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Wheel offset?

Jesper Slattengren
So when I modify the tire/wheel, there is a field for wheel_offset. Which makes perfect sense. The wheel center is a design position on the intersection between the spin axis and the mating surface where the wheel is bolted on. On this design, different wheels can be used with different offsets. That will among other things change the scrub radius.
The problems are
  1. This parameter is not used by anything. Changing it does not move the tire in or out.
  2. Using the suspension testrig, there is nowhere to set this parameter. As this is using a testrig tire that does not expose this parameter. I can change it by manually search for this variable and change it. But it looks like an oversight. And it does not change the scrub radius or anything else in the simulation
 
OK, it is easy to fix for the full vehicle tire template, but it seems wrong to me.
 
Anyone else looked into this? @Martin Kieltsch​ you must have fixed this?
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    I was understanding the first one: Cm Offset as moving the CG of the wheel part, and second one center offset just as visualisation of center of wheel (with that cylinder).
     
    in help is written: Enter the offset of the wheel-center geometry along the z-axis of the wheel part. And i was thinkining as geometry for part.
    Capture
  • 0
    Visualization... It is useful to have a visual feedback. But more important is where the forces from the wheel acts.
    But it is really a question of where the center plane of the tire is. And that is disconnected from the wheel center.
    As I explained, the wheel center is a design parameter of the suspension (really a sort of misnomer as it is not connected to the wheel). On that suspension you can put on any wheel that is the right size and the right bolt pattern (and clears the calipers). It is not uncommon to have different wheel offsets on the same suspension to fit a wider tire for a stronger engine. And I don't want to have to change my suspension model to test the behavior for different wheels.
    So the offset will move the tire itself in or out.
  • 0
    Well, that was an interesting picture. But as I said, it's only geometry and does not matter.
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    I was always using hardpoint to move wheel center. I was thinking about center offset in wheel part as just geometry offset without real usage apart visualisation (but if see hardpoint wheel center, why i need cylinder).
     
    Your clarifation about center offset was interesting with real usage, maybe this was intended use for center offset and there is just bug.
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    As usual it's better to have important things implemented on your own.
    So just use own suspension templates that have a construction frame parametrized that's later held by the communicator wheel_center. (i.e. all A/Car stuff is attached to that relocated CF)
    In our case we have a parameter variable for the offset in question ("Einpresstiefe" in German) that moves the wheel_center marker along the spin axis relative to a hardpoint for "wheel center".
    Unfortunately that sometimes creates user misunderstandings as they expected the wheel center at the hardpoint and did not check for the parameter being unequal to zero.
    In the standard wheel subsystem you have to use a zero offset as it's already done in the suspension template.
     
    The advantage of this method: You can easily adjust the offset the same way in suspension and full vehicle analysis
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    Concerning the variable set by the wheel modify dbox:
    .ACAR.macros.mac_tem_whe_smo is setting $wheel.center_offset
    That's only used in $wheel.geo_ctr which is (according to database navigator) which is only used by "$wheel.wheel_hub.cm"
    WheelHubInfo
     
    Just that there is no $wheel.wheel_hub.cm as wheel_hub is a cylinder and not a part.
    Without digging deeper, I simply assume
    that the intended behaviour was to move $wheel.cm and as a consequence it'd be bug.
  • 0
    in FTire, we have wheel offset (=ET=Einpresstiefe, as Martin said) in the tire/rim data file. If this value is set, Adams is expected to give the location/motion of the *geometrical* center point of the rim as input to FTire; FTire takes into account the ET.
    If you prefer to handle wheel offset directly in your Adams model, this is no problem. In this case, you must set ET=0 in the tir-file (which obviously is the default).
    Very small disadvantage of the first method (ET set in the tir-file): you will not see the wheel offset in the Adams online animation. But you *will* see it in FTire's own animation window, and in the ogl-file-based offline animation in Adams/ PPT.
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    @Martin Kieltsch​  the way you propose is the safe way as it would work with the suspension testrig wheel, but I hate to do it that way as the offset is a property of the wheel, not the suspension.
    Regarding your second answer: It seems like a big confusion from whoever created this template in the first place (likely not with MSC anymore) as there is a separate field for cm-offset compared to geometric offset. It seems like these two variables have been confused at some time.
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