rear panhard bar tech

[redracersmod]

Ok guys I was talking with a fellow racer yesterday about panhard bars and adjustment he said he searched the forum and found lots of conflicting info on adjustment and was left with even more confusion. So maybe someone with more knowledge then I do can help make all of us more informed. Let's start by looking at what each adjustment does individually. What does it do (tighten or loosen and where) if you only raise the panhard bar on the frame? What if you lower it? What about if you only change it on pinion up or down? Lastly both together up or down. Thanks guys

[let-r-eat]

http://www.afcodynapro.com/afco-tech-tips

[Anonymous24]

The panhard bar dictates rear roll center. If running a balanced setup, rarely should the panhard bar be adjusted in anyway.(RARELY!). Keep in mind each track has its own unique setup that is required. I have learned that if you must adjust the panhard bar, it should be equally adjusted on the pinion plate and chassis mount. Adjusting only one side WILL change rear roll center location. Rear roll center should be paired with the front roll center so the chassis rotates upon the same axis.

[redracersmod]

So your saying put it at the recommended height and location and never touch it because it will be right? There is a reason its adjustable its to adjust it. What I'm asking is what affect does it have if you move the frame side up and leave pinion alone. Does it tighten the car does it loosen the car? Does it affect middle or entry or both? What happens if you just move pinion side up?

[Anonymous24]

Yes I am saying once configured correctly, for that specific track, yes leave it alone. As I stated above, the panhard bar dictates rear roll center, and you want the front and rear roll centers paired. Its adjustable because each track requires a specific setup. Flat tracks require roll center placement more to the left than a high banked race track. Adjusting the panhard bar in the manner you are describing may help handling issues, but in reality, your setup may(probably) have a flaw in another area. Panhard bar should NOT be adjusted to correct handling issues.

[Anonymous24]

Also recommended heights are all just educated GUESSES. Every car is different. Base set up sheets are for racers who haven't taken the time to learn vehicle dynamics. They are provided by chassis builders so the racer can be relatively fast without proper education and understanding of how every component works. Balanced setups are CRUCIAL. I have yet to come across a base setup that is truly balanced.

[redracersmod]

Ok so then how do you adjust it to find the correct placement?

[propit21]

would you not want to adjust from heat to main where the track drys out and more roll is needed in the car to help gain rr traction?

[let-r-eat]

Why does NASCRAP make panhard bar adjustments throughout the night? They haven't dialed in their front and rear roll centers?I don't agree with Anonymous24. The front and rear roll centers and their placement is an important tuning tool.

[Anonymous24]

No. As I stated above, the panhard configuration is setup specific per track that you are running. If you need more RR for the feature, you also need more RF. Its crucial to keep the setup balanced. I recommend adding ballast to the right side of the chassis for both the RF and RR in optimum locations to achieve more side bite. There are a few other adjustments that could be made, but adjusting the panhard bar isn't one of them. If you would like more detailed information, please PM me, and we can go from there.

[Anonymous24]

QUOTE=let-r-eat;1807003]Why does NASCRAP make panhard bar adjustments throughout the night? They haven't dialed in their front and rear roll centers?I don't agree with Anonymous24. The front and rear roll centers and their placement is an important tuning tool.[/QUOTE]Its OK to disagree with me. I went to college to work NASCAR or NHRA. I have obtained the education those fellow racers have. Mechanical Engineering specializing in Vehicle Dynamics. I was unable to finish college due to having children. Full time work/full time school/racing every weekend 2-3 nights don't mix. I'm sharing knowledge that is accurate and track tested.

[MasterSbilt_Racer]

I love this thread!

[MasterSbilt_Racer]

would you not want to adjust from heat to main where the track drys out and more roll is needed in the car to help gain rr traction?

Why is more roll needed to gain traction? Do you want more rr traction on exit?

[Anonymous24]

Why is more roll needed to gain traction? Do you want more rr traction on exit?Excellent question MasterSbilt_Racer. I look forward to the upcoming responses regarding your question.

[redracersmod]

Actually from what I have read is body roll doesn't permote more traction on the RR tire. Correct me if I'm wrong.

[washeduptoo]

IMO body roll doesn't have to create side bite, but side bite does create body roll. Again, JMO and best of luck.

