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Old 04-13-2011, 12:04 PM
Jason M Jason M is offline
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Default Bumpsteer Analysis Among Other Things...

6/5/2011 I edited the title to bring this thread on topic, The Hunter is not an easy thing to use for bumpsteer right now, I need to work on the process. So for now I'am using a Long Acre single Dial indicator bumpsteer gauge & a Fowler digital protractor to take measurements.

(( Old intro...)I have access to a Hunter alignment machine ($50k machine). I'am game planning different setups to check on my s13. My s13 is a good test candidate becuase every suspension link is adjustable, and every pivot point rotates on spherical bearings or rod ends. There is minimal deflection/compliance which should give us repeatable & accurate results. I will use a 12" and 24" caliper to measure suspension link lengths. I will document and report all my findings.)

If anybody has a combination of adjustments & test strategy in mind that they think should be tested, post it up in this thread & I'll report the findings.

Front Suspension

I can check camber curve's during bump only, bumpsteer during bump only, and camber & bumpsteer during bump at different turning angles to see how SAI and & Caster effect things. (Camber curve at 5 deg's,10degs,15degs,20degs, etc turning angle, at specific sai, and caster adjustment's.

-Toe out on turns (ackerman)

I would also like to see how shortening the flca length, & adjusting front roll center via spacing the ball joint stud effect things with various combinations of upper camber plate adjustments.

Rear Suspension
-bumpsteer & camber curve factory length links
-bumpsteer & camber curve with slightly longer upper links in (??? certain increments)
-bumpsteer & camber curve with different RLCA & toe link lengths
-bumpsteer & camber curve with roll center adjustments via lower ball joint spacers
-roll steer (wheel base changes)
-track width changes

Last edited by Jason M; 06-05-2011 at 04:45 PM.. Reason: note to self...
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  #2  
Old 04-13-2011, 05:37 PM
Def Def is online now
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Definitely bumpsteer with stock link lengths and links that are 0.25" longer (traction and camber roughly).
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Old 05-10-2011, 11:26 PM
Jason M Jason M is offline
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My car is not drivable so I have not been able to use the Hunter ***yet***, but I had a chance to dust off the old LongAcre bumpsteer gauge. It will be intersting to compare the two. I used a Fowler digital protractor for camber & spindle roll measurments.



Here is my raw data. Can anyone make some nice looking graphs & post them up?

Setup #1
S13 SUBFRAME
Camber arm 12 1/8" eccentric full negative
Trac Rod 8.275"
Toe Rod approx 13 7/8" eccentric fully inboard
RLCA ball joint pivot spaced down .750" below oem.
front rod end .385" longer then oem, rear rod end .495" longer then oem.

Zero point 2.7 deg's neg camber approx 12 7/8 from fender to center of axle.

Setup #2 was the same as above except the camber arm eccentric was full postive camber. Zero point was 12 7/8 to the center of the axle. -1.9 deg's camber. I'll post up setup #2 curve later. The eccentric had no noticable effect on the camber curve.

Notes: Toe Rod initally hit's subframe at 2.5", I clearanced the bushing collar which gave me another .75" of travel for setup 1 & 2.

Setup 3 the same execpt camber arm 12.375" trac rod 8.5" (as requested .25" longer then oem)

Setup 4 eccentric for camber arm max negative camber (from -1.2 to -1.9)

notes: You guy's really screwed up my setup, my ball joint bound up super quick. ( I have half the articulation as the oem ball joint) Funny things happen when the ball joint starts to bind. You can see it in the data. I did not touch the toe rod after changing the lengths of the camber and trac rod. The toe rod length *may be impotant* in making things work correctly. I have a theory on why the longer arms did not work well. I think it may be ok with an oem RLCA. I need some oem tapered cones to bolt on the oem rlca's though. Anybody want to let me borrow some for testing?


Camber setup#1 / Bumpsteer setup #2 / Bump setup #3/ bump setup #4/ Spindle Roll setup #1
3.25" / -6.40 / .033 /
3.00"/ -6.05 / .043 / . bjb /.115 / 6.2 deg's
2.75"/ -5.70 / .055 / . bjb / .115
2.50"/ -5.40 / .061 / . bjb / .117 /
2.25"/ -5.10 / .061 / . bjb / .114
2.00"/ -4.80 / .058 /. bjb / .106 / 4.15 deg's
1.75"/ -4.50 / .056 / .107 / .098 /
1.50"/ -4.25 / .052 / .098 / .090
1.25"/ -3.95 / .046 / .082 / .076
1.00"/ -3.70 / .039 / .067 / .062 / 2.15 deg's
0.75"/ -3.45 / .031 / .053 / .047
0.50"/ -3.20 / .022 / .036 / .030
0.25"/ -2.95 / .011 / 017 / .015
0.00"/ -2.70 / .000 / .000 / .000 / 0.00 deg's
droop...
0.25"/ -2.50 /.011 / .017 / .014
0.50"/ -2.25 / .022 / .036 / .027
0.75"/ -2.05 / .033 / .056 / .041
1.00"/ -1.85 / .045 / .075 / .057 / 1.8 deg's
1.25"/ -1.60 / .059 / .097 / .076
1.50"/ -1.40 / .072 / .122 / .092 / 2.7 deg's
1.75"/ -1.25 / .086 / . bjb / .100
2.00"/ -1.05 / .098 / .bjb / .bjb / 3.75
2.25"/ -0.85 / .111 /.bjb
2.50"/ -0.70 / .124 / .bjb
2.75"/ -0.50 / .138 /.bjb
3.00"/ -0.30 / .151 / .bjb/.bjb / 5.7 deg's
3.25"/ 0.00/ ..na /
3.50"/ 0.00 / ..na /.bjb/.bjb / 6.55 deg's
3.75"/ 0.00
4.00 +0.25
ball joint binds at 4.25"

Last edited by Jason M; 05-11-2011 at 11:09 PM.. Reason: ADDED S13 SUBFRAME TO THE SETUP SHEET
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Old 05-11-2011, 04:55 AM
Black R Black R is offline
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Is this with the s13 rear subframe? *assume it is, but just double checking.

