Everything you need to know about PAX Factors

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Everything you need to know about PAX Factors

Postby Jeff Thill » Tue Aug 29, 2017 7:20 pm

This used to be a sticky at the top of every year in the forums but somehow it doesn't do that anymore so I thought I would re-post it so its not lost in the shuffle. After writing this back in 2013, Rick Ruth himself and someone at the national level asked to share my PAX/RTP explanation with others, to which I said yes of course. So anyway, I hope you enjoy reading this and now you will know what they are talking about at the race track when they say PAX factors.

Recently it has come to my attention that several people (racers and fans alike) don't know what "PAX Factors" are. So I emailed the current godfather of PAX (Rick Ruth) for some info and did some searching on the internet. I plagiarized most this, changed some things and added some new, to make up as good of an explanation as possible. So read on and enjoy.

What is PAX/RTP?

RTP stands for Racers Theoretical Performance. There used to be an index called PAX, which is no longer used, but people often still use the terms PAX and RTP interchangeably.

PAX stands for Professional AutoX. It was the established Index that was created by Jim McKamey and George Saxton in the 70s. Dave Beck later maintained them. RTP is what Rick Ruth called his index system in the early 90s. When Rick took over the PAX factors (2002), the two systems were combined and enhanced, thus PAX/RTP. Rick toyed with the idea of eliminating the PAX designation, but folks will still always call it that.

PAX/RTP is a (per SCCA Solo racing class, not per car) multiplier that is intended to take the car’s performance out of the equation and rate just the driver. It basically gives you the theoretical time you would have gotten if you had been driving a car in the fastest class, A-Mod. This way you can directly compare times between two different classes. It also allows classes such as Pro and Novice to exist… giving equalized times between drivers of cars with radically different performance potential. In essence, it is a handicapping system designed to even the playing field and let the best drivers, not the fastest cars, get recognition.

Here is how it works. Let's say you have a car that runs in the B-Stock class. Your best time for the last event was 32.301 seconds. B-Stock’s PAX/RTP factor is: 0.845. So you multiply 0.845 by 32.301 and you get 27.294. That is the theoretical time you would have run if you had been driving an A-Mod car. So, say someone in E-Modified (EM) ran a 31.256. E-Mod’s PAX/RTP is 0.928 which gives an indexed time of 29.006. So, even though the E-Modified (EM) car ran a faster raw time than you, you ran a faster PAX/RTP time. In addition, you would have theoretically been faster had you both been driving the same A-Mod car the factor is based off. The theoretical conclusion being, you are a better driver.

So how are there PAX/RTP factors derived? They are developed by Rick Ruth and reflect studies of results from well over 500 nationwide Solo events. Each year new data is collected in the form of results from around the country and the RTP factors are modified to adjust for current trends per class. This data is compiled from the Tire Rack® Solo National Championships, National Tour, Alabama Region, Atlanta Region, Chicago Region, California Sports Car Club, Central Florida Region, Equipe Rapide (Florida & Texas), Great Lakes Solo Series, Hawaii Region, Houston Region, Midwest Divisional Series, Milwaukee Region, Minnesota Autosports Club, New England Region, Northwest Region, Northern New Jersey Region, Oregon Region, Philadelphia Region, Rocky Mountain Series, San Francisco Region, San Diego Region, South Jersey Region, St. Louis Region, Tri-State Sports Car Council, Texas Region, Washington DC Region, Wisconsin Autocrossers Inc., and many, many others.

And Straight from Rick Ruth, he monitors our regions results and uses them when compiling data!!!!! We are honored!!!!! Thank you Rick for doing such a labor intensive job. Our club certainly appreciates it!

Here are the current 2013 PAX/RTP factors for you to review.

SS 0.859
AS 0.847
BS 0.845
CS 0.834
DS 0.826
ES 0.828
FS 0.830
GS 0.816
HS 0.804
SSP 0.871
ASP 0.866
BSP 0.858
CSP 0.861
DSP 0.855
ESP 0.849
FSP 0.838
XP 0.901
BP 0.878
CP 0.862
DP 0.874
EP 0.875
FP 0.877
GP 0.850
AM 1.000
BM 0.962
CM 0.910
DM 0.918
EM 0.928
FM 0.917
FSAE 0.989
SM 0.867
SMF 0.852
SSM 0.881
STF 0.795
STC 0.824
STS 0.829
STR 0.839
STX 0.827
STU 0.846
KM 0.955
JA 0.879
JB 0.842
JC 0.743

If you want to see past years PAX/RTP factors, please visit

Motocross hurts. With age comes a roll cage.
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Jeff Thill
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