Help me choose a suspension setup

Discussion in 'Corner Carver Racing Tech Discussion' started by Screamin_dutch, Dec 12, 2018.

  1. Norm Peterson

    Norm Peterson corner barstool sitter

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    Plane of Chassis when RR is off the ground  and the RF is about to lift, outline rear view.jpg Plane of Chassis when RR is off the ground  and the RF is about to lift, outline side view.jpg I also took a crack at displaying the presence or absence of chassis twist. Within the limits of accuracy of my measurements (I do question a couple of them) and the ability of Excel to display a surface chart, there isn't much. You'd be looking for the front and rear lines in rear view and the right side and left side lines in side view to not be parallel to each other if the chassis was twisting enough to measure to within about 1/32".

    View attachment 68904 View attachment 68906


    Norm
     
    Last edited: Jan 10, 2019
  2. Norm Peterson

    Norm Peterson corner barstool sitter

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    I also ran an abbreviated test lifting from 12" forward of the RR jack point (with a 2x4 to spread the load. Instead of taking 6.75" at the rear fender opening to get the RF off the ground, it only took 5". So this is pretty sensitive to actual jack location.

    I also have some idea how much the loaded sidewall height varies with inflation pressure (roughly 1/8" going between 25 and 35 psi, 285/35-18 tires on 11" wide rims).


    Norm
     
  3. Norm Peterson

    Norm Peterson corner barstool sitter

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    Minor correction to the 3D twist plots. Width is 72", not 62".

    Yes, there is some chassis twist, but it's really small. Like a round 0.06°, which with a chassis stiffness of 21,000 ft*lbs/deg corresponds to an applied torque of about 1200 ft*lbs.

    Initial chassis twist and chassis twist due to jacking.jpg


    Norm
     
  4. Pentalab

    Pentalab forum member

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    I'm still trying to fathom how u ended up with just .058 deg of twist? And also same .058 deg, regardless of whether u lifted RR 4.56"..... or 6.75".

    OK, put another way, IF you placed a digital level on the rear trunk lid, dead center...and it read '0.0 degs' , (no jack), what will the same digital level read when RR lifted 6.75" ?? Is it really 2.586 degs ? If that is the case, the digital level reading at front end of car should be LESS. You depict it as MORE...like 2.690 degs. Or am I reading this all wrong ? I'm talking about the level positioned so it's parallel to axle/ transverse to center line of car.
     
  5. Norm Peterson

    Norm Peterson corner barstool sitter

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    Yes, I noticed the same things. The measurements are the measurements, except for the LR fender @ 4" which is suspect.

    One thing is that jacking the car up isn't the same thing as applying a pure torque about the car's longitudinal axis. It's also possible that there's some sta-bar effect happening.

    I may eventually re-run the sequence, but for its original purpose the measurements were careful enough to show that the actual twist due to jacking is very low.


    Norm
     
  6. Norm Peterson

    Norm Peterson corner barstool sitter

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    XenForo strikes again . . . not saying post was submitted or returning me to the thread on submittal. I hate XenForo :angry1: :banghead:


    Norm
     
  7. Pentalab

    Pentalab forum member

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    Ok, so what's the next step ? If that 6.75" could be reduced to 2" or less, with the use of SFC's, and your tests / measurement re-run, it would provide for some interesting observations. Then in part 2, test the sfc's out on the rd / hwy / local twisties /auto X / road course. Then perhaps some minor suspension tweaks, if required. Then re-evaluate.
     
  8. eighty6gt

    eighty6gt forum member

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    OK, the car is level lifting it with a jack

    that has little to no material difference on handling.
     
  9. Norm Peterson

    Norm Peterson corner barstool sitter

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    Not sure where I'm going to take this next, though I do have a couple of thoughts that'll at least make the measuring/remeasuring process easier and hopefully better.

    With my springs and sta-bars, 4.56" is what it takes just to get the RR lifted free of the ground, lifting at the Ford jack point - that being defined by rear shock rebound travel. Rebound travel is a function of any amount lowered (I'm lowered somewhere around 15 or 20 mm in the rear, and there is 100 lbs or so in the trunk which is worth about another quarter of an inch). So I'd still need to lift the car at the rear axle line about 4.56", as currently loaded.


    Norm
     
    Last edited: Jan 11, 2019
  10. Pentalab

    Pentalab forum member

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    It's not level ! He has to lift the RR 6.75" to get the RF off the ground. That could potentially affect handling..and probably does. I'll comment on the handling part..after I install the steeda jacking rails..and welded into place. The rear steeda box tube / frame braces are already installed and welded. Well welded at 2 of the 3 corners of the triangular rack. We will weld the 3rd corner this spring. Steeda's 2" wide x 1.5" tall 4130 CM rectangular tubing jacking rails are bolted with 2 x bolts at each end. The game plan is to also weld the rect tubes, on the inboard side..on the edge..in about 5 x places. Ok, now it's my idea of solidly installed.

    To keep the finish intact, a hockey puck placed dead center on my low profile floor jack may well do the trick. A puck is 1" tall x 3" diameter.
     
    Last edited: Jan 11, 2019
  11. Norm Peterson

    Norm Peterson corner barstool sitter

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    That 6.75" applies only when lifting at Ford's jack point. Move the jack one foot further forward and you only have to raise the RR fender opening up 5" (I ran that one). Move the jack point as far back as you can (risk being on anybody who tries this; I have not) and I'm sure you'd have to lift the fender at the axle line 7" or more.

    This would be related to handling when encountering a road surface that's sort of 'warped', where when even going dead straight ahead the crossweight percentage would not be the same as when measured on a flat surface. Jacking could be considered a crossweight problem, taken to extremes.


    That's one of my little tricks . . .


    Norm
     
  12. Juice

    Juice forum member

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    I will be installing the Steeda X, 555 5093 brace so I can keep the rear seats intact. I will have a review after my next track day at WGI. I have hard data from last year's event (lateral G force, and lap times) to compare with. Stay tuned....event is a few months away still..
     
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  13. Pentalab

    Pentalab forum member

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    Finally got a Fedex tracking # for the steeda X brace and the pair of Steeda jacking rails. WX still sucks, so this will have to wait a bit.
     
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