How Does the Driver Control the Car? ( Introduction to the article in the “Technical Pages”.)

1. How Does the Driver Control the Car?(Introduction to the article in the “Technical Pages”.) • The Driver and Car Handling - accelerating, braking and cornering. • From a control point of view, cornering is the most demanding and interesting for analysis. • A new perspective. Dale Thompson Racing Car Technology www.racing-car-technology.com.au info@racing-car-technology.com.au Note: In vehicle dynamics terminology, cornering or turning of the vehicle is referred to as “yaw” or “yawing” of the vehicle. For more details see our web site at www.racing-car-technology.com.au

2. The Weight Transfer Worksheet • In this web site, we recommend to you our spreadsheet calculations, the Racing Car Technology Weight Transfer Worksheet (WTW). Weight transfer considerations are now common in procedures for suspension tuning. Working with race cars over a number of years, we have shown the WTW can give good results. The WTW remains the only fully tested, fully documented weight transfer “calculator”, that anyone can use. • But it does not represent how the car works. Some will say at this point, “How else could it work?” The predominant view amongst the racing and performance car community is that handling and control must be about the weight transfer and chassis roll. • At universities all around the world, engineers are now taught the “single track model”. The Society of Automotive Engineers have mandated a whole raft of standards and conventions that allow vehicle dynamics engineers to talk the same language. • Using the ideas, we can gain a truer understanding of oversteer and understeer. We highlight how the driver controls the car. • Of the TV show “Top Gear”, How can The Stig drive really, really Fast? This video explains our ideas in general terms. See www.youtube.com/racingcartech. For more details see our web site at www.racing-car-technology.com.au

3. Driver “Feel” for the Car The interaction between the driver and racing car, his feel for the car, is described by Michael Schumacher (circa 1995), "You have to have the senses in your whole body, that come up to your brain, and then, in the end, you have to transfer the information to the steering wheel. It is how you do this that is the difference between drivers, between those who are sensitive, who have more feeling, and those who may be as sensitive but are not able to transfer that into their driving.“ He expresses a level of uncertainty about whether it is the feeling, or what you do with it, that counts. What it is the driver is sensing? How does the driver control the car? We’ll start with what happens to the car in a corner. (The following diagrams are based on the “single track model”) For more details see our web site at www.racing-car-technology.com.au

4. Cornering – Very Slow Copyright C Racing Car Technology 2007 CofG b Vehicle C/L Inst. Dir. Travel R Vehicle path Very slow turning, no “slip angles” at the tyres. The curved path of the CofG is shown. Instantaneous direction of travel is at right angles to turn radius, R.b is the “attitude angle”Car is pointing out from the turn. Instantaneous Turn Centre For more details see our web site at www.racing-car-technology.com.au

5. Cornering – Neutral Steer, maintain the intended path… Copyright C Racing Car Technology 2007 a Vehicle C/L CofG a a Inst. Dir. Travel R b a Vehicle path, Inst. Dir. Of Travel, turn radius, R all the same as previous diagram. But now the lateral force acting on the tyres forces “slip angles”, a , front and rear. The vehicle rotates in the direction of the turn. The car is now pointing into the corner. Vehicle path The neutral vehicle maintains the intended path Instantaneous Turn Centre For more details see our web site at www.racing-car-technology.com.au

6. Cornering – Oversteer, a tighter path.… Copyright C Racing Car Technology 2007 Note: The rear tyres are not sliding a Vehicle C/L CofG a a Inst. Dir. Travel R b a Intended Vehicle Path If slip angles increase at the rear, faster than the front, the car will rotate further in the direction of the turn, increasing the attitude angle, b. The turn radius, R will shorten as shown. The vehicle will steer a tighter path, as shown. Oversteer Vehicle Path Instantaneous Turn Centre For more details see our web site at www.racing-car-technology.com.au

7. Cornering – Understeer, a wider path…. Copyright C Racing Car Technology 2007 Note: The front tyres are not sliding. Understeer Vehicle Path a Vehicle C/L CofG a Inst. Dir. Travel a b R a If slip angles increase at the front, faster than the rear, the car will rotate out of the turn, reducing the attitude angle. Turn radius, R is lengthened, as shown. The vehicle will steer a wider path as shown. Intended Vehicle path Instantaneous Turn Centre For more details see our web site at www.racing-car-technology.com.au

8. Attitude Angle at the Centre of Gravity Rear axle attitude angle Front axle attitude angle Attitude Angle Attitude angle, the angle between vehicle centre line and direction of travel, is also known as “float angle”, “body slip angle”, “beta angle”. It is a function of the front and rear slip angles, as shown in previous diagrams. The attitude angle varies at different points along the centre line of the car. For our purposes, we consider it at the centre of gravity. In the next slide we demonstrate how unbalanced lateral forces at the front and rear tyres will cause a change in attitude angle, and thus be an instant indicator to the driver of the understeer/oversteer balance of the car. For more details see our web site at www.racing-car-technology.com.au

9. Balanced, or unbalanced lateral forces at the tyres… Moments around the centre of gravity will leave us with a net rotational force around the CG. b a CG Front Attitude Angle FR FF For neutral steer, FF x a = FR x b, ie the rotational forces are balanced. FF x a > FR x b, the car is in oversteer – increasing attitude angle. FF x a < FR x b, the car is in understeer – decreasing attitude angle. It is clear from the previous slides that the car is not rotating around the CG. The turn centre is moving and turn radius is lengthening and shortening. For more details see our web site at www.racing-car-technology.com.au

10. Oversteer and Understeer • Maximising grip at all four tyres is the initial aim. So tyre selection, temps, pressures, cambers, toe etc are of prime importantance. But because of the transient nature of handling, (corner entry, mid corner, exit), it also works out we also maximise overall grip with attention to spring frequency - springs, ARB’s and shocks controlling ride, roll pitch rate. • But suspension tuners also have to be able to balance the car for oversteer/understeer - grip of the front wheel pair versus grip of the rear wheel pair as per previous slides. Ideally we look to “stick the loose end” so as to increase overall grip. Sometimes that cannot be done. So for example, we might choose a compromise balance that optimises corner exit acceleration at the expense of some mid corner grip. For more details see our web site at www.racing-car-technology.com.au

11. What’s ahead in the Technical Pages? • The article further explores the notion of the attitude angle being the primary source of feedback to the driver. The driver can feel the change in attitude of the car, over and above the expected attitude angle generated by the vehicle when in neutral steer. The driver is extremely sensitive to the car balance, but largely unaware of overall grip. But give him/her a little extra grip and he will use it and go faster, while reporting the car unchanged. • Although a very intuitive concept for drivers, it remains largely ignored by mainstream suspension tuners and race engineers. This may be because of the difficulty of constructing a reasonable, easy to understand model. By taking a new perspective on understeer and oversteer, as per the diagrams in this intro, we offer a model that can predict and explain the motion of the car. • To get the full article, please subscribe on the front page of our web site. Or contact me direct about subscribing without using Paypal, if you prefer. info@racing-car-technology.com.au For more details see our web site at www.racing-car-technology.com.au