More Momentum Maintenance

In my last post I claimed that learning to determine and drive a momentum-maintenance line was one of three basic skills that the beginning autocrosser must acquire in order to Save Time. In this post I’ll give another example, from the same event discussed in the last post, of how I approached a particular section, determined what line I wanted to drive and how I actually drove it as recorded by GPS data.

The course designer was Charles Krampert. Charles posted the course map prior to the event and challenged folks to state how they were going to drive the 180 degree turnaround section. This generated lots of interesting pre-event discussion on the TAC/TVR website (you can see it at http://teamtac.org/e107/e107_plugins/forum/forum_viewtopic.php?104840) with various ideas of how it should be done.

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Figure 1

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Figure 2

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Figure 3

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Figure 4

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Figure 5

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Figure 6

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Figure 7

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Beginning Autocross- What’s Important?

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E-Street 944 I’m Developing

I’ve been thinking lately on what’s most basic and important to Saving Time on the autocross course.

First of all, we have to learn to drive at the limit. Let’s call this Skill #1.

We have to learn to be so sensitive that we can drive right at the maximum capability of the tires and hold it there, or a little below or somewhat above, depending on the need.

Want to be sensitive? You gotta relax. Nothing will impair sensitively like being stiff. Of course, being relaxed while competing is tough. There are some simple signs, like do you have your hands together near the top of the steering wheel? This all but guarantees your shoulders are bunched up, with the bones out of the sockets and you have little sensitivity in your hands. Shoulders need to be relaxed down into the sockets for good connections to the torso to allow the most sensitive control of what happens at the hands.

To hold a car right on the limit, getting every last 1/4 mph out of a sweeper, we’ve got to be sensitive and fast. By fast, I mean we must react fast and early, because a car on the limit is a high-wire balancing act, ready to do something bad (that will slow us down, usually by taking us off our line) at any second. The steering wheel may not move much, but it moves with high-frequency, if relatively small amplitude, motions. As I’ve noted elsewhere, this will produce a smoothly driven car to the outside observer but the driver may feel furiously busy on the inside.

Couple the sensitive, fast hands to steering with the right foot, in order to shift weight forward and back to adjust the line with slight understeer and oversteer and you have basic skill #1 necessary to get the most out of your tires. Right foot steering only works near the limit of tire adhesion. Below the limit the car goes where the tires point. What’s the fun in that?

Skill #1 also includes becoming comfortable with exceeding the tire’s peak capability when needed. For instance, if we need to rotate the car in a corner to exit on the power earlier, then somehow we have to induce the rear tires to take a normally inefficient, excessive slip angle. For a moment. This is why many really good drivers dislike cars that are difficult to rotate. It makes it harder for them to employ a strategy that Saves Time.

Here’s the opposite situation. I rode with a guy this weekend who had an interesting cornering technique. He would take a much too straight and tight line toward a corner, turn late and sharply around the cone, and then mash the throttle. Just past the cone the tires would break loose, the back end would step out, the rear tires would slip with acceleration and then the car would be off toward the next corner. This sort of worked, but he’s still usually last in class.

Why did it work? He runs a late-model, modern sports car with the very capable traction control and stability management on at all times. The car would oversteer a little and the rear tires would spin a little, all under the control of the computer and the car is never going to spin. He had learned to let the computer do about 50% of the turning control and all of the stability and wheel-spin management. I’d never seen anyone use the nannies to such obvious and intentional effect. Do you think he will ever become a fast driver? I don’t either. Not in this lifetime. But, he is relatively safe on a site that has a ditch on one side and poles that can be reached if you are sufficiently crazy/stupid and he’s quite certain his wife would kill him if he damaged the car.

I just tried to get him to open his line up so he didn’t have to brake so much into every turn.

Another aspect of Skill #1: I’ve heard Sam Strano teach a concept called turning at the cones. (No, he doesn’t mean wait ’till we get to the cone to start the turn!) Once I figured out what this meant and was able to do it regularly, I got faster.

