Autocross Car Classifications

From the Blog

Autocross Car Classifications

As our autocross schedule continues to not sync well with the Nugget deadlines, a full report on Saturday’s just completed Carlsen Porsche Autocross School, followed by Sunday’s Carlsen Porsche Autocross Series Event #5, will have to wait until next month.   No time for the results to be complied before his Nugget’s deadline.

In brief, however, both events went very well. Nothing but good feedback and complements from the 50 new students introduced to the world of autocross. And many thanks to the indomitable pair of John Seidell and Howard Yao for organizing this event yet again. They’ve been doing it so long none of us can remember how long they’ve actually being doing it. Your efforts are much appreciated, gentlemen!

Sunday’s autocross was also very well attended, with 116 drivers taking times, including many new students from the school.

As Autocross Chair, I field a lot of questions about car classifications for the autocross series, so I’ve been intending to write a more thorough explanation of the process for the web site. I thought I’d take the opportunity of this off month for autocross event reports to address that topic.

First a bit of history. GGR’s autocross series started somewhere in the dim mists of the past, well before written history and perhaps time itself. So the systems for classifying cars into fair and competitive groups has gone through many versions over the years. But the basic concept was always been pretty much the same: divide cars into classes by model, and then further differentiate by the amount of “preparation.” In the GGR lingo, the modification steps were stock, improved, prepared, and finally modified. (And when a finer graduation was eventually inserted between prepared and modified, it was named…what else but “prodified!”) But over the years, as Porsche added more models, multiplied by 4 or 5 modification levels, the system had reached about 40 classes by 2005. With that many classes, any sense of the series being a “competition” was dwindling. A few classes had enough drivers of the same car model and modification level to generate some meaningful competition, but only a few. Everyone else had little or no competition. We reached a point where we had to choose between being a true competition series or a hobby where everyone gets a trophy just for showing up.

A group of long time club members and autocross participants then got together to try to work out a better way. The solution they constructed is our current points-based classification system. The basic concept is simple: assign each car model a base number of points that reflects its performance potential, and then add points for any modifications that increase that potential. Different class are then simply an arbitrary range of points. Within a narrow range of points, no matter how diverse the cars (front engine, rear engine, stock late model, or a highly modified classic), they should all be fairly competitive. How wide or narrow the points range for each class is a simple compromise between the number of classes and the amount of performance variation considered fair within a class.

The base points are established by a formula incorporating three factors: power to weight ratio, model year of the car (the technology incorporated in newer cars makes them inherently faster), and wheel width (reflecting ultimate cornering grip.) The base points vary from 100 for the oldest 356s to 1055 for the 918.

Modifications points were then assigned for all the things usually done to a car to make it go faster: engine modifications, suspension modifications, brake modifications, chassis stiffening, removal of the interior and other lightening schemes, aerodynamic aids, etc, coming to 73 items in total.

Points are also assigned for running wider wheels running tires that are stickier than normal street tires. (Some might wonder why we regulate wheel width rather than tire width. The tire is where the rubber meets the road, literally, so why not directly regulate that? The answer is that tires are made of flexible rubber and wheels are made of rigid metal. It can be very difficult to measure a tire accurately. Where does the tread end and the side wall begin? And tire manufacturers vary greatly in how they label tires. One manufacturer’s 205 width tire could be as much as an inch different from another’s 205. Much arguing can ensue. Wheels, on the other hand, are very consistent. Everybody’s 6” rim measures exactly 6” inside the mounting flanges, regardless who manufactured it. Much simpler, much less arguing.) The oldest Porsches originally came with 4.5” or 5” wide wheels, but anyone interested in performance driving usually ran at least 6” wide wheels. For that reason, 6” wide wheels, front and rear, was chosen as the 0 points level. You gain 10 points for each additional ½” in width above that level.

The tire points are based on the Department of Transportation’s UTQG (Uniform Tire Quality Grade Standards) tread life rating that is imprinted on all tires. This rating varies from around 25 up to around 600. It is intended to be a linear measure of expected tire life. So a tire rated at 200 can be expected to last twice as long as a 100 rated tire. In our system, tires with a rating of 200 or more are considered normal “street tires”, incurring no added points. 101 to 199 gets you 25 points, 50 to 100 gets you 50 points, less than 50 gets you 75 points, and racing tires (which have no UTQG rating) get you 175 points.

The committee’s compromise for the number of classes was fixed at 16. The AX16 class covers cars from 0 to 250 points, AX15 from 250 to 300, and so on, up to AX1 with all cars over 1150 points.

The process for figuring out your car classification is then fairly simple: look up the base points for your model, add the wheel points for your wheel widths, add the tire points for the rating of your tires, and then add modification points for all the performance modifications done to the car. You can look all of this up in the GGR Competition Rules available on the GGR web site, but we also have a special web site, originally developed by the original points system committee, that will step you through the process:

For a highly modified race car, this process might take as much as 5 minutes, but for a stock car, it will be less than a minute. The key of course is having a few pieces of information at your finger-tips: The car model and year, the wheel widths, the tire rating, and then knowing what has been modified on the car. For most people who have bought their car new, or if bought used, have some knowledge that nothing has been changed from the stock configuration, it’s a very simple process. The only situation in which it can be a bit difficult is when acquiring a highly modified car. To be fair to your fellow competitors, you need to put in the effort to discover exactly what has been modified and what is still stock.

No one checks or verifies your classification. We are a club of ladies and gentlemen, and we expect everyone to behave in a fair and sportsperson-like manner. But ultimately, if a competitor in your class suspects that your classification is inaccurate, they can protest your classification. You will then be asked to document and justify your points total.

As simple as I think this process is, there was a contingent in the club who wanted something simpler for those running completely stock cars. So they petitioned for a parallel set of classes called Showroom Stock. These class definitions are taken from the PCA National competition rules used for the Parade Autocross competition. At Parade, they use a total of 13 Showroom Stock classes, but for the convenience of regions using the Parade rules for smaller events, PCA also publishes versions for Small, Medium, and Large regions. We use the Large region version, which compacts the 13 classes down to 7. These are our SS01 to SS07 classes.

To qualify for Showroom Stock, a car must be as delivered from the dealer with no modifications other than factory or dealer supplied options. Tires must have a treadwear rating of less than 180. And only fairly recently manufactured modes are included (a 1989 964 is the oldest car currently listed). The full set of rules for the Showroom Stock classes are available from the PCA web site.

Personally, I’m not a big fan of Showroom Stock classes. I don’t believe classifying a car in the points system is so onerously difficult that a simpler system is necessary, and they are just removing cars from the regular AX classes and reducing the level of competition for all.

46 car models are listed in the Showroom Stock classes. That’s an average of over 7 models per class. How fair is the competition in a class with 7 or more different models? Surely each class will end up with one model that has a significant, is not unassailable, advantage over all the others. It just seems like an inherently flawed and unfair system to me. I have much more faith that the competition in your points system class will be more equitable. But that’s just me.

But finally, you have a third and final classification choice: the FUN class. If you’re not the competitive type, you can always avoid all the above by just running for FUN!  Which is what it’s all about anyway. Whatever classification system you chose; I sincerely hope you’re having a ball.

Don’t hesitate to contact me is you need any help with your classification.

Go Fast!

Andrew Blyholder
GGR Autocross Chair


Remaining 2017 GGR Carlsen Porsche Autocross Series Calendar

Saturday, August 26th – GGR #6, Alameda
Sunday, September 17th – GGR #7, Marina (Zone Event)
Sunday, October 29th – GGR #8, Alameda (Zone Event)
Saturday, November 18th – GGR #9, Alameda



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