C6Z06 Solo Nationals Super-Stock/A-Street Competition History

I’ve followed Super-Stock and then A-Street closely over the years. While I’ve never owned an A-Street car, I have co-driven in the class on occasion. A-Street and it’s predecessor Super-Stock have been two of our premier classes with interesting cars, compelling marque competition and they always draw top driving talent.

Charles Krampert, 2021 A-Street National Champion, in his C6Z06 (Photo by Chris Morey)

A-street class has been dominated in recent years by the sixth-generation Corvette Z06 model (C6Z06), so much that people newer to the sport may think this is the way it’s always been. Prompted by comments from some of the old hands I did some investigation to see just how the classes has gotten on since 2006, the first year of the C6Z06.

The first surprising thing that I found is that the C6Z06 never won its class (Super-Stock) at Nationals during its production years from 2006 to 2013. People ran the car during those years but it was beaten over and over again by the Porsche GT3, the Dodge Viper, the Lotus Elise and the C5Z06. For whatever reason, it looks to me like no really top-level driver drove it, either. I don’t know why, but I suspect that the perception was that it just wasn’t quite as good as the GT3, plus it was not cheap.

In 2010 the C6 Grandsport model was released and some top drivers, like Sam Strano, did give that car a try. The Grandsport never won, but Strano came in 2nd in 2011 to Braun in the Elise.

I don’t understand why people thought more of the Grandsport than the Z06. It’s gearing made it only equal to the C6Z06 in acceleration, at best. It weighed significantly more for the exact same tires and the suspension was effectively softer. As a new car it was at best equal in cost (or more expensive) than an early C6Z06. By then the issue with the cylinder heads had become known, but the true extent, cause and the proper fix were not well understood. Maybe this issue kept some people away from the car.

2014 was the first year of Street on 200TW tires and the classes were reconstituted. For the first time the C6Z06 was separated from the GT3 and Elise. The C6Z06 went into A-Street while the other two went into Super-Street and it won at Nats for the first time with Daddio, one of the best autocross drivers ever. C5Z06 cars were 2nd and 3rd, with an S2000CR in 4th. Compared to the “super-200” tires we have now, those first 200TW tires were really pretty bad. You just couldn’t use much power coming off a corner.

In the meantime the GT3 went on a tear in Super-Street, winning in 2014, 2015, 2016 and 2017. In 2018 a GT4 won. In 2019 the new NSX won.

Then in A-Street in 2015 Yom won in a C5Z06, beating Daddio who was again driving the C6Z06. The next year Daddio won A-Street again in his C6Z06 with C5Z06 drivers taking 2nd and 3rd.

In another swap-around in 2017 Frank, in a C5Z06, beat Daddio in his C6Z06 to take the win in A-Street. Beginning to see a pattern? Or the lack of one?

In 2018 C5Z06 cars took 1st and 2nd with a C6Z06 in 3rd. In total, over the first 5 years of Street the C5Z06 won three times vs. two wins for the C6Z06.

It was not until 2019 that the tide began to change. C6Z06 cars took 1st and 2nd. A Cayman S took 3rd and a C5Z06 took 4th. This was the first time that a C5Z06 was not either 1st or 2nd in A-Street.

Nationals were not held in 2020 due to Covid. In 2021 C6Z06 cars took 1st (Charles Krampert in the car in the picture above), 2nd and 3rd. This was the first year you could say that the C6Z06 dominated A-Street, with Cayman GTS drivers in 4th and 5th. C5Z06s were 7th and 9th, driven by excellent but, I think most would say, somewhat lesser talents than some who had piloted that car in previous years, no disrespect intended. The C5Z06 may have finally lost favor, probably due more to the age of the car than any performance reason, except possibly for one thing. 

In my estimation, the courses at National Tours have been getting faster, though perhaps not at Nationals itself. Newer cars in almost all Street classes have been getting more powerful. They have also been getting heavier, but in general the power increases have outpaced the weight increases. I think some course designers have been, perhaps unconsciously, catering to these higher power cars by setting up courses that have at least one location where more acceleration and thus a faster top speed than previously typical can be achieved. The C5Z06 tops out in 2nd gear at about 70mph. Up to that speed it’s a close match to the C6Z06 thanks to its gearing. But, if the course allows a higher top speed, the C6Z06 will continue to accelerate extremely quickly on up to 75mph, even 80mph. The C5Z06 is then at a marked disadvantage as the car either sits on the rev limiter or the driver is forced to upshift. It is rarely advantageous overall to upshift in such a situation unless you can really use 3rd gear for a while. That happens almost never, so it makes sense to favor the C6.

