J-Bar Theory

[fastford]

While there is no way to say for sure, I'd be willing to bet yes by a large margin. I've done tons of private tests for the last 12-13 years with several racers and at times that can get upwards of 20 times a year. This isn't including open practices nights at a track as I don't generally accept them as gathering good data.

Not a 100% if Austin meant total hours testing or all the different types of stuff I've tested over the years.

and i would be willing to take that bet if , like you said , if there was a way to say for sure , ive been involved with building and racing dirt cars going on 25 years and drag cars 15 years before that , i have a heap of hrs testing my self , but one thing i will say , you never stop testing and learning , or you will go backwards , I have defiantly gained knowledge from your post and i do appreciate it..........

[Austin34471]

I would stay away from the tethers because you would obviously have to attach them to the rearend in a few places... which would, you know, increase the unsprung weight.....

Heh.. heheh.... heh......

[Matt49]

I would stay away from the tethers because you would obviously have to attach them to the rearend in a few places... which would, you know, increase the unsprung weight.....

Heh.. heheh.... heh......

Now you've really got me thinking! Maybe my left side tether needs to weigh WAY more than my right side tether. Ha ha

[Jking24]

I have seen what billet it's describing at lakeside quite a few times and in my opinion it is a very experience related change. Example if the driver had not lifted when he initialy turns the car in but then burps the throttle to let the car rotate. The weight transfer has already happened so the effect of going up on jbar (on frame) tightening entry ie. Decel has already happened. The right sides are loaded their for minimal effect from added loading. More jbar would keep the car up during the off throttle and late straight away periods then when the driver did get back to the fuel which was probably still pre apex the added angle adds rr traction and general car attitude witch rotate the car more across the center. I don't know if that came out right but their is alot of what where and how that goes into what effect the j bar will or won't have

[95shaw]

These points have my curious about one other change. When would someone move the j-bar right or left without changing angles or lengths?

Generally speaking, moving the j-bar right or left, moves the point of weight application on the axle.
Meaning weight that is applied by the j bar is moved closer to one tire.

Of course, moving the both ends to keep bar length the same, moves the frame end in relation to the center of gravity, changing which spring the weight is coming from. Dynamically, could net a zero change in wheel weights.

[let-r-eat]

Years back when I started smashing tires together with springs I learned some things about the J Bar that I never realized before. The placement of that JBar is more critical than I ever expected. Leaving the J Bar in a box stock configuration could be a big compromise.

[Kromulous]

Reviving this thread, i wanted to ask more questions. Ran this past Saturday night, when the track has some water in it the car is pretty good overall decent, but not great. Florence Speedway BTW.

Now when it gets slick, we struggle.

What i see is, the car has a lot of rear lift, LR and the RR it seems, the RR it is not compressing at all, and probably against the chain on the RR, and the LR for that matter. I run a chain on both sides. Now that i think about it, its probably maxed out on both, against the chain.

Does the amount of bar angle, on the LR, and the RR, play into how much angle is in the J bar? I mean if you have a lot of angle on the LR bars, and angle in the J-bar it should make it easier to lift the LR, correct?

I am thinking i need to lower the J bar on both sides, maybe 1/2" pinion, and 1" on the frame. and try to get it to roll on the RR better on entry, the car is lose on entry, but he says its not horrible. Its just terrible off, no grip.

RF is pinned, 2300 lbs at 4" about 160 lbs extended load on the LR. Droop travel on the LR is about 5.5" Stagger was 1.5" RR spring is a 250 lb.

I will see if i can find a video to help, this car has me cornfused, it doesn't behave properly LOL. We're almost ready to dig out a Reveloution we have in the back of the shop in the weeds!

[rjs21]

I appreciate the conversation that you guys have had on J-bars. I have a question and the modified section doesn't seem to have much discussion.

Do any of these theories relate to an IMCA Sportmod with a straight panhard bar behind the axle housing?

[Lizardracing]

Yes it does with some small differences.
Mounted behind. The panhard bar is longer so the side to side change is less, the axle mount moves up and down less, so it's less of a reaction than pinion mounted but the roll center theory still applies if you into that sorta thing.

[rjs21]

My car has a slider on the frame side so it is adjustable in small increments. The housing side has 4 holes on it 1" apart, not a small increment adjustment.

My question is; what is more important if I was to adjust the frame side? The height, which would affect roll center? Or the angle?

Suppose I wanted to snug up entry with a 1/2" panhard adjustment. Would I raise it on the frame to get more angle but a higher roll center? Or lower it with less angle but a lower roll center?

Which aspect of the adjustment is more critical?

I was wanting to avoid the housing side adjustment because it seems to be a big change.

[Lizardracing]

Generally speaking the height will be felt more by the driver on a long PH bar.

[billetbirdcage]

My car has a slider on the frame side so it is adjustable in small increments. The housing side has 4 holes on it 1" apart, not a small increment adjustment.

My question is; what is more important if I was to adjust the frame side? The height, which would affect roll center? Or the angle?

Suppose I wanted to snug up entry with a 1/2" panhard adjustment. Would I raise it on the frame to get more angle but a higher roll center? Or lower it with less angle but a lower roll center?

Which aspect of the adjustment is more critical?

I was wanting to avoid the housing side adjustment because it seems to be a big change.

Just to be clear, how is the panhard mounted? Left side frame and right side axle/rear end or left side axle/rear end and right side frame? That will make a huge difference on adjustments!

[rjs21]

Panhard mounted on left frame rail to axle housing about 4" right of the pinion.

[hipower17]

wasn't it moyer that tried the jbar on the right side won a lot of races then quit using it? why is this setup used more often looks like this would work on certain tracks?

[MasterSbilt_Racer]

wasn't it moyer that tried the jbar on the right side won a lot of races then quit using it? why is this setup used more often looks like this would work on certain tracks?

I have first hand experience making a Rayburn bad fast with the panhard on the right. The front and rear need to roll/work together. It can certainly be made to work.