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Author Topic: Bump Steer  (Read 6814 times)

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fabr

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Bump Steer
« on: February 13, 2014, 09:02:00 PM »
How long did it take you to eliminate nearly all of it? Usually takes a while to get close and for sand close is plenty close enough. Current build will be on road also so really good handling ,absent of "twitchiness" is a must. It took over 16 hours of manipulation of rack positioning and inner tie rod positioning to get to where I have 21" of travel and only 1/8" bumpsteer. I'm happy and damn sure glad that's over.  ;D
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dsrace

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Re: Bump Steer
« Reply #1 on: February 14, 2014, 02:18:58 PM »
with my first one or last one?  ;D :)
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fabr

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Re: Bump Steer
« Reply #2 on: February 14, 2014, 02:54:44 PM »
LOL!!!!! Bad thing is that even with a suspension CAD the TR positions will be off due to minute differences in a arm mounts and minor camber/caster inaccuracies that influence the final sweet spot. I ended up 1/2" higher and 1/2" out on each TR from the CAD results.
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"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

Carlriddle

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Re: Bump Steer
« Reply #3 on: February 14, 2014, 03:16:49 PM »
I let DS bang his head against the wall.  I might have 1/4" froom top to bottom.  Prob get some of that out but is offroad only so.  I'd like to get a tag, wonder what  bs1 that may be. 
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fabr

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Re: Bump Steer
« Reply #4 on: February 14, 2014, 03:49:57 PM »
If I start out with zero toe at full droop I have 1/8" total toe change over 21" On the other hand,changing nothing else other than changing toe in to 1/4" at full droop will change total toe change to 1/2 inch over 21" . It also shows how a small amount of wear in the components will greatly change the cars handling.Just an example of how sensitive any small change will be. Just an FYI,we use rack and pinion steering on most off road buggies. Rack and pinion steering will only have near perfect bumpsteer when the wheels are pointed straight forward. Any steering input to the left or right will alter,dramatically, toe numbers.
« Last Edit: February 14, 2014, 03:51:35 PM by fabr »
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"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

dsrace

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Re: Bump Steer
« Reply #5 on: February 15, 2014, 10:46:24 PM »
you are absolutely correct on minute diff's or slop affecting a huge amount of bump. I do include some adjustment in the spindle up right and steering arm to make the 1/16" shim changes to adjust it out if one chooses to take the time as carl said.   nothing ever holds still in the jigs or turn out EXACTLY as we shoot for but that just makes it a challenge lol  the small amount you have will never be felt in the sand or on the dirt and I bet if you set it with 1/8" toe out at full droop you'll see it toe in right away in the first 1 to 2" of stroke setting you straight of course I know you already know this but for those that don't.
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dsrace

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Re: Bump Steer
« Reply #6 on: February 15, 2014, 10:49:00 PM »
ya know not only does the slop in the rack play a huge roll in bump but as the heims wear the slop in all of them adds up and setting the alignment and getting it on the money will change after the first run or two once the steel and welds have settled a little and that too can change it a touch as well. really come down to how much time one wants to spend setting it or I think the term I have been told is anal!!  LMAO LMAO LMAO LMAO
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fabr

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Re: Bump Steer
« Reply #7 on: February 16, 2014, 10:06:13 AM »
you are absolutely correct on minute diff's or slop affecting a huge amount of bump. I do include some adjustment in the spindle up right and steering arm to make the 1/16" shim changes to adjust it out if one chooses to take the time as carl said.   nothing ever holds still in the jigs or turn out EXACTLY as we shoot for but that just makes it a challenge lol  the small amount you have will never be felt in the sand or on the dirt and I bet if you set it with 1/8" toe out at full droop you'll see it toe in right away in the first 1 to 2" of stroke setting you straight of course I know you already know this but for those that don't.
All very true!  This part especially. My front will cycle thru 26" of travel but there is no reason to use that much. At 26" (with my track width) the toe change is uncontrollable. Limited to 21" with 5" ground clearance at full bump I have ,with 1/8" static toe ,a total toe change of 1/8" in. If I try for 22" travel eferything goes to hell quickly with massive toe out that cannot be eliminated with a decent toe change/camber curve.
« Last Edit: February 16, 2014, 10:08:27 AM by fabr »
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"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

