Q: “I get annoyed when people talk about rotating a car in to a corner. To me rotating is something it does when it is out of control, as in “I rotated the car 720 degrees or the car rotated under hard braking.” I’d rather think about differing slip angles. What am I missing?”
A: Sorry to annoy you! To most drivers, the idea of rotating a car is easier to picture than slip angles. Having taught slip angles, friction circles, and all sorts of other bits of vehicle dynamics to thousands of drivers, I’ve learned what sinks in and resonates with the majority of drivers. That’s why “rotating a car” is a phrase I – and most drivers at every level – use.
Question: If the minute hand on a clock moves from the 12 o’clock position to the 5-after position, has it rotated, if even a small amount?
Here’s how I define rotating the car: Imagine looking down on a car from above as it enters a left-hand corner. If, as the car follows the line from the Turn-in to Apex points, the slip angle of the rear tires are slightly higher than of the front tires, the car will appear to rotate like it’s on the face of a clock or compass. In the case of the left-hand corner, it will have rotated counter-clockwise, if only just a few degrees or seconds of the clock. Taken to the extreme, watch World of Outlaw sprint cars. They rotate the car in with dramatically higher slip angles on the rear tires than the front. But on a road racing circuit slip angles are nowhere near that level. It may be so subtle that it’s next to impossible to notice if watching from the outside, but the driver should be able to feel it.
What’s the difference between rotating a car and oversteer? I’m glad you asked! I think of oversteer as something you don’t particularly want, or it’s what the car is doing to you. Rotating the car is a deliberate act by the driver, done to the car. And the reason for rotating the car is to help point it in a direction that allows getting back to full throttle sooner.
I’m sure I’ve either confused you or annoyed you even more with this reply! 🙂