I think turning at the cones means, say, when approaching and turning toward an offset gate, we aim the car at the inside cone so that the car’s path, if projected forward and around the arc at that moment, will clearly intersect with and hit the cone.

That sounds kinda stupid, I know. But, here’s the trick: We gotta speed up.

If you speed up then the slip angle of all four tires increases while cornering. The car drifts on a new, larger arc than it would have, an arc that magically passes the car just outside the cone. Without a specific steering input.

In the old days of road racing, when even race tires had huge slip angles, all the corners at race tracks were clearly taken this way. You’ve seen those old movies of races in the 1920’s up through the 1950’s with the car pointing one way but the actual path determined as much by the amount of 4-wheel drift as which way the axis of the car or the front wheels were pointing. We see this a little now in modern-day Drifting competitions, though that type of “drift” used to be more accurately termed a power slide. (They also make it very easy to observe that power sliding from corner to corner, while dramatic, creates a slow way to get around a course.) Modern day Formula 1 cars exhibit slip angles of about 0.0001 degree. They don’t appear to drift at all. This is why mere mortals can’t drive one worth a flip.

I think this drift effect accounts for the common occurrence among the moderately skilled (I include myself in this category) that it requires a slightly out of control run to be fast. It’s easier to carve an arc with a slip angle that is just below or perhaps right up to the most efficient angle for the tire, the angle of maximum lateral G. When you do that you can predict with assurance from the moment of turn-in that you will make the gate. Turning at the cones requires playing on the other side of the peak slip angle. It can be hairy out there. We have to turn-in such that, without a significant amount of 4-wheel drift, we won’t make the gate without hitting the inside cone.

When we say a particular tire is easy to drive, this is what we mean. We can play with the grip on the other side of slip more easily, more controllably. I expect this is why I find the Rival-S easier, and perhaps for me faster, than the RE71R I drove last year, even if it doesn’t produce the better lateral-G number in a skid-pad test.

Skill #2: Driving the momentum-maintenance line

I’ve heard it said that all autocross cars, even super high power-to-weight cars, are momentum cars. I think this is a key insight and mostly true.

I’m not saying there is no difference in driving high-power vs. low-power. If you’re a regular reader you know that I’ve spent a lot of time trying to figure out how different the line should be based upon acceleration capability.

I started autocrossing in a relatively high-power, heavy car (400hp CTS-V) then went to medium weight, relatively high-power car (345hp Corvette) but have now bought a old Porsche 944 with all of 162hp (once upon a time) to drive in E-street. (No, I don’t think it’s the car the have in E-Street.) One of the reasons I did this was because I came to believe that I was never going to master momentum maintenance (in the time available) unless I was forced to by driving a low-power car in a “momentum-maintenance” class. I’m taking advantage of the fact that, for me at least, losing is a great motivator.

To my advantage I have at hand locally one of the greatest masters of momentum-maintenance that ever came down the pike. He headed up Twickenham Automobile Club’s autocross school in Huntspatch last Saturday. I was lucky enough to be invited to attend in the role of an instructor. I think I learned as much as the students I was coaching. I just didn’t get to actually practice the concepts until the autocross the next day.

I don’t pretend to be an expert in the techniques of momentum-maintenance. I’m going to do my best to give you the gist. The school this past weekend showed me how inept at this I am. Give me a couple more years, please. I’m just saying that no matter what class you’re in, you won’t be really fast unless you master the techniques of this skill. Then you can layer other skills, knowledge and techniques on top.

The basic concepts of momentum maintenance, as I understand them, are:

  • Find the simplest, largest radius arcs possible through the tightest, slowest features
  • Work backwards from these largest possible radius arcs to determine the correct approach position so you can drive that large radius arc through the feature
  • Extend these largest possible radius arcs from one feature to the other until they intersect tangentially between the features, usually about half-way in between
  • At the tangent/intersection points turn the steering wheel as fast as possible, within the car’s ability to transition, to produce as much of an instantaneous flip from cornering in one direction to cornering in another direction, just as if you are driving a slalom

Followed with complete rigor, this method of determining the line through a course will produce nothing but arcs, with no straights at all, if the course is tight and busy. Of course, this is not 100% correct 100% of the time, but this is the basic idea. If there’s a long distance between the features then probably the arcs will not intersect. Consider those instances your chance to drive in a straight line, or nearly straight line, remembering that most cars can accelerate fully in 2nd gear and still be turning.