In 2022 C6Z06 drivers took 7 of 8 trophies in A-Street, with a C5Z06 in 5th. The best Cayman S, the same car and driver that took 3rd in 2019, was 10th. Though the courses did not allow the Z06 to use its power advantage, grip ruled on both courses. C6Z06s have more grip than the Porsches, more grip than most anything else in Street, at least as measured by weight to total rim-width ratio. Plus they have a negative camber advantage over the Porsches on the front end, a wider track and probably a lower center of gravity, all things that tend to produce grip. It’s like that old saying, “There’s three things most important in autocross: grip, grip and grip.”

OK, maybe I made up that old saying.

Autocrossing 5 Mid-Engined Porschees*

In the span of two seasons I scored co-drives in several Boxsters and Caymans at local autocross events. I was in between nationally competitive cars, the last being a 1989 944 in E-Street, and wanted to find out if a mid-engined Porsche might be my next autocross tool. In the end, as many of you already know, I bought a 6th generation Corvette after it was moved down from A-Street to B-Street.

The five cars, in the order I drove them, were a 2008 Cayman, a 2005 Boxster, a 2008 Cayman S, a 2011 Cayman and a 2019 Cayman GTS.

The relevant specs are:

-2008 (987.1) Cayman, 2.7ltr, manual trans, stiffer front sway bar, aftermarket struts & stock springs, autocross alignment, near-dead Bridgestone RE71R tires (I think they were 255/285) on 8.5″ & 10″ rims, competing in B-Street

-2005 (987.1) Boxster, 2.7ltr, manual trans, all stock, autocross alignment (of dubious pedigree) well-used 245/275 Hoosier A7 tires on 8” & 9” rims, competing in A-Street-Prepared just because the owner wanted to try R-comp tires

-2008 (987.1) Cayman S, 3.4ltr, manual trans, all stock, autocross alignment, 235 Michelin Pilot Sport tires on an 8” rim in front and 265 Falken RT660 tires on a 9” rim in the rear, competing in B-Street.

-2011 (987.2) Cayman, 2.9ltr, manual trans, Bilstein B8 replacement struts (w/stock springs), stiffer front sway bar, autocross alignment, 245/275 Falken RT660 tires on 8.5″ and 10″ rims, competing in B-Street

-2019 (718) Cayman GTS, 2.5ltr turbo, manual trans, PASM, Sport-Chrono, track alignment, 235/265 Michelin Pilot 4S tires on 8.5″ and 10.5″ rims, competing in Super-Street

2008 Cayman

I drove this car in one event for eight runs in the warm and dry. It had gone through several autocross owners, at least one who had the knowledge to set it up right. It was as sharp as a scalpel, transitioned beautifully, did not push excessively and was held back only by the old tires and low-torque engine. Luckily it was a very tight, super-transitiony course that day with little place to use much power, so I had exactly the right tool for the job and I knew it before the first run. Even so, the start was a straight-up drag race up through first gear and half of second. With the 245hp engine it seemed like it took forever, coming from my C5. After the four morning runs I was top PAX of 61 drivers. In the afternoon I was eclipsed only by a soon-to-be national champ in an A-Street Corvette. Those eight morning runs (with co-driver) seemed to kill the tires once and for all. I was unable to match my morning times in the afternoon, as was the owner.

This car showed me how capable the lightweight, big-tired base Cayman can be. On the right course, anyway.

2005 Boxster

I drove this car in three events for a total of 16 runs, some of which were wet. This car handled very well, felt usefully lighter than the next three cars and did not push. This was surprising and I half-suspect that some previous owner had done something to create this situation, or it could just as easily be a wonky alignment like some toe-out in the rear. (The present owner thinks the suspension is stock and I could not see anything non-stock when I examined it in my garage.) With Porsche Stability Management turned off this car actually tended to oversteer at the limit, so I had to be careful with it at first. Braking was good as was transition speed, though nothing great in spite of the mid-engined design, I was a little surprised to discover. I credit the aftermarket struts and stiffer FSB on the 2008 Cayman (above) for its better transition speed as compared to this car. Being a non-S, everything (springs, shocks and bushings) is probably relatively soft in typical Porsche fashion, but that means excellent grip on our bumpy lot. The 2.7ltr motor is not torquey. Pulling off slow corners was painful.

