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Discussion Starter #1
Has anyone heard any tuner comments on making slight suspension adjustments? I wouldn't want to do anything crazy, but I could see a slightly larger rear sway bar doing a little bit of good, but I haven't completely decided that's a good thing on an AWD car.

Do AWD cars leave body roll in to help keep the force on the tires vertical for traction purposes?
 

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not sure about your second question, but in the beginning, before people really had a good handle on how to tune the wrx suspension, a lot of people tried out larger/adjustable rear sway bars. the general feeling was that it helped get rid of some of the understeer.

if that's what you're after it could work, tell us how it feels when you're done. you can also try alignment settings, they have a big effect on handling. you could also try a rear strut bar, probably a minimal effect, but easy and reversible.

what are you trying to do? you don't say in your post, and having goals is very helpful when suspension tuning. it will give you something to shoot for, and will help other people help you. (that last comment is more for other people reading this, i assume you know this, clone.)
 

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Discussion Starter #3
I'd like to get some of the rear end roll out of the car. I'm becoming accustomed to it, but it isn't the feeling I'm used to. This being my first AWD vehicle, I was curious if there was a performance reason that body roll is allowed as it is.

With a rear sway bar, the body roll comes out of the car, but the force it changed from a vertical force downward on the tire (body rolls over top) to a sideways force. I didn't know if this would be detrimental to the setup.

I'm rather used to sideways stability in a car (as in slalom). I know a sway bar isn't the cure all and can make things worse (especially with progressive springs), but I was thinking that would be a simple starting point to fixing the problem.

I love the overall feel of the suspension, but I just wish there was a little more stability side-to-side, speaking of body roll.
 

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The STi suspension is meant to slide through corners at higher speeds. I autocrossed my stock WRX suspension and easily kept up with people who heavily modded it. The STi is even better, but likes to be smoothly finessed more than WRX likes to be manhanlded.

The body roll is there for suspension travel which is necessary in a rally car and a street car. What you need to realize and what sakura-iro mentions is alignment. Even though the body rolls, the tires remain in proper alignment with the tarmac. This is what is important. The body roll, now that i think about it can actually help weight transfer to the outside wheels where you want the loading. I would go with a slightly negative camber setup and even a little toe out in the front and neutral to a touch of toe in at the rear. This will definitely help the car rotate. I personally think the car rotates very well if you power through corners and have good tires (better than the RE070's if you are autocrossing).

Since this is your first AWD car, I would say you should get used to how the car wants to be driven, not how you want to drive the car. This is a world class suspension and changing it with good intentions can have the opposite effect.

That's my two cents.
 

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Discussion Starter #5
I don't see how you are correlating body roll and suspension travel. A sway bar has nothing to do with that. If you have a large sway bar, the force will be more horizontal to the contact patch, but this will still cause the tire to resist the turning motion, pushing the tire 'over', which would be aided by a negative camber setup as you said. Body roll or not, this should occur, would it not?

The added rear bar would only serve to load the inside wheel as well, actually using that traction more effectively, would it not?

Rotation.....yes, I can see the rotation being aided by everything you have mentioned. I'm more concerned with transitioning, not so much rotation. If you are in a slalom and have loaded one side of the car and then need to transfer to the other side, it takes time for the body to do so. With what time I've spent in the car, it seems that rapid side-to-side transitioning is not so stable and cannot be handled as accurately as I I've felt in other setups.

I could be wrong...this might be the way all AWD vehicles feel..but I'm willing to bet there is a way to make the car a little more stable in this respect....that's all I'm trying to investigate.

Don't get me wrong...I'm not looking to go completely changing the setup of the car. I was just curious what a slightly larger rear bar might do for the car. And just so that you might think I'm not completely crazy, Shiv has recommended a larger rear bar for the EVO, which apparently is more neutral than the STi.

I've given the lecture you just gave me to people wanting to do coil-over change overs. I didn't think a discussion about a minor setup change would require such. :roll:
 

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CloNeGTS said:
I don't see how you are correlating body roll and suspension travel. A sway bar has nothing to do with that. If you have a large sway bar, the force will be more horizontal to the contact patch, but this will still cause the tire to resist the turning motion, pushing the tire 'over', which would be aided by a negative camber setup as you said. Body roll or not, this should occur, would it not?
I am simply trying to state that as the body rolls, the outside suspension goes into compression and the inside goes into droop, thus the suspension travel effects the alignment (the same phenomenon that we all know creates bump steer and why you have to get an alignement when you lower a car).