Anywhere the largest possible arcs through the slowest features do not intersect is a distinct advantage to the higher power car or class. Course designers please take note. In fact, it occurs to me that the ratio of total course distance to distance between non-intersecting arcs (or arcs above a certain radius) might be a scientific measure of how much a course favors high-power vs. low-power.

Braking, including trail-braking, and accelerating is generally required only to transition from one radius arc to another, which may include increasing and decreasing radius turns, either explicit in the course design, or implicit in order to connect arcs.

As a real-world example, here’s the starting section of last Sunday’s course, as designed by Charles Krampert:

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First Section of TAC/TVR #4

 

I felt the most important thing in this first section was to enter the increasing slalom at high speed. The slalom cones were offset the easy way and with increasing spacing so it was full throttle for me end to end, equivalent to a road-race corner leading to a long straight. We will be faster everywhere along that straight the faster we exit the preceding corner. The faster we enter the slalom, the more time is saved.

So, the first thing I do is draw the biggest feasible circle that properly leads into the slalom:

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Big Circle To Allow Fast Entrance To Full-Throttle Slalom

Now we know that if we get onto this circle we can enter the slalom at the fastest possible speed, with the limitation of coming from another corner. If the circle were drawn much larger, no way to get onto it from the previous corner.

Next, we work back to the previous corner and draw another circle, as big as possible that connects to the first circle, but that we know will connect to a circle coming before it and meeting about half-way between. This second circle is necessarily a little smaller than the first one, because of the shorter distance to the previous feature. Just like in a slalom, the shorter the distance between cones the smaller the radius of the arcs and the slower the speed for a given lateral-G capability.

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Second Circle Tangent to First

Here I’ve worked back one more circle:

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Third Circle Reaching About Halfway Between Features

 

From the start to the third circle there are only two turns, so two more circles. These two are necessarily smaller because the distance between the features is shorter.

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Five Circles Means Five Turns

Now, we draw the momentum-maintenance line, using the tangentially connected sectors of the circles. This is the line I drove and the line that won the class that day. There wasn’t a straight section anywhere. I lined up to start turning immediately from the staging location.

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Five-Arc Momentum Maintenance Line

We normally have to do this circle drawing in our head at the event and “see” the resulting path in front of us while driving.

Now you know everything I think I know about momentum-maintenance. Please don’t get too excited and tell me, well, you haven’t even mentioned looking ahead, you fool! My instructor told me that’s the most important thing in autocross.

Of course your instructor is correct. You can’t properly drive the line I show above without looking ahead and a lot of other things as well. I just can’t put everything in one post. For now, I want to answer the question, “What am I supposed to be looking ahead at?” The answer is not only the cones in front of you, but the path you want to follow through those cones. That path you have to imagine and project onto the pavement.

Which brings up an interesting point. What if someone invented a heads up display that projected the path in front of the car as an assist to the driver. Would it be legal?

Skill #3 is car setup. Even in Street, the lowest preparation class, this is vitally important.

Not many production cars come off the assembly line optimized for autocross. They don’t even have autocross tires as an option! What are the manufacturers thinking? This is annoying, but just the way it is. So, we have to pick up the slack and optimize the car for autocross as God intended.

I’ve never been in anything but the lowest preparation class, so forget about me writing a book on car setup. Not gonna happen. I started this sport late in life. I don’t have time to learn everything.

But, for the raw beginner, I’ll just list the major things that in general need to be done to a Street class car to produce maximum competitiveness.

