NCR PAX Information

What is PAX?

The PAX (Professional Auto-X) Index has been used by SCCA and other clubs for years. It is a handicapping system that attempts to account for performance differences between car classes, allowing the drivers' performances to be compared. A PAX factor is assigned to each class; the faster the class, the higher the factor. The fastest cars have a PAX factor of 1.000; other PAX factors are a percentage based on performance potential relative to the fastest cars. Each driver's actual time around the course is multiplied by their car's PAX factor to calculate their PAX time. This PAX time is also called their indexed time or factored time. PAX times can then be compared across classes.

It is impossible to come up with a PAX index that is perfect just as it is impossible to come up with a class system that is perfect. Everyone believes that someone else has a softer(i.e. easier) PAX factor.

What is an Indexed Class?

An indexed class is a class that combines several classes into one class and uses factored times to compare the results. For several categories we do not get enough entries to populate the individual classes so we need to combine multiple classes. By forming indexed classes, the factored (aka indexed) times provide a more fair comparison of the results than the raw times.

NCR Autocross uses several indexed classes:

  • The Strict Stock Classes S1-S9 are combined into a single indexed class.
  • The Improved Classes I1-I6 (formerly Classes 13 & 14) are combined into a single indexed class.
  • The Modified Classes M1-M6 (formerly Class 15) are combined into a single indexed class.
  • The non-Porsche Class, X (formerly Class 16), combines all non-Porsches into a single indexed class.




If you are in one of these classes, simply register for the base class, e.g. S7, I2, ... For the non-Porsche class, you enter class X/ + the SCCA class for your car, e.g. X/AS, X/SM2, ...

The NCR PAX Index

The 2008 NCR PAX Index index is based on the 2008 PAX/RTP Index, developed by Rick Ruth, that is based on hundreds of autocross events nationwide. Some explanation of the NCR charts and how we arrived at the numbers we use follows. First for the Production Stock and Strict Stock chart:

Column Description
Class NCR Production Stock and Strict Stock class names.
Models The car models which make up each respective class. This information is from our Autocross Rules.
SCCA Class The SCCA class for each model.
SCCA PAX The SCCA class we use for each of our Production Stock classes. All models which make up one of our classes are generally in the same SCCA class. This makes coming up with a PAX factor easy because we just used the SCCA class PAX For example, three different car models make up our Class P2, but each one of them is in the SCCA E-stock (ES) class, so we use the ES PAX factor).
The SCCA PAX factor for the Production Stock class.
Strict Stock
The SCCA PAX factor for the Strict Stock class. These factors are calculated using a two second handicap over the same production class. This is based on the commonly accepted assumption that the R-compound tires allowed in the Production Classes make a car about two seconds faster.
60 sec Shows the factored time for a 60 second raw time in this class. Here you can see how much time you'll be giving, or gaining, from your friends.

The Improved and Modified charts are similar but these categories are more of a problem because these classes do not map easily to the SCCA classes. However, the Improved Category is similar to the SCCA Street Prepared (SP) Category so we mapped the Improved classes to SP classes although the matching is not exact. The SCCA Prepared and Street Modified Categories are similar to our Modified Category so we mapped our Modified classes to some of these classes. Again, the mapping is not perfect but it does provide a progression of PAX factors allowing for a more equitable comparison of results between the individual Modified Classes that are all included in the indexed class.

For Class X, we simply use the PAX factors for the non-Porsches' SCCA classes.