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Author Topic:   Trick in 06, redux !
Kromulous
Dirt Forum Champ
Total posts: 856
posted December 07, 2005 10:46 AM  

 
Another:


Kromulous
Dirt Forum Champ
Total posts: 856
posted December 07, 2005 10:51 AM  
Ok some miscommunication is going on here, i should of stated "effective" and "dynamic" more clearly.

According to AFCO's theory, the old theory of the mid point of the bar is way off. That i can buy, because using the old theory some adjustments i have made in the past did not produce the proper results, according to the old theory.

I can agree with that, and it makes since. The only reason i went to the AFCO site to begin with was i was trying to find some pics of your theory so i could understand it better.

Now after clearing that up, i am trying to learn more about effective and dynamic RC locations and how it migrates.

Krom.

Kromulous
Dirt Forum Champ
Total posts: 856
posted December 07, 2005 10:53 AM  
Link to the entire article:
http://www.afcoracing.com/tech_pages/panhard.shtml

zeroracing
Dirt Forum Champ
Total posts: 1932
posted December 07, 2005 11:05 AM  
awkwardjeff
Why dont you draw it out and post it on here? That away everybody can see exactly how you recomend doing it. A diagram speaks volumes over a paragraph.
Post a diagram of how you find your rear roll center, then we can debate this if people agree or disagree.

As for personal attacks they have no place on this forum, that is the reason this forum is so great. Other forums you go to you ask a question and some guy will call you 6 names before your done. So dont result to personal attacks.

But a diagram would be great to help the understanding of your method, maybe once we see it drawn out we will say wow that is great, and really easy to follow according to the diagram, or we might say I dont like that idea therefor choose not to follow it.

Dont try to start a battle of know it alls, sooner or later somebody will step in and make you look foolish. Just state your idea's in a respectful manner.

Now, lets see a diagram of your method.

Thanks
Jason

wfoondirt
Dirt Forum Champ
Total posts: 533
posted December 07, 2005 11:18 AM  
Since we are posting references here's some more fuel for the fire.


Roll Centers

Short Panhards

J-bar Roll Center

author reference

Personally I think this whole discussion has become one of symantics. There are several different theories out there reguading roll center location. Each takes into account different factors that contribute to the roll center location. What is important to realize is that no matter what theory you use to find the roll center you have to take into account at some point all the factors that effect the suspension (panhard bar height/angle, spring location/split/rate, track width etc.) to determine how a car will behave. Remember that the RC is a THEORETICAL point. Every RC theory has its positive points and negative points.

awkwardjeff
Dirt Forum Champ
Total posts: 589
posted December 07, 2005 12:02 PM  
Jason,

My way of figuring rear roll center on a chassis with a pan bar is simple and shouldn't need a drawing. I'm not sure I could draw it out and post it......drawing it is simple getting it loaded would be hard for me...... i'm not a computer person.

my way, find the center of the tire contact patches......draw a line from the floor to the sky....vertical. then draw a line through the pan bar until it crosses the vertical line.......to me that is roll center. The only place I differ from the drawing Krom posted was AFCO's picture uses the top spring locations ......I have debated this with many people, including some very smart people. a few still believe in the spring mount location to find roll center.....others I have converted to believe tire contact patch..... My arguement is this.....if you move the spring you change the effect?? or you change the location???? if you move the bottom of the spring out you will need to stiffen the spring to have the same amount of roll, because of leverage, correct? then if you move the top mount of the spring are you changing the leverage or moving the roll center???? Their arguement to me becomes, if you go from a 2 off wheel to a 4 off wheel on the right rear did you move the roll center or did you just change the effect?? All the sprint car guys I have discussed this with I have converted to my way of thinking. The stock car guys seem to be a little more stuck on the spring mount way of figuring location. I think the sprint car guys understand it better because of the front axle on a sprint car, the rear of a stock car wraps with torque so it rotates, then with the other locating divices, weather 2link, Z-link, 4 link....they seem to think it much more complicated. The chassis tries to rotate around the rear roll center, we all agree. We can change how the chassis rolls many ways, moving roll center, stiffer springs, wheel offsets, spring location.....but those things don't change the location, the effect the amount of roll...... The reason to add to this post was adjustment from one car don't effect every car the same way. We have a car with the roll enter located right of center and one car with the roll center located left of center, one is a raising roll center.......as the chassis rolls the roll center raises and will limit the amount of roll. The other car has a falling roll center, so as the chassis rolls the roll center moves lower, this promotes the chassis to continue rolling........ one car the pan bar ends right of center the other car the pan bar ends left of center so the adjustments are backward from one car to the other.........along with the dynamic changes being much different.

