Rotation - Your Primary Sense of Feel in Controlling the Race Car

 

As a racing driver, “seat of the pants” feeling, or feel for oversteer rotation, is a notion you're most likely comfortable with in principle.

But exactly how it fits in with the overall sensing you use in controlling the race car is probably very much up in the air for you.

How can you settle this in your mind when nobody talks about the real mechanics of what’s going on here?

Yet now, you can get all the facts on this important concept of rotation that can transform how you approach your racing.   

Gleaned from the world of race car vehicle dynamics, I am showing you a whole new mindset on your race driving that could help you take your racing to the next level.

Here's a summary of the ideas:

Rotation is a very specific motion of the car that is of most interest in car control. Other motions, such as roll, pitch and lateral G may well be part of the sensing mix but are not felt as precisely.

The rotation motion is a direct message from the tyre contact patch to the driver about the grip availability at the tyres and occurs fast and precisely enough to allow “closed loop control”. Closed loop control works as follows:

Driver feels the excessive rotation -
Driver response e.g. quick counter steer -
Feel stability i.e. can't feel rotation–
Repeat -

By continuing to monitor the rotation and responding accordingly, finer and finer control of the race car is possible. 

• Looking from above the race car, the rotation we are talking about is the rotation of the chassis around a vertical axis through the centre of gravity.
• Rotation is measured in degrees of rotation per second and is known as the yaw rate.
• The driver does not feel a fixed yaw rate as happens in the mid corner (steady state cornering). The driver only feels the angular acceleration, the rate of change in the yaw rate such as we have in the so-called "transitions" of corner entry and corner exit.
• When racing drivers say “rotation”, in respect of driver feeling, we should interpret this as meaning the "rate of change of yaw rate".

Key Insight - Rotation and Tyre Slip Angle

(has not been shown to racing drivers before)

• In the corner entry, as the driver rotates the steering wheel to turn into the corner, the driver can feel this highly nuanced "blip of rotation" as grip builds at the tyres. Looking at the vehicle dynamics involved, we can identify that the tyres are not sliding. The rotation is coming from the generation of tyre slip angle. And further, it is only the rear tyre slip angle rotating the chassis. (Front tyre slip angle does not cause any rotation of the chassis. The driver just steers a little further into the corner and the extra steering is not noticed by the driver.) 
• As the car takes a set in the corner the rotation feeling goes away. The car feels stable.
• But if the car feels nervous, like the rotation wants to go on with it, this is a warning that the car will oversteer unless corrective action is taken. 
• The nature of the connection between slip angle and driver feel is quite eloquently described in this short and sharp quote from the book, "Optimum Drive" by Paul Gerrard.
  

  "Slip angle feels like sliding, but it's actually elastic twist between the contact patch and the rim" (while the contact patch stays stuck to the road) - Paul Gerrard. My words in brackets.

  The idea of the tyre slip angle coming from "elastic twist between the tyre contact patch and the rim" is incredibly insightful and should be at the heart of the way you build out your understanding of rotation and what it means for you in your racing.     

  Can you see where we are going with this? And how this new mindset will help you in:

  • Analyzing your driving and in particular, interpreting U/S O/S balance. (This is brand new. Many of my students have a light bulb moment when shown this U/S O/S insight.) 
  • Giving context and vocabulary to your communication with your team that will empower your discussions about the suspension set-up.
  • Guiding the process of setting up the suspension on your race car through a better appreciation of how handling works.
    
    

  My new on-line training, the “Science of Race Car Driving“, gives you an end-to-end mindset around driving and setting up the suspension on your race car. The role of rotation in your thinking is a new key part of the training.

  To find out more, click on the button:

New Insights on Race Driving and Suspension Set-Up