[Anonymous24]

Actually from what I have read is body roll doesn't permote more traction on the RR tire. Correct me if I'm wrong.No correction needed.

[let-r-eat]

I'm glad you have such high credentials. Could you divulge into the mechanical concepts that justify this? Why would we want to restrict the placement of the rear roll center when we don't have to? The rulebook isn't limiting us?I see no reason to couple the front and rear roll centers in anyway. Providing optimal slip angles for the intended configuration doesn't require us to limit our adjustability.. I'll let Chad Knaus and Chip know they might as well weld up those adjustable mounts. Is their an optimal position for a particular slip coefficient? Sure. Does it change constantly? Sure.I'll take adjustability.

[propit21]

I enjoy these thread great learning, am going to go ahead and take the bait. We found by adding angle in the j bar when the track went dry and slick, it helped with side bite in on entry and middle, considering your panhard bar/j bar doesn't have much effect on exit.

I didn't go to college to become a engineer or do I think I know that much about chassis dynamics so am just going off what the driver have told me and what we have done and seems like it helped. I would love to know other adjustments to make.

What I've have heard or read is that the angle in the bar works as leverage of weight from left to right. You can also move statically your rear roll center up or down or left to right depending on where you mount you bar, angle, or how high or low it is. (Other things also play a part as well) So an easy adjustment for us if we need more "side bite" is just just add angle in the bar whether right or wrong we feel we get good results from that adjustment, it's also easier then moving ballast for us.

[redracersmod]

I moved my panhard up on the frame and left the rear end location the same it seemed to loosen my car.

[Anonymous24]

I'm glad you have such high credentials. Could you divulge into the mechanical concepts that justify this? Why would we want to restrict the placement of the rear roll center when we don't have to? The rulebook isn't limiting us?I see no reason to couple the front and rear roll centers in anyway. Providing optimal slip angles for the intended configuration doesn't require us to limit our adjustability.. I'll let Chad Knaus and Chip know they might as well weld up those adjustable mounts. Is their an optimal position for a particular slip coefficient? Sure. Does it change constantly? Sure.I'll take adjustability.You are taking an orange and comparing it to an apple. Us dirt racers don't run 500 miles in a single run. They don't have time to changes like we do in between runs. NASCAR pit stops are around 15 seconds. Its very hard to make changes to other components in a timely manner. So they are very limited on changes they can make to improve handling. Air pressure adjustments, spring rubbers, and track bar movement is about all the "quick" adjustments they can make. Adding/removing wedge, shock changes, adding ballast, etc. all take too long. Like i stated above, you can't compare an orange to an apple and expect it to be the same. Both fruit, both spherical in shape, both completely different.

[let-r-eat]

I'll just agree to disagree. I'll select adjustability. You won't see any non adjustable mounts on my panhard bar anytime soon unless the rules require. Apparently your racing somewhere I know nothing about.

[dirtplay18]

I run a mod with a rules package similar to an imca sport mod, solid pullbar, panhard bar behind rear end. Contrary to everything I've read, when I raise the bar on the frame (left side mounted) it tightens the car. My rear housing bracket is not adjustable, but I'm going to change that and see if I can gain anything from it. I don't think you can ever have too much adjustability in a race car.

[Dirtrunner35]

What ever adjustment you do at one end of the car the opposite will happen at the other end.

[redracersmod]

Well still no one has answered my question directly. Is this one of those that it affects every car differently there is no right or wrong answer and that's why you see so many answers saying the same adjustment did the opposite?

[MasterSbilt_Racer]

Well still no one has answered my question directly. Is this one of those that it affects every car differently there is no right or wrong answer and that's why you see so many answers saying the same adjustment did the opposite?

There is no one right answer. As there isn't for most things in the chassis tuning world. Raising the j bar on the frame will tighten your car if it isn't too high already.

[el paso mod 19]

Are you saying that if you already to high on frame, that if you raise it more it will make car loose. Just trying to understand. Thanks

[redracersmod]

I have checked several setup adjustment guides and they all say raising it will loosen the car. The same could be said for just raising the frame side as this Will raise the roll center slightly. That is my thinking on it.

[MasterSbilt_Racer]

I have checked several setup adjustment guides and they all say raising it will loosen the car. The same could be said for just raising the frame side as this Will raise the roll center slightly. That is my thinking on it.

