Q: “What I was wondering is how to describe the difference between turning the car and car rotation. We talk about car rotation and using the brakes to effect it, but what is the difference from that compared to turning car with the steering?”
A: Rotating the car involves more slip angle at the rear tires than at the front. Traveling at 5 MPH, for example, the slip angle at the front and rear tires would be equal, and the only thing making the car change direction is the steering angle – the driver turning the steering wheel. At speed – at, near, or over the limit – the car’s balance (load transfer front to rear), and it’s handling characteristics, can result in higher slip angles on the rear tires, and that will result in the car rotating.
Think of rotating a car this way: imagine looking directly down on your car from above, and there is a clockface overlaid on it. Let’s say that you’ve turned the steering wheel enough to make your car point at the 2 o’clock position, but because you’re also trail braking into the corner, there’s more load on the front tires than there is on the rears. That could result in the rear tires having slightly less traction than the fronts — the rear tires have a greater slip angle — and now the car rotates on that clockface so your car is now pointing towards 3 o’clock.
I also look at as the difference between oversteer and rotation is… oversteer is what the car is doing to us; rotation is what we’re doing to the car.
When I was working alongside a number of really great rally instructors, they used to say that the steering wheel was used to “suggest” a direction change, and then everything else was done with the feet. I like that, and it’s related exactly to what you’re asking about.
In the rallycross car I turn the car with the steering wheel, I rotate the car with the brake pedal.
My biggest question on “Rotation” is tire wear… Surely, ‘sliding the rear around’ has to badly scrub off tire surface. Many will say that tires are “Sacrificial” and no one expects them to last for a long time. BUT is the ‘time’ you make up, in fragments of a second, at each turn, eaten away if you have to stop for new tires in the pit? … Or degraded traction as the race nears the end…?
And how much of this “translates” to street Driving. It is similar to “Drifting” in the same way as to Rallye Driving. But many of us do not have “Tire Sponsors” to replace our efforts to “Re-Pave the race Course” with a thick layer of tire rubber…
The amount of tire wear from rotation is minimal, and no more than the wear on the front tires from a little understeer. All of this is based on driving the car to the limit, so I certainly hope no one is reading into what I’ve said as saying you should do this on the street!! And rotation is a long ways from drifting a car. Of course, if you drive below the limits of the tires on the track, you will not wear your tires as quickly as if you drive at the limit. It’s a choice each driver needs to make, and I’m only giving the information so that a driver who chooses to drive at the limit can do so better.