As for making personal attacts, I agree, I felt Krom was being a flamer with me.....just pouring gas on the fire and watch what happend. I agree this is a great site because Jammin keeps this type of BS out of the conversations..... Krom joined in 04, you joined in 02, and I joined in 00. It doesn't matter how long any of us have been here, I was here when this was a rather small site and gave many people help, and have been thanked many times.....out of this discussion I have recieved PM's reguading the roll center location stuff. My point is my ideas and thoughts are well respected from the people that have been here a long time. I hate people that tend to argue with my thoughts without providing information to support their arguement. people tend to say that a idea or thought is wrong but don't know the right way.......if someone doesn't know the right way how can they support their idea of the other person being wrong. Krom agrees the old thought on center of the pan bar is wrong and out-dated...... Steve Smith is a author, not a chassis builder. He went to many shops and took what those people said as the truth.......right or wrong.

Kromulous
Dirt Forum Champ
Total posts: 856
posted December 07, 2005 12:42 PM  
If my posts came off as being inflamatory, they came out wrong. I was just trying to understand your theory, i didnt understand the vertical lines, now i do.

Which i am beginning to see the merit in it. Once i seen the AFCO pictures, i was better able to grasp what you were saying.

I know using the old theory, some adjustments didnt add up. On a 3/8ths paper clip track, the car was tight in the middle, the car would come in hard and fall off the bars and get tight. So i thought i would raise the rear RC, i raised the frame side, it got tighter. That was on a front mounted J-bar by the way.

Good discussion noe the less, learning alot.

Krom.

leapinlizard
Dirt Freak

Total posts: 437
posted December 07, 2005 12:57 PM  
So we all agree you have to decide where the RC is before you can manipulate it?

It seems that the only thing I have learned in my 1 year career is that RC are NOT an exct science. No one has a formula to find or manipulate Front or Rear RC. I say the Front is included because I've read many theory's ther as well as new technolgy and advances in science.

Let's say for a moment the RC is located on a intersection of a tanget line drawn thru the panhard bar and center contact patch'a. If the panhard bar axle mount is located dead center of the contact patches then moving the bar up or down on the axle end or frame end will have no affect. True?

awkwardjeff
Dirt Forum Champ
Total posts: 589
posted December 07, 2005 01:18 PM  
I'm off to work for a day or two, for anyone wanting to argue or debate this I have a question you will need to answer before we discuss this any more. why does a sprint car have the ladder located on the right side of the chassis? and what would be the effect of mounting it on the left rear? I hear all the time you want as much left weight as you can get, wouldn't left side be better? I will tell you that one of the locations is a falling rear roll center the other is a raising roll center. You tell me which is which......... to draw out the jacobs ladder, draw a line along both straps until they intersect, use that point as your inside point, then use the clevis point as the outside point......that is the line that would be the pan bar..........

awkwardjeff
Dirt Forum Champ
Total posts: 589
posted December 07, 2005 01:29 PM  
quote:
Let's say for a moment the RC is located on a intersection of a tanget line drawn thru the panhard bar and center contact patch'a. If the panhard bar axle mount is located dead center of the contact patches then moving the bar up or down on the axle end or frame end will have no affect. True?[/B]

That is NOT true, if you move the mount of the frame you didn't change the location, if you moved it on the housing you now moved the location......... if you moved the rear housing mount up you will raise the roll center and the chassis will not roll as much. If you move the mount down you lower the roll center. And the chassis will roll more.......everything else being equal.

we have all seen cars with three wheels off the ground, car is on right rear tire only off a turn, driver is on the gas...... where is the roll center???? it must be way out past the right rear outside the chassis?????? I don't think so, The EFFECTIVE roll center is way out there, because of springs, locations of mounts, angles of bars, and many other things. I think Krom can agree with that thought??? the chassis starts to roll then because things aren't balanced the effects of the un-balance spring split, locations, ect. start moving the effective roll center location. to me this isn't called "effective roll center" this is called leverage.......


