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jr18
08-06-2007, 05:06 AM
If you raise the jbar up on the pinion what efect does it have? and if i raise it on the pinion do you have to raise it on the frame at the sametime?

billetbirdcage
08-06-2007, 04:07 PM
Raising it on the frame or lowering it on the pinion increases the rake in the j-bar and will tighten the car up to a point, sometimes going over a certain point of rake can loosen the car thru the center by keeping it up and steering.

Generally lowering it on the pinion is a bigger adjustment then moving the same amount up on the frame.

Moving both up or down is like raising or lowering the Rear COG of the car, basically you are moving the rollcenter in relation to the COG. So moving the whole bar up evenly is like lowering the COG.

jr18
08-07-2007, 05:10 AM
Moving both up or down is like raising or lowering the Rear COG of the car, basically you are moving the rollcenter in relation to the COG. So moving the whole bar up evenly is like lowering the COG.





when would you us this adjustment?
when would you raise of lower the whole bar evenly and what type of track would you do this on?

MasterSbilt_Racer
08-07-2007, 10:42 AM
You would raise the bar on a fast track. Probably high banks. Too low when you have too much corner speed makes the car hike up too much and roll over too much.

jr18
08-07-2007, 11:59 AM
So you would raise the the Jbar (pinion and frame) when you run a fast high bank and lower it (pinion and frame) on a dry slick flat track if I have it right. That was what i was thinking (But keep the same amount of rake).

billetbirdcage
08-07-2007, 12:44 PM
For me I almost never move the whole bar up or down. The most common adjustment is to add rake or reduce rake.


MasterSbilt_Racer is correct if your going to move the whole bar up or down. However I disagree with a high banked track, should be fast or slow.

MasterSbilt_Racer
08-07-2007, 01:34 PM
Yeah, that was poorly worded. I was equating high bank to fast, but that is not always true. I also agree about moving on the pinion. A move of 1" will kill your car. If you can move .5", I have found that to be useful at times. I usually just adjust on the frame as Billet does.

billetbirdcage
08-07-2007, 01:59 PM
I figured you just misworded.

Explaination for others not following:

When you get to a certain amount of banking (picture 90 degrees of banking) the centrifical force is pushing straight down on the car into the surface so it isn't rolling to the right but pushing down on the left and right sides. So more banking can actually hinder the left side rolling up and you may need more j-bar to lift the left side up going in and to the middle of the corner.

Mason5
08-07-2007, 06:10 PM
So you guys are saying if you take angle out this will loosen the car on entry move down on chassis . Move up on chassis add angle to tighten. I do know on my pinion mount hole to hole is 1 1/4. The way i take it when you raise on chassis you lower roll center when you lower on chassis you raise. How much drop of rake or added rake where you could see a differce. thanks

jr18
08-07-2007, 06:37 PM
you guys have lost me

billetbirdcage
08-07-2007, 06:41 PM
Yes,

More rake tighter
Less rake looser
same rake but both ends higher looser
same rake but both ends lower tighter

But as I said once you go past a certain amount of rake it can start going the other way especially in the middle.

How much of an adjustment (say a 1/2" is) is dependant on the amount of rake you have and the length of the j-bar.

assuming a 1/2" adjustment:

Longer the bar is the less noticable the adjustment is
Shorter the bar the more noticable it is.
The more initial rake you have the bigger an additional 1/2" will act
The less inital rake you have the smaller the additional 1/2' will act.

Generally a 1/2" on the frame is fairly noticable and on the pinion a 1/4" is noticable.

billetbirdcage
08-07-2007, 06:48 PM
you guys have lost me

Moving the bar (both ends) up or down isn't a real common adjustment.

Most generally you add or reduce rake to tighten or lossen the car (raise or lower one end). Rake: The difference in height of the frame side verses the pinion side.

Tighten: increase rake

Raise on frame
Lower on pinion

Loose : reduce rake

Lower on frame
Raise on pinion

Generally if you move a 1/2" on either side moving the pinion is more dramatic of an adjustment. This just means you see a bigger effect if you move the pinion side a 1/2" verses moving the frame side the same amount.

billetbirdcage
08-07-2007, 06:51 PM
So you guys are saying if you take angle out this will loosen the car on entry move down on chassis . Move up on chassis add angle to tighten. I do know on my pinion mount hole to hole is 1 1/4. The way i take it when you raise on chassis you lower roll center when you lower on chassis you raise. How much drop of rake or added rake where you could see a differce. thanks

Forgot to add, I'm talking about a j-bar mounted to the right side of pinion NOT a straight bar mounted to the left side of pinion -- slightly different effects on entry.

Mason5
08-07-2007, 08:47 PM
Ok that what i run is a straight about 14.5 in long on the left side of the pinion.

jr18
08-08-2007, 04:22 AM
I got it now.

Thanks
JR18

Pitcrew
08-14-2007, 07:40 PM
So when adjusting the rake on the frame, is it necessary to still center the rearend after adjusting the rake or does the adjustment have to be really significant. Do you adjust the hiem on the bar to center the rearend? I've heard some leave the rearend alone and some center the rearend. We have a Rocket.

billetbirdcage
08-14-2007, 08:26 PM
Yes, keep the rear end centered by adjusting the length of the j-bar or using a frame mount that keep it correct.

However sometimes raising the j-bar on the frame (which will move it left if you don'thave an adjustable or raduised frame mount) isn't totally a bad thing as it will help tighten the car by moving it left. But, you have to adjust for the loss of LR bite from moving it left.

It is best to keep the rearend center though.

Pitcrew
08-14-2007, 08:40 PM
Thanks Billet, we do have a raduised mount for it to.