Quote:
Originally Posted by csmith12
Drifting is another example of pivoting that is in between a circle burnout and unicycle, but yet... still a very good example of steering with the rear. Too much gas sends the car in a spinout, too little and the car snaps back inline changing the direction quickly just like a bike.
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From the textbook, drifting is kind of a special case. The driver is manipulating multiple variables at once.
Understeer at steady state is defined as the front tires losing traction before the rear, measured in positive degrees of steering wheel change per g of lateral acceleration.
Oversteer at steady state is defined as the rear tires losing traction before the front, measured in negative degrees of steering wheel change per g of lateral acceleration. The interesting part about oversteer is that there exists some critical speed where an oversteering car is able to complete a steady state corner with 0 steering angle and it continuously slides/rotates with some slip angle relative to the direction it is traveling.
Drifting is unique because the driver intentionally reduces traction at the rear in order to require a large negative change in the steering wheel to keep a constant radius of turn. The driver then modulates both the throttle and the steering input (assuming they're not already at full opposite lock) to manipulate the vehicle's slip angle. We know this is true because the coefficient of static friction between tire and road is always higher than the respective coefficient of kinetic friction. I'm not so sure I'd describe drifting as steering with the rear because by spinning the tires faster or slower (modulating the throttle), the driver is actually changing the amount of both lateral and tractive force at the rear wheel and changing that special critical speed to keep a steady turn radius while sliding. It's not really
steering, per say.
Vehicle dynamics are fascinating and complex. I highly recommend checking out Fundamentals of Vehicle Dynamics by Thomas Gillespie (easy to read and good explainations) or Race Car Vehicle Dynamics by Douglas Milliken (much more technical and harder to follow as a newbie, but is the accepted bible of vehicle dynamics).