  • Install wider than stock, top-performing autocross tires. The right brand/model changes over time, but is always a major discussion topic on the internet.
  • Take advantage of the one sway bar change rule. For RWD and AWD, this usually means a much stiffer front bar. FWD cars often do the opposite.
  • Maximize negative camber within the car’s adjustability. Not many production cars allow so much negative camber (approaching 3 degrees) that it will kill your tires in daily driving.
  • Optimize front and rear toe. This is very car specific, but can be done at the site (with a portable jack) and restored closer to stock for the daily drive to prevent rapid tire wear. Test until you know the best settings for your car. I usually adjust one front tire for some total toe-out, then put it back to toe-in after the event by counting flats while turning the tie-rod. Who cares if the steering wheel is a little off-center during the run? (If you do, you can adjust each side equally. But, ain’t nobody got time for that. You should be walking the course, thinking and planning.)
  • Test until you understand the effect of tire pressure and know the range for best grip. This may vary by site surface, ambient temperature, sunlight, etc.
  • Install high-performance adjustable shocks and test until you know what settings work for what level of site grip and bumpiness and how to adjust to conditions on the fly

For most of us, our only opportunity to test is at the events themselves. This is the big bummer of autocross. We must be willing to give up the near (beating someone today) to seek the far (beating many later.)

The higher preparation classes involve exponentially more knowledge and money to be nationally competitive. Of course, you can be fast, have a fast car and have a lot of fun without being totally committed to getting to the pointy end of the spear at any preparation level.

 

 

 

 

 

GRM Gets Shock Tuning Wrong

Today, I was reading the latest issue of one of my favorite magazines, Grass Roots Motorsports. In an article about setting up a Mustang with high-dollar shock absorbers I found that what the author says about shock tuning is incorrect.

I don’t mean a little bit off, I mean totally backwards.

Like this: “For example, maybe you want to reduce the rate of dive when trail-braking. You can add some compression at the front of the car, but you can also take some rebound out of the back and accomplish a similar goal.”

What?

Since the rear shocks are extending during braking, the complement to increasing compression resistance in the front shocks is increasing rebound damping force in the rears. You wouldn’t “take some out” you’d add more if you want to slow the rate of dive.

At first, I’m thinking that maybe this was just a simple mistake? The part about reducing the “rate” of dive with added compression was right, if not exactly clear why it might be useful.

Then I got to this statement with regard to cornering: “So, if we speed up weight transfer in the front (by lowering the front compression and rebound settings)…” and my heart sank. I realized that this is not a simple mistake in terms but rather a major misconception about what shocks do on a car.

I suspect the author thinks that by “reducing the rate of dive while trail-braking” he thinks things will happen slower and softer and be more controllable. It seems like he thinks that reducing compression and rebound forces will speed up weight transfer across the axle when cornering, or to the front wheels when braking, presumably on the grounds that this frees the suspension to achieve the final, rolled-over state quicker.  Bzzzzt! 40 lashes!

This misconception absolutely guarantees that you can never figure out how to tune your car’s handling by making shock adjustments.

The truth is just the opposite.

This case illustrates a concept that is difficult to grasp and, I’m here to tell you, difficult to explain. I’ve had this discussion several times with various people and I don’t seem to be able to get it across effectively. (I suspect the shock company representative quoted in the article had the same problem with the author of the article.) I see this as a personal failing. I’m going to try again here, in writing. I suspect it’s hard to understand because it’s a dynamic situation that’s over very quickly and, well, like the author says in the article, people just don’t understand what shocks do.  Man, he got that right!

Every time you touch the brakes, move the accelerator in either direction or make even the slightest steering input the shocks do two main things: create forces and absorb energy. Absorbing energy from the oscillation of the springs “damps” the spring (and car) motion and is usually said to be the primary function of the shock (damper).

What shocks do is complex, and we are going to only scratch the surface, but understanding the forces they create is the easy place to start. The textbooks all start with damping. Forget about damping. Forget you ever heard the word. It’s much more important for the autocrosser to understand shock forces first. Focussing on force creation rather than energy absorption is the key insight that I hope will allow me to get my main point across.