PEwaste
Dirt Full Roller

Total posts: 67
posted December 07, 2005 01:54 PM  
If I remember right, Greggie, you have a Dirtworks car? On the Hoffman/Dirtworks style cars, along with the Harris cars that I have been around, we always adjusted the way I stated. Now is it the right way... maybe for us but not for you. Adjusting the panhard bar isn't just raising or lowering it anymore... with the way the chassis rolls, lifts up... it is a whole new ball game... but adjusting it the way I was taught never did me wrong.

Awkward.. I never attacked you, but obviously you have superior knowledge to me or Krom. He asked a question and didn't ask to be belittled. Roll centers are rather confusing, and to some people are easy to find. It is just like adjusting a race car to fit your needs, what one guy does might be the complete opposite of what it takes to get the same car to do for another person.


Kromulous
Dirt Forum Champ
Total posts: 856
posted December 07, 2005 02:07 PM  
Right side jacobs ladder would be the falling rear RC, left side would raise, right?

Krom.

awkwardjeff
Dirt Forum Champ
Total posts: 589
posted December 08, 2005 09:19 AM  
Krom, I just got up and have to go back to work soon, so I don't have lots of time today. You are NOT correct, sorry....

to figure it out i'm sure you used the 3 point of the ladder drew a line through each strap until they crossed, then used that point to draw a line from there to the clevis point.....these two points represent the pan bar......I believe you got all that correct. The next thing you did was moved the CLEVIS end up and down......is that how you figured it???? Don't feel bad, that is exactly what almost everyone does.

The clevis end is mounted to the birdcage, which is located on the axle......that is the point that stays stationary.....

To figure it out correctly you would need to draw the ladder level and draw out you lines, then draw a complete new ladder with the outer points (chassis) mounts lower, you will see the bottom strap goes from say 45 degrees to 65 degrees pointing up hill at the top strap would go from 45 degrees down hill to about 25 degrees....the top strap gets more level...... if that all makes sense.... so you raised the frame mount location.......that means you raised the rear roll center during chassis roll, mounted on the right side.

I'm sorry if I came across as a know-it-all
its' not my intent to show what I know, or to show what someone else doesn't understand. I post information I feel will be useful and help others, I hope some of this discussion has helped you have a better understanding of what is going on with roll centers and adjustments. And now that you and I have a better understanding of each other we could debate more if you would enjoy the conversation.

[This message has been edited by awkwardjeff (edited December 08, 2005).]

Kromulous
Dirt Forum Champ
Total posts: 856
posted December 08, 2005 10:25 AM  
Your right, i figured it that way, but i forgot that the clevis end was connected to the birdcage. A friend of mine runs a Sprint car, and i help with it sometimes when we race at the same track, but i dont get to involved with it, i'm just a grunt guy on that team.

You seem to know alot about Sprint cars, you race around the Midwest area? DO you know Steve Stapp "Bopper" or Joe Kerr?

Anyway, i still dont quite understand how and when the RC moves outside of the panhard bar, can you go over that a little? Like in the AFCO pics above.

And your posts are very helpfull, i dont think they come off as being a know it all, at all. I appreciate you sharing the knowledge.

Keep the thread going, alot of folks can benifit from it, i know i have already and there is alot of confusion out there about Panhard bars.

