En kanonartikel som jag hittade här: http://www.napylon.com/
Jag VILL logga så jag kan se min traction circle (den lär vara väldigt taggig o dan iof )



Dr. Strelnieks operates on the North Course

By Byron D. Short

one of my favorite autocrossing oxymorons is "controlled aggression." The idea of aggressiveness on course conjures up images of violence, at least inside the cockpit. I'm sure most of us had ridden with someone who made us perhaps more than a little bit uneasy as they attacked the course with seeming reckless abandon. But when we think of taking a "controlled" drive we think of a rather sedate effort, a drive with great skill to maintain consistency.

Dr. Erik Strelnieks seems to have a good grip on how to execute this seeming conflict in terms. At the 1999 Tire Rack Solo II National Championships, Erik showed exceptional skill, and truly defined "controlled aggression."

If you are a steady reader of this column, you are familiar with the concept of "Usage." Vehicle Usage is a rating which GEEZ software puts on a run by measuring a variety of things all the way around the course. Usage numbers come from the highest of either the closeness to the edge of the implied friction circle, the speed of the transition rate, or, barring those two, the percentage of available forward acceleration.

Essentially this means that the computer figures you'd better be at the edge of the friction circle, or transitioning quickly if you are in the middle of the friction circle. And if neither of those is true, your last resort is to be standing on the gas as hard as you can.

All three of these measurements are expressed as a percentage, and the highest of the three is your Usage score. As you drive around the course your Usage score will undoubtedly use each of the three different metrics at various points. Typically, on most courses, the one used the most is the first: staying at the edge of the friction circle. For a really great explanation of how to stay at the edge of the friction circle, we are going to let the good Dr. Strelnieks take us for a quick spin on Roger H. Johnson's North Course.

Taking a look at Erik's friction circle diagram with the entire course traced into it we see that we have a classic "apple" shape. The sections of the friction circle that incorporate both braking and lateral components together (the areas around 4:30 and 7:30 when you view it like a clock) are fully developed and well rounded. This shows Erik's skill at making his hands and feet work together, by combining braking and steering inputs to keep him at the edge of the friction circle.

of particular note here is the section from 7.2 to 11.4 seconds. As you will see in a moment, this section includes a complete trip around the friction circle in a scant four seconds. It includes Erik's deepest braking point on the course, as he exits the tricky "Great Walls of Topeka" section of the course, and enters the quick two-cone slalom prior to the "Tunnell of Love."

The first thing that strikes me here is just the fact that the doctor exited the "Great Walls" turn with so much speed that he needed this much braking. To exit "Great Walls" with this kind of speed required excellent car control, and early throttle application. But to just stand on the gas would have thrown the car into the walls that Roger H. Johnson put along the outside of this turn.

Note the gentle application of throttle Erik shows from 7.2 to the acceleration peak at 9.3. Now at that peak Erik is putting over 200 rear-wheel horsepower on the ground. Adjusted for driveline frictions and aerodynamic losses this is essentially the peak power the RX7TT is rated to make. And here Erik is making all of that power at a part of the course where most of us were still unsure if it was okay to get on the gas yet! That's aggressiveness!

The application of all of that power begins Erik's full tour of the friction circle. But before we look at that, let's examine more closely Erik's Accel strip chart and specifically the braking spike at 10.75. Note that it's perfectly symmetrical, meaning that Erik released the brake at the same speed he had applied it. However, you may note Erik and the RX7TT are capable of faster transitions from gas to brake. The points on the course at 21.1, 33.1, and 38.7 all show much faster transitions from gas to brake pedal.

So was Erik "lazy" at 10.75, and that's why he failed to maximize the transition from gas to brake? Well, no. He was just aware of the friction circle. At the point that Erik initiated the transition to the brakes, about 10.2, he was already pulling over 1 g of lateral-left acceleration. If he had made the same aggressive stab on the brakes that he made at those other spots he would have attempted to leave the RX7's friction circle, which generally results in a significant slide.

Likewise with the release of the brakes at 11.25 a sudden release of the brakes would have brought Eric's friction circle trace straight up, and kept him from using the full measure of the RX7's friction circle limits. So instead he releases the brakes more slowly while feeding in more steering to stay at the right edge of the friction circle.

For an even more detailed graph of this, look at the inset Friction Circle diagram (labeled "CIRCLE"). This little snippet shows the trace of the friction circle that Erik made from 7.2 to 11.4. With the rest of the run cut away you can really see and admire Erik's perfect circumnavigation of the RX7TT's friction circle.

At the start of the "CIRCLE" diagram, Erik starts out at nearly full right lateral gs coupled with significant forward acceleration. He then traverses counter-clockwise to the full left lateral limit. Erik steps into the brake and blends the release of the turning force with the rise of the braking force, reaching full braking gs at 10.75. Then he gently blends the release of brake pressure to the increase of steering input to keep the trace at the right edge of the friction circle until he's back to his starting point at the top right corner.

Through the entire maneuver, the Doctor stays right on the vehicle's limits. Talk about control! And aggression? How else would you describe that much gas and brake in such a tough section of the course?! If ever there was a good explanation of "controlled aggression," this is it!

This was Erik's second run on Roger Johnson's tricky North Course. His excellent overall score of 90.71% is all the more impressive for his 94% Usage rating, one of the highest I've ever seen in National Championship competition. Although he coned away a slightly faster third run, Erik stood on this fast run to capture the 1999 Super Stock National Championship.

Byron Short is the president of Extreme GEEZ, Inc., and invites your questions and comments by e-mail to bshort@extremegeez.com, or phone at 1-800-775-9511. You may learn more about Extreme GEEZ products at our website, http://www.extremegeez.com.

Här är lite traction circles från Ringen (i GPL )

Citat:

shows Erik's skill at making his hands and feet work together, by combining braking and steering inputs to keep him at the edge of the friction circle.

Det är naturlgtvis detta som skiljer de riktigt duktiga från oss vanliga dödliga.

JohanR