Author Topic: Bump Steer  (Read 9201 times)

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Offline sandycrack

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Re: Bump Steer
« Reply #15 on: February 17, 2014, 07:40:33 AM »
Lots of great info there!  Some great tips I had not thought of.  I really appreciate the info!
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Online fabr

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Re: Bump Steer
« Reply #16 on: February 17, 2014, 08:25:10 PM »
Well,I wrote up my method of getting the rack properly positioned as well as determining rack spreader bar tie rod positions. Only problem is I didn't hit send before leaving work. Oh well,I'll post it in the morning. I also hit upon what,IMO,are things to never,ever do.  DS and I pretty much agree on things relating to front end stuff. He just takes a slightly different road to the same result.
"There can be no divided allegiance here.  Any man who says he is an American,
but something else also, isn't an American at all.  We have room for but one
flag, the American flag... We have room for but one language here, and that is
the English language... and we have room for but one sole loyalty and that is a
loyalty to the American people."
Theodore Roosevelt 1907

-----------------------------------------------------------
"I fear the day that technology will surpass our human interaction. The world will have a generation of idiots" Albert Einstein  (IT'S OFFICIAL THAT DAY IS HERE NOW!)

Offline sandycrack

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Re: Bump Steer
« Reply #17 on: February 18, 2014, 05:29:15 AM »
Great!  Thanks guys.
You smell that?

Online fabr

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Re: Bump Steer
« Reply #18 on: February 18, 2014, 07:41:44 AM »
I always start with the basics that are extremely important . If they are ignored there will be no way to get anything correct after that.. I make a dummy bulkhead with vertical slots to allow vertical adjustment of the r&p, I also make a dummy spreader bar with slots to allow unlimited adjustment of center to center tie rod spacing. When done I make final bulkhead with correct hole positions and also tha same for the spreader bar.
 1. Center rack and pinion body in car perfectly! I do not mean almost centered.
2. Center rack in car . Also perfect,not almost .
3. Accurately set camber/caster to specs @ ride heightwith desired toe .Set it,cycle suspension thru travel,recheck ,reset if necessary. At this point make absolutely certain that upper and lower outer heims are equidistant from center of car so that left and right sides are perfect mirror images of the other. This is as critical as being certain rack and spreader is centered .
4. After all that is perfect,just resign yourself to the fact it is not.  rofl
5. Assuming the camber/castor curve is as desired, it is time to determine inner tie rod spacing and position in car fore/aft of spindle center line and above/below outer tie rod to outer tie rod horizon line. This is what is so tricky. It can only be done trial and error. I have a very good suspension CAD program that will design all this for you and put you in the ballpark BUT,as DS said, minor build differences will skew the inner tie rod positions from the ideal to real world needs.
6. Sooooo,how to determine inner tie rod positions? First off,take a valium.  ;D ;D
7. I begin with the tie rods parallel with each other when the tie rods are level with the ground. This will make the outer rod positions and inner tie rod positions in the same vertical plane. This may or may not need to be fiddled with later.
8.  I start with toe set as desired with suspension at ride height. I then cycle suspension thru full travel and recheck toe. Once again cycle thru travel and plot the toe change curve.Never check anything without cycling the suspension first. It will make a difference!
9.Now it is time to experiment with TR spacing from center I make a rack spreader with slots for this purpose. Makes life much simpler. Move inner tie rod position,reset toe,cycle,plot toe change. Repeat about a zillion times.
10.WHen it gets as good as it can be  ,it is time to adjust the height. Again cycle suspension,plot toe change over full travel,adjust till as good as it gets.
11. What now? Take another Valium.  drowning Start over with the inner tie rod spacing and get the toe change curve better yet and then fiddle with the height. Lastly I look at the fore/aft position of the rack itself to see if there is any room for improvement.  12. Remember ,it will be worth the effort to get it right NOW.


 I want to mention that when plotting the toe change curve,it is very important that there is never any toe out . There must always be some toe in for directional stabiity especially at higher speeds on hardpack or asphalt,in the sand it is not as important but why not get it right? I try to see 1/8" toe in at full droop and see slight additional toe in at full bump.

Bear in mind the rack MUST be dead center when doing all of this and the a arms must be identical so far as picot points are concerned.







