Nats was a wake-up call. My driving discipline broke down.

By discipline I mean the ability to calmly and constantly test for and drive at the limit, given whatever the particular conditions are, even if the limit is getting lower as the run proceeds, and not succumb to the desire to sacrifice position for speed. That means never overdrive and aways let correct position produce more speed.

In the pressure of the moment at Nats I didn’t do that.

So, I was really looking forward to a 2-day event in Columbus, MS followed the next week by the Charlotte Tour, thinking of both as opportunities to practice good driving discipline. This is my plan and goal for the foreseeable future.

The surface at Columbus Air Force Base is clean concrete and the layout is very similar to Peru, if you happen to know that site. On Day 1 of the two day event I had last year’s A-Street national champ as co-driver in my car. We rode with each other the first two of four runs in the morning and the first two of four more in the afternoon. It had been a couple years since I’d ridden with him and, frankly, I was a little shocked at how fast he was in my car. Another wake-up call. I really need to up my game.

Overall, I was reasonably satisfied with how I drove at Columbus, successfully working on being fast and driving at the limit but disciplined and controlled. I was looking forward to Charlotte. My co-driver mentioned that, while my car was very fast (he took top PAX in it) he thought it was a little too loose.

Once at Charlotte and reunited with my regular co-driver, Tom, I asked him if he also thought the car was too loose. He said, a little exasperated, “That’s what I’ve been telling you all year!”

I finally got the message.

I said, “Okay, let’s add some toe-in to the rear.”

“Did you bring toe-plates?” he asked. (Tom had flown in to Charlotte.)

“Don’t need them,” I answered.

I knew that the toe setting was absolutely zero both front and rear on the car having been intentionally set this way after it was repaired earlier in the Spring. (These are the stock toe settings… I’d wanted to try it, though I always used a little rear toe-in on my C5 and sometimes front toe-out) I proceeded to jack up the rear end of the car and put in two flats of toe-in on each wheel. I know from experience that this is enough to make a noticeable change.

The car was clearly easier to drive at Charlotte compared to Columbus. It was more stable at the limit. Once home I measured the new rear toe at 3/32nds of an inch total. My toe plates are 22 inches in between measuring points. This turns out to be a total toe angle of 0.24 degrees. (I use Rob Robinette’s convenient on-line calculator for converting toe inches to degrees.)

While working course on Day 2 at Charlotte I watched the faster ES Miatas not brake at a certain point like the slower cars and instead carry more speed into the section followed by aggressively sliding the car through the next turn, letting the slide bleed off the speed as necessary to make the next feature. The net result was an increase in average speed in that section, but you had to really trust that you could control the slide. I attempted to copy. I’ve always considered that dynamically a Corvette is really just a bigger, heavier Miata except with more power. It worked great and the slide was stable thanks to the revised rear toe setting. I’m not sure it would have been possible otherwise.

I was satisfied with my driving both days and took 2nd in a class of six.

While my car is not set up for CAM-S, neither were two of the other three cars. The only well-set up car per the class rules was the winner by a sizeable margin. I got lucky and snagged the only additional trophy spot.

Nats is well over and done with. I have mixed feelings about it and waited a while before starting to write this post. My results were, well, underwhelming. And well underwhelming, too.

Mental mistakes and driving errors forcibly reminded me that I’m still an amateur, which pisses me off after 12 years in this sport. I once heard the definition of an amateur to be someone who practices until they can do it right.

By contrast, a professional is someone who practices until they can no longer do it wrong.

We don’t get much practice in autocross. Most of us couldn’t afford the tires if we did. (Can you imagine the cost of doing a minimum of 4 hours of practice driving drills a day, 6 days a week, like you must do in any other sport to be good? Now you can understand why several of the best drivers in the sport are tire test engineers.) This means that you must make the most of each run you do get to really develop a disciplined, decisive and consistent driving style that eliminates big mistakes entirely.

That’s not me in autocross. At least not yet on courses as challenging as we had this year at Nats. But, I know what it should feel like. I’ve learned and taught another type of mental/physical endeavor and I remember that it was often difficult to properly demonstrate the wrong way to do things for the students even when it was called for.