Shock absorbers produce forces that always resist motion. They resist pitch, roll and twist of the car. In so doing, they speed up weight transfer and slow down the motion they resist.

This speed-up-weight-transfer/slow-down-the-motion concept strikes many as paradoxical and may be why it get misunderstood. But, really, it’s not very complicated.

Let’s start by imagining we have a car with springs but no shocks.

Now, apply the brakes.

The dive downward that results is resisted by increasing force in the front springs as they compress. (The opposite happens at the rear.) Where does the force go? It goes into the tires. They do the braking, not the springs, right? So, that’s where the forward dive load (forward weight shift) ends up. It goes into the tire contact patches and, as we all know, this increases the braking capability from the front end of the car while reducing it at the rear.  Remember, the additional compressive loads in the springs are “reacted” immediately by the road at the contact patches. There’s no other place for it to go. Newton’s third law, etc.

Now, with just the springs, it would take some finite time, let’s say 2 seconds, for the sake of argument, for the extra load to build up on the tire patches. (I say “extra’ load because the front tires always had their share of the car’s weight on them to begin with.) It builds up linearly with spring compression distance because the springs are generally linear in their action. That’s why one number, the spring rate, can usually describe how they work. 200 lbs increase in force for each inch of compression, for instance, might be the spring rate for each front spring on a stock car. If there are no shocks this is exactly the same thing as saying the weight transfer isn’t complete until the dive motion ends. And you won’t achieve full braking at the front (full load at the contact patches) until the forward dive has reached it’s final position.

This sounds suspiciously like what the author of the GRM article was thinking. Remember, this is with no shocks on the car.

How much weight transfer occurs? If we assume our 200 lb/in spring compresses 3 inches in those 2 seconds, then we’ve got 3 in x 200 lbs/in = 600 lbs of weight transfer to each wheel, or 1200 lbs total that wasn’t there before. That 1200 lbs has been transferred off the rear wheels, of course, which is why rear brakes are smaller in size and heat capacity than front brakes on most cars.

Now, reinstall the shocks and brake again.

The front shocks will develop a compression (bump) force more or less proportional to the rate at which the shock shaft moves (the shock shaft velocity) as the dive begins. This force resists the compression of the shock. These forces can be very high if we want them to be. For instance, a shock could develop 400 lbs at 1 inch per second of shaft speed. (Ok, so it’s a little on the high side of normal practice. Please bear with me.) So, now, when the springs might have compressed 1 inch and the shock shaft is moving 1 inch per second we have 200 lbs of new force from the spring and another 400 lbs of new force created by the shock.  Again, all such force is reacted by the road at the contact patches of the tires. The shock has barely moved, the dive has just begun and we already have our full 600 lbs of weight transfer to each front wheel. All that extra weight that the front tires “feel” came off the rear tires and it got transferred in approximately one-third the time (only 1 inch of motion out of 3 inches total that will eventually occur) as without the shock in place. This is the essence of “increasing the rate of weight transfer.”

The resistance to compressive motion provided by the shocks adds to the resistance from the springs and it happens as soon as the shaft starts moving. It starts to happen early, long before the springs have reached their final, compressed state. Just like the spring resistance created a load increase (weight transfer) into the front contact patches, the shock resistance does the same thing.

Imagine that the front shock has so much resistance to compressive motion that it would only let the shaft move at, say, 1 inch per hour, even if you pushed on it with a million pounds of force. In that case, weight transfer will be essentially instantaneous without hardly any dive motion ever taking place. Hit the brake and the loads at the tire patches instantly increase due to weight shift. A little bit of the load increase (weight shift) comes from the springs, a whole lot comes from the shocks. And essentially no dive rotation has taken place! We need to get this point: thanks to the shocks, weight shift need not be directly coupled with body rotation, either in pitch or roll or combined pitch and roll (twist).

The super-stiff shocks in the thought experiment have now created a kart. You can’t get weight transfer faster than with a solid, non-movable suspension like on a kart. You don’t doubt that weight transfer occurs in karts, do you?