"There can be no divided allegiance here.  Any man who says he is an American,
but something else also, isn't an American at all.  We have room for but one
flag, the American flag... We have room for but one language here, and that is
the English language... and we have room for but one sole loyalty and that is a
loyalty to the American people."
Theodore Roosevelt 1907

-----------------------------------------------------------
"I fear the day that technology will surpass our human interaction. The world will have a generation of idiots" Albert Einstein  (IT'S OFFICIAL THAT DAY IS HERE NOW!)

Offline dsrace

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Re: Bump Steer
« Reply #19 on: February 18, 2014, 10:01:00 AM »
well fabr took the time to say it better lol he is absolutly correct and 1 thing i would like to add for those with others front end designs that can't seem to get the bump out.......if it wasn't designed right in the first place you will never be able to adjust the bump out at best tone it down!!!!!   there is a lot involved with getting a front end correct and time consuming if you want it right like fabbr explained but it is needed for the best end result and yet soooo many short cut it and don't care and even more don't know the difference!!
Don't never argue with an Idiot!
Because he will drag you down to his level and beat you with experience

Offline dsrace

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Re: Bump Steer
« Reply #20 on: February 18, 2014, 11:35:51 AM »
fabbr , now I know this may be a silly question but humor me.....have you measured each wheel individually to see which one is more of the prob? did you design anti dive into the front? what is your -camber arc? just curious
Don't never argue with an Idiot!
Because he will drag you down to his level and beat you with experience

Offline Carlriddle

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Re: Bump Steer
« Reply #21 on: February 18, 2014, 12:15:43 PM »
Well, heres how I'm gonna do it;


Grab
1 chair
2 valium
1 bottle of Jack Daniels
12 beers

Give 2 valium to Fabr, bottle of Jack to DS, grab chair for me and drink the 12 beer while they do it.  Sure hope I have enough beer.

 LMAO LMAO LMAO LMAO
You can keep your CHANGE, I'd like to keep my DOLLAR.

Online fabr

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Re: Bump Steer
« Reply #22 on: February 18, 2014, 12:50:20 PM »
Yes,ds you nailed it. As he says,if the arm geometry is crap everything is crap no matter what you do. A proper camber/castor curve is essential and must be finalized before any bump steer elimination can be attempted. ANY change to the camber/camber will seriously affect any efforts you have made towards elimination of bump steer. In other words,DO NOT ALTER CAMBER/CASTOR AFTER SPENDING BOAT LOADS OF TIME ELIMINATING BUMP STEER!!!!!!! ;D ;D ;D ;D
"There can be no divided allegiance here.  Any man who says he is an American,
but something else also, isn't an American at all.  We have room for but one
flag, the American flag... We have room for but one language here, and that is
the English language... and we have room for but one sole loyalty and that is a
loyalty to the American people."
Theodore Roosevelt 1907

-----------------------------------------------------------
"I fear the day that technology will surpass our human interaction. The world will have a generation of idiots" Albert Einstein  (IT'S OFFICIAL THAT DAY IS HERE NOW!)

Online fabr

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Re: Bump Steer
« Reply #23 on: February 18, 2014, 01:01:46 PM »
fabbr , now I know this may be a silly question but humor me.....have you measured each wheel individually to see which one is more of the prob? did you design anti dive into the front? what is your -camber arc? just curious
  Yes ,I do each side individually and then check to see that the combined results add up correctly. Yes,there is usually a difference due to whatever. If built on jigs it will be minor differences but there will be differences as you and I know. Mine this time were almost non existant.  ;D I got lucky.
  Didn't try to eff with antidive as there is a great deal of controversy as to whether or not it is a good thing offroad. I don't really have an opinion to voice at this time as I am very wishy-washy on the subject.
  Camber goes from .5-3.5 at full droopIIRC today.Don't quote me on it tho. Need to check paperwork.
"There can be no divided allegiance here.  Any man who says he is an American,
but something else also, isn't an American at all.  We have room for but one
flag, the American flag... We have room for but one language here, and that is
the English language... and we have room for but one sole loyalty and that is a
loyalty to the American people."
Theodore Roosevelt 1907

-----------------------------------------------------------
"I fear the day that technology will surpass our human interaction. The world will have a generation of idiots" Albert Einstein  (IT'S OFFICIAL THAT DAY IS HERE NOW!)

