Let’s take an in-depth look at tires and how they affect your driving, beginning with a review of slip angles.
A tire’s slip angle, measured in degrees, is the amount the tire slips sideways while cornering – as your cornering forces and speed increase, the tire ends up pointing in a slightly different direction than the wheel is actually pointing. The angle between the direction the tire is pointing and the path the wheel is following is the slip angle. And, each tire has its optimum slip angle range. Up until that optimum slip angle range is reached, the tire is not generating its maximum traction capabilities. If the cornering speed or steering angle is increased, the slip angle will increase along with tire traction until it reaches a point where tire traction then begins to decrease again.
If you look at a "Slip Angle vs. Traction" graph, you will notice the peak traction limit, or lateral acceleration, is when the tires are in a certain range; for example, 6 to 10 degrees of slip angle. Below 6 degrees, and the tires are not at their limit; above 10 degrees, and they are beyond the limit. Let's look at four hypothetical drivers to see where on the graph it's best to drive.
Our first driver is probably inexperienced, and definitely a little conservative. He consistently drives through the corners with the tires in the 2 to 5 degree slip angle range. The tires are not at their maximum traction limit. Driver 1 is not driving at the limit, and therefore will be slow.
Driver 2 has a bit more experience and is known to be a little on the wild side. He consistently overdrives the car. But what does that mean? Well, he always drives through the corners with a slip angle above 10 degrees. In other words, he is sliding the car too much. It may look great, with the car in a big slide all the way through the corner, but the traction limit of the tires has begun to decrease from maximum. Plus, all this sliding about will increase the temperature of the tires to the point where they are overheated, further reducing the traction capabilities of the tires. Can you think of anyone that drives like this?
Our final two drivers are consistently cornering in the 6 to 10 degree slip angle range. Both are very fast. Both are cornering at about the same speed. Both are driving the car with the tires at the limit. So, what's the difference? Driver 3 is cornering in the upper end of the 6 to 10 degree range – about 9 or 10 – while Driver 4 is around 6 or 7 degrees. Again, the cornering speed is the same, but Driver 3 is sliding a little more than Driver 4, causing more heat build-up in the tires.
Both drivers will run at the front of the pack early in the race, but eventually Driver 3's tires will overheat and he will fade. He's the one complaining at the end of the race about his "tires going off." Meanwhile, our winner – Driver 4 – has gone on, consistently driving with the tires in the 6 or 7 degree slip angle range, and is praising the tire manufacturer for making a "great tire" and his crew for a "great handling car."
The goal, as this example demonstrates, is to consistently drive at the lowest possible slip angle that maintains maximum traction.
And, understand that the difference in speed between cornering with a slip angle of 2 degrees and 12 degrees may be one or two miles per hour – or even less. So, you can imagine how much skill, sensitivity and practice it takes to be able to control the car well enough to stay between 6 and 7 degrees of slip angle! That’s the kind of precise “traction sensing” that the truly great drivers have.
Now, I'm going to contradict myself. Sometimes you have to drive in the upper end of the ideal slip angle range. If the tires are too hard a compound for your car (perhaps they were designed for another type of car), or the track temperature is very low, you may have a difficult time getting the tires to their optimum temperature range. In this case, you may want to slide the car a little more, drive in the upper end of the optimum slip angle range to generate more heat in the tires to achieve maximum traction. The consistent winner has learned to "feel" this and interpret his tire temperature readings, then adapt his driving style to suit.
For more information about Ross’s tips, coaching, eCourses, newsletter, Virtual Track Walk videos, and other resources to help you drive at your best, go to www.SpeedSecrets.com
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