Krom.

awkwardjeff
Dirt Forum Champ
Total posts: 589
posted December 08, 2005 11:18 AM  
Krom,

roll center outside the pan bar is this. use AFCO's thoughts and use your spring mounts to draw your vertical line from floor to sky...... or use my thoughts and use center to tire contact patches, if BOTH ends of the bar are on one side of that vertical line the roll center will be OUTSIDE the bar. The bar and the vertical line don't cross......only when you continue the line of you pan bar do they cross.

A pan bar with a mount on each side of the vertical line is known as "roll center INSIDE the bar"

To me the rear roll center is a exact science, not some theory. If you built the car equal on both sides, same locating links, spring locations, spring rates, center of gravity, ect. this would be the point the chassis will ROTATE...... as the chassis rotates the roll center location is moving, also known as dynamic..... the dynamic change is what is backward from inside or outside locations .......one moves the roll center lower, one moves the roll center high. The more you understand what is going on the better you can control the outcome. Do you agree with my thoughts on a car that is standing on the right rear tire only? the roll center isn't outside the chassis, but that is exactly what it's acting like........you seem to refer to that as effective roll center, I personaly like to call it leverage.

I got a task for you ....get a pair of sissors and a leather shoe string. put the shoe string at the tip of the sissors and cut, now open the sissors all the way and put the shoe string all the way in and cut again.......which was easy and which was hard??? why? I don't think you moved the center, you had more leverage because you moved the shoe string.....I'm not sure this is a good example, but it's the one I used on my wife the other day and she seemed to understand better.

leapinlizard
Dirt Freak

Total posts: 437
posted December 08, 2005 11:42 AM  
So with your ideas, a roll center placed nearer the RR tire will cuase the body to roll around that point. This causes the LS side rise more then the RR side compresses.

A roll center closer to the LR tie will make the RR compress further than the LR will rise.

A roll center nearer the right side tire can help more with side bite by loading the RS but it doesn't allow the LR trailing links to index(move) as far. Possible calling for a change there.

A roll center placed nearer the LS tire will create a little less side bite but more indexing of the LR bars angles.

Placing the front and rear roll axis at the same "x" and "y" will provide a balanced set up that keeps the front and rear working together rather than trying to twist up your frame.

Changing wheel offset's moves the Roll center.

I'm a getting it?

awkwardjeff
Dirt Forum Champ
Total posts: 589
posted December 08, 2005 11:59 AM  
Krom, and everyone:

I'm must apologize for giving mis-information.....I deleted part of a post, and must correct myself before someone(krom),,,LOL finds my mistake. if the pan bar is mounted on the right the adjustments will still be backwards from inside the bar to outside the pan bar. I haven't had this discussion in a year or so and thought I remembered EVERYTHING.......but it wasn't making sense to me, so I had to draw the right side mount stuff out all over again for myself...... and my memory wasn't THAT good.

The right side mounted bar WILL be backwards if the rear roll center is inside the pan bar or outside the pan bar. again i'm sorry if I cause any confussion.....

Kromulous
Dirt Forum Champ
Total posts: 856
posted December 08, 2005 12:54 PM  
Leverage works, effective RC was just a term i read on another page. Using the term leverage will actually help you remember what your trying to do with the panhard bar.

Like pulling a nail with a claw hammer, grip out at the end of the hammer, its easy, grip it by the head of the hammer and its harder.

Krom.


awkwardjeff
Dirt Forum Champ
Total posts: 589
posted December 08, 2005 02:13 PM  
Leapinlizard,
Are you getting this?? heck, maybe, at least part of it..... I agree if you have the front roll center and the rear roll center located proper .....and the line between the front and rear is the roll axis, that is why at the start I didn't use the word axis.....a axis is a line between two points, like front and rear. Roll center is talking about one single point, that is why at the start of this discussion I choose that wording. But yes, if the front and rear are located proper to keep a balnaced roll axis it will keep from twisting the chassis. Remember my question of a car with 3 wheels off the ground, standing on the right rear tire off the turn?? the chassis is acting like on big lever or leaver depending on who you are talking to, twisting the chassis to plant the car. This set-up can be fast, but hard to drive.

