J-Bar Theory

[Jim11h]

Billet, have you thought that maybe you was already at max adjustment for desired effect and went more which can (usually does) give opposite effect? Seems to me where you was at and effectively learned how to use as tuning device where other folks it throws them and they start chasing their tail

[fastford]

i had a driver that used the rear brakes to get in the turn , raised the j bar 2 inches on frame , he could still get in pretty good , but he could drive off the corner on the right rear liker a bullet , this fit his driving style better than a driver that likes to keep the car straighter in and through the turn , point is , sometimes you have to go against the norm to find a balance between driver , car and track.....i also use to think there was nothing better than a short strait bar , that was before all this soft rt frt stuff ,

[billetbirdcage]

more than any one on this thread combined ? thats saying a lot billet , what say you?????

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.

[Matt49]

A little off topic but along the same thread of thinking about j-bar...
Has anybody thought about or experimented with some type of tether system for the rear end as a safety net in the event the j-bar (or something holding it on) breaks. Not sure if any of you have ever broken a j-bar but suffice to say that the j-bar isn't the only thing you'll be replacing if you ever do. The shocks and birdcages are usually going to end up destroyed. It seems like some sort of tether system could be easily developed to "save" some of this additional damage and potentially increase safety. I was sitting still the time mine broke (got hit square in the LR while at a complete stop sideways) but breaking one at speed in the corner could get ugly.
I think it's something to consider. I've thought of putting tabs on the rear frame rails some sort of mounting mechanism above the center of the rear end and then just using some old harness belts. The belts being adjustable would make it sort of a universal design. Thoughts?

[billetbirdcage]

Billet, have you thought that maybe you was already at max adjustment for desired effect and went more which can (usually does) give opposite effect? Seems to me where you was at and effectively learned how to use as tuning device where other folks it throws them and they start chasing their tail

Sure it can happen, but in these instances typically doing that adjustment would not loosen them up. It's on of those deals where it's situational and a lot of it is based on experience with it and knowing the drivers/cars well from being with them for a long time. Now if every time I got over that certain point it did that, then I would agree but that wasn't the case here.

The experience I'm talking about isn't all that different then knowing/guessing from experience when to do 4 soft tires, 3 soft and 1 hard, or left soft and right hard. While not exactly the same, sometimes you just know or base what is gonna work the best off experience. Like knowing that the soft tires tonight isn't gonna work as well as it typically does and they are gonna give up.

[billetbirdcage]

A little off topic but along the same thread of thinking about j-bar...
Has anybody thought about or experimented with some type of tether system for the rear end as a safety net in the event the j-bar (or something holding it on) breaks. Not sure if any of you have ever broken a j-bar but suffice to say that the j-bar isn't the only thing you'll be replacing if you ever do. The shocks and birdcages are usually going to end up destroyed. It seems like some sort of tether system could be easily developed to "save" some of this additional damage and potentially increase safety. I was sitting still the time mine broke (got hit square in the LR while at a complete stop sideways) but breaking one at speed in the corner could get ugly.
I think it's something to consider. I've thought of putting tabs on the rear frame rails some sort of mounting mechanism above the center of the rear end and then just using some old harness belts. The belts being adjustable would make it sort of a universal design. Thoughts?

The drive shaft as it gets into the tunnel/(not a nice word)(not a nice word)(not a nice word)(not a nice word)pit or when the RR tire hits the 4 link bracket or frame, is our safety stops, lol

Not saying it isn't a good idea but what about back ups for other things? I've torn up way more when the torque arm or 6th coil chain breaks, so where do you stop on back up's?

[Matt49]

The drive shaft as it gets into the tunnel/(not a nice word)(not a nice word)(not a nice word)(not a nice word)pit or when the RR tire hits the 4 link bracket or frame, is our safety stops, lol

Not saying it isn't a good idea but what about back ups for other things? I've torn up way more when the torque arm or 6th coil chain breaks, so where do you stop on back up's?

Billet, I realize you're kind of playing devil's advocate (maybe not) but if NOT destroying the drive shaft is the outcome of a tether system, it kind of supports my point. I just look at single points of failure and try to think of ways I can limit the damage if/when those failures occur. Obviously routine maintenance is our best friend but things do fail outside of what a small team can reasonably quality control. With a failure like I'm describing, you're obviously out of the race, but if you can salvage some form of financial losses and/or increase safety, it has to be worth evaluating, right?

Love this discussion by the way. 4m tech section has been lacking these in the past few months.

[95shaw]

Billet, I realize you're kind of playing devil's advocate (maybe not) but if NOT destroying the drive shaft is the outcome of a tether system, it kind of supports my point. I just look at single points of failure and try to think of ways I can limit the damage if/when those failures occur. Obviously routine maintenance is our best friend but things do fail outside of what a small team can reasonably quality control. With a failure like I'm describing, you're obviously out of the race, but if you can salvage some form of financial losses and/or increase safety, it has to be worth evaluating, right?

Love this discussion by the way. 4m tech section has been lacking these in the past few months.

Are we thinking of creating another tether which can be morphed by someone into a tuning device?
My other concern would be that we are simply moving the stress points when the failure occurs.


Thoughts?

[billetbirdcage]

Are we thinking of creating another tether which can be morphed by someone into a tuning device?
My other concern would be that we are simply moving the stress points when the failure occurs.


Thoughts?

You mean like the bungee cord type chains/limiters guys are using now? Joking. . .

















or am I. Shrugs

[billetbirdcage]

Billet, I realize you're kind of playing devil's advocate (maybe not)

Yes, I’m playing devils advocate. My point was if you had a back up/safety for every item on the car, it might weigh 100# over weight or have so much stuff in the way it’s hard to work on or something else to get tangled and cause issues while racing. If you can do it without causing additional problems or things I listed for such a rare occurrence, absolutely nothing wrong with doing it.

[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.