Raising on frame only affects average height and angle. Those two things are having opposite effects. That is why it gets tricky.

[drtrkr244]

I think you are reading the adj. guides wrong.

Grt and Shaw both say to raise panhard bar on frame to tighten entry, which from my experience is correct.

[Dirtrunner35]

lowering the rear roll center will put more dynamic wedge in car

[autoshop]

raising the frame only will tighten the car due to the angle has a short sweeping angle thus pulling the rearend to the left and under the car more almost the same as moving the wheel offsets to the left more

[let-r-eat]

roll center height and it's relationship to the center of gravity of the race car. Lower the J bar will lengthen this relationship and raising will shorten. That is why most say to raise the bar to loosen entry and lower to tighten entry. Most believe that the j-bar relationship is for mid corner handling changes, per the afco tuning guide. The roll axis relationship of the placement of the front and rear roll centers is important. If the roll center on the front of the car is lower than the rear then forces acting upon the center of gravity and the roll center up front are greater than out back. There is a whole bunch of stuff that is going on. Whole bunch because you have dynamic forces changing with the application of throttle/brakes. Think about the center of gravity of your race car and the placement of these roll centers. The center of gravity will be around cam height. That's why placing weight above or below the center of gravity matters. As to the J-bar excessive angle. Excessive angle can loosen because when the center of gravity move vertically the resistive forces may not be enough *traction of the tires* creating a loose condition. You can only create leverage with resistance............hence you need traction to get up on the bars.

[Krooser]

Time for a snack…

Hey Anonymous 24… you brought up 'wedge'…. I haven't heard that in years. Makes me want to go get my 5/8" socket and my floor jack so I can adjust the car for the feature (another old term).

[Anonymous24]

[QUOTE=Krooser;1812067]Time for a snack…Hey Anonymous 24… you brought up 'wedge'…. I haven't heard that in years. Makes me want to go get my 5/8" socket and my floor jack so I can adjust the car for the feature (another old term).[/QUOTyes wedge.....that tells ya how long i have been doing this

[oldtrackchamp4x]

That's how i do mine. Set ride heights, jack up in center of rear end and measure how much rr comes off ground before lr, i have that measurement wrote down. Of course i put car on scales every four or five races to be sure. Works for me. JMO

[Anonymous24]

I only add wedge at the track if needed. All tracks have their own setup and that work is done at the shop. Rarely I put wedge in it. I prefer to hang ballast for the feature. That is if any adjustment is needed to be made.

[Krooser]

Now we know who the old farts are….

Last year I spoke to a new 'driver' who was bemoaning the high cost of going racing… his Dad had just bought a tractor and 53' stacker trailer but they hadn't started racing yet because they were waiting to be able to buy $3,000.00 wireless scales...

[HEAVY DUTY]

Now we know who the old farts are….

Last year I spoke to a new 'driver' who was bemoaning the high cost of going racing… his Dad had just bought a tractor and 53' stacker trailer but they hadn't started racing yet because they were waiting to be able to buy $3,000.00 wireless scales...

I am an old fart. I have been known to use a jack and a socket. I agree on the cost of racing, but I have yet to see a stacker trailer win a race. I love these so called racers who have never raced before, that have their T-shirts, window stickers, and wrap on their car before they ever get an engine. Ive raced for 37 years, and I have never had a window sticker. I must be going about it the wrong way.

[7uptruckracer]

Wedge is for asphalt, Bite is for dirt, I consult with a lot of both, Nascar Cup cars are on bumpstops, the lower series are on coilbind setups, when your on packers and stops a lot of times the easiest adjustment is a panhard bar there are to many variables and temp changes, weather conditions or maybe you missed the setup, there are many times I'd love to change something in the race on a dirt car because my LR TO RR balance isn't right, If you wanna put yourself in a box and say never change something go ahead, it will eventually bite you so its best to know how it works right? You need to understand rake and how your arc moving effects how your body moves in relationship to your rear end, Raising both ends of any rear track bar j bar front or rear mounted will raise your roll center and free up the car on a left side frame mounted J bar, Raising your frame side will lower roll center and tighten car, raising pinion side will raise roll center and free up car. If your on and other setup then a Left side frame Jbar post it and we can tell you how it works. But any panhard bar you need to know the rake (mounting bolts to ground) and just pay attention to your overall height. on anything other then a jbar where its mounted on the tube changes week to week so what Anonymous24 tries to sound informed about doesn't hold water I work on the cars it all depends on asphalt what your trying to do with rear steer what your bumpstop package is and what your rules package is just like on dirt you can change your effective bar length to change your reaction speed, or move it closer to one tube and change loadings and rear steer properties. KNOW HOW IT WORKS as fast as your tire loadings and adjust to the driver don't get wrapped up in numbers and put yourself in a box understand how it works the rest doesn't matter as long as it works if you need a general baseline most people in here will help Mastersbilt know his stuff!