I'm going to try another example before I leave for work, get a 4X4 piece of lumber about 8 feet long. Place one end under the car along with a jackstand close to the car and push down on the other end to lift the car. Then move the jackstand away from the car, you see it gets much harder to lift the chassis. the jackstand is your roll center, let's say you have 1 foot of the lumber from the jackstand to the chassis, 7 feet from the jackstand to the end. If you are lifting say 1250 pounds you need to use ABOUT 178 pounds of force to BALANCE......

So if you start trying to move your roll center left or right that far ......well you see what you need for spring rates.

My thoughts are the rear roll center is one specific point, everything else affects the amount of roll on one side or the other of that point. If both sides of the roll center aren't the same you start to have leverage, or effective roll center.....

You can't change springs mid-turn while racing, you can't change spring location, you can't change center of gravity, ect. But what you can change mid-turn while racing is the location of one specific point (rear roll center) you can raise this point or lower this point. it works like moving the jackstand. on some tracks you want to move the point higher to limit the amount of roll, other tracks you want to lower the roll center to encourage the chassis to continue rolling. In my opinion, and this may start another disagreement is you can't move a rear roll center side to side with chassis roll during racing. I believe some people believe they moved it right because the chassis didn't roll as much.....but people that believe that way don't seem to understand the differance between roll center and EFFECTIVE ROLL CENTER or the leverage affect. these people believe in a roll center and the chassis is rotating ONLY, they don't believe in a leverage affect in any of their equations...it just doesn't exist to them.

fastow
Dirt Maniac

Total posts: 179
posted December 17, 2005 11:14 PM  
Where is the roll center on a leaf car. Even better one where is the roll center if we had a car with a stack leaf on the left 2 inch lowering block and 4 link or z link on the right?

awkwardjeff
Dirt Forum Champ
Total posts: 589
posted December 18, 2005 06:00 AM  
do you need help locating your rear roll center or just tossing that in for arguement? If you ran a stacked leaf left and a 4link or Z-link right I assume you are using a panbar still?

quote:
Originally posted by fastow:
Where is the roll center on a leaf car. Even better one where is the roll center if we had a car with a stack leaf on the left 2 inch lowering block and 4 link or z link on the right?


fastow
Dirt Maniac

Total posts: 179
posted December 18, 2005 11:47 AM  
I was not looking for arguement but discussion. But I have seen a car once that had leaf left rear and bars on the right and no panhard bar it used the left leaf to hold rear end in place.

Kromulous
Dirt Forum Champ
Total posts: 856
posted December 19, 2005 06:54 AM  
Thats a good question, where is the RC on a leaf both sides car?

I've always been to scared to work on a Leaf car, my brother bought one, and i got the torch out first thing, and put bars under it, LOL.

Krom.

fastow
Dirt Maniac

Total posts: 179
posted December 19, 2005 08:26 AM  
If remember right the roll center is like between the axle and spring. Adding lowering blocks lowers roll center. But when your talking left to right don't think I have ever looked at that andd with just on leaf I would guess it would be all the way over to the left?

wfoondirt
Dirt Forum Champ
Total posts: 533
posted December 19, 2005 08:30 AM  
The RC for a leaf car is located by drawing a line through the front mounting point and the rear shackle mount. Where that line crosses the centerline of the axle is the height of the roll center.

Here is a copy of the diagram from Milliken's RCVD.


Kromulous
Dirt Forum Champ
Total posts: 856
posted December 19, 2005 08:54 AM  
That must be why i see them leaf guys always talking about re-arching thier sprins, and keeping them jacked up in the pits all the time.

Krom.

fastow
Dirt Maniac

Total posts: 179
posted December 19, 2005 08:13 PM  
That makes sense but still don't say about left to right location of the roll center
. Where did you find that pic anyway don't think I ever seen it before
?

wfoondirt
Dirt Forum Champ
Total posts: 533
posted December 20, 2005 07:36 AM  
Lateral location is typically assumed to be at the middle of the track width. On an asymetric car it would be closer to the stiffest spring but it still won't be far off center.

The diagram is from Milliken & Milliken's Race Car Vehicle Dynamics.

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