Online fabr

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Re: Bump Steer
« Reply #24 on: February 18, 2014, 01:07:27 PM »
Carl,no way will that be enough beer. Better bring a 30 pack
"There can be no divided allegiance here.  Any man who says he is an American,
but something else also, isn't an American at all.  We have room for but one
flag, the American flag... We have room for but one language here, and that is
the English language... and we have room for but one sole loyalty and that is a
loyalty to the American people."
Theodore Roosevelt 1907

-----------------------------------------------------------
"I fear the day that technology will surpass our human interaction. The world will have a generation of idiots" Albert Einstein  (IT'S OFFICIAL THAT DAY IS HERE NOW!)

Offline sandycrack

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Re: Bump Steer
« Reply #25 on: February 18, 2014, 01:46:01 PM »
Ok now you guys have me spinning.  I am not sure what they call my front arms as the rear part of the arm is toward the rear connecting on the side of the passenger compartment.  I call it a modified A arm and I'm sure most of you call it fooked up!  rofl My point is that now I see where the camber/caster will change at a different angle than a true A arm.  I am seeing why you guys like a true A arm so much. 
You smell that?

Online fabr

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Re: Bump Steer
« Reply #26 on: February 18, 2014, 02:14:13 PM »
Ya,I hate the design(no offense meant!) . You can get similar results of bump steer reduction but only if the castor/camber curve is not too wild.The process is the same.
"There can be no divided allegiance here.  Any man who says he is an American,
but something else also, isn't an American at all.  We have room for but one
flag, the American flag... We have room for but one language here, and that is
the English language... and we have room for but one sole loyalty and that is a
loyalty to the American people."
Theodore Roosevelt 1907

-----------------------------------------------------------
"I fear the day that technology will surpass our human interaction. The world will have a generation of idiots" Albert Einstein  (IT'S OFFICIAL THAT DAY IS HERE NOW!)

Offline dsrace

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Re: Bump Steer
« Reply #27 on: February 18, 2014, 04:42:10 PM »
Ok now you guys have me spinning.  I am not sure what they call my front arms as the rear part of the arm is toward the rear connecting on the side of the passenger compartment.  I call it a modified A arm and I'm sure most of you call it fooked up!  rofl My point is that now I see where the camber/caster will change at a different angle than a true A arm.  I am seeing why you guys like a true A arm so much.

got a pic?
Don't never argue with an Idiot!
Because he will drag you down to his level and beat you with experience

Offline dsrace

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Re: Bump Steer
« Reply #28 on: February 18, 2014, 04:47:01 PM »
Carl,no way will that be enough beer. Better bring a 30 pack

I designed it so about 20 min's and i'll have it knocked out lol   whoo back up let me re-phrase that....depending on how many beers carl drank while putting it together 20 min's or so  rofl rofl

fabbr I did design in 5* anti dive ( apprx 5 *) to try on just my front end and either it wasn't enough or I simply can't tell the diff between my front ends w/o brakes nd this one since none of them really took a dive when I hit the brakes lol    but it does through a funny caster change in the mix which is tricky to adjust out and I can't get the toe in completely out using a full 24" of wheel stroke but now that it's all broke in ( I mean that litteraly after my near roll over in the front yard lol lol  that sent all 4 wheels off the ground and nearly blew two beads lol ) I have 1/4" toe in front full droop to full bump and If I cared to spend a little more time on it I am pretty sure I could cut that in half but it doesn't effect anything that I can notice yet.
« Last Edit: February 18, 2014, 04:51:08 PM by Dsrace »
Don't never argue with an Idiot!
Because he will drag you down to his level and beat you with experience

Offline dsrace

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Re: Bump Steer
« Reply #29 on: February 18, 2014, 04:49:51 PM »
  Yes ,I do each side individually and then check to see that the combined results add up correctly. Yes,there is usually a difference due to whatever. If built on jigs it will be minor differences but there will be differences as you and I know. Mine this time were almost non existant.  ;D I got lucky.
  Didn't try to eff with antidive as there is a great deal of controversy as to whether or not it is a good thing offroad. I don't really have an opinion to voice at this time as I am very wishy-washy on the subject.
  Camber goes from .5-3.5 at full droopIIRC today.Don't quote me on it tho. Need to check paperwork.

I set mine -.5 at full droop and achieve -3* full bump....no positive camber and I like the way it handles.  I did not set the rear up for a - camber arc but have been thinking about to see if it would do any better or not. I could make a new carrier to test this w/o changing the chassis side.
Don't never argue with an Idiot!
Because he will drag you down to his level and beat you with experience