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Thread: Using Optimum K for analyzing bumpsteer

  1. #1

    Using Optimum K for analyzing bumpsteer

    Hi all,
    I'm working on steering for Columbia University's team, and I'm wondering if there's a feature on Optimum K that can help with analyzing bump steer. Specifically, analyzing bump steer with different sized steering racks. I'm very new to Optimum K, so I apologize if this is a stupid question.

    Thanks!

  2. #2
    Senior Member
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    Oct 2007
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    Bolton, CT
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    Apologies if this is not what you're looking for since I'm not familiar with Optimum K, but there should be some output which can show toe change with vertical suspension travel (aka bumpsteer). You should just be able to change the inner tie rod (track rod) XYZ position and assess the toe change outputs.
    Jim
    "Old guy #1" at UCONN Racing

  3. #3
    Senior Member
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    Quote Originally Posted by GwenArch View Post
    Hi all,
    I'm working on steering for Columbia University's team, and I'm wondering if there's a feature on Optimum K that can help with analyzing bump steer. Specifically, analyzing bump steer with different sized steering racks. I'm very new to Optimum K, so I apologize if this is a stupid question.

    Thanks!
    Yes it can. Read the user manual.
    Trent Strunk
    University of Kansas
    Jayhawk Motorsports
    2010-2014

    Now in NASCAR land. Boogity.
    Opinions Are My Own

  4. #4
    I can only agree with Trent.

    There are 2 rules in software use
    1. You can't use the software unless you read the user manual
    2. Except a few (very rare) exceptions, nobody reads the user manual.

    Believe it or not, whether questions our support engineers receive are about OptimumLap, OptimumTire, OptimumKinemantics, or OptimumDynamics, whether they come from professionals or from students, in 90 % of the cases most of our replies consist in a CTRL C + CTRL V of some specific pages of the user manual / help file.

    The time students took the necessary time to find an answer at the public or university library is gone. The Google generation has its strengths but patience and studiousness are not part of it.
    Claude Rouelle
    OptimumG president
    Vehicle Dynamics & Race Car Engineering
    Training / Consulting / Simulation Software
    FS & FSAE design judge USA / Canada / UK / Germany / Spain / Italy / China / Brazil / Australia
    [url]www.optimumg.com[/u

  5. #5
    Senior Member
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    Mar 2008
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    Brighton, MI
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    Bum Steer

    Young professional would be wise to refer to it as Ride Steer or Roll Steer to differentiate whether knuckles are in or out of vertical phase. There is usually a difference between the procedure values and I will leave it to you to discover why that is so.

    And, it is properly characterized as a derivative of steer by roll or ride, not as a simple fraction. The only 'error' in the technical vernacular is referring to it as a percent. That means 0.02 deg/deg at some trim height or roll angle would be called '2 percent'. The nonlinear nature of this mechanism has often been bumped around, but using it in simulation and specification requires more precise nomenclature. You'll find out why whenever you make use of high cornering stiffness tires.

    Same deal for camber.

  6. #6

    Bump steer with compliances

    Additional perspectives

    Bump steer (or Roll steer) could be VERY different with and without compliance.

    Here is a little test to do

    A No compliance; no spring no damper no ARB
    1. Cut a few pieces of wood of 20, 40, 60, 80, and 100 mm.
    2. Put them under your car ideally not too far away from a vertical plane to the ground passing though the wheel center of one axle (front or rear)
    3. For each step measure the toe angle at each wheel
    4. Create a spreadsheet of toe or toe variation Vs ride height or ride height variation (which is the same as wheel movement Vs the chassis)
    5. Use this test opportunity to also measure the camber variation and the damper eye-to-eye length. That will give you your motion ratio.

    B. With compliance
    Drill 2 holes on each side of the car, insert an plastic anchor and a hook in each hole, then put the straps (the ones you use to secure the car on the trailer will do the job) over the car from one hook to another
    Use the straps ratchet to pull the car down.
    Make the same measurements made in test A but this time make sure you also carefully measure the wheel center height variations (taht will gibve you the tire deflection that you will have to subtract from the ride height variations). Or use solid, dummy wheels

    I guarantee you will find VERY different camber or toe or motion ratio Vs ride height curves

    If you do thees measurements make sure you take picture and create a good document to show the design judges.

    If you have scale under each tire that would be better. Warning: read the scale user manual (ahaha again) to amke sure you do not overload the scales. If necessary use 2 scales side by side on which you will have put a piece of wood between the scales and the tire to distribute the tire load on the 2 scales.

    But you will also have to show them how you use these curves in your car design and tuning.

    Also remember that in this test these are only vertical compliance, no major lateral or longitudinal or torsional efforts are exerted on the tires
    Claude Rouelle
    OptimumG president
    Vehicle Dynamics & Race Car Engineering
    Training / Consulting / Simulation Software
    FS & FSAE design judge USA / Canada / UK / Germany / Spain / Italy / China / Brazil / Australia
    [url]www.optimumg.com[/u

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