Author Topic: Bump Steer  (Read 8781 times)

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Offline fabr

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Re: Bump Steer
« Reply #45 on: February 19, 2014, 07:00:19 PM »
Big subject ,ds, one that really is only answered by defining what the handling objective is.
"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

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"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 #46 on: February 20, 2014, 09:07:32 AM »
your are correct but interesting topic none the less. all suspension settings are based on end use to truly tune a rail or car for ones app but many many don't know and don't do it.
Don't never argue with an Idiot!
Because he will drag you down to his level and beat you with experience

Offline sandycrack

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Re: Bump Steer
« Reply #47 on: February 20, 2014, 06:29:17 PM »
Her are a couple of pics of the front arms.




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Offline fabr

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Re: Bump Steer
« Reply #48 on: February 20, 2014, 09:08:53 PM »
your are correct but interesting topic none the less. all suspension settings are based on end use to truly tune a rail or car for ones app but many many don't know and don't do it.
+1!
"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 fabr

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Re: Bump Steer
« Reply #49 on: February 20, 2014, 09:13:04 PM »
SAndy,have you checked to see that your rack travel will turn the wheels the steering angle needed? Reason I ask is because it appears to be a rather long tie rod "stem". I assume that is a fortin widespread rack?
"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 Carlriddle

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Re: Bump Steer
« Reply #50 on: February 21, 2014, 05:33:06 AM »
SAndy,have you checked to see that your rack travel will turn the wheels the steering angle needed? Reason I ask is because it appears to be a rather long tie rod "stem". I assume that is a fortin widespread rack?
Beat me to it.

How about a shot from front w/arms level.  Hard to tell but rack looks high.
You can keep your CHANGE, I'd like to keep my DOLLAR.

Offline fabr

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Re: Bump Steer
« Reply #51 on: February 21, 2014, 08:31:15 AM »
I don't wish to come across too skeptical but I think this has been "eyeball" designed. I have to admit some 35 years ago I built my first steering setup from scratch including building the struts for a drag car. To put it mildly,it was a huge learning curve. I had no one to turn to for help either and the internet just did not exist. LOTS of books later I had a firm grasp of suspension design/s. Because of that I will make a couple of guesses. It appears that the pivot point of the tie rod heim on the splindle is maybe 5" or more from spindle centerline. Around 4" approx  is more like it. In other words,make sure that when turning lock to lock that the outer tie rod travel matches the rack travel lock to lock.  Doing so will determine the center to center dimension necessary from spindle centerline to outer tie rod heim pivot point.   I would determine that before I did anything else so far as mounting the rack or building the rack spreader.
« Last Edit: February 21, 2014, 08:37:02 AM by fabr »
"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 #52 on: February 21, 2014, 11:12:52 AM »
The rack is just sitting up top not mounted.  I will get some time Sunday and mount the rack back up put the tie rods on and take a couple of pics.  Still have to grease the wheel bearings and then start the final alignment process, not that that has any bearing on alignment.

Fabr, if you are referencing the tie rod connecting stem on the spindle it is just long enough for the tie rod to clear the Howe power steering unit.  I have not tried full stop to stop so will need to get the wheel and Sweet steering servo mounted up. 

You smell that?

Offline fabr

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Re: Bump Steer
« Reply #53 on: February 21, 2014, 12:36:37 PM »
The rack is just sitting up top not mounted.  I will get some time Sunday and mount the rack back up put the tie rods on and take a couple of pics.  Still have to grease the wheel bearings and then start the final alignment process, not that that has any bearing on alignment.