Here’s the summary: 1) I was the 2nd fastest B-Street car in the Pro-Solo Finale. (I wish I knew how to put the accent above the “e” in the WordPress editor. Sorry.) That result also gave me 2nd place in the years’ points championship for BS, which was good for a trophy. I admit that a lot of it was luck, plus a smaller than usual number of competitors in BS this year, but I’ll politely take it. The car was great, just like it had been the entire second half of the year once we figured out set-up and pressures.

2) I was 9th of 19 drivers in BS Solo, the SCCA trademarked name for autocross. No trophy and none deserved. Both the car and the driver were terrible. Very lucky not to be at the bottom.

How can the same car on the same tires at the same site be great in one event and terrible a few days later?

For one thing it wasn’t the same site. More on that later. For another thing, don’t ever underestimate the bad effects from a lack of disciplined driving. It’s really so very easy to give up time in big chunks.

The Pro-Solo, which always occurs the weekend before Solo Nationals, is an event for which you must qualify by garnering good results in at least two events during the year, plus there’s an attendance cap set at 275 total competitors spanning all the classes. (Actually only 266 drivers had times this year.) As a result, the surface gradually rubbered-in nicely over the course of two days of competition and the moderate temperatures meant the gap sealant between the concrete slabs largely stayed put in the gaps. I used the wet skidpad to clean the tires after each four-run session, but the grip stayed consistent (or got better as heat built in the tires) during the four runs of each of three sessions. During the last session I was finally able to restrain my over-driving for one run on each side and avoid major mistakes. The other 10 runs of the total 12 were real garbage from poor reaction times to slow 60-foot times, on into mistake-riddled course driving, all caused by emotional, out-of-control over-driving. What a jerk!

So, I squeaked by with an OK result, though way off the winning pace. A real Pro would have done the opposite of me: 10 good runs and (maybe) 2 poor ones. That’s what the BS Pro-Solo Finale winner, Geoffrey Wolpert, appears to have done. (I don’t know how he actually felt about his runs.) Maybe a really top driver, say, an SCCA Driver of Eminence, might have 10 good runs and 2 great ones. (Not that Geoff isn’t a top driver!) I got to interview one of that species, Bartek Borowski, as part of my reporting duties for Sportscar magazine, after he won his 10th National Championship in ES this year. I think I learned something just by talking to him for a moment. About his third run on Day 1 that put him in the lead he said, “Finally under control.” All three runs that day looked perfect and under control to me!

For the Solo competition held during the following four days there were approximately 1100 competitors on the same piece of concrete, half competing the first two days and half the second two days, with, perhaps crucially, much warmer temperatures. My co-driver (who hadn’t driven an autocross in over a month due to requirements of his work) and I ran the last two days. They sweep the surface with a machine each evening, so big chunks of accumulated rubber were never a problem.

What was the problem? I put it into a mock formula: OPR (Other People’s Rubber) + crack sealant + wrong tire type + >80 degrees F = grip that gets worse during each run and from one run to another as a film of rubber mixed with sticky crack sealant accumulates in an ever-thickening layer on the hot tire surfaces as the run progresses.

Even though we had a team of friends helping to jack up the car after every run and remove this layer from the tires with oscillating tool cutters, good grip would only last for the first 1/3rd of each run. By the last third both lateral and longitudinal grip were down nearly 10%. I was unable to mentally adapt to this change and consistently braked too late on corner entry and ran wide at least twice during the 2nd half of each run. The upshot was that I was both slow and hit cones on two of the three runs each day. This was very abnormal for me. I just don’t hit very many cones. Usually.

One of our volunteer tire cutters was also working a competitor’s tires, which were a different brand. (I wanted and tried to obtain that brand, but failed due to shortages.) That car accumulated barely anything, perhaps because of a different rubber compound and perhaps partially because those tires need to be hit with water after each run while my tires need to get quite warm for best grip. So, we used no water. (In retrospect it may have been better if we had watered our tires after each run and kept them as cold as possible, but I can’t be sure how much that would’ve helped. We’d had no way to test for that during the year.)

