em5m
Pit Crew
Posts: 19
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Post by em5m on May 16, 2014 21:15:26 GMT -6
Where should the j bar be mounted at pinion? And what effects does it have being above pinion or below, ect..? Hughes 4/4 with lr spring behind shock in front ect..
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Post by flipflopoo1oo on May 16, 2014 22:27:37 GMT -6
Finding a happy spot at the pinion is related to roll center! Different set-ups and adjustments of the same car can change roll center locations and free movement there of to binding! Most are found by starting one hole off the bottom and keeping angle when moved on both ends up or down at a 5-7 inch rake! We never got to use the third hole on any chassis as it was binding there and would not coast and roll in easily! A free roll when steering back and forth is the free pivot point of the roll center! A walking gear slider at the pinion makes it easier to find but more likely to break! Some brackets may be reversible as to have a better hole location in-between! It should just hold the rear end under the car and lift a bit as too much angle will not let it roll unless in the throttle! Pull bar spring movement can send it hiking or change from free to binding as to pinion location changing to the roll center! Hot laps per setup changes is the best way to get it dialed in! I do hope others have a more precise answer for you that run a Hughes!
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em5m
Pit Crew
Posts: 19
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Post by em5m on May 17, 2014 6:59:29 GMT -6
Finding a happy spot at the pinion is related to roll center! Different set-ups and adjustments of the same car can change roll center locations and free movement there of to binding! Most are found by starting one hole off the bottom and keeping angle when moved on both ends up or down at a 5-7 inch rake! We never got to use the third hole on any chassis as it was binding there and would not coast and roll in easily! A free roll when steering back and forth is the free pivot point of the roll center! A walking gear slider at the pinion makes it easier to find but more likely to break! Some brackets may be reversible as to have a better hole location in-between! It should just hold the rear end under the car and lift a bit as too much angle will not let it roll unless in the throttle! Pull bar spring movement can send it hiking or change from free to binding as to pinion location changing to the roll center! Hot laps per setup changes is the best way to get it dialed in! I do hope others have a more precise answer for you that run a Hughes! it has a sliding adjustment up and down and right now is almost maxed out "up" and is about 2" ?? Higher than the pinion! The car seemed to not want to turn in and through the middle on or coasting in! ?? Let me know, i thought i have heard people say level with pinion or lower? ?
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Post by flipflopoo1oo on May 17, 2014 9:03:42 GMT -6
Yes indeed, at the lower edge of the pinion for us but using my set-up! Short bars may work better on some set-ups depending on the roll center movement changing if using a hiking set-up! Wrong makes it tight along with the fact that any too much angle when lifting movement or not is holding the left side down until throttle torque raises the front of the pinion to lift or get to a free spot in some cases! This factor can make you tight (not rolling to steer) or too loose by hiking quickly with more steer than you need! With the shock timing and link angles in-mind as to how fast it hikes also! A minimal angle works to allow the rest to work at a smoother transition when rolling going in and less sudden change when looking good in the turn as not to upset the process of roll steer! Not using the j-bar as a traction device or left bar angles to over steer when lifting gives less bite if hiking to run the left forward for more weight on the left rear to hook! I prefer higher right side bars and even traction with shocks and springs to transfer weight to the left rear under throttle! A pan hard long bar is more drivable when correctly placed! Getting a set-up that holds cross and left rear with out a ton of steer and less roll center to deal with is a easer car to adjust and race! Its old school, 4 wheel but passes a three wheel high or low for us! Nothing new about 4 links hiking but the cost of a chassis these days! How much rake on the angle? This is the holding factor other than sweet spot at the pinion! Spring poundage, shocks and location of them along with lengths of bars and angles may give me or someone running about the same set-up that works for them a clue to roll center (with ride heights in mind) to give better answers! Scale numbers if you have them! Cross can move roll centers quickly right to left and twisted! Too much cross is the roll center leaving moment center with no where to go, thus needs hiking to add rear percent and bar angles of steer higher on the left to get that to work! The poor jay bar is caught in the middle with no where to go but up higher than designed to work properly! Shorter left bars adds fuel to the fire but the lift burns out quicker with limited hiking! Just tie it down like the bull-dog it is and I will take my old hounds and go hunting for first place! How much movement do you get on the left rear? If hiking too easy a softer spring or stiffer shock but if tight and hiking a lot, indexing may be at fault if roll is happening! If no roll, j-bar angle too much or location at pinion, shocks holding too much left side weight or too much or too little cross to match with left! Left front too soft not helping roll or not compressed as to help roll, Too stiff right front lot nosing and moving load to lt. ft. and through the cross to rock the car over! Too much front split if stronger on the right! Too even rear springs or moving lower perches in the wrong direction by indexing and bar lengths and angles! A j-bar car usually uses a 50-75 pound left front gain and weaker on left rear to control hiking and toping out with j-bar and bar angles making up for the spring! Using nosing hard and hiking to steer more than roll! More negative caster helps twist the chassis to roll if steering left to get in and right to tighten and transfer weight to the left rear! This should not all be blamed on the j-bar location but it is a key if on a car, to start and finish a change of set up any kind! I recommend moving it down and leveling out the top if a five to 7 inch rake and adjust elsewhere if problems persist!
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Post by flipflopoo1oo on May 17, 2014 9:19:36 GMT -6
I don't like or use them although have won lots with them when limiting differential movement with indexing, steer, solid pull bars and limiting all bar angles just to have a free moving car! A biscuit-ed j-bar allows a little more freedom from bind! This saves changing with small adjustments with every time you adjust something else in the mix!
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