rear panhard bar tech

[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]

Question

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 ?