Question on vehicle dynamic

Discussion in 'General Discussion' started by Comante, Oct 16, 2020.

  1. Comante

    Comante Registered

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    Driving the Radical at Silverstone I encountered a car dynamic that I don't fully understand and thus I don't know how or if can be cured with a little setup change, or driving change.
    Doing Luffield turn I experience this phenomenom: I turn the car to the right, the car "settle" with the back, while the front begin a lateral wobbling, if I apply throttle in the wrong phase the car understeer, if I apply throttle in the right moment, the car take it all and I can manage to exit the turn pretty fast and in line.
    The problem is that waiting for the phase seems a waste of time, anticipating the throttle opening because you see the turn unfold ahead of you into the straight end in a wasted time due understeery outcome.
    Any idea of what is going on?
     
  2. CrimsonEminence

    CrimsonEminence Registered

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    Are your front tyres already warmed up (fully sufficient) in this moment?

    Could be something strange but i almost assume more likely actually something, i call "tyre chatter", when your front tyres aren't fully warmed up, they can lose and regain grip in an interval over and over again and actually result in wobbling/oscillations/little jumpyness at the front. I experienced it with some cars and also had a conversation about it with somebody, confirming me, rF2 actually simulating this behaviour.

    (I always suspected rF2 to lack some features in the tyre model, but i experienced some eye openers, that teached me otherwise, like the Huracan Super Trofeo mod in the workshop, also having a slightly wobbly/jumpy front, when tyres aren't in operational condition, for example. This car even needs actual temp and pressure management, instead of putting pressures to the minimum and go for it, like often in rF2. Also i heard about it in relation to Porsche GT cars, to chatter so much, you can feel it in the wheel in real life.)

    Maybe it's something else (oscillations in the suspension maybe, try 1-2 clicks more damper, especially rebound), but make sure, your front tyres are nice and steady in temps to eliminate this possibility.^^
     
    Last edited: Oct 16, 2020
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  3. Comante

    Comante Registered

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    My feeling is that being the turn a U turn , the left rear suspension has the time to compress fully, unloading the right front. The left front heat quite a lot, this generate an oscillating movement. Probably a stiffer damper in the rear could slow down the suspension, delaying the pumping action. Will make some trials.
     
  4. John R Denman

    John R Denman Registered

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    There are a couple of versions of the Radical. If its the one with the live rear axle (no differential) its probably due to binding.

    Binding is when the slip differential between the inside & outside rear tires are forced to skid through a turn; its almost always the inside rear that skids. Going through a long tight turn the load on the inside rear changes
    1. under braking on entry the rear is light, front has grip
    2. rolling into the apex the load shifts back to neutral as brakes are released, front has less grip
    3. as grip increases on rears binding increases pushing into understeer

    The best way to manage that is to add more rear ARB, less spring rate with a slight height increase. And maybe go the other way on the front; less ARB, more spring. That tends to reduce binding of the inside rear tire.

    Also play with Caster a bit. Increased caster reduces inside rear & outside front corner load a bit as the suspension will actually rise & droop though the turning radius as well as increase/decrease camber angles depending on the adjustment. That's an old karting tuning aid that's relevant to all live axles vehicles.
     
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