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throttle and radius

Discussion in 'General' started by Ra.Ge. Raptor, Oct 26, 2020.

  1. Ra.Ge. Raptor

    Ra.Ge. Raptor wanna_be_fast

  2. notbostrom

    notbostrom DaveK broke the interwebs

    This will end worse than airplane on a treadmill
     
    t500racer and turbulence like this.
  3. nlzmo400r

    nlzmo400r Well-Known Member

    Motorcycles in motion have some of the most complicated physics of any vehicle, especially when suspension design is taken into account. The whole 'the bike wants to tighten the radius when the throttle is opened' isn't necessarily wrong, but it's definitely not the complete story.

    Most sportbikes have quite a bit of antisquat geometry built into the rear suspension linkage that will drive the front tire into the ground and extend the rear shock when throttle is applied. The obvious other forces in action during throttle application is chain pull which acts in the opposite direction of the antisquat in addition to weight transfer rearward. Ultimately of course the rear squats under acceleration and weight is transfered away from the front axle causing a reduction in friction and therefore making it impossible for the radius to become tighter when throttle is applied given all other factors remain equal.
     
  4. Ra.Ge. Raptor

    Ra.Ge. Raptor wanna_be_fast

    It's complicated. :D

    The ycrs guys say keep it simple, forget about swingarm angles etc have in mind that more mph results in a wider radius,so maintenance throttle (steady r) untill you can see your exit and truly accelerate, giving away lean angle simultaneously.

    Keep it simple, keep it safe.
    Trying to "steer on the gas" might lead to painful highsides.
     
    mpusch and Monsterdood like this.
  5. Trainwreck

    Trainwreck I could give a heck

    Doesn't the rear raise under acceleration? They seem to on the dyno anyway.

    I've also noticed it on TV when watching SBK. When they are exiting some corners the rear raises a bit and the bike starts to wheelie.
     
  6. cha0s#242

    cha0s#242 Ignorance and prejudice and fear walk hand in hand

    That's because the front is tied down.
     
    Ra.Ge. Raptor likes this.
  7. Banditracer

    Banditracer Dogs - because people suck

    And what happens when you throw an alternative / non fork front end into the mix ? That's another can of worms, should add to the page count. :D
     
  8. Phl218

    Phl218 .

    Or different grip levels front and rear...
     
  9. Ra.Ge. Raptor

    Ra.Ge. Raptor wanna_be_fast

    Or different anti-squat properties of the geometry of the rear suspension/swingarm.
     
    nlzmo400r likes this.
  10. mpusch

    mpusch Well-Known Member



    I'll go with this.
     
    bacolmm, 5axis, 2blueYam and 4 others like this.
  11. Ra.Ge. Raptor

    Ra.Ge. Raptor wanna_be_fast

    Good call :beer:
     
    bacolmm and Monsterdood like this.
  12. nlzmo400r

    nlzmo400r Well-Known Member

    Yes it does, but the force of the chain pull is greater than the force of the antisquat of rear suspension and therefore ultimately the bike does shift weight rearward, not forward.
     
  13. nlzmo400r

    nlzmo400r Well-Known Member

    The front end actually doesn't play a roll under throttle input, so regardless of it being a coil over shock in the front, or a traditional inverted (or non) fork tube setup, the chain pull and antisquat geometry of the rear of the bike is what determines how the weight is transferred rearward.
     
  14. JCW

    JCW Well-Known Member

    https://global.yamaha-motor.com/about/technology/urbanlegend/#no02

    I think there is a split second when you open the throttle before the bike gains any meaningful speed to widen your radius that geometry can be more advantageous to turning. But as the bike gains mph, the bike can do nothing but increase the radius for a given lean angle.

    The rear extending does not eliminate weight transferring from acceleration. In some cases it could increase it due to change in cog height.
     
  15. Ra.Ge. Raptor

    Ra.Ge. Raptor wanna_be_fast

    Exactly at the moment of transition from brake to throttle.
     
  16. Ra.Ge. Raptor

    Ra.Ge. Raptor wanna_be_fast

    Any telemetry guys to tell us what "usually" happens when a sportbike is accelerating?
    Does the rear squat in any case or is it just our perception ?
     
  17. Monsterdood

    Monsterdood Well-Known Member

    Pretty sure it depends on swingarm angle and the height of CG and getting this just right is that ever elusive hunt for corner exit traction.

    The question of what happens as you add speed probably needs to be divided into small speed additions where geometry might be relevant and larger speed additions where basic speed, lean angle and radius are all that matters. This is the basic YCRS r=mph per above posts. I think this is the main principle at work and the minor speed changes and geometry impacts are secondary.
     
  18. JCW

    JCW Well-Known Member

    Alberto naska's video posted above shows his telemetry and the rear extending. His channel has some awesome stuff, imo. A lot of fluff too.
     
  19. Ra.Ge. Raptor

    Ra.Ge. Raptor wanna_be_fast

    around 9:40

    Ducati test rider Alessandro Valia on the advantages of cf wheels regarding mid-corner throttle opening:

    "reduction of the tendency to close the throttle line. what I'm talking about is the mid-cornering phase , when you begin to accelerate and the bike tends to tighten the line on its own"

    the above were mentioned during the Panigale V4 SP's presentation at the "Physics & Motion interactive and didactive laboratory" , dedicated to students and enthusiasts who want to understand how the laws of physics influence the dynamics of motorcycling.
     
    Phl218 and JCW like this.
  20. tophyr

    tophyr Grid Filler

    what
     

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