After Day 1 we knew that for Day 2 we had to be fast, clean and tight on the first run as that would be the only run with anything like the good grip we were accustomed to receive from the car. I was able to get a clean first run, though far from mistake-free. It was just enough to retain a mid-pack position. Unfortunately, my co-driver coned his first two runs, so he had to be super careful on the last one just to take 18th and avoid last place.

I’m anxious to do a lot more events this Fall. Much to work on.

A Word On The Competitiveness of the C6 Base in BS

Several people, both in person at Nationals and other events during the year and on-line, have asked me what I think about the competitiveness of the C6 Base in B-Street. Some of these inquiries came from people not presently in the class but considering joining. I’ve thought some on this question and now have an opinion.

I can say without reservation that in every national and local event I’ve competed in this year, whether it was on asphalt or concrete, with the possible exception of Solo Nationals itself due to the specific course designs and local conditions that were outliers compared with all other courses/events I’ve driven this year, the performance of the C6, the M2, M2C and M3, and the early and late Supra were exactly commensurate with the performance of the driver at that particular event. As far as I can determine, the driver that drove the best on that day won every time. These six cars are very, very close in performance, given the present tire technology and the various strengths and limitations inherent to each car. I just don’t think there’s a lot of course dependency, either. So, at least for this year and next, if you are in a C6 and you drive best you will win.

I would also say that I doubt this situation will remain static for very long. The M2 and Supra in particular are being improved basically each model year, while the C6 will always be what it is. (And I like what it is very much!) Both the M2 and Supra, significantly underrated in power by their manufacturer(1) from the start, now have considerably increased power compared to their initial configurations and with no end in sight. I think that wheel width and tire technology limitations are what keep the C6 competitive for now.

The C6 Base accelerates in a straight line in 2nd gear just as fast as the C6Z06, given equal rear tire diameters, until it runs out of RPM. Both the M2C and the later Supra accelerate significantly faster. But what counts most in regard to power in autocross is how fast you can accelerate beyond the apex of a slow corner, which is a very different and much more complex thing. If either the M2 or Supra got even a half-inch increase in rear rim width the C6 would then be at a significant disadvantage, I believe.

The manual transmission version of the Supra coming out in model year 2023 along with certain suspension improvements intended to make it drive better at the limit may vault it to the top of the class. It could be a class killer. Right up until a newer M2 out-paces it! As one Street Activity Committee member remarked, “B-Street is the wild west!”

(1) I have no idea how BMW is accomplishing this, legally. They have obviously found a loop-hole in the European regulations, whereas the Corvette LS3 engine met the newer SAE standard that required any randomly chosen engine to dyno test within +/-1% of the rated power level under strictly controlled conditions. That Chevrolet was confident they could meet this voluntary standard is a testament to the precision and consistency reached by their V8 engine design, part manufacturing and assembly processes at that time. BTW, the LS7 motor in the C6Z06, when it first came out, was not submitted for certification to this standard.

Most people seem to find the effect of compression forces from shock absorbers and what they do fairly easy to understand. How rebound forces from the shocks affect the car seems to be more difficult. This may be a clue that most of us are thinking incorrectly about what the shocks do during a turn.

Time for a thought experiment. I’m not going to help you out with diagrams or pictures. You can find those lots of places. Consider this a challenge. Just THINK about it.

Say you turn the steering wheel left. The car turns left and at nearly the same time weight begins to shift from left to right. The body of the car, because it is supported by suspension springs, begins to roll to the right. The right-front spring compresses, putting more load onto the right-front tire. The left-front spring extends and removes from the left-front tire. The additional vertical load from the springs on the right-front tire is directly proportional to the extra spring compression. The reduced vertical load on the left-front tire is directly proportional to the reduced spring compression. Voila! We now understand weight transfer. Right?

Are you sure?

Caveat: For the purpose of this thought experiment please forget about the energy dissipation effect of shock absorbers. That amount of energy is small, in any case, and has more to do with how the tires are controlled over bumps, and with controlling resonances of the sprung mass, which we are not talking about here.

Let’s go with this idea a little longer even though most of you already know it’s wrong, or at least incomplete, and consider the shocks.

