Rear aarm rake

[Carlriddle]

So the tire goes fromt +9*(tilt out) at droop to -9*(tilt in) at bump?  Thats a lot of change.  0* at ride hight going to a - at bump.  Some desert and short coarse cars run higher - #'s but cant think of any reaso to have + camber.

[fabr]

Ok Im here to learn.Why is that much a bad thing -9*+9*?
Im in east texas,no sand,but were I live I have miles of dirt roads with lots of hard curves and pipelines.I want it to handle good in turns.I had about the some change before with 15'' of travel and put a big wing on back and it turned like it was on a rail.
I know it will have body roll because it did before so why would I want to drag a tire around a turn at speed?
If im missing something let me know.

Body roll should never be considered in relation to camber change. On a side note a rear a arm car will inherently exhibit less body roll than a trailing arm. If that +/- camber car handled like it was on a rail a well designed camber curve would have made it amazing. Remember that most of the steering and suspension travel occur when going mostly straight. IMO,and nearly all the rest of the world,you do not want + camber in the equation.

[mr.bob]

I see + camber being a little high and I played with the R.A calc. for a few hours and could not get good - without getting + camber.I see how 9*+ is not the best thing to have when it unloads so if I set r.h. at -1 or so that would help some.
What I may do is see were it only gets 3-4* + camber and strap it,I dont need 23 1/2'' of travel.

[mr.bob]

Also the upright has to be leaned in the way it is to clear the break,as of now it is almost rubbing I may need to give it a touch with the grinder to be good.
this is the R.A calc,go x2.5
http://www.racingaspirations.com/suspensiongeometry.php?tcx=50&tcy=164&thx=294&thy=164&bcx=50&bcy=230&bhx=320&bhy=263&scl=1

[fabr]

I see + camber being a little high and I played with the R.A calc. for a few hours and could not get good - without getting + camber.I see how 9*+ is not the best thing to have when it unloads so if I set r.h. at -1 or so that would help some.
What I may do is see were it only gets 3-4* + camber and strap it,I dont need 23 1/2'' of travel.

The -1 at ride height is good but you need to be sure that you never have + throughout the entire travel range. See what you have with a reasonable travel of 18-20". If the target camber curve cannot be met then ,no choice about it, you will need to redesign mount points and maybe the arms themselves .

[dsrace]

think of it this way, there is a reason vw got rid of the swing axle design!  it pivoted at the trans only so there was extreme camber change in the rear but they only used the middle 4" of wheel stroke so that minimized it for street use or there design designation. when people try and add wheel travel to the swing axle design, it looks like a bird flapping it's wings and at + camber the wheel is not square with the earth for a complete contact patch and the rear now slides or swaps out uncontrollably, but most who still utilize this design don't know any better and must think it is just how it is. the use of the swing axle was for simplicity for most i have to imagine but if you have ever tore down one of those transaxles I don't know how anyone could have thought that! lol lol

in your case for dirt runs I understand you are trying to take into consideration body roll for your reasons of -9 to +9 camber arc being acceptable but have you measured the amount of body roll to confirm that you truly need -9 * of camber? this would be extreme body roll imo.  at no point do you want +* of camber at all! this is a bad thing and will amplify bump steer and grossly create problems.

I understand peoples thinking of the tie rod being parallel to the a-arms so it tracks accordingly but that is not correct in all cases. you have to find the sweet spot where the tie rod tracks the a-arm in it's curve/arc. if you cannot find this spot you will have to change the design. simply using the center or small amount of travel say the middle 10" out of 20" capable wheel stroke, to tame the problem down,  still requires re-design to make it right, other wise you are just putting a band aid on it or using duct tape to fix something like red green. lol lol

