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Bench Racers Index

In 2002 we introduced the Bench Racers Index (BRI) – a handicapping system used to calculate a “corrected time”, allowing us bench racers to compare our relative performances and talk some trash regarding the amazing results we would have achieved if only . . . . .

Our 2002 handicapping system was based on the PAX (Professional Auto-X) system used by SCCA. We realized from the outset that applying an SCCA system to our PCA classes would have some problems, but what the heck, it was just for bragging rights anyway and it might give us some insight into how to create a system better geared for Porsches. Now that we’ve had several season’s experience with the BRI, we have indeed been able to identify some significant flaws – in spite of which, the winners generally thought the system worked pretty well.

I suppose that if one were smart enough, it should be possible to create a sophisticated model of vehicle performance that accounts for power, weight, tire compound, suspension geometry, brakes, gearing, etc. However most of us are not that knