PDA

View Full Version : Sway Bar Adjustment



Eagle7
04-12-2004, 08:33 PM
Got a new adjustable front sway bar (Suspension Techniques). Now I've got to figure out how to use it. http://Forum.ImprovedTouring.com/it/smile.gif

My motivation was to tame down the tail wagging, although I have to confess I'm still learning what a neutral setup feels like.

Anyway, the bar has two positions for the links to the control arm. The "outer" position is a "softer" bar that should result in relatively more oversteer. The "inner" position is "stiffer" for less oversteer. (hope I got that right)

Q1) Is there a middle setting, with one link in each position? Or is that non-symetrical? I r an engineer and I still don't know.

Q2) Since both the sway bar and the shocks affect under/oversteer, how much of each should I use. I'm thinking I should leave the front/rear shocks at a middle setting to find the optimal sway bar setting, then tweak with the shocks.

Q3) Now for the really newby question. Is there an easy way to tell when the car is neutral? Or is there a different answer for that for every driver?

Thanks,

------------------
Marty Doane
ITS RX7 #13
CenDiv WMR

Jake
04-12-2004, 09:01 PM
I'll go first.

1. I would think that one on each would work as a middle setting. I don't think Symmetry is an issue, because you only care about the relationship between L+R

2. The Bar deals with steady state cornering balance. The Shocks deal with transistional. If you are trying to prevent oversteer from a quick tranisiton (quick throttle off for instance) than you should look at stiff shock setting up front and a softer one in the back. If you are getting oversteer in long steady-speed sweepers, than you need to stiffen up that front bar.

3. I would suggest driving at a constant spead in a corner at the limit and see what end slides out first. Use that to set your bar stiffness. I think in many ways, people like to set the car up for as much oversteer as they seem comfortable with.

My preference is a car that oversteers in steady state (easier to control), but understeers a bit in a quick transistion. A quick oversteer in a transition is harder to control and can cause a spin.

m glassburner
04-12-2004, 09:11 PM
Ummmm ... first question,what are you driving?fwd or rwd ,awd? When I have one end of the car misbehaving I will adjust that end first... unless im out of adjustment at that end... http://Forum.ImprovedTouring.com/it/smile.gif

ITSRX7
04-12-2004, 09:19 PM
Marty,

Call me and we will talk. WAY to much info to consider in just a post.

508.697.8111

Up till 10:00pm weekdays

AB

------------------
Andy Bettencourt
06 ITS RX-7
FlatOut Motorsports
New England Region
www.flatout-motorsports.com (http://www.flatout-motorsports.com)

m glassburner
04-12-2004, 09:30 PM
I second that!!! http://Forum.ImprovedTouring.com/it/smile.gif

Eagle7
04-12-2004, 10:23 PM
Jake - ding, the light went on. Thanks.
m - RWD '86 RX-7 with no rear bar.
Andy - I'll try you later in the week. Thanks.

More background. My first (only) race weekend last year I had two or three white-knuckle experiences - one at about 90 MPH under full throttle. Fortunately I saved it each time, but I'd rather have better control of the car (a desire which my co-racers, and my wife, share, I'm sure). Post race analysis: stock front bar, worn out front shocks, Khumos past their limit, and front toe knocked out.
This year: the aforementioned front bar, new front shocks, new Hoosier R3S04s. My only track day so far was temp in the mid 40s - I couldn't get enuf heat in the tires (~ 110 deg) to know what I had.

------------------
Marty Doane
ITS RX7 #13
CenDiv WMR

Quickshoe
04-12-2004, 11:00 PM
Easy way for a newbie to know when the car is "Neutral": (1)The car goes where you point it, when you point it. And (2)the back end isn't trying to pass the front end.

At this point in the game, you need to find a setting that you are comfortable with. Don't keep changing things on the car (other than shot shocks and tires http://Forum.ImprovedTouring.com/it/wink.gif ) and learn to be consistant.

It is important to learn what input you gave the car that caused the undesired effect. This is important because later you will know whether the problem is you or the car or a combination. Further, when you are stuck in a race with a handling problem you will know how to change your driving to compensate for a handling issue.

Get with somebody, such as Andy, who can give you a good baseline setup to start with.
I'd like to help you out in that area as well but my seat time behind the wheel of an ITS Rx7 is limited to a few laps and a stint in an enduro.