Thanks to multiple events I got comfortable to where I could really throw this car around, slippin’ and slidin’ even in the wet. It was great fun with the R-comp grip, especially in sections where you can keep the speed up. If this car were in C-Street I might very well run it even though no way it can take the Mazda ND2 MX-5. It’s a much more comfortable and practical car than the MX-5.

The owner (we rode with each other on some runs in each event) was amazed that it was possible to slide the car around, even in the wet on R-comps, and not spin with PSM off. He had developed an almost comical ability (always leaving PSM on, wet or dry) to approach each apex cone way too shallow and fast, wildly throw the car into the turn and allow the stability control to figure out how to prevent a spin. The apex he made for each corner was, therefore, about 15 yards beyond the theoretically correct location. This did not bother him at all! Once PSM had done its magic he’d go on to the next corner and do the same thing over again. When I first rode with him I couldn’t stop laughing. It was almost half-fast.

The car was not competitive in ASP or on PAX, being simply a stock car on R-comps, like the old days of Stock classing before Street.

2008 Cayman S

I was in this car in one event for five runs in the warm and dry. Falken RT660 tires for the front were on back-order so we were running on Michelins with new Falkens in the rear. Slightly sharper handling than the 2005 Boxster, probably due to stiffer springs and bushings on the S model, but it was limited by a push that was easy to provoke on either corner entry or exit, probably exaggerated by the front to rear tire mismatch. Somewhat more torque than the base models, but of limited usefulness in this case due to the corner exit push.

Transition speed was lacking. Could that be down to the relatively narrow Michelins in front instead of the wider Hoosiers on the 2005? I guess so. The 3.4ltr motor still lacks low-end torque coming off really slow corners but feels adequate in the mid-range. This car needed a thicker front sway bar, wider wheels and better front tires, and a more extreme alignment, so it was not representative of what it could be as an autocross machine.

I was faster than the owner but got pounded in the overall standings.

2011 Cayman

In the left seat for one event for eight runs in the dry, cool to warm conditions. This car was a well-prepped example for B-Street, though without the ultra-rare LSD. (I doubt it needs it.)

Handling was sharp, grip was good, transition speed good, could provoke push if you tried hard enough, but corner exit behavior was very nice. Torque is still lacking with the 2.9 and not great gearing (by this time Porsche was putting in their too-high second gears, for some unfathomable, fun-killing reason in their “fun” car) though significantly improved from the older 2.7. I had raced against this car and owner several times in B-Street at regionals against my full-prep C5 and we were always very close. I think he’s one of those rare fast guys who’s never been to a national event. (He has a Lemons team and for all I know he’s done hundreds of regional autocrosses.) We leapfrogged each other every run this day as conditions warmed. I lost to him by a small margin in the end. We were both top 10 PAX at a smallish event.

I think in B-Street I might rather have this 987.2 non-S than a 987.1S, especially if I factor in how much nicer the 2nd-gen cars are in general and how bullet-proof the non-direct-injected 2.9ltr engine has proven to be, but my vision may be clouded by the unprepared 987.1S I drove. I once saw a unicorn 987.2 non-S car for sale, all the right autocross options including LSD and none of the wrong options. For all I know it was the only one made, having been specified by a buyer who wanted the most track-worthy, non-S car possible, for some strange reason. (Maybe he didn’t trust direct-injection.)

2019 718 Cayman GTS

I drove this car in one event for six runs in the dry. This was one of the more difficult cars to autocross I’ve driven, entirely because of the turbo-lag at low rpm in 2nd. It’s quite horrible, even with the variable-geometry turbo. Then, when the huge torque finally comes in (usually so late it’s at the wrong time) it hits like a 2by4 to the back of the head and there’s no telling where you end up. This is a very quick car from corner to corner if the motor is on boost.

In all fairness the owner was definitely better at throttle modulation than I, able to often settle for a smaller amount of boost even though more would have been usable but not practically achievable. Maybe I could eventually master it, though I can’t see myself ever warming to it. The owner says that on the track (where he spends the majority of his time) the lag is much less noticeable because the motor is higher in the rpm range even in the slowest corners. He was amused at my frustration.