How about with 12.25" ruca and 8.5" traction rods?
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Old 05-11-2011, 01:30 PM
Jason M Jason M is offline
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Quote:
Originally Posted by Black R View Post
Is this with the s13 rear subframe? *assume it is, but just double checking.

How about with 12.25" ruca and 8.5" traction rods?
I need to measure the oem camber arm with my mill toight, and then I will start messing with camber & trac arm lengths.

Keep checking my second post, I plan on editing it with future data. Anyone care to make up some nice looking graphs???
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Old 05-11-2011, 10:58 PM
Jason M Jason M is offline
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I'am not sure why every one wants to adjust both the camber arm & trac rod the same amount. The arms are at about 42.5 degs apart. The camber & trac rod rolls, pivots/rotates, tilt's (camber), moves the hub rearward/forward. Multi link is super complicated.

I think there is a ratio of how much the trac rod should be adjusted vs the camber arm in order for only the camber adjustment to change. (or atleast have a minimal effect on other settings)

Relationship of trac rod & camber arm on the spindle...



picture of my setup...


I measured two camber arms, neither one was the same length, one had an oem bushing, the other a poly bushing. I measured 12.129 / 308mm's on the oem bushed arm. But who knows with bushing wear and tear it's as close as I can get right now. lets just call it 12 1/8" Trac rod is 8.275".

Last edited by Jason M; 05-12-2011 at 08:35 AM..
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Old 05-12-2011, 07:11 AM
V1A V1A is offline
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Blue Line = Linear Regression










Last edited by V1A; 05-13-2011 at 12:06 PM..
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  #8  
Old 05-12-2011, 05:41 PM
Jason M Jason M is offline
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V1A, Thank you very much for making the charts.

I'am going to work on my process a little before I post anymore data.
Here's some stuff on my todo list.
1. Measure ride height change of hub with a dial indiactor.
2. Figure out a better way to set the zero point of the suspension travel height for better comparisions.
3. Easy one todo, but I'll list it here anyways. Calculate exactly how many inches per turn of a flat of the hex's, on both the camber arm, and the 5/8"-18 threaded 7/8" trac & toe rods. That way I don't have to unbolt any arms or disturb any eccentric's. That should help make comparison's more consistent. Once I initailly setup the arm lengths I should be able to quickly make accurate changes.
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Old 05-12-2011, 05:46 PM
V1A V1A is offline
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No problem. Thanks for the data.

I sent you a PM about the concial spacers, just in case you didn't notice.
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  #10  
Old 05-12-2011, 09:26 PM
Jason M Jason M is offline
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***Warning Theory Alert*** Maybe I'am just now starting to catch up to the current understanding of the S chassis's multilink suspension, but let me put these thought's out there for review.

Why is the outboard (spindle) toe arm pivot located behind (rearward of) the inboard toe pivot (subframe)? Why does the spindle roll at such a fast rate? Why does the spindle roll at all? Certianly the Nissan engineers would not design in spindle roll, or misaligned the toe arm so badly on accident. The spindle roll must be compensating for something. I suspect it's controlling bumpsteer.

My thoughts are that when the outboard toe pivot starts it's arc under bump the spindle toe's out (can't argue with that), the spindle also rolls forward under bump (also can't argue with that), when the spindle rolls forward the outboard toe pivot aligns with the inboard pivot causing the spindle to toe inward, cancling each other out to a certain extent.

One of my observation's is that with the toe arm disconnected, the spindle rotates (toe's in & out) on the lower ball joint & on the trac & camber arm sphericals, but is otherwise very rigid. It seems simple to me now, but the toe arm is literally just along for the ride pivoting the spindle on it's axis, to control toe-in. (Maybe thats why the tourqe specs are lower for the toe arm in the fsm)

Something I want to experiment with is camber arm & trac rod lengths. My thought's are:
1. Set all of your suspension arms to factory lengths.
2. Measure and note your suspension settings, camber, toe, wheel base, ride height.
3. Support the suspension so the ride height can't change. (wheels are off at this point with the vehicle on jack stands, or lifted somehow)
4. Unbolt the toe arm. (optional)
5. Lengthen the camber arm to achieve your desired camber
6. Lengthen the trac rod to move (pivot) the toe-in of the spindle back to previous setting, and confrim your camber setting.
7. Adjust toe arm length until spindle is set to the previous toe setting.

I'am not sure that will give you the same setback of the toe arm pivots, and thats not something thats easy to measure. Lengthening the camber arm pivots the outboard toe pivot rearwards. Lengthening the trac rod moves the outboard toe rod pivot forwards. The objective of adjusting camber with my method is to tilt the top of the spindle without moving the toe pivot forward or backward.

Last edited by Jason M; 05-12-2011 at 10:24 PM..
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