Eagle7
04-13-2004, 07:04 AM
Originally posted by Quickshoe:
Easy way for a newbie to know when the car is "Neutral": (1)The car goes where you point it, when you point it. And (2)the back end isn't trying to pass the front end.
Ever? Doesn't this depend on intelligent and consistent car control techniques?

<font face=\"Verdana, Arial\" size=\"2\">At this point in the game, you need to find a setting that you are comfortable with. Don't keep changing things on the car (other than shot shocks and tires http://Forum.ImprovedTouring.com/it/wink.gif ) and learn to be consistant. </font>
Yeah, that's what I'm trying to do.

<font face=\"Verdana, Arial\" size=\"2\">It is important to learn what input you gave the car that caused the undesired effect.</font>
I'm not sure whether some of them were from driver input. For instance, the 90 MPH incident - at Grattan there are two turns leading onto the main straight that are taken flat out (at least in my car). The exit of the second turn has some large bumps, so the whole car is heaving up and down. 99 times out of 100 my car has stuck there, and I've never seen another car get loose there. One time it didn't. Driver input or bad shocks? I don't know.

<font face=\"Verdana, Arial\" size=\"2\">This is important because later you will know whether the problem is you or the car or a combination.</font>
Exactly!

<font face=\"Verdana, Arial\" size=\"2\">Get with somebody, such as Andy, who can give you a good baseline setup to start with.</font>
Thanks, I will.

------------------
Marty Doane
ITS RX7 #13
CenDiv WMR

John Herman
04-13-2004, 08:25 AM
Marty, I know the corners well. I have seen many cars lose it (big time) in the area you're talking. If your shocks are shot, you're not going to go through those corners fast or comfortably. Second, as you get faster, you HAVE TO get smoother through those corners. Any jerking of the wheel, throttle lifts, etc., will cause problems. One thing to watch out for on the first turn to the right, when the car gets light as it hits the bump, you may need to "breath" the throttle as the rear lightens. This will keep the rears from breaking loose, because if the rr is spinning a bit when you make the transition back to the right, you have lost a bit of valuable traction in the rr. Finally, because this is such a fast, but violent transition, the car never takes a set. With shot front shocks, this would contribute to nasty transitional oversteer, which you experienced. I find at Grattan, you'll adjust your handling more with shock settings, so good shocks are a must! You still need something close for springs and bars, which it looks like people here are willing to help with. The best corner to evaluate your steady state handling is turn 1, because its the flatest and longest, or the right hander after the yump.

dyoungre
04-13-2004, 09:47 AM
As far as a 'mid point' adjustment: putting one link short and one link long is not a good idea, because you get weight transfer under jounce. Think about it - if both sides go up 2 inches (lets say, under braking), but one side has a longer lever arm, the rotation of the longer arm is a smaller ARC than the short arm - so you end up with weight transferred from the longer side to the shorter. Not good.

------------------
Dave Youngren
NER ITA RX7 #61

Jake
04-13-2004, 11:35 AM
Dave has a good point, I didn't think about that.

If your front shocks are worn, that is probably the cause of a quick transitional tail-out. More dampening in the rear than the front will cause the tail to slide in a quick transition. A stiffer front bar will not fix that.

Greg Gauper
04-13-2004, 02:01 PM
But isn't that the way a cockpit adjustable bar works? By sliding one link up and down the length of one arm? And since you see those on (cross weight sensative) formula cars, if there was a bad side effect nobody would use them.

I would think that the net effect of one long arm and one short arm would be the average of the two arm lengths.

Now if you didn't readjust the lengths of your links, you could put preload into the bar which is a bad thing on symmetrical tracks.



[This message has been edited by Greg Gauper (edited April 13, 2004).]

zracer22
04-13-2004, 03:31 PM
As a newbie, it's more about the seat time and less about the car. Instead of neutral, tighten up the front and soften the rear until you have just a touch of understeer. When you are at that point, you can feel quite good about the rear not breaking loose. A slight push is easy to correct, you just lift a little. "Tight is safe, loose is fast" is a fairly consistant generalization. As you get a better feel for your car and racing, then begin to head towards neutral with adjustments. If you spend too much time setting up the car you won't be focused on your driving as much as you should be. Another good idea is to find an experienced racer to help you. Someone that's been doing it for years can jump in your car for a few laps and then make recommendations.