[Matt49]

I’m going to provide “my” answer and then get back out of the way.

There are things that need to be understood about rear roll center that are not very well known which is one reason there is a lot of conflicting information on this topic. There is a VERY common (and often published) misconception that the roll-center on a car with a j-bar is a point right between the mounting locations on each end. It simply isn’t true. This comes from an extension of OLD logic from panhard bar cars with VERY long bars and cars with springs matched on either side. A lot of stuff found in college level vehicle dynamics text books where the real world is the last thing considered. It’s “road car” vehicle dynamics and it doesn’t completely apply to late model or modified j-bar setups. This is reason number one why there isn’t a straight answer to the OP’s question.
The actual roll center location on a j-bar car is dictated (somewhat) by the j-bar mounting locations BUT it is also dictated by the upper spring mounting locations and the effective spring rates. That’s as much as I’m going to say about that because I could write for hours trying to explain it completely.

Reason number two that there isn’t a straight answer is that modern dirt cars on j-bars get a TON of motion which means that the roll center migrates quite a bit as the j-bar mounting positions move relative to the ground. And yes, BOTH mounting points move relative to the ground. Couple this with the face that both upper shock mounts move and the spring angles change which changes the effective rate and you’ve got a math problem that I have not the time or patience to go through right now. This is why we have computers.

Reason number three also has to do with the motion but more so because the vertical center of gravity is moving up at the same time the axle is moving left.

Bottom line is there is a lot going here and there are no “straight” answers but there are some “in general” answers that work for most people and those have already been provided.

[7uptruckracer]

Well said the bad thing is there are published diagrams that give people these ideas, and they don't hold water the best thing to do is to know how it works and adjust accordingly, take good notes, so you know how it effected the car and make your own adjustment guide. I have one on a asphalt mod that runs from the left side of the pinion diagonal to the RR trailing arm mount.....try explaining how that works to someone.....unless you know your spring tables your rear roll rates, you can have springs mounted toward the center or way out by the calipers all of it effects how it works and rolls

[dukeofpaducha]

Well said the bad thing is there are published diagrams that give people these ideas, and they don't hold water the best thing to do is to know how it works and adjust accordingly, take good notes, so you know how it effected the car and make your own adjustment guide. I have one on a asphalt mod that runs from the left side of the pinion diagonal to the RR trailing arm mount.....try explaining how that works to someone.....unless you know your spring tables your rear roll rates, you can have springs mounted toward the center or way out by the calipers all of it effects how it works and rolls

Why did a left side frame mounted panhard rod become the convention in dirt cars? Would a panhard rod mounted to the frame on the right lower the roll center as the car rolled over on the right rear?

[MasterSbilt_Racer]

Why did a left side frame mounted panhard rod become the convention in dirt cars? Would a panhard rod mounted to the frame on the right lower the roll center as the car rolled over on the right rear?

It may. But what does the front roll center do? Especially with the dynamic camber some are running today. I have had luck with a panhard like you describe, but I don't think it is a magic bullet.

[dukeofpaducha]

Thanks for the reply MasterSbilt_Racer. All else being equal would the right side frame mount panhard bar shift the dynamic roll couple resistance toward the front allowing the rear to roll over easier ?

[MasterSbilt_Racer]

Thanks for the reply MasterSbilt_Racer. All else being equal would the right side frame mount panhard bar shift the dynamic roll couple resistance toward the front allowing the rear to roll over easier ?

That has been my experience.

[Dirtrunner35]

Ever look at a data acquisition on a car, great stuff.