Fabr, if you are referencing the tie rod connecting stem on the spindle it is just long enough for the tie rod to clear the Howe power steering unit.  I have not tried full stop to stop so will need to get the wheel and Sweet steering servo mounted up.
Yes,the outer tir rod heim will travel X inches lock to lock and so will the rack. Those travel numbers should very closely match. To do so will require a definite length. It appears too far from the steering axis (term I should have used earlier) to do so at this point.
 From reading your post I have to ask if you are just assuming the holes in the rack that appear to be where to mount the inner tie rod heims are in the correct position ??  If so I have to also ask if you know what we are talking about when we say something about a rack spreader bar? Not trying to be a dick in any way,just trying to help and that takes us knowing if you fully understand what we are talking about.  8)
"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 #54 on: February 21, 2014, 01:29:46 PM »
No offense taken by me at all.  I am eager to understand this for sure!
My understanding of the spreader is a bar that has the tierod mountpoints and is bolted to the rack.  To me this set up is designed to use the factory bolts and believe me I could be wrong since I have never put one together.  The Howe site shows 2 different billet bars one has the tierods close to center and the other has them midway to the end of the rack.  Am I understanding the spreader correctly?
The rack is the Howe 2.0 wide unit they said the set up was designed for and the tierods seem to be the correct length when bolted up.  Ill mount it back up and put the tierods back on and take pics and we can go from there.

Here is a pic of the way they set up the rack on the exact setup I have.
« Last Edit: February 21, 2014, 01:42:25 PM by sandycrack »
You smell that?

Offline fabr

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Re: Bump Steer
« Reply #55 on: February 21, 2014, 06:49:17 PM »
Yes you understand what a spreader bar is. What you don't understand is why the one you have is likely not going to work. I don't think your setup is that exact setup. Same design ,yes. but not exact ,as in every little mount point is exactly the same position and spacing as the car you posted. In other words ,is your car an exact copy of the one pictured down to the most minute detail of the mounting points of everything? From your pics I don't believe it is.  Now,back to the spreader bar,there is no such thing as "the right bar" for your setup unless it is an exact copy,as described above,of the car it was designed for. Therefore you,as all of us,will need to make your own. Start out by making the dummy bar as I described in an earlier post.  By far the most technically difficult thing about building cars of any type is the front steering. Everything,and I mean everything ,affects everything else. If you change one parameter ,all the others change.It really is not too difficult if doing a 2-3" travel drag car but add another 20+ inches to that travel and things get difficult in a hurry.
"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 #56 on: February 21, 2014, 09:45:05 PM »
We all know no 2 cars will be exactly the same even off the same jig, but should be close.  This car is off of the same exact jig as the one in the pic so I would think it should be very close.  The bulkhead for the rack is laser cnc produced.  I'll get it together and we will start from there.  I am sure I will have many more questions.
You smell that?

Offline fabr

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Re: Bump Steer
« Reply #57 on: February 21, 2014, 10:05:15 PM »
We all know no 2 cars will be exactly the same even off the same jig, but should be close.  This car is off of the same exact jig as the one in the pic so I would think it should be very close.  The bulkhead for the rack is laser cnc produced.  I'll get it together and we will start from there.  I am sure I will have many more questions.
COOL!!!!!!!!! That means you are light years ahead(if the original was designed right to start with)of the game. Do you know what the suspension specs were/are for the original you posted pic of? WHen I say specs,I mean you will have to reproduce the same camber/caster curve over the desired travel range as the original . Start with camber and caster set as the original was spec'd and post back.
"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 WelderPat

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Re: Bump Steer
« Reply #58 on: February 22, 2014, 07:19:58 AM »
 Take four pieces of square tubing drill holes in them to simulate shocks sitting at ride level and put the straps away.
 You want the suspension sitting at ride level , and even side to side  when you work on these matters
 Check the king pin inclination angle first I think it is a problem .
 If the rack sits in a straight line between the attachment points looking at it from the top and front .
And the pivots of the rack to the tie rod are on the same plane as the pivot points for the a arms where they mount to the frame you will be pretty close.
There is always free cheese in a mouse trap.

Offline fabr

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Re: Bump Steer
« Reply #59 on: February 22, 2014, 07:50:38 AM »
+1 on the straps.

-1 on the tube simulating the shock. Use stands under the lower heil and be sure,as ds said earlier,that all points are snugged up to eliminate slop. You must be able to cycle the suspension thru its' full travel to check bumpsteer.

I agree on getting the rack in the ballpark tho.


"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!)