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Re: ROLL CENTER
[Re: 67autocross]
#1993084
01/18/16 01:24 AM
01/18/16 01:24 AM
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Joined: Jan 2003
Posts: 27,451
So Cal
autoxcuda
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,451
So Cal
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1/8 of movement/turning of the spindle is a lot at the tie rod end, probably 3/8" of movement of the tire back and forth...that is more than I would like to get in my b-body 1/8" of movement is a lot at 3 inches of compression? Think about what is going on a 3" of compression....low speed high G corner... The spindle will be at a high turning angle and straight line bump steer doesn't apply much. The two measuring points on my commonly used bump steer gauge are 16.5" apart. A typical tire is 26".  I showed my results shown below with a guy that crew chiefs K&N Pro Series championship cars and full time designs and builds his own multi track championship car. 1/8" of bump with the same style gauge I used at 3" is still good and he said don't mess with it. He did say 1/16" would be very good. Of course we're talking cars set up for handling. Not Drag cars. Getting .001" at jounce AND rebound at 3" is nearly impossible. That's not reality if you've ever did this or did it regularly. How much wheel travel do you have with your set up? I don't remember exactly. But it's at least 3" up and down. I ran the gauge with my upper control arm bumper (jounce) and the removed bumper setup I run all the time. Neither hit the limits.
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Re: ROLL CENTER
[Re: BergmanAutoCraft]
#1993313
01/18/16 02:32 PM
01/18/16 02:32 PM
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Joined: Feb 2011
Posts: 4,302
Nebraska
72Swinger
master
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master
Joined: Feb 2011
Posts: 4,302
Nebraska
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Shock travel and wheel travel are not always the same, shock is at an angle and mounted inboard of balljoint obviously. I know you all know this.
Mopar to the bone!!!
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Re: ROLL CENTER
[Re: BergmanAutoCraft]
#1994544
01/20/16 12:28 AM
01/20/16 12:28 AM
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Joined: Nov 2004
Posts: 25,050
Texas
GoodysGotaCuda
5.7L Hemi, 6spd
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5.7L Hemi, 6spd
Joined: Nov 2004
Posts: 25,050
Texas
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Shock is only 5" in an A body, so it can't be any more than 2.5" in either direction. ..does an Abody have a 1:1 motion ratio?
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Re: ROLL CENTER
[Re: BergmanAutoCraft]
#1994949
01/20/16 03:55 PM
01/20/16 03:55 PM
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Joined: Feb 2011
Posts: 4,302
Nebraska
72Swinger
master
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master
Joined: Feb 2011
Posts: 4,302
Nebraska
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The last few inches of compression are probably 1:1 ish but on rebound you get over it on my Dart. My guess is with no bump stops and a 5" shock, travel at the tire is more like 6".
Mopar to the bone!!!
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Re: ROLL CENTER
[Re: autoxcuda]
#2177944
10/18/16 05:59 PM
10/18/16 05:59 PM
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Joined: Mar 2005
Posts: 1,545
Seattle, WA
375inStroke
Special needs person
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Special needs person
Joined: Mar 2005
Posts: 1,545
Seattle, WA
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1/8" of movement is a lot at 3 inches of compression?
I was getting 1/4" toe change per inch of travel on my road course car. Couldn't touch the brakes on corners or it would pull into the turn hard. Installed a bolt and heim joint style tie rod end and got it down to less than .010" toe change per inch of travel, and that problem went away. I don't want to use a heim joint on a street car, though. How do you adjust bump steer on your car?
Last edited by 375inStroke; 10/18/16 06:00 PM.
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Re: ROLL CENTER
[Re: 375inStroke]
#2178010
10/18/16 07:12 PM
10/18/16 07:12 PM
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Joined: Jan 2003
Posts: 27,451
So Cal
autoxcuda
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,451
So Cal
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1/8" of movement is a lot at 3 inches of compression?
I was getting 1/4" toe change per inch of travel on my road course car. Couldn't touch the brakes on corners or it would pull into the turn hard. Installed a bolt and heim joint style tie rod end and got it down to less than .010" toe change per inch of travel, and that problem went away. I don't want to use a heim joint on a street car, though. How do you adjust bump steer on your car? And that would equal 0.03" of toe change per 3" of travel. I have 0.082" per 3" in compression. I have the Hotchkis hiems tie rod kit. The measurements I got where with no adjustments (lucked out). The hiems are worn now though.
Last edited by autoxcuda; 10/18/16 10:40 PM.
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Re: ROLL CENTER
[Re: autoxcuda]
#2178174
10/18/16 10:50 PM
10/18/16 10:50 PM
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Joined: Mar 2005
Posts: 1,545
Seattle, WA
375inStroke
Special needs person
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Special needs person
Joined: Mar 2005
Posts: 1,545
Seattle, WA
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And that would equal 0.3" of toe change per 3" of travel. I have 0.082" per 3" in compression.
I have the Hotchkis hiems tie rod kit. The measurements I got where with no adjustments (lucked out). The hiems are worn now though.
.010", not .100", so .030" for 3" of travel. It started out .250" to .300" per inch of travel, so we're talking over an inch of toe change over full suspension travel. The instructions for the kit said rule of thumb is to keep it less than .020" per inch of travel.
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Re: ROLL CENTER
[Re: dusterpt440]
#2185174
10/29/16 10:18 AM
10/29/16 10:18 AM
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Joined: Dec 2003
Posts: 22,695
Bitopia
jcc
If you can't dazzle em with diamonds..
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If you can't dazzle em with diamonds..
Joined: Dec 2003
Posts: 22,695
Bitopia
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Since there seems to be a wide range of understanding of the terms discussed here, to make sure everyone is on same page, roll center is the geometric location on a chassis determined by the suspension linkages as they move thru their respective arcs, and the height of that derived roll center in regards to the measured height of the COG, determines how long the theoretical vertical lever arm is between those two points. That distance is important, as it determines how much the chassis "rolls" when cornering, longer=more. The front and rear usually have different values, intentionally. How did I do? 
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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