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Author Topic:   straight bar vs. j bar
dirtracr
Dirt Full Roller

Total posts: 34
posted July 16, 2001 08:44 PM
any thoughts on this..the j bar seems easy to figure out but since switching to the straight bar, ive yet to have real success with it..ive heard five inches of rake to zero inches...i used to almost bottom out the rr shock with the j bar but with the straight, it feels like its rolling over fine but ive lost about two inches of travel on my rr shock..also if you get alot of rake in the straight bar, can you lose the shock travel on the rr and still be overextending the shock on the lr, picking up the lr...

rjs
Dirt Full Roller

Total posts: 38
posted July 16, 2001 10:05 PM
One reason you may lose shock travel is that with a J-bar the chassis roll is being transfered on a shorter arch so the same amount of lift moves the rearend over to one side more with the straight bar which I assume is longer. I hate to assume things because when you do it makes an *** out of u and me. Other factors include center of gravity- roll centers- and dynamic movement. With rebound or up travel LR what is the rearend doing in relation to the car's center line? Are you pushing the rr into the track or is the opposite true- think of the side bite. With out knowing other factors such as spring rates, rear roll center,and ballast placement it is impossible to make an accurate picture of what is really happening. By changing this one thing it affects several others in how they interact as a suspension unit.

wfoondirt
Dirt Maniac

Total posts: 142
posted July 17, 2001 01:58 PM
are you talking about a long straight bar or a short one mounted to the pinion?

dirtracr
Dirt Full Roller

Total posts: 34
posted July 17, 2001 05:09 PM
my bad, its the little short one mounted to the left side of the pinion...200lr, 150rr..its an eight inch sleeve with a heim on each end..this ends up being the size it is to keep my driveshaft straight..

wfoondirt
Dirt Maniac

Total posts: 142
posted July 18, 2001 02:00 PM
I'm not a big advocate of the short panhard bar. I ran one about 4 years ago and was never real happy with the effects, granted in some cases it helps with off the corner but other wise i think it hurts the handling, but thats personal opinion.

Here are the typical effects of switching to the short bar. For one it moves the roll center more to the left and usually higher because of packaging constraints. also depending upon the angle it moves the rearend more laterally through ride/roll than a j-bar or long bar.

What happens with the short bar is that as the car rolls it will jack wedge into the car which will typically loosen entry and tighten exit. This is probably the reason for the changes in shock travel.
Another consideration in loosing rr shock travel is suspension bind, the short bar moves the rearend ALOT more that a long bar so be sure nothing is binding as the chassis moves.

dirtracr
Dirt Full Roller

Total posts: 34
posted July 18, 2001 08:48 PM
thanks for your input...a couple of my main competitors who are also in dirt works chassis are running this..one has a swing arm and the other has the four bar like mine, except his is a dw8, mines a 7...we tape all of our races and its really raising the chassis on the left rear and its crawling up under but it not hooking up on this slick track...what angle would you recommend..ive had five inches in it and about two and a half, not real happy with it...the one competitor ive mentioned with the four bar has it figured out cause hes kickin **** with it..my car seems to have a four wheel drift to it from the center off, right when i start picking up the throttle, it has like a four wheel drift, never had that before..ive had to burp the gas to keep from getting the wall...ive run softer rf than lf and vice versa on the springs..went back to the stiffer rf when it would not come off the corner..ive also got the rr spring in front of the axle and lr behind...im going to give it another week or so, weve been experimenting alot lately, so if it doesnt come around ill go back to the j bar and the set up from last year.....ive done all the normal adjustments for the slick track thats why im a bit lost..the car seems to have good sidebite, it sticks where i put it gettin in and turns good, its just at that point when i pick up the throttle that im having the problem with the drifting..

[This message has been edited by dirtracr (edited July 18, 2001).]

rjs
Dirt Full Roller

Total posts: 38
posted July 18, 2001 11:12 PM
How long are your trailing arms? The new Dirt Works have blocks for 7inch trailing arms this hooks up faster and hav much more roll. Look closely at your competition I bet they have other differences like the lr underslung is curved or has a dip to provide more roll without the rearend banging the frame rail. The only time I would run the short bar is on a smooth super dry track.

dirtracr
Dirt Full Roller

Total posts: 34
posted July 19, 2001 05:00 PM
the uppers are 17 3/8 on left and 1/8 on right...lowers are two inches shorter...this is a smooth super slick track and yes they do have the dip in their underslung..the rear end hitting the underslung was something i was going to check, thats possible..never did before with the j bar and i had more shock travel with the j bar..would like to get something figured out, the short bar seems to be the fast way on this track right now...this car doesnt have the mount for the seven inch rod..so short of putting on a new mount could i shorten the bottom rod on the lr...if so how much do you think and do i do it on the lr only..thanks for your input...

[This message has been edited by dirtracr (edited July 19, 2001).]

jlfastride
Dirt Full Roller

Total posts: 27
posted July 21, 2001 05:27 PM
like the guy said earlier the shorty jacks wedge in the car , no longer is the car simply rolling over in the turns it is actually raising the lr thus reducing the downward travel on rr. jl

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