Given this scenario, the car never gets to full compression of the front springs. Not in any reasonable amount of time. But, full weight transfer was achieved (except for the extra that would have happened due to the suspension motion, which is mostly bad anyway, especially when cornering) and it happened fast, long before the springs were ever fully compressed.

Shocks make more of the weight transfer happen earlier by creating forces that resist the shaft motion. They front-load the weight transfer. At the same time, they reduce the rate of pitch or roll, making the car take longer to achieve the final, stable position, on which the shocks have no effect, neglecting the effect of pressure in gas-pressurized shocks.

Do we care how long it takes to achieve the final position? Not much. We got our braking force earlier in the braking process than otherwise. We didn’t have to wait those agonizing 2 seconds for the full dive to occur. That means we stop in a shorter distance.

Yep. Shocks can have a big effect on real-world stopping distances, even though the tires and the brakes haven’t changed. Worn shocks can kill you on the street, not only with increased braking distances but also due to poor handling.

The same thing happens when cornering. The compression damping from the outside shocks and the rebound damping on the inside shocks both create forces that resist roll, slowing it down, and, by doing so, increase the rate of weight transfer across the axles because all forces created are reacted only at, and immediately by, the road at the tire contact patches.

So, one way to tune the car with the shocks is to set how fast we load up the tire patches and to control which ones load up earlier or later than others in the differing conditions of pitch and roll the car encounters. Loading up the contact patches too fast makes the car hard to drive and lose traction due to loss of compliance. You may be forced to slow your hands when cornering for instance, to keep from impacting the tire contact patch so hard and fast that it loses traction.

Too slow is terrible, at least in autocross where transient response is so important. A big difference in load rate front to rear will create an unbalanced car because one end will load up and reach the limit faster than the other end. When that happens, that end of the car starts to slide.

If a car is naturally unbalanced due to other factors, then we may be able to re-balance it with shock tuning.

To sum up, slowing the rate of pitch or roll is achieved by resisting it. To do this we design the shock to create a force that resists the motion of the shock shaft. Resisting shock shaft motion increases the rate of contact patch load change because the resisting force is created immediately with any shaft motion and very quickly reacted (through the structure of the suspension, wheel and tire) by the road at the contact patch. You might say the force is “created” in the shock, “travels” to the tire contact patch and is resisted by the road.

Here’a real-world example of the forces developed by shocks intended for street-class autocross where the springs cannot be changed. These are the force curves for the shocks I’ve been running on my Corvette. The positive curves are for compression and the negative curves are for extension (rebound). At only 1 inch per second of shaft velocity each front shock produces about 220 lbs of force resisting the compressive direction with the adjuster 5 clicks down from the maximum. The rears are a little less. At the maximum adjustment the force values are even higher.

Above 8 inches per second the forces are over 400 lbs in both the compression (bump) and extension (rebound) directions.

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Slalom vs. Slalom

I’ve always assumed that there are parallels to be found between downhill ski competition and autocross. I never bothered to look into it, until now.

Full disclosure: I never became anything more than an intermediate recreational skier. So, you ski-racers out there can comment and tell me where I’ve got it all wrong.

Four main types of ski-racing events seem to exist at the world-championship level. The event called Giant Slalom (GS) most closely parallels autocross, I think. It runs about 1 second between gates, basically the same as an autocross slalom. The distance between gates varies a bit and sometimes there are two gates to pass on one side, but there are ranges for proper course design based on vertical drop. From Wikipedia, based on a formula: “… a course with a vertical drop of 300m would have 33 to 45 direction changes for an adult race.”

Maybe we could learn something about standardized course design for national autocross events from ski-racing.

The second type of event, Slalom, is shorter in length than GS with faster transitions and only about .82 seconds (I saw this number somewhere) between gates. I think this was the first type of ski-racing of the four to be established. Slalom transitions are faster than most, but not all, cars can achieve.