This car was clearly the best handler of the five, probably because it was lower, with stiffer springs and bushings and was a later generation chassis. Porsche always continuously improves their models. This car also remained distressingly pushy in spite of dialing in all the camber possible in the front. Why, Porsche, why? Why do you feel the necessity to save us from ourselves even in a GTS model, making it impossible to have a sports-car that’s balanced at the limit without resorting to artificially degrading grip at one end or replacing expensive suspension components? If Chevrolet can give us the adjustability needed in their car why can’t you? Is it because the mid-engined design is too easy to spin at the limit for the typical driver so you must enforce a plow, baby, plow at all costs rule?

We were limited by the marginal grip of the Michelins in the cold of morning, but the 4S tires improved tremendously in the warm afternoon with two drivers. Once warm they were really not far off the Falken RT660 in my estimation. It was an enjoyable car to autocross, in spite of the tendency to push, excepting the awful turbo dynamics. On a high-speed but transitiony course with no really slow corners this car might very well be a match for the C6Z06 in A-Street. But one slow corner and you give away a half-second, easy. (I can’t imagine trying to campaign a base 718 with the non-variable venturi turbo in A-Street… talk about tilting at windmills!) After driving this car I have even more respect for Rachel Baker’s Super-Street win in a 718 GTS at Bristol Tour in 2020 over Foley, a national champion, in a Porsche GT3. I was working course during that heat and she was really driving that thing smoothly, if on a bigger, faster course than I had. Still, it was something I could not do during this first event in the car with some tight corners and maybe never could do. Yes, I’m definitely spoiled by the instant, linear torque of a big naturally-aspirated motor. I bet the 4-liter naturally aspirated motor they put in this chassis later is a revelation.

Summary

-I think that any of the first four cars can be made into a very pleasurable autocross car with proper attention to & knowledge of setup detail. In Street, where more front camber is not available, probably all will tend to pushiness, less you intentionally degrade rear grip, and all will therefore be hard on front tires given the paltry one degree of negative camber available. Maybe testing with a very small amount of toe-out in the rear could produce the best compromise for a skilled driver. Or maybe replacing the rear anti-sway bar with an adjustable unit instead of the front (only one or the other can be replaced in Street class) could be the ticket to balanced handling and reduced roll.

-The turbo GTS will often be frustrating on the autocross course, I think, due to the power characteristics. If it were well-classed maybe we’d learn to live with it in the interest of winning, but it’s not well-classed, so why bother? For contrast, I’ve done some autocrossing in a Mazadaspeed Miata in BSP where class rules limit it to the small, old-school, stock turbo. It has less than 2/3rds as much power but is such a better autocross engine due to the negligible turbo lag given the other modifications that are legal in that class that help it to spool a little faster. (I still don’t care for the non-linear torque curve.) That car is 600lbs lighter, I admit.

-None of these cars can hold a candle to the transitional ability of a Mazda MX-5 ND in spite of the mid-engined design. The Mazda is just so much lighter. They do change direction faster than fifth and sixth generation Corvettes and that’s fun.

-In my totally subjective opinion none of these cars brake as well as the 2011 base C6 Corvette (non-Z51) on Falken RT660s I drove just after the GTS, except maybe the GTS. I really don’t know why this should be. Seems like they should brake better given the weight distribution. Maybe it’s down to pad differences, but braking didn’t seem to be as controllable or direct as the Corvette. C5 and C6 base brakes are, admittedly, marginal on a racetrack in the hands of a decently fast driver. They just don’t have the heat capacity to take lap after lap of hard driving on a course that’s tough on brakes. Corvette track rats must upgrade at least the fronts, but for autocross the Corvette brakes are fine. Porsche brakes typically are much better on-track in my experience and do not require upgrading on a stock or near-stock car for track-days, even in the hands of a fast driver, though we must recognize the horsepower differences. The GTS I drove had full-race pads that were high-torque and quick to bite when warm but with poor modulation characteristics. It was therefore not optimum for autocross, though we were sure to drag the brakes on the way to the start so that we began each run on consistently warm pads and rotors. I think on a softer, less radical pad it would have been fine and a match for the Corvette. The 2011 Cayman had performance pads, but not full race, which should have been perfect for autocross. It had the same front rim width as the C6 Corvette and the same tire, with less camber and less weight in front, yet it didn’t brake as well. The other Porsches were on stock pads. Their braking was nothing to write home about either. I admit that I don’t understand this. I was consistently slightly disappointed in the autocross braking from the first to the last of these five cars. I suspect that it had nothing to do with the brakes and more to do with soft springs and bushings. Possibly the lower polar moment also makes the cars feel less settled under braking as compared to the high-polar moment Corvette, in which case the issue I have has nothing to do with the brakes, per se, at all.

