for not overlooking something ....

dmitrik4 05-31-2011 08:54 PM

true enough.


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