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Author Topic:   Panhard Bar Theory ?
Kromulous
Dirt Forum Champ
Total posts: 796
posted June 22, 2005 07:07 AM  
I've seen alot posts about panhard bars, alot of different ways to adjust them etc. So now i am getting confused about what ways to adjust for certain situations.

Understanding that the panhard bar controls the rear roll center is pretty basic. Adjusting it can become a little tricky.

Some say if the car is tight in the middle, raise the frame side, well ok, but that seems a little off to me. Wouldnt raising the frame side induce more side bite via the added angle ?

Angle in the panhard bar is supposed to induce more side bite, which i can understand. As well raising it or lowering it both sides at the same time can raise or lower the RC, which is understandable as well, but the confusing part is how people adjust it, at least it is to me.

Anyone care to share there theories on adjusting a car with the panhard bar?

Our current situation on our car is this. 4-link LR behind, 225 spring, swing arm z-link (18" lower swing arm), spring on the arm 300lb spring. Running a J-bar even with the pinion, and about 5" total rake. Running a 26" Pull bar at 10* and right at 100lbs LR bite.

The car is really smooth and easy to drive, we had it out on a bigger, faster track and i was really happy, since i built the entire front & rear suspension. Only thing is it had a little to much side bite, little tight in but not bad but got tighter in the middle as you went.

Now, i was going to lower the J-bar frame side to shed off some side bite, or is that wrong thinking?

Another adjustment i considered is a softer RR spring, but i did want to change my scale numbers. So i want to adjust the panhard if i can.

Kromulous
Dirt Forum Champ
Total posts: 796
posted June 22, 2005 07:17 AM  
Stole this from a Circle track article, interview with Joe Garrison from GRT.

“By raising the J-bar up on the frame to create more of an angle, it makes it easier for the car to roll over onto the right side,” says Long. “If you’re drifting across the track going into the turn, then raise the chassis mount for the J-bar, and it will help the weight transfer to the right side.”


“We use a 19 to 20 inch, and it has probably anywhere from seven to nine inches of angle in it for our standard setup,” says Garrison. “By angle, I mean the mounting point on the pinion versus the mounting point on the chassis. If the track is extremely slick, you need a lot of angle in the J-bar to help induce roll in the car and create side bite and drive. On a bigger track where you can carry more speed, you don’t need as much angle in the J-bar. You might even use a longer bar, say as much as 25 inches. On a real tight, stop-and-go racetrack, we might even use a short, straight Panhard bar if we have to get the car to turn quickly.”

Garrison continues, “Actually, on our standard J-bar setup, with it mounted on the right side of the pinion, I think it helps tighten the car on entry but allows it to turn through the middle and coming off. In contrast, the straight bar that mounts on the left side of the pinion makes the race car more loose on entry and gives the drive coming off—perfect for a short, stop-and-go racetrack.”

rpm20
Dirt Freak

Total posts: 338
posted June 22, 2005 07:40 AM  
i can really relate to the confusion you have also krom....

our dw8 was the same way , 4-z and tight in and through. we recently tested the 4 link rear and i liked how it got in, it was great in and in the middle it was actually a little loose.
i atributed that to the fact that we went from a 225lr behind ,180rrin front to a 225lr behind and rr200 in front.

we dropped the p bar just on the pinion side to about 1.5" below the pinion and it was good in but the middle and out it was a push monster and i was in the way of everyone.

i think in the future i will lower both sides equally.

now last night i was reading some p bar tech and it recommended to lower both sides when lowering and also stated tha if you raise just the outside or lower just the inside , you are then creating an unstable roll center that may actually be lower than you wanted and induce further poor handling.........boy can i relate to that.
i am still fixing the stuff that got wrecked sat. night when one of the guys ran over my rf because i was out to lunch.
i start with my frame side 7-8" up from the bottom of the frame rail and the pinion side even with the middle or even a touch higher.
about 5" diff. in each height.
seems to work good.....if you dont mess up and adjust it tight again.
also with our 4-z we found that too much top bar angle makes it tight on the gas .
i ran as much as 3/4" trail on the z to get it in better.

wfoondirt
Dirt Forum Champ
Total posts: 505
posted June 22, 2005 08:34 AM  
There are 2 factors to consider when adjusting the panhard bar. Number one of course is the change in r/c. Number two is the jacking effect caused by inclining the panhard bar. This jacking effect typically moves the r/c to the left creating more roll.