fabr

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Re: Bump Steer
« Reply #8 on: February 16, 2014, 10:15:00 AM »
YES!!!! Rack slop and initial break in of heims and rack along with the initial movement of thechassis as it settles in will make revisiting the toe issue needed soon after first run. I agree that in the sand it is very forgiving but on hardpack or asphalt,it needs to be right if running 100+ mph . Many people who run their car on the street say that the car is "twitchy" and blame it on the power assist in the car making it so. IMO,it is the simple fact it needs a proper alignment and possibly a remake of the geometry.
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"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

sandycrack

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Re: Bump Steer
« Reply #9 on: February 16, 2014, 07:36:49 PM »
Would you guys please help me with a list of progressive steps for final set up and alignment of the front end?  1st timer you see and my other buggy was set up and running when I bought it.  I am doing final assembly now now can probably get close the hard way, but am hoping there is a sequence that will make it a little easier.  Any help would be greatly appreciated.
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Carlriddle

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Re: Bump Steer
« Reply #10 on: February 16, 2014, 08:02:08 PM »
You setting alignment and toe at ride.  ESP for rd and hard pack.
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sandycrack

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Re: Bump Steer
« Reply #11 on: February 16, 2014, 10:07:06 PM »
yes ride height sand and hard pack. 
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fabr

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Re: Bump Steer
« Reply #12 on: February 16, 2014, 10:50:04 PM »
Sorry,didn't see this till now. i'll post some of my thoughts tomorrow sometime. It's a very involved subject actually.
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"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

dsrace

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Re: Bump Steer
« Reply #13 on: February 16, 2014, 10:56:09 PM »
that is a difficult request with out knowing the design so I will tell you that I always jack my front end up off the ground so at full droop and set the alignment. I set caster first them camber then double check caster then double check camber once both are right then I set toe. now I'll tell you one thing out of all the front end kits I have sold that people always forget to do......center the rack before you set toe!!!!!!!!!!!!   if you do not and it is off 1/8" to one side it will mess you all up. fabbr and many others know what 1/16" up or down on the steering arm does for bump so one side steering faster than the other really fooks you up lol  I go out side the box on offroad norm's but I set 10* caster and 1/2* neg camber and 0 on toe. it is impossible to get an actual 0 on toe with the slop in the heims and rack even with a rack snuggy from fast ( which is a major diff on getting most the slop out!!!!! ) there is always a little. I can actually account for 3/8" toe play from the slop in heims and rack  when they are a little loose. another thing and I know this will get old but if you leave the nuts and bolts loose while setting alignment you will never get right lol use  some standard nuts to spin on and off and snug them all up so all of that isn't slipping back and fourth on ya.   if you run limit straps then bolt them on before you set toe. I designed spindles with 1/8" wider gap than heims for my front end kits so I can pull and swap a washer rather than pulling heims for finer adjustments on all 3 points of the spindle. I can actually change 1* of caster with them. remember when you change caster you change camber and visa versa so it will take some time to get it right one. I can align my font end kits down to 0 toe change at 24" wheel travel but that's getting real picky and has to be done again after break in. 
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dsrace

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Re: Bump Steer
« Reply #14 on: February 16, 2014, 11:08:16 PM »
also make sure ( if you have slop in the rack mounting point ) that the rack is level and also need to make sure your tie rods are equal length. so if they are the same length then screw the heims in all the way and screw them out 1 turn at a time each until you get it and the wheels need to be pretty close to square when you go to set caster and camber. this is all of course if the front end is built correctly and I don't care what jig you have for building a-arms they will all come out of it slightly diff. maybe not noticeable to the naked eye but slightly different so bushings become a little trickier to set but doable if done right.   just take some time to do it right and once it settles it won't be bad or re-do it. good heims will make a big diff as well over steel on steel.
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