Hello again. I am still here, though my car hasn't moved except for a couple of feet every week to keep flat spots from forming on my tires. Time and money aren't always easy to come by. I'm busy juggling wedding plans, moving to Virginia and job hunting. So, if this part seems rather far from Woodwork, don't worry. It's just me in a time warp. Ever onwards...
A WORD FROM OUR SPONSOR - YOU
I finally got some feedback from people at Woodwork, and there are two comments which I should
address. Our Amish-Indian Slater posed the question (to which I gathered he already knew the answer)
concerning the difference in the line through a curve with a straight in front of the curve versus a straight at the
end of the curve. To qualify my discussion in Part 4 where I discussed driving a single curve, I am only
considering a single isolated curve with a straight both in front of and behind the curve. Also the Part 4 discussion
uses a generic corner whereas there are really two types of corners: a slow corner, and a fast corner. The slow
corner is one you take at slow speeds (it's tight). The fast corner is one you take at fast speeds (it's wide). The
lines for these two types differ some, but the techniques for handling them are quite different and have to do with
how you control the weight of your car through each. The differing techniques, which I will discuss in Part 7,
explain an observation made by Mark Nast concerning cornering in an autocross. Having only autocrossed once
and being more interested in circuit and road driving I never analyzed autocross driving requirements. Basically
an autocross is comprised of lots of slow corners and short straights. For those of you who autocross, next
segment's discussion on slow corners will explain the dynamics of what you are trying to accomplish.
Back to Slater... A discussion of straights with curves belongs in Part 5 under "More Curves," but was completely forgotten in my excitement over explaining the physics of tire adhesion with force ovals.
The shortest distance between two points is a straight line. OK, so you've heard that. When you traverse multiple curves, you generally make a sacrifice of the ideal line through one curve in order to get through another curve in the set. This becomes even more apparent when the series of curves is either preceded or succeeded by a straight. The rule is to give precedence to the faster element of the road. In the case of curves and a straight, the straight is the faster element. Time is made on the straights. So, you've heard that one too. To illustrate what this means, consider two identical corners followed by a straight (and preceded by curves). If the driver takes the first corner using the ideal line for a single corner, the car will have to slow down a lot to make the now tight turn 2 which means that the car will be going slow as it enters the straight (line 1). If the driver sacrifices turn 1 by slowing down more and turning in late, the car will have an ideal entrance into turn 2 and will be able to speed up during turn 2 and exit into the straight at a much higher speed (line 2). Either way, one, or both, of the turns couldn't be taken on the ideal line, so the slower element is sacrificed so that the faster element can be taken advantage of. The philosophy of line 2 also holds for a tight corner followed by a gradual corner, since the gradual corner is the faster element.
Now, let's consider the opposite case where two identical corners
are preceded by a straight (and followed by curves). The best attack is for
the driver to gently turn in early to use as much of the straight as possible. Turn 1 is taken as quickly as possible
while ignoring the fact that there is a turn 2. Turn 2 is then taken tight and slow, but the overall time through the
straight-turn-turn is the quickest obtainable. Like the first example, this basic line holds for a gradual corner
followed by a tight corner.
Get the picture? Now you start considering more combinations of fast curves, slow curves and straights and you get the road you're driving on. Remember, Give precedence to the faster element of the road.
THROWING YOUR WEIGHT AROUND
The force oval we examined last time was for a static tire patch. The purpose in throwing your weight around is to create the most useful tire patches for the maneuver you are executing. Actually, I've been misusing the term "throwing your weight around." People who drive using the point-and-go methodology are throwing their weight around to their detriment (though, not all of the time - more later). What we want to accomplish is the setting of our chassis into a balanced state which provides us with the most beneficial tire patches.
Besides the sloshing of your fuel, oil, and coolant you are not truly moving any weight around your car. What happens to your car as you drive is that you alter the balance of the chassis about the car's center of mass causing differing "weights" to be exerted on the tires causing varying tire contact patches. The center of mass of an object is the point about which all of the mass of the object is equally balanced. If you shot your car out of a cannon the center of mass of your car would trace the same parabola that an equivalent cannonball would travel (neglecting aerodynamic effects). Your car would probably pitch, twist and tumble, but it would do so about the center of mass and the center of mass would not be affected. If you could stand far enough away so that you couldn't see the tumbling of the car you wouldn't be able to distinguish it from the equivalent cannonball by its overall flight path. Whether your car is flying out of a cannon or flying down the road it rolls and pitches about its center of mass causing the weight supported by each tire to continuously change, thereby causing the tire patches to constantly change. (Later in the series I will describe a way to set up your chassis to optimize its balance.)
SEAT OF YOUR PANTS
Drivers take the phrase "driving by seat of your pants" very literally. I didn't emphasize this enough in Part 1 concerning your driving position, but your seat is where your car tells you what is going on. When you start to lose the rear you feel it through the seat. If you're hunched forward hanging onto the steering wheel you won't be able to tell whether it is the car sliding or you being pushed around by momentum. Likewise, if you're using the steering wheel as an oh-shit handle you won't be able to tell how the traction up front is. Driving by the seat of your pants is the best way to get an accurate picture of your car's current balance and traction status.
Next time I will cover car balance dynamics and how to set your car's balance with the brakes and throttle as you go through corners. Until next time happy flying.
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