WINE, SONG, AND OTHER DIVERSIONS
FRICTION AND SCRUB
Before I delve into road handling techniques I wish to make a few excursions. I have mentioned scrubbing as
an acceptable form of wheel slip. This is so, because I over-simplified my explanation of static versus kinetic friction.
The transition between static and kinetic friction is not clean. Friction actually increases with a small amount of wheel
slip, after which thermodynamic phenomena take over and friction decreases sharply to the kinetic friction level. Scrub
is the term used to describe that nebulous region between straight rolling, static friction, and complete skidding, kinetic
friction. The scrub angle is the angle between the line through the center of the tire as if it was rolling and the line
created by the path of tire contact with the road. In other
words, scrubbing is when the tires are rolling with a
small amount of lateral slip. The car is still in control
and will still respond to steering input. It will just
respond less sharply than when the tires are not
scrubbing. If you drive smoothly, your car will make a
gradual transition to a state of scrubbing when pushed to
the limit. If you drive smoothly, you will feel this
transition and will be able to handle it accordingly. And
unlike a skid you can make the transition back to pure
rolling when you choose by backing off smoothly.
Smooth cannot be over-stressed. During my first run on
a track, I was at MY limit going into a turn and
panicked, took my foot off the gas and got a panoramic
view of turns 5 through 9. Had I backed off the gas
smoothly I may still have started to lose my rear end, but
it would have been recoverable. Keep it smooth.
(Upon reviewing this I want to clarify one thing. Smooth has nothing to do with slow. When they tell you to "draw the bow smoothly" you do it slowly and evenly. Driving need not be like that. What I want you to do is drive in an analog manner in which you make a fluid transition from one state (direction and/or speed) to another. I know digital is in but if you're going into a 20 mph marked bend at 60 and you yank the wheel, you'll be making a body shop very happy.)
Since I haven't made it clear why I brought this up in the first place, I'll tell you. I wanted you to be aware of a car handling condition which you will notice when your car is at its limit, but which is not bad. Steering response is less sharp, but you are still in control. If you are in control, you're driving correctly.
GETTING IT STRAIGHT
While I was driving the other day I realized that I had forgotten one aspect of steering which can be useful. Due to the front suspension steering geometry of most cars, the steering wheel tends to straighten by itself. While a racing purist would point out that this means that one must always fight this straightening force while steering, there is one benefit to be derived. And particularly since most street cars, including to some extent TVRs, do a self-straightening dance, you might as well make use of it. When you're coming out of a turn let go of the wheel and let the car straighten itself out. You can use the pressure of your hands against the wheel to control the rate at which your car straightens. So, what's the catch? DON'T GRAB THE STEERING WHEEL WHEN YOU'RE STRAIGHT. The rear end of your car might not realize that you've decided that the car is going straight and you'll get a quick lesson on Newton's First Law of Motion. The trick is to know how far your car will straighten at all speeds and to gradually slow the steering wheel down before it stops abruptly by itself, thereby providing a smooth transition between the turning car and the straight car. This way the full straightening process (the car's self-straightening and whatever you need to do to straighten it the rest of the way) will be smooth. My Suzuki Samurai will straighten itself completely at all speeds, so all I do is slow the steering wheel down a bit before I'm straight. My TVR straightens itself to about 30 degrees from straight at average corner speeds, and will getter straighter the faster I am going. This allows me to force the car to straighten itself more by accelerating out of a turn. My Lotus was never taught the word straight so it's crank into the turn and crank out of the turn.
SPIDERS AND TIGHT CURVES
Some of you may have already discovered that spider steering can't get you through some of those tight curves. Shuffle steering may even be inadequate. Smooth, small-increment steering is always important, and what I'm about to discuss is not a replacement. Rather, it is an exception for use when the turn is too tight and the speed too high for small-increment steering. You may have guessed that I'm going to bring up grabbing the wheel with two hands and giving it a twist. The majority of people get through the majority of turns this way, but we're going to modify the method. If you grab the wheel and turn it 135 degrees to the right your hands are now in the 1:30-7:30 position. You're travelling too fast to relocate your hands because you need them to keep you from slipping away. In this position how well can you micro-adjust your steering wheel? You really want to have your hands in the 9-3 position in which you can very easily micro-adjust you turn. Drivers from F1 to autocross accomplish this by gauging the steering wheel angle (call it A) required for the turn and placing their hands A degrees in the opposite direction of the turn from the 9-3 position. This way their arms will only be twisted as they enter the turn. While traveling through the turn, their hands will be in the 9-3 position allowing them to keep their car right in the limit of adhesion. For our 135 degree right hand steer you would place your left-right hands at 4:30-10:30. Turn the steering wheel 135 degrees to the right and your hands will be at 9 and 3.
Next issue I will cover Road Handling techniques (I know you've heard that before). Until next time happy flying.
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