When the right-front spring compresses the shock is also compressed. The shock resists this motion with a compression force. That force pushes down on the tire via the suspension linkages and up on the body. So, the shock adds to the weight transfer and slows the body roll. There’s more downward force on the right tire while the shock is moving, which is prior to the steady-state condition, so it speeds up weight transfer. Once the body stops rolling the shock force becomes zero but by then it has been traded for spring force and we are steady-state cornering, fat, dumb and happy, as they say.

This is the way I thought about shock forces for a long time and it’s not wrong. But, then I started thinking about the left-side shock during this same turn. It’s extending as we enter the turn as the body begins to roll and is therefore resisting that extension with rebound force. So, it pulls up on the tire, reducing the load at the tire patch and at the same time pulls down on the body of the car, again slowing the roll and, again, somehow speeding up the weight transfer. Note: Rebound forces always pull weight/load off the tire just like compression forces always add weight/load to the tire.

Now I have a question for you: Where did the load go that got pulled off the left tire?

Well, the only place it can go is over to the right tire. That’s the definition of weight transfer. It can’t vanish. It has no buddy it can turn to and say, “Hold my beer.” So, how does it get to the right tire?

Think about that for a minute.

See the problem? How does the load that the left shock picks up from the tire patch get over to the right side and push down on that tire? It’s not the force that the right shock puts down to the right tire. (It would still transfer weight to the right even if there were no compression force in the right shock.) Do all the free body diagrams you want… I don’t think you’ll find it. We think we understand how the right shock pushes down on the tire with compression force, but how does the left shock, all by its lonesome, send weight over to the right?

Maybe it will help to understand or at least appreciate the dilemma if we remove the right shock entirely. The left shock is over there, still resisting the roll of the sprung mass of the car by picking load up from the tire patch, but how does it speed up weight transfer and create a load on the right tire? Magic?

One way out of this thought-experiment dilemma is found by gradually stiffening up the shocks until they won’t move at all. Just replace them with solid bars. You can leave the springs in there, but they can’t do anything if the shock is locked up, right?

Now we have a kart. The suspension cannot articulate. The springs are just dead weight.

Is there any weight transfer when we turn our new kart-like car? Of course there is. Turn the wheel left and it still wants to throw you out the right door. Plenty of weight shift from one side to the other. The tires on the outside of the corner see much higher vertical (and horizontal) loads during a turn even though there is no working suspension.

This is called unsprung weight transfer and it happens faaast, i.e. instantaneously, as long as we neglect the elasticity of the tires and the structure. If the tires produce a lateral force there is instant, unsprung weight transfer. Can’t get faster than that. (Please don’t bring quantum physics into this!)

All cars with a working suspension have both unsprung (fast) and sprung (slow) weight transfer. Sprung weight transfer is often called “elastic” weight transfer and has been discussed previously here.

Springs create (or allow) the sprung weight transfer at the expense of unsprung weight transfer and then add a little extra to the total thanks to lateral movement of the CG as the body rolls. The softer the spring, the more and slower the sprung weight transfer. The full weight transfer cannot be complete until the sprung weight transfer is complete, i.e. the body stops rolling. In the end the total weight transfer is the unsprung weight transfer that happened instantly plus the sprung weight transfer that took a finite amount of time.

If the shock is replaced with a solid bar and prevents the spring from moving then you get the fastest possible weight transfer. Effectively, you have converted the sprung weight transfer (that would have taken some time to accomplish) into unsprung weight transfer that happened instantly. You have also slightly decreased the total weight transfer by eliminating the extra bit that comes from allowing the body to roll.

Now you know the answer: both shocks, left and right, by acting to some degree like stiff, solid bars and resisting body roll during the transient event, temporarily convert some of the elastic, sprung weight transfer into unsprung weight transfer. They speed up weight transfer by “borrowing” some elastic weight transfer from half a second in the future and bringing it into the RIGHT NOW. The stiffer the shock the more like a solid bar, the more like a kart, and the more weight transfer gets borrowed from the future. This also makes it all the easier to dynamically overload the tire.

This is why shock forces that are too high, compression OR rebound, can contribute equally to causing that right front tire to go over its lateral grip limit during turn-in to a left corner and start to slide, producing understeer. It’s the total of the shock forces that matters.