CloNeGTS said:
The added rear bar would only serve to load the inside wheel as well, actually using that traction more effectively, would it not?
absolutely, but I have seen WRX's so rigid that they are unweighting the inside wheel. The chassis is so stiff, that the car can three wheel, which is exceedingly bad :(

CloNeGTS said:
Rotation.....yes, I can see the rotation being aided by everything you have mentioned. I'm more concerned with transitioning, not so much rotation. If you are in a slalom and have loaded one side of the car and then need to transfer to the other side, it takes time for the body to do so. With what time I've spent in the car, it seems that rapid side-to-side transitioning is not so stable and cannot be handled as accurately as I I've felt in other setups.
yeah, I have noticed this too, but if you can get the car to slide on the tires the transitions are much less dramatic. I have found that smoothness and throttle on oversteer does wonders for the slaloms. Not to mention tires that are somewhat progressive at their limits. I am running Kumho Victoracer Ecsta's and love them for autocross. I am not as wild about the RE070's as they are not nearly as progressive and obviously lack the ultimate grip of R comps. For the street, the RE070's are fantastic. :wink:

CloNeGTS said:
I could be wrong...this might be the way all AWD vehicles feel..but I'm willing to bet there is a way to make the car a little more stable in this respect....that's all I'm trying to investigate.
Subaru's fell totally different than any other car i have driven hard, but once you get used to them, they are extremely well handling cars. Ther is definitely more roll than other rock stable cars, but the Subarus are designed for it an do not seem to suffer. No wonder some rally co-drivers get motion sickness :D

CloNeGTS said:
Don't get me wrong...I'm not looking to go completely changing the setup of the car. I was just curious what a slightly larger rear bar might do for the car. And just so that you might think I'm not completely crazy, Shiv has recommended a larger rear bar for the EVO, which apparently is more neutral than the STi.

I've given the lecture you just gave me to people wanting to do coil-over change overs. I didn't think a discussion about a minor setup change would require such. :roll:
The words of warning were more for others reading than directly at you. :oops:


very interesting topic, you've really got me thinking.... :D
 

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Discussion Starter #7
Right back at ya RE: "got me thinking"

When you related it back to the whole 3-wheel stance thing, I can see where that might not be so hot. You're very right to say that the suspension travel has been matched (or hopefully has been) to the body roll so that the given travel gives the perfect angle on the wheel itself. I can see where defeating the body roll may load the suspension (changing the angle of the wheel), but not allow the body to get up and over the wheel in a way that would use that new angle.

And just a side note, which is almost embarrasing.....I have been running around without one of my rear sway bar bushings for the past week which is when I started thinking about all of this. After putting the replacement bushing back in yesterday, the car feels more like it should again. ;)
 

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Discussion Starter #8
Oh, one other thing....you run the Victoracer's on the street as well? How do they hold up under regular street driving mileage wise? I know I'll need to replace the RE070s before long, and I'd like a great summer tire that I can run on the street and still be perfectly happy with come autox weekends.
 

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Just to add few cents worth on info:

Chassis setup and tuning is not directly related to where the driven wheels are. Principal physics are the same for all cars.

There is no such thing as eliminating weight transfer front/rear, side/side. No matter what is put on a car, weight transfer is always the same. Suspension geometries, A/R bars, or springs, etc. do not eliminate weight transfer. For example, a go-kart has no suspension components at all and it is one of the vehicles that is effected the most by weight transfer due to its small size and overall weight.

Suspension systems are used to "manage" weight transfer to make the car handle better in a given situation. So, what does all this mean?

During cornering, weight will be transfered to the outside wheels; however, the question is can you get this additional load for higher grip on the outside without loosing too much inside grip and without deforming the tires and alignment. Body roll, deflects wheel alignment relative to the surface by adding camber. This positive camber results in higher tire slip angles. As you would know, a certain degree of tire slip angle is a good thing, usually between 8 to 12 deg. However, if body roll is excessive, you can get as much as 3-4 deg. positive camber. Obviously, this is not a good thing, hence you want to minimize body roll. The rule of thumb is to limit body roll between 1.5 to 2 degrees under 1g cornering force; higher for street cars and lower for higher-performance cars. F1 cars for example have less than 0.2-0.3 deg body roll at 1g, but they are also able to pull much higher cornering powers, so you will sometimes see noticeble body roll on them as well.