JohnRW
04-13-2004, 03:50 PM
I'm with Greg on this one. The chassis doesn't know and doesn't care if you're using different length arms at each end of the sway bar. The swaybar pivots independantly of the chassis, and it's the total resistivity to a twisting/bending moment that is transferred to the chassis.

As Greg mentioned, cockpit adjustable bars usually have one fixed end, and one longer blade-type arm that can pivot to change the characteristic of the WHOLE bar, not just one end. In essence, it's a way of varying the length of that end of the bar, without actually varying length.

Jake
04-14-2004, 10:06 AM
Well, Dave is right about the mixed settings. In reality it may not make much of a difference - but if the suspension compresses uniformly left and right (not in a corner), the loads on the left and right wheels will vary through the travel in a mixed setting. When there is no roll, ideally you want no preload on the bar. It would be impossible to have no preload through (a symetrical left and right jounce) range of travel if you have different settings left and right.

dickita15
04-14-2004, 10:18 AM
Originally posted by Jake:
but if the suspension compresses uniformly left and right (not in a corner), the loads on the left and right wheels will vary through the travel in a mixed setting. When there is no roll, ideally you want no preload on the bar. It would be impossible to have no preload through (a symetrical left and right jounce) range of travel if you have different settings left and right.

jake, i am not so sure about this. i can see where at different points in the travel there might be a different efective spring rate for the bar based on changing geometery of the links but i think it would still be even right to left.
dick

dyoungre
04-14-2004, 10:49 AM
With an blade type adjuster, you are changing stiffness, not moment arm length; this issue would not occur. With cable style, single sided adjustment, this issue occurs - although you are not only changing the moment arm, you are changing the reaction vector as well. How do you get a free body diagram in this thread? Anyway, the amount of weight transfer depends on the amount of jounce; on a formula style car, there probably isn't enough jounce to cause a measureable issue.
In any case, while the theory is true, the total 'real world' impact *may* be negligible. Any time I have to make an assumption, though, I'd rather stick with the theory until proven otherwise.

------------------
Dave Youngren
NER ITA RX7 #61

SpeedyDave
04-14-2004, 03:12 PM
Originally posted by Jake:
Well, Dave is right about the mixed settings. In reality it may not make much of a difference - but if the suspension compresses uniformly left and right (not in a corner), the loads on the left and right wheels will vary through the travel in a mixed setting. When there is no roll, ideally you want no preload on the bar. It would be impossible to have no preload through (a symetrical left and right jounce) range of travel if you have different settings left and right.

Hey Jake! I actually disagree with this, shouldn't a sway bar provide NO resistance if both sides are traveling the same? Ie braking zone. The bar should simply pivot. It should only provide resistance when unequal left-right load is applied and tries to "bend" the bar.

Jake
04-14-2004, 03:48 PM
Both Dave's are right. Speedy - as you point out there should be no preload in the bar in a straight braking zone. If you use different attachment points to the bar, you have different radius arms that act on the bar. Unless I put a free body diagram here, I probably won't be able to explain this any better, but I'll try anyway.

Think of it this way: You adjust your front bar to zero preload L/R but use different bar setting on either side. In a straight braking zone you compress the front end of the vehicle equally left and right. The endlink that acts on the longer radius arm of the bar will rotate the bar more than than the side with the shorter radius arm. This will twist the bar (something that shouldn't happen in a straight braking zone!) This, in turn, will change your corner weights and load one of the front wheels more than the other.

In reality, this may not make all that much of a difference because the radius change isn't all that much and none of us have all that much suspension travel anyway. But I still don't think I would use a mixed setting considering this.

dickita15
04-14-2004, 04:53 PM
good explanation thanks you

Eagle7
04-20-2004, 09:34 PM
Originally posted by ITSRX7:
Call me and we will talk. WAY to much info to consider in just a post.
And the master says...my current car setup is pretty loose. Suggested stiffer front springs and sway bar setting and shock adjustment. Should save me a lot of testing time (and money) trying to figure it out.

Kudos to Andy - very knowledgeable and helpful.

Thanks,

------------------
Marty Doane
ITS RX7 #13
CenDiv WMR