Of the two so-called speed events, Super Giant Slalom (Super-G) I’d say is most similar to Solo Trials and the Downhill is more comparable to road racing. The speed events have gates set farther apart, thus allowing higher velocities, are longer, have big radius turns and not much in the way of quick transitions.

From my brief reconnaissance of the sport, ski-racing technique has evolved rapidly over the last 20 years and maybe much longer. Much of this change has been driven by the evolution of equipment, in particular the advent of scalloped (side-cut) skis. As equipment got better humans have had to adapt technique to take full advantage.

The ski-racing authorities have imposed limits on the equipment to keep things from getting out of hand, to keep things (somewhat) safe. They’ve had to impose minimum ski length and side-cut radii for each of the four types, for instance. They’ve had to change these requirements more than once. We call those “take-backs” in autocross, of course.

Something vaguely similar to equipment limits is happening in autocross. As power-to-weight ratios go up along with lateral-g’s in the lower prep classes, the courses at most venues have to necessarily get tighter to get keep the maximum speeds in the safe range.

In general,  however, I’m not sure we can say that autocross evolution has been much driven by equipment evolution. While street tires have increased rapidly in performance, and street cars certainly handle better straight off the showroom floor than ever before, there have always been race tires and race cars at a much higher level of performance. That’s where most evolution due to technology has occurred. Someone with more knowledge than me will have to discuss whether better race tires have caused evolution in the classes where pure race tires are used.

Not that I think autocross is static. Far from it. I think it has been evolving fairly rapidly over the last 15 years or so. I think the best drivers of today are better than those of 25 years ago. The reason? One word: Data.

It’s almost comical what some people considered gospel 25 years ago. Data has cleared away a lot of the rubbish, the old wives tales, and the many ideas borrowed from the more mature sport of road-racing that just don’t apply to autocross. I think data is still driving autocross (and, for that matter, road racing) evolution today.

So, most of the talk/forums/instruction in ski-racing deals with human technique, and rightly so, especially since there are significant physical dangers in the sport, but there is some thinking about line and course strategy.

For instance, “high and early” vs. “low and late” discussions about apexing gates are common, especially with respect to the best line for beginner vs intermediate vs expert. Most teachers seem to recommend completing about 2/3rds of the turn prior to the gate, except for an expert skier who may do more of the turn after the gate. I’m sure the reader will recognize the direct parallel to autocross. I’ve done quite a bit of related data analysis elsewhere in this blog. Turning high and early is equivalent to late apexing in most peoples’ minds (not mine… I think that phrase should be banned from autocross as it is almost invariably misused) or, more properly, “back-siding the cones.”

I was particularly struck by the thoughts of Bob Harwood in an essay entitled The Road Not Taken- A philosophical approach to line and tactics, published on-line at modernskiracing.com.

Mr. Harwood writes “…what Bode [Miller] has taught us is that the old myth of one right line, the high line, is simply not true. Bode has learned that if he rocks his weight back a bit at the apex of his turn, he can ski a lower, tighter turn and still carve. Bode is able to bend the tail of the ski with more arc to carve a small radius turn with a high degree of confidence. Bode also has an amazing ability to shift his weight forward at the end of a turn so he can initiate the next turn smoothly and not get caught on the back of his skis at the start of the next turn. The end result: Bode’s balance and skills let him ski a lower, straighter line with less chance of DNF-ing than a more tradition skier…”

Sound eerily familiar? Race car driving has often been boiled down to the aphorism “The driver is simply a manager of shifting weight.”

Example: I recently co-drove a BS S2000 at the last two regionals of the year. I’d never autocrossed an S2000 before. The first event I wasn’t particularly fast. I focused on an efficient line and not spinning. (I spun anyway.)

Several places I took too slow of a line and dropped out of VTEC, which you really don’t want to do in an S2000 if you can help it. By the end of the day I had managed to get a feel for how much I could slither the rear of the car and yet not spin. I managed to beat the owner by a small amount but we were both down in the standings… I PAXed 17th of 112 and 8th of 9 in Pro, far down from my average position.