Obviously, the "anti-roll bar" is one tool to combat body roll. The biggest negative about A/R bar is that it makes the suspension system not so independent, and we sometimes get a result in which the inside rear wheel takes off the ground during hard cornering as you have mentioned before. That is definetly not a good thing, and means that rear A/R bar is too stiff. For this particular reason, many club racers and specifically F1 cars before 1995 did not use A/R bar on the rears.

An alternative way to manage the weight transfer is obviously the springs. With higher spring rates and stiffer shocks, you can reduce body roll, and in return you give up comfort :) But more importantly, if you have too stiff of a setup, the car would be too bouncy for certain roads, and you just cannot get the power down enough to take advantage of the lesser body roll. In this particular scenario, a 4WD setup helps as there is power at some corner on a bouncy tarmac.

Adding negative camber is a very popular way as well, but how much camber will you keeping adding? I personally would not put more than -2 camber on the fronts and -0.5 on the rears of the STi. The downsides of the any camber are reduced braking capacity, reduced straight line stability, and increased tire wear. Hence, keeping camber adjustments sensible and managing weight via the combination of springs, shocks and A/R bar has been the preferred way for several decades now :)

Specific to the STi, I do not have the definitive answer at this time as we just received our development STi. We will be running tests for the next 2-3 months and hopefully come up with multiple ways to modify the suspension system per driver preferrence.

I do hope I did not bore anyone reading this, just wanted to add some information.

Thanks.
 

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I personally cannot wait to get through testing for baseline and start testing of alternative shocks and springs. We will leave the A/R bar alone for a while until such time that we feel shocks and springs are too stiff for daily driving.
 

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CloNeGTS said:
Oh, one other thing....you run the Victoracer's on the street as well? How do they hold up under regular street driving mileage wise? I know I'll need to replace the RE070s before long, and I'd like a great summer tire that I can run on the street and still be perfectly happy with come autox weekends.
I do not run the victoracer ECSTA's on the street. I did run them on a "short" 50 mile round trip highway excursion, and they showed the wear pretty dramatically. I would not recommend these for regular street use as they would probably last less than 1k miles.

I will be looking at the ECSTA MX as well as a few other tires from Dunlop, Yokohama, Falken and Bridgestone but I won't need tires until next spring, so I am waiting for more feedback on the newer models before I make any decisions.
 

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CloNeGTS said:
Oh, one other thing....you run the Victoracer's on the street as well? How do they hold up under regular street driving mileage wise? I know I'll need to replace the RE070s before long, and I'd like a great summer tire that I can run on the street and still be perfectly happy with come autox weekends.
fyi, I have victoracer 700's on my Cobra. It's mostly driven on the streets nowdays, and they hold up ok - I had to change the fronts last year, but that's because I have something like -2.0 camber in the front.
 

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im thinking of adding a larger RSB myself...which makes me wonder about the diameter of our stock sti bar. also, would perrin be a good way to go?
 

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CloNeGTS said:
I'd like to get some of the rear end roll out of the car. I'm becoming accustomed to it, but it isn't the feeling I'm used to. This being my first AWD vehicle, I was curious if there was a performance reason that body roll is allowed as it is.

With a rear sway bar, the body roll comes out of the car, but the force it changed from a vertical force downward on the tire (body rolls over top) to a sideways force. I didn't know if this would be detrimental to the setup.

I'm rather used to sideways stability in a car (as in slalom). I know a sway bar isn't the cure all and can make things worse (especially with progressive springs), but I was thinking that would be a simple starting point to fixing the problem.

I love the overall feel of the suspension, but I just wish there was a little more stability side-to-side, speaking of body roll.
have you thought of the STi pinks? people have been saying they make the sti feel "right". Maybe that will solve some issues you're having?

Robert~
 

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Just a little input - i have no definite answers - but i would like to point out that after installing my F&R strut bars and "sti pinks" it is a very stiff and well handling setup now. ill have to do a lot of more driving and cornering to figure out what areas would need further improvement. i would suggest upgrading the springs before looking into the RSB from what ive seen so far. im off to drive now.
 
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