I personally pre-set -.5* of camber at full droop for a total of -3 * at full bump. I square the toe with 10* of caster , 10* of kpi (sai ) and with 3* of anti dive set at the frame ( I use front brakes currently ) I get a very small caster change that effects bump steer ( from the anti dive ) so my tie rod does not run parallel with my a-arms exactly, but close. I have 1/8" of bump ( toe in ) through a 26" wheel stroke but limit the suspension to 24" travel. now I could adjust that bump out to 0 but it's not a big enough problem imo for myself to maintain control of my rail on the dirt or sand nor has it posed a problem on the asphalt either. If I were to introduce + camber I would never be able to control bump in any shape form or fashion that would allow my rail to steer or handle worth a darn.

it sounds to me like you need to cut some parts off and re-locate or re-design and this might not be what you want to hear but is what is needed to make it right. if you can't find this spot on your computer software try it the old fashion way of by hand. move the rack and tie rod to radical spots to see what changes it makes. if you have + camber then I would say you have a problem stemming from the mounting points of your a-arms at your frame in relation to your spindle to start. if your trying to induce - camber with those mounting points then the distance between the upper and lower a-arm at the frame should be less than at the spindle ie. 8.5" at the spindle and 8" at the frame. with kpi ( sai ) built into the spindle upright to get the load applied to the contact patch of the wheel on the ground you desired then you will need shorter upper a-arms to match this design thus unequal length a-arms.

when you push and pull the top of the spindle up right in and out 9* +/- there is noooooooo way the tie rod could ever follow that arc/swing! you MUST address this problem first if you want to correct the problem. 

I am not there to see the problem but if your a-arms are mounted on the out side of the frame itself at a rake or angle to following to the nose then you have 2 angles during the susp stroke. the a-arms are moving up and down and forward and back to an extent and this compounds the problem as well to a point. I looked at you pics but it was hard to see do to the size on photo bucket to help really.  for a camber arc that extreme you upper a-arm must not be moving with the lower at the same time or it is arcing forward before the lower is.

[dsrace]

ok I looked again and it looks like your not mounted on the outside but rather on the inside looks to be a center load rack?

if you have soo much body roll that you require -9 to +9 in an attempt to keep the wheel square on the ground then I think it might also be time to re-valve your shocks and add sway bars to minimize or reduce some of that.

I am not trying to knock your rail or design in any way so don't take my posts or replies as negative, I am only trying pass along info to help from my experience with diff designs.

[mr.bob]

yes it will have a center load rack.In a few Im going to play with it and see what I can come up with.
Thanks for all the help every one.

[dsrace]

when the rack is centered and where the tie rods bolt on, is the center of the tie rods  in line with the pivot points of the a-arms? in other words if you ran 2 pieces of all thread through the tabs your a-arms bolt onto and then took a piece of tape from top to bottom of the all thread, would that tape intersect the center of the pivot of the tie rod at the rack mount point?  just wondering is all because this is where it should be to start.

[mr.bob]

I havent put it on yet but I think it may need a bump steer bar.But it may depend on the steer tabs,havent put that on ether.

[dsrace]

i am unfamiliar with a bump steer bar. if you don't have steering arms on yet don't bother until you get the camber arc addressed, this will save you time and stress.

[fabr]

To simplify what ds is saying: correct the camber curve...........................before you do anything else.  DS,bump steer bar= rack spreader.

[dsrace]

To simplify what ds is saying: correct the camber curve...........................before you do anything else.  DS,bump steer bar= rack spreader.

that makes sense 

[mr.bob]

the wheel hub was not in flush and the top and bottom arms were not to the rake of the frame.So now it has -6* bump and +5* droop@ 23'' with -1 at r.h..In the last 4'' of down travel is were camber changes fast and scrub.So with 19'' of travel it has + 3* and about 2'' less scrub.

So new #s are -6* +3*@19''.
I did a quick check on bump steer with card board and a pen and it looks good,@23'' it wasent bad ether maby 1/4'' that would be at droop.but @ 19'' I THINK all is good.

[fabr]

You gotta get rid of that +. All there is to it my friend.