In between events I watched a particular video (here) over and over again. This video shows a split-screen comparison of the best runs of Geoff Walker and co-driver Matthew Braun in an STR S2000 at the 2014 Wilmington champ tour.

Geoff  Walker is one of the guys from an adjoining region that I’ve always considered quite fast. I’ve been trying to match him for years. He trophied in STR at Nationals in 2013, one of the very toughest of classes.

Matthew Braun is simply one of the fastest autocrossers alive with multiple Solo National Championships and podium trophy positions. Lately he’s been 3rd in SSR in both 2015 and 2016, having been the SS National Champion in 2006, 2010 and 2012 and the A-Stock champion in 2003, just to name of few of his accomplishments. I’ve been lucky enough to meet him on occasion.

Walker was driving great, by my standards. As far as I can tell he only makes one slight mistake in the entire run, getting a little bit late in the first slalom. That’s it. Everything else is just perfect. Perfect, that is, until you see what Braun does on the same course.

I see a consistent difference between the two. Braun takes a slightly smaller radius at each offset cone. He then rotates the car while going past and is able to get on the throttle earlier as a result of the car being pointed in the new direction sooner. He walks away from Walker with a higher average speed (and possibly a shorter distance traveled) at every point in the course.

Braun and Miller: Both take a tighter radius by controlling weight shift. Braun manipulates weight over, and lateral forces at, the rear tires and gets them to slide at just the right spot and rotate the car during a tighter radius turn. According to Harwood, Miller manipulates his body weight, bending the rear of his skis more, allowing him to carve tighter at the apex and take a more direct, and thus faster, downhill line. The parallelism between these techniques is striking to me.

Cause and effect are often difficult to sort out in autocross, but the 2nd event in the S2000 I beat the owner by a much larger margin, took 2nd of 6 in Pro and PAXed 6th out of 74. This is about normal for me, maybe even better than normal.

axsm033

 

Zennish Autocrossing Survives!

Two things of note have happened since my last post. One, the Solo Nationals Appeals Committee upheld the decision by the Solo Nationals Protest Committee to reinstate the first 3 runs taken, wet or dry, in the weather-interrupted Heat 5 on the last day of Nationals. Two, Howard Duncan sent out an apology for letting the Steward’s appeal get in the way of awarding trophies to the people who deserved them. Well done and well said, Howard.

Zennish autocrossing survives!

Not only was it affirmed that the Steward did not have the power to invalidate legitimate  runs, it was affirmed that the Steward’s action, which she claimed to be enforcing the intent of the rules, was, in fact, contrary to the intent of the rules.

Did she actually believe otherwise? I doubt it. All indications are this is a woman with significant experience in both driving and officiating autocross. Many of her even more experienced fellow competitors told her she was wrong. She threw out the dry runs anyway. Then they officially disagreed with her by filing multiple protests. She could have stopped it all then, but she did not.

So, the Protest Committee heard the protests and told her she was wrong by upholding four of them and reinstating the runs taken before the delay. By appealing their ruling, she revealed the final act in a misguided attempt to single-handedly change autocross… to make autocross more fair. I’m confident she thinks it was for the good of the sport. What she really did was to attempt an end run around the rules-making process, an attempt which, if successful, might also save some face. Sort of like going to the Supreme Court in hopes of making new law via creative interpretation. Ain’t the way it’s supposed to work, that’s the legislature’s job, but in the words of the comic Judy Tenuta, “It could happen!”

Not taking multiple no’s for an answer, she attempted to get her fairness improvement encoded in an appeals committee ruling. Hoping they would say, “well, it was within her power as Steward and things surely were more fair in the end…” Thank God they didn’t!

Instead, the Appeals Committee said, “…it has long been the tradition and understanding in Solo that the weather “is what it is”…”

They went on to say, “We believe the lack of a rule addressing fairness and changes in weather [especially as the Solo Events Board has declined to enact any such rule when suggested in the past] reflects an intent that changes in weather not be the basis for discarding runs or declaring results “unfair.”

Now go howl at the moon, autocross zen-doggies.