-If the first four cars in the list above were in C-Street I don’t think they could win against the ND2 very often, though it would be great fun to try. Performance-wise the GTS is probably a B-Street car, able to hold its own against the M2 and Supra, probably beat them more often than not. I don’t think it could win very often in A-Street, much less in Super-Street where it is presently classed, but Rachel Baker did it at least once, so what do I know?

-As street cars any of these would be excellent and fun cars to own. I think they’re designed to be tremendously rewarding at 90% effort on a twisty road. I certainly understand that design focus from a business standpoint. I never drive more than 80% to 90% on any public road and I remember to this day how astounded I was by the first Boxster I test-drove, a 1999 model. (This was before I started autocrossing.) I had test-driven the newly redesigned 2003 Honda Accord Coupe off the showroom floor only an hour before. It was getting rave reviews for its handling. It drove like a schoolbus compared to the Boxster.

Only when pushed to the limits of traction do the shortcomings of these cars manifest, but what mass-produced sports car is any different? Certainly, both my fifth and sixth generation Corvettes were much worse cars at 90% as they came from the factory, especially the C5 on those early run-flat tires. I remember when, intending to sell it, I once returned the C5 back to near-stock, including the original shocks that had only 13k miles on them, after autocrossing it fully prepped for B-Street for several years on expensive, specially valved dampers. It felt shockingly bad even though it was not on run-flats any longer.**

*As my wife pronounces the marque

**When I did finally sell it it was aligned well on Koni shocks, had a moderate front bar and had Z06 titanium mufflers with a by-pass mod that made it sound killer without being very loud. It was a much better-driving car at that point than stock.

An Autocross Season- Part 18: Post-Nats Reset at Columbus and Charlotte

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

In CAM-S Grid at the Charlotte Tour. The car to the right is backwards in his spot for a reason. We all jockeyed for position prior to the start of the runs in order to get sun on the tires in the cool conditions.

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.)

The horizontal bar with threads on the right is the toe link that sets the angle of the wheel with respect to the forward direction. Notice the hex section with six flats. This is where the toe angle is set, one link on each side. If you’re careful, you can loosen the lock nut (on the right) and then rotate each link with a wrench the same number of flats and thus keep your thrust angle centered. (Yes, the bottom of the shock shaft needs to be cleaned! The grit-covered o-ring shows that this shock has never bottomed into the bump stop.)

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.

Donna L., unofficial ambassador for CAM-S, with her beautiful C7. She made my co-driver and I welcome in the class. She also stormed back on Day 2, overcoming a Day 1 deficit to my co-driver to take 3rd place.

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.

An Autocross Season- Part 17: Nationals

Walking The Courses At Sunset In Lincoln, Nebraska

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.

Silver Ghost in Bump Class Grid at the Pro: 4 BS drivers and 1 EVX

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.

2nd Place 2022 Points Trophy, Pro-Solo B-Street Class

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!

B-Street Grid At Solo Nationals- Silver Ghost On The Right

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.

Oscillating Tool For Cutting OPR From The Tires

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.)

In Solo Grid, L. to R.: Nick L. and Rachel O., Pit Crew Volunteers, with Co-driver Tom H. Pit crew not pictured were also Charles K., Jessica, and the Goofy Gomers (Dave R. & Mike R.) Big thanks to all for helping Tom and I so much.

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.

Rain On Saturday Morning As We Pulled Off The Site

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.

Compression vs. Rebound- Not What You Think

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 load is removed from the left 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, 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 sped 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. But, then I started thinking about the left-side shock. It’s extending as we enter the turn and 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. 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. 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?

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 shocks 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 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?

The 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 and the springs are just dead weight.

Is there any weight transfer when we turn a kart? Of course there is. Turn the wheel left and it wants to throw you out the right side of the kart. 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 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 itself. 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 it’s a bit complicated to calculate (and has been discussed previously here) but we don’t need to worry about calculating it now.

Springs create (or allow) the sprung weight transfer at the expense of unsprung weight transfer and then add a little extra to the total. 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, 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 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, making it all the more easy to dynamically overload the tire.

This is why shock forces that are too high, compression and/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 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.

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