Yes, the extra compression force from the right side shock pressing down on the tire helps to counteract the increase in instantaneous weight transfer. But, similarly, by jerking weight off the left front tire with too high rebound force you can start an oversteer sliding event from the inside tire which then cascades to the outside tire. Maybe some very experienced and sensitive drivers can actually feel the difference between compression-produced understeer vs. rebound produced. I doubt that I can.

Moral of the story: Even if you have near zero of shock force in one direction, say very little compression, if the rebound forces are too high you can make the same bad things happen. And vice-versus.

I’ve been on pins and needles hoping that one of my three orders for rear tires at Tirerack would come through. Finally, a set of 305/30-19 Falken 660s arrived. This will allow me to do another event before Nats. The present tires have 84 runs, so I wouldn’t have run them again until the test & tune course in Lincoln.

I still have an order for a pair of the new 315s, but they are tentatively expected in October, not soon enough for Nats.

One of the other orders was for a pair of Yokohamas. Just got an email from Tirerack saying they are now expected Spring of 2023!

After the last local event we had a good setup. We thought.

Aaaand, we were right!

At Bristol Silver Ghost was great! Grip for miles, transitioned well, no bad habits. I mean, you can provoke understeer if you ask too much, too fast on corner entry, and you can produce oversteer if you give it too many beans on corner exit, but you really have to try hard. You can slither it in the slaloms and 4-wheel drift it around offset cones like nobody’s business.

Pro-Solo

The drivers were not quite as good as the car. At the Pro-Solo I moved from 4th and out of the trophies to a trophy and 2nd place when I finally combined a good start with a good run in the last session. 2nd, 3rd and 4th were extremely close, but we were all far behind first. This is only my second trophy at a Pro. I was pleased to be 3rd on the Masters index, got into the Super Challenge, won the first round and should have won the second, but a 1+ second reaction time (due to forgetting to switch off traction control until the yellow lights were counting down) put an end to the Challenges for me. I lost that challenge match by 0.04s after giving away ~0.40s at the start.

The Pro-Solo courses were unusual, even by Bristol standards. Each side, though not symmetrical, had the longest acceleration zone I’ve ever seen at a national event, good for 80mph for the C6Z06 AS cars on the left side. My car maxes out at 70mph in 2nd gear, so I had to sit on the rev limiter for 1.5s on the left side and 1.0s on the right while my auto-box competition continued speeding up. I expect entering a slalom at 70 to 80mph was a new thing for many drivers…. it sure was for me. Such unusually long, high-speed sections damage fairness both within the class index system and within different cars in specific classes and endanger course workers. I saw a worker run to avoid being hit by a car sliding through what would normally have been a safe location given slower speeds. The car slid directly over the spot where he and others, including a person from my region, had been standing earlier.

Then there were the mid-site bumps, which are always a consideration at Bristol and part of the site’s charm and challenge. In the Pro they were located at the 60-65mph point of the long acceleration zone on both sides. The coneage was incredible. If the driver made an input, or otherwise had the car unevenly loaded when crossing the bumps, the car would take a big hop one way or the other, at the least, or spin, at the most. (My work assignment gave me a perfect rear view of the shenanigans.) The Porsche GT3s had a terrible time of it. The back end would violently bounce. (With the exception of the 96/196 SSP car. That one traversed the bumps relatively smoothly. Better shock valving? Less stiff springs?)* The mid-engined cars were next worse. My front-engined Corvette on Penske’s? After the first round someone asked me how my car was handling the bumps. I answered, “What bumps?” Only after that did I really take note of them while driving. But, on one run my co-driver proved that if you didn’t have the wheel straight when hitting the bumps bad things (like an off-course) would happen even to my car.

Solo Tour

The courses for the Tour event were the best I’ve seen on this site. Kudos to course designers Dave Marcus and Charles Krampert! The day 1 course really kicked my butt. I was a full second off the pace and don’t really know why. If I had to guess I’d say I was slow to appreciate how much speed you could carry through certain sections. Plus, I’m consistently not as fast through slaloms as my co-driver. I think I’ve been slow to find the dynamic limits of the car now that it has such good lateral grip. This put me in fourth place at the end of day 1, one spot and half a second out of the trophies. On day 2 I was right up there, however. I turned in the second fastest time in the class on my second run with a good chance to improve on the third. It didn’t happen. I totally blew the first big turn by entering it too fast after doing it well previously. I’ll present a technical discussion of that turn below. I stayed in 4th and my co-driver took 5th.

