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Thread: Tire Analysis Best Approach?

  1. #11
    The Pacejka model isn't the end all, be all either. GM and older Pratt and Miller fits use piece-wise functions to fit the tire characteristics.
    Those work really well too as the tire steady state response is generally able to be categorize as linear, transitional, or frictional for where it is on the curve.


    Bill your steering compliance fit might be representative of some of the FSAE cars I had seen in my day, possibly even polite at that.
    You are just missing the +/- 8 degrees of on-center steering lash.
    Kettering University Vehicle Dynamics
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  2. #12
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    Lash Track

    Quote Originally Posted by MCoach View Post
    Bill your steering compliance fit might be representative of some of the FSAE cars I had seen in my day, possibly even polite at that.
    You are just missing the +/- 8 degrees of on-center steering lash.
    I've got data from a Cup car that was pretty loose, too. These were cases of engine power enhancement by using a dummy pump and also a drive belt that mysteriously would break just before the hood pins were secured.

    But a Corvette R&P valve fitted into a 600 RB gear: Priceless !

  3. #13

    Off track...

    Quote Originally Posted by BillCobb View Post
    I've got data from a Cup car that was pretty loose, too. These were cases of engine power enhancement by using a dummy pump and also a drive belt that mysteriously would break just before the hood pins were secured.

    But a Corvette R&P valve fitted into a 600 RB gear: Priceless !

    Off topic, but I'm still surprised at how much "wind up" is considered acceptable in the steering system with these cars under load.
    If you clamp the wheels or hubs in place and try to steer the car you can get a good +/- 25 degrees of elastic steering wheel angle from center.
    Kettering University Vehicle Dynamics
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  4. #14
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    Put the Pressure on

    Quote Originally Posted by MCoach View Post
    Off topic, but I'm still surprised at how much "wind up" is considered acceptable in the steering system with these cars under load.
    If you clamp the wheels or hubs in place and try to steer the car you can get a good +/- 25 degrees of elastic steering wheel angle from center.
    Is that with the pump motored or with an auxillary hydraulic supply plumbed in ? Otherwise, that's normal for the range of T-bar windup in the valve body. You would be twisting the T-bar up against the stops.

    To edumacate yourself, take a valve body and clamp it in a vise. Then put a Vice-Grips on the pinion shaft and twist away. Under flowrate/pressure conditions and with an input torque, the valve body opens and the pressure pushes the power piston to try to close the valve.

    Think of it as a high capacity power transistor: A little bit of input is amplified to produce a very large output. And you should know what that means: It's an unstable system in the absence of damping (friction) or flow limiting. People complain about the lack of road feel with power steering, but with an "optimized" (get that Z ?) damping setup and very low friction, and nimble fingers, the feel can be totally haptic.

  5. #15
    Quote Originally Posted by BillCobb View Post
    BTW: My admittedly scant search of Round 1 thru 7 tire files seems to indicate that there is really just one good tire and more rim doesn't help it.
    Are you referring to the data itself (I saw on a recent ttc post you we're mentioning some irregularities with data) or are you suggesting there really is one tire to rule them all (by this testing metric).
    Noah
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  6. #16
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    May I have the Envelope, Please ? And the Winner for the FSAE Best Tire Award is Clea

    My challenge is to have you easily answer your own question. I've put together pics of the tools needed to produce a certifiable, high confidence decision. Now its time to discover this for yourself. No need to "optimize" your tire selection. TIRF already has done the hard work.

    Stay tuned to the TTC Forum. I'll show you how to best paddle thru the swamp.

  7. #17
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    Quote Originally Posted by MCoach View Post
    Off topic, but I'm still surprised at how much "wind up" is considered acceptable in the steering system with these cars under load.
    If you clamp the wheels or hubs in place and try to steer the car you can get a good +/- 25 degrees of elastic steering wheel angle from center.
    Like Bill touched on already, these steering systems are just inherently prone to lots of compliance. Not sure what team you are working for, but take a look inside your pumps and see how "stock" they really are. Lots of R&D work has been done on them already just to get them to the level they are at currently. Ultimately I think it's why so many open wheel drivers struggle in stock cars, you really can't trust what your hands are feeling most of the time. Which in a good open wheel or prototype car is not the case.
    Trent Strunk
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  8. #18
    Quote Originally Posted by theTTshark View Post
    Like Bill touched on already, these steering systems are just inherently prone to lots of compliance. Not sure what team you are working for, but take a look inside your pumps and see how "stock" they really are. Lots of R&D work has been done on them already just to get them to the level they are at currently. Ultimately I think it's why so many open wheel drivers struggle in stock cars, you really can't trust what your hands are feeling most of the time. Which in a good open wheel or prototype car is not the case.
    I certainly have seen the internals, and I understand, it's just not the same as a rack. There really isn't a lot of reverse efficiency inherent to the design either. Almost every single part of those pumps been modified from a back yard bottle rocket and made it into a NASA shuttle.
    Kettering University Vehicle Dynamics
    Formula SAE 2010 - 2015
    Clean Snowmobile Powertrain 2012 - 2015

    Boogityland 2015 - Present

  9. #19
    Quote Originally Posted by BillCobb View Post
    My challenge is to have you easily answer your own question. I've put together pics of the tools needed to produce a certifiable, high confidence decision. Now its time to discover this for yourself. No need to "optimize" your tire selection. TIRF already has done the hard work.

    Stay tuned to the TTC Forum. I'll show you how to best paddle thru the swamp.
    Ready to row my boat for sure.

    Worth noting, we have done our own analysis on tires and at least using our methods there are some pretty clear trade offs between compounds and sizes that can make the answer less clearcut.
    Noah
    Student

  10. #20
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    Noah, It's starting to rain ...

    OK, so you have preliminary results for tire model functions. Analyze them with a vehicle dynamics simulation and evaluate their capability and suitability. FSAE car's are not that complicated mechanisms and the tires are essentially mono-ported, so warm up the weapons.

    Now lets get back to that quintessential problem of locking your nuts.

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