J-Bar Help

[Kevin20ump]

What are some negative effects of having too much J-Bar angle?

[talclipse]

What are some negative effects of having too much J-Bar angle?

The car will pogo, lose forward drive and become very radical.

[rubbinsracin]

we found that when we have put to much angle on the jbar it will make the car much harder to drive off the corner. i like alot of angle in the bar but when we find the max we can put in it before it starts to get erratic, then we go down one hole on the frame side.

[hall99]

We went for years running to much angle, we are now running 1 or 2 clicks below the center of the pinion on really dry tracks and our car has never worked better. Matter of fact we haven't moved the J-Bar in almost 3 months. Running 2011 Gen X.

[MasterSbilt_Racer]

No forward drive. Back of the car just looks "stiff" and doesn't work.

[JB1K]

How much angle / rake is too much?

[merc123]

Doesn't drive right...

[rubbinsracin]

JB1K - Everyone likes a different amount of angle. i personally like about 7.5-8.5" or so in mine. we run ours just below the pinion on that side and in the next to top hole or top hole in our setup on the frame side slider. there has been a couple of times where we have went to the 3rd hole down on the frame side. but not very often. usually when we were chasing forward drive.

[JB1K]

JB1K - Everyone likes a different amount of angle. i personally like about 7.5-8.5" or so in mine. we run ours just below the pinion on that side and in the next to top hole or top hole in our setup on the frame side slider. there has been a couple of times where we have went to the 3rd hole down on the frame side. but not very often. usually when we were chasing forward drive.

Is that 7.5"-8.5" of rake? or 7.5"-8.5" from the bottom of the chassis (chassis mount). The setup sheets always spec x distance up on the frame and x "clicks" (whatever that means) from the pinion. For reference it would be nice to know how much rake that amounts to.

I have been moving mine around all year, and it seems like there is really a sweet spot where it works decent. I still can’t get my head around what changing the rake / angle VS. raising / lowering it at both ends accomplishes.

For instance, raising it at the frame (only) lowers the rear roll center -right? How is this different than lowering it at both ends? Seems like you could arrive at the same vertical roll center, but L to R it would be different?

[rubbinsracin]

we measure our rake from the ground up. our frame mount is 7.5 to 8.5" higher on the frame side than the pinion side. we have never measured from the frame up to get that measurement sorry.

roll center is changed anytime you move the jbar up or down. if you move it up on either side you raise it. if you move it down on either side you lower it. i would suggest you contact your chassis builder about where a good starting point is for your chassis/track/driving style.

[JB1K]

I can understand and agree that moving it up at the pinion raises the RC. But if you just move it up at the frame, increasing the angle, does this not move the RC downhill?

[MasterSbilt_Racer]

I can understand and agree that moving it up at the pinion raises the RC. But if you just move it up at the frame, increasing the angle, does this not move the RC downhill?

There are different theories on this and I don't think any of them are very useful. You can't really pick a "roll center" with a solid axle/panhard type suspension.

I can tell you from practice that with too much angle your car rolls less. That doesn't support the theory that more angle means a lower RC.

The thing to realize is that a certain load is going through your lateral locating device. The angle is going to effect that loading. More vertical, more vertical load on tires. Whatever tire the bar is closer to gets more of the load as well.

[Jim11h]

not to mention, a tire has only "so much" grip and basically with too much angle you go past the point of "grip" that tire has and thus creating the problem of "blowing the tires off" coming out of corner. take masterbilt_racer last statement and then this and it should all make more sense