First Turn On Day 2

The First Turn on Day 2 was similar to ones I’ve seen several times previously at that location on this site. It’s quite complicated to look at and maybe confuses some people, but the fast way to do it, I think, is simple in theory if difficult to accomplish in practice.

Below is the turn as drawn on the course map, except that I think cone 503 had been removed. The exit was not as pinched as shown below.

I think most of us, with nothing more to go on than the map, would plan to drive this corner something like the dotted line path as shown below. Enter wide, be on cone 523, cross from 523 to 502 as fast and shallow as possible, exit on 502 at the angle that allows maximum acceleration yet still make the 500/501 gate.

In reality there is a complication, i.e. a complex slope. Take a look at the next three figures to see that we have a downward slope from left to right that flattens out in the corner exit path, plus another slope that rises from front to back in the center of the corner.

Section A-A from Fig. 6 shows a slope from above cone 523 down through 502, extending a distance beyond 502 and then flattening out. Section B-B shows another camber from an axis through cones 523 to 502 sloping upward to the rear of the corner as defined by cone 515 and others creating a back wall.(These figures are not to scale. In reality the Sect. B-B slope is less than the Sect. A-A slope.) You may need to think about the sections for a while to understand the two slopes I’m trying to illustrate if you’re not familiar with section views.

What happens to most drivers when they attempt to drive the path shown in Fig. 6 is that the slope shown in Section A-A makes them understeer wide of cone 502, fall down the slope crossing the chalk line with the left-side tires and land in the flat below 502 where they struggle to get turned and then back up the slope toward cone 449 while not hitting cone 501. Therefore, the vast majority of drivers find themselves on a path similar to, or worse than, what I’ve shown in Fig. 8. It feels terrible to an experienced autocrosser. It feels, and is, very slow. I got sucked into this line plenty of times at previous events held on this site. I vowed not to let it happen again!

When walking the course my plan was to take advantage of the slope shown in Sect. B-B. Everyone seems to see and worry about the other, more severe slope, the one shown in Sect. A-A, but taking advantage of the B-B slope seemed to me to be the solution. My thought was to go deeper into the turn, effectively using the discredited “late apex” strategy, but using the B-B camber to help slow the car down in the first half of the turn and increase the efficiency of the entire turn to allow an exit close to cone 502 and at an exit angle that allowed the car to 1) stay on the A-A slope, never venturing lower than necessary and especially not all the way down to the flatlands, and 2) achieve an early acceleration into the next, fairly significant acceleration zone. This would also give the advantage of not spending as much horsepower having to climb back up the A-A slope on the way to cone 449. This planned path is shown in Fig. 9 and is basically what I drove on my first run as verified by data and video.

Below is a video clip of this corner as I actually drove it in Run 1.

Well, the first turn felt pretty good in Run 1. The 180 degree turn in the back of the corner seemed efficient and quick. But, I was way off of the entry cone, cone 523, and thought it could be done better, i.e. shorter. (It always Saves Time to go shorter and slower in a smaller arc than longer and faster on a bigger arc.)

On the next run I tried to do essentially the same thing but wanted to be right on cone 523 and slow down more so that I could turn sharper with less distance traveled. The result was a line similar to what’s shown in Fig. 11, though I over-slowed a bit on entry and flattened out the arc in the middle, meaning that the tires fell below their multi-tasking limit for a moment and costing time. (You can see the double move with the steering wheel.) The clip of the actual run is shown in Fig. 12.

While I think I was faster than most in this corner in Run 1, the path taken in Run 2 was 0.20s faster than Run 1 as measured from the entry braking point to the next braking point.

Let me know in the comments how you think this corner should really have been done! I’d like to hear your thoughts.

One more thing: this is one big reason why the Bristol events are so successful:

• *I later learned that this car had electronic shocks with aftermarket tuning, something only allowed in Super Street class at present.