Until you reach an extreme amount of angle in the panhard bar the height of the bar is the dominant factor in determining the r/c location. At extreme angles the jacking forces become dominant.

So at moderate angles raising just the frame side of the j-bar will loosen the car by raising the roll center. Ideally though you would want to raise both ends of the bar, but changing just the frame side is often done out of conveinence. Typically if you want to create side bite you would lower the bar on the pinion.

As with any kind of jacking force in a race car adding angle to the panhard bar makes spring changes less effective and bar angles more sensitive.

Kromulous
Dirt Forum Champ
Total posts: 796
posted June 22, 2005 08:52 AM  
Ok, what would you do for my situation, concerning a panhard bar situation?

Our current situation on our car is this. 4-link LR behind, 225 spring, RR is a swing arm z-link (18" lower swing arm), spring on the arm 300lb spring. Running a J-bar even with the pinion, and about 5" total rake. Running a 26" Pull bar at 10* and right at 100lbs LR bite.

The car is really smooth and easy to drive, we had it out on a bigger, faster track and i was really happy, since i built the entire front & rear suspension. Only thing is it had a little to much side bite, little tight in but not bad but got tighter in the middle as you went.

Now, i was going to lower the J-bar frame side to shed off some side bite, or is that wrong thinking?

[This message has been edited by Kromulous (edited June 22, 2005).]

Kromulous
Dirt Forum Champ
Total posts: 796
posted June 22, 2005 08:56 AM  
quote:
Originally posted by wfoondirt:
There are 2 factors to consider when adjusting the panhard bar. Number one of course is the change in r/c. Number two is the jacking effect caused by inclining the panhard bar. This jacking effect typically moves the r/c to the left creating more roll.

Until you reach an extreme amount of angle in the panhard bar the height of the bar is the dominant factor in determining the r/c location. At extreme angles the jacking forces become dominant.

So at moderate angles raising just the frame side of the j-bar will loosen the car by raising the roll center. Ideally though you would want to raise both ends of the bar, but changing just the frame side is often done out of conveinence. Typically if you want to create side bite you would lower the bar on the pinion.

As with any kind of jacking force in a race car adding angle to the panhard bar makes spring changes less effective and bar angles more sensitive.


So from this post, my thinking of lowering the panhard bar (to shed off some side bite) would be the wrong effect i am looking for, which is to loosen the car in and in the middle of the turns.


dirtbuster
Dirt Forum Champ
Total posts: 2007
posted June 22, 2005 09:00 AM  
Was it tighter in the middle as you got on the gas? If it was tighter on the gas then i wouldnt mess with the pbar, id look somewhere else.

What left% do you have? IF it is just a little tight in you might try moving some lead to the left. or lowering it a little in the chassis and leave your panhard bar alone.

5" isnt a lot of rake. We have close to 9 in ours. I dont think that is uncommon for spring behind cars. We started with it lower and needed more sidebite so we raised it almost 2". We were already in the bottom pinion hole so we couldnt go any lower there otherwise I would have dropped it there.

[This message has been edited by dirtbuster (edited June 22, 2005).]

wfoondirt
Dirt Forum Champ
Total posts: 505
posted June 22, 2005 09:14 AM  
You would want to raise the bar overall. The extent of how much depends on how tight the car is. I raise the pinion a hole first and tune from there with the frame mount. It also depends upon the timing, if the car is tight early I would take some angle out, if its tighter closer to the middle of the corner I would try and maintain the angle and raise the bar evenly.

[This message has been edited by wfoondirt (edited June 22, 2005).]

wfoondirt
Dirt Forum Champ
Total posts: 505
posted June 22, 2005 09:24 AM  
quote:
Originally posted by dirtbuster:


What left% do you have? IF it is just a little tight in you might try moving some lead to the left. or lowering it a little in the chassis and leave your panhard bar alone.


This is something that is often missed when discussing setup and I was going to bring up but didn't want to confuse the topic.

ls% has a big effect on mid corner speed/sidebite. The past couple years I've started working more and more with ls% to tune the car as the track changes. If your car is light enough that you have a couple hundred pounds to move around it can make a big difference.

