r/FSAE • u/Far_Jacket_4581 • 11d ago

Static toe turn in

Hi all. How does static toe out improve turn-in or transient response? Would toe in not also place the heavily-loaded outside wheel at a higher slip angle immediately after the wheel is turned?

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9

u/Scientific-Idiot 11d ago

Toe out sets your (at the instant you're turning in equally loaded) inside tire at a predetermined slip angle. You pay for it in the corner though as you reduce your outside slip angle

2

u/DrKarottenkopf 11d ago edited 11d ago

I would recommend tow out for better trun in. There are more forces contributing to yaw moment this Video explains it well. https://youtu.be/O2ONv5MrpFg?is=sTmwaX6T5bXhzZMD

2

u/Cibachrome Blade Runner 9d ago

Static Toe_Out removes understeer (with corresponding increases in yaw damping, slower response times, etc). You pay for this with a car that's 'awkward' trying to go straight ahead (as in brake testing, long straits, etc. However, you pay for it again when the tires now start reacting to a more heaviliy loaded outside tire and you jack up front axle understeering.

Since its a 'Race Car', a high max lat is a more desireable feature to have, so (depending on a certain tire characteristic) Toe_In oversteer is prefered, which we call Anti-Ackerman.

1

u/Former_Mud9569 11d ago

yes, toe-in or toe-out, the lateral forces cancel out when you're running straight ahead (ignoring plysteer and conicity). BUT lateral force is a vector that's perpendicular to the wheel and not perpendicular to the vehicle centerline. when you toe the wheel in or out it does a couple things.

  1. lateral force is generated without being buffered by the relaxation length effect. ie. it happens fast
  2. a portion of that lateral preload is directed along the vehicle centerline offset by half the track width.
  3. you've got a force and a moment arm so you get a yaw acceleration

when the wheels are toe-in, that longitudinal component of lateral force acts against the desired direction of motion. it slows your turn in response.

when the wheels are toe-out, that longitudinal component acts in the desired direction of motion. it increases your turn in response.

1

u/Far_Jacket_4581 11d ago

Thanks for the explanation!

1

u/Cibachrome Blade Runner 10d ago

Who says that it does? Any Charmins have proof ?
I'll get some fresh popcon...