Ls% also effects the lateral location of your r/c.


[This message has been edited by wfoondirt (edited June 22, 2005).]

happy
Dirt Full Roller

Total posts: 73
posted June 22, 2005 10:15 AM  
We run a 1\4 high bank and the track went black in the heats enough to see the car a little tight on entry. Our thoughts were to lower the bar equally on the pinion and frame, come feature time we ended up with a car that did a 4 wheel "drift" looking back I think the bar should have been left at the same point on the frame and lowered on the pinion one hole to try and give more side bite, does this sound correct?

Kromulous
Dirt Forum Champ
Total posts: 796
posted June 22, 2005 10:21 AM  
It sure is confusing RPM, i hear alot of different theories. Sorry to hear about your crash as well.

I was considering 1 or 2 adjustments, dropping the RR spring down to a 275lb (on the swing arm) or lowering the P-bar. Now i'll change that to raising it, gonna raise it a 1" on the frame side first.

Our left side is at 53%, our car is real heavy its at 2500lbs with driver and fuel. So we dont have any ballast to work with. Although i can move the fuel cell laterally, and move the battery from high left side to high right side.

Could you go over some of your theories on left side % and how to work with it for all of us?

Thanks, for the great discussion so far, Krom.


wfoondirt
Dirt Forum Champ
Total posts: 505
posted June 22, 2005 12:02 PM  
quote:

gonna raise it a 1" on the frame side first.


I would consider raising the pinion end first to avoid getting too much angle in the bar and creating unwanted body roll. I like to error on the side of less angle than more. Too much angle and the car gets hard to drive on a hooked up track.

quick and dirty explination of ls%:

Basically the idea is to shoot for 50/50 lateral weight distribution at steady state cornering. Lateral weight transfer is calculated by (lsw*cgh*g)/tw (banking angle also has an effect but the equations get more complicated). Given that equation you see that as cornering g's decrease (track slicks off) you need to decrease ls% to maintain the same tire loading. Since a tires vertical loading vs potential grip relationship is not linear, too much weight transfer will cause a loss in overall traction also.

As far as tuning goes I typically time mid corner speed and work from there. On the modified I would make as much as a 4% change in ls% from tacky to slick track, but I had ~250lbs of ballast to work with. Being that you are already overweight I would work on getting a good typical feature balance and give a little up in the feature since ls% is not easy to change without ballast and I'd sacrifice setup for total weight anyday.

Sorry I don't have time for a more detailed post but work calls.

[This message has been edited by wfoondirt (edited June 22, 2005).]

Kromulous
Dirt Forum Champ
Total posts: 796
posted June 22, 2005 12:25 PM  
So, you decrease left side %, basicly your putting more weight back over on the right side tires, instead of the left.

Since the track gets slicker, you dont need a high left side % to combat high siding the car in corners.

I used to race RC cars (carpet oval) years ago in the winter, boredom, and back then we actually played with moving all the weight to the right side of the car and over loading the right side with weight. And it worked, well to, it was very fast. Your theory would support that, although thats not recomended for real cars but it works non the less.

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted June 22, 2005 12:39 PM  
Think of it this way. When the track is tacky the tires stick on their own and the car will transfer a certain amount of weight to the right side. In order to keep the car balanced you need to have enough left% so that after transfer the tires are still loaded somewhat evenly. Now as the track dries out the tires lose grip and with the same amount of left% the right side is not getting loaded as much and therefore has less sidebite. Taking left% out, or moving lead to the right will help rebalance a car on a dry track because you are getting back to that balanced condition at the tire patch. But go to far and you will either make the car too tight on entry or overload the Rr all together.

Also when dry you may want to raise you lead to induce more roll and weight transfer to make the car think its still tacky. With the lead low on the chassis the tires wont stick well enough on their own to induce transfer, raising the lead gives it more leverage to roll over and transfer and stick the right side. This can also by used to tune the car on different tracks. To some extent you can run more left% when dry if you keep it high on the left so that it will still transfer to the right, but in some cases you still need to take left% out.

Now does that mean when tacky to put all your lead low and left and dry high and right...NO. You have to tune it and find a balance that works for you. But in general as the tracks dry out you want to move lead up and to the right. Maybe not all at once but try a little at a time and see how it affects you then go from there.


wfoondirt
Dirt Forum Champ
Total posts: 505
posted June 22, 2005 01:11 PM  
db is right on, good explaination.

I run rc cars too and due to their nature most setups don't apply to real cars.

I wouldn't suggest overloading the right side tires. The idea is not to overload them, the idea is to load the ls and rs more evenly as cornering g's decrease as the track slicks off. The problem with running high ls% is that when it slicks off you can't transfer enough weight to the right side. As db eluded to without some kind of data aquisition its a trial and error situation.

If you are interested in all the mathematics behind this I would reccomend Milikin's Race Car Vehicle Dynamics.

[This message has been edited by wfoondirt (edited June 22, 2005).]

Kromulous
Dirt Forum Champ
Total posts: 796
posted June 22, 2005 01:53 PM  
Set up's dont apply, but i often find the theory does.

Nice book by the way, gonna order a couple of them, should make for some nice reading and learning.


leapinlizard
Dirt Freak

Total posts: 402
posted June 22, 2005 02:18 PM  
Math is math, physics are physics and the rules are unchangable. If you had a scale dirt RC car with a track scaled down and all the real life traction and everything. Not theory, but the exact same physics would work for the RC car. But since we can't control everything to such a minute amount we are stuck living with acceptable variances. Moving weight up creates higher mechanical leverage arm by moving the CG. Moving that CG right loads the right side tires by increasing the weight carried by them at a given moment. IF you have to induce a transfer of energy beyond adding more weight you move it right. To lengthen the mechanical arm. You do it this way so you don't have to add more total weight but you get the same results. Higher banked tracks need less weight to transfer because the ground is already making up some of that weight. In the form of inertia force.

I'm really just babbling here. I just though that a different way might help some people understand it.

wfoondirt
Dirt Forum Champ
Total posts: 505
posted June 22, 2005 02:38 PM  
[highjack]
Physics do apply to rc cars the same as anything I totally aggree. At least with the nitro cars the setups tend to be extreme as a crutch for the drivers reactions. We built some pretty wild stadium trucks for dirt oval racing a few years ago that were ~75% ls% with huge side boards and wings that were eventually outlawed at our local track even though it was a run what you brung class...go figure.
[/highjack]


Kromulous
Dirt Forum Champ
Total posts: 796
posted June 23, 2005 07:26 AM  
Your right, its easy to go to extreme with RC cars, like the right side weight we were doing.

The reason for this post was to try and get a better understanding of panhard bars. I believe there is alot of misinformation out there about adjusting them.

I think there is some good info here, but if you got any more ideas on panhard bars and adjusting them post it please.

wissota3x
Dirt Forum Racer

Total posts: 86
posted June 23, 2005 08:23 AM  
We run panhard behind the rearend about 21" long.Don't have much experience with the J-bars.Sounds like J-bars run more angle than the behind bars for some reason.We have been running about 2& 1/2 inchs of angle and moving both ends together. The vertical location of the balast,battery,fuel cell,etc; has alot to do with side bite and roll over. Our typical adjustment from heavy to slick track would be to add fuel which raises the center of gravity and adds more rear %.We lower both ends of the panhard also.Putting too much angle in the panhard makes a rough riding car and doesn't allow the springs and shocks to work properly.We mount the battery and balast about shoulder high to the driver.We are on hoosiers and our LS % is in that 55 to 56% range.Rectangle 32 gallon fuel cell mounted just to the left of center.JMO

wfoondirt
Dirt Forum Champ
Total posts: 505
posted June 23, 2005 08:55 AM  
Not really much to add. I generally use the panhard bar to tune mid corner. I try to avoid running too much angle, I will usually add angle until it starts to get tight on late entry then back off some. I don't like to use alot of angle because once you do it starts effecting other areas of the corner and makes tuning the car harder. It can also make the car more unpredictable to the driver. I like to run right side frame mounted panhard bars (ala rayburn) mainly for strength since the bar is in tension instead of compression. The right side panhard also makes the r/c more stable.

Here is a link to one of Mark Ortiz's newsletters that talks a little about panhard bars. In case you have never seen his newsletters they are definnately worth substcribing to. The auto-ware site also has an archive of some of the back issues also.

[This message has been edited by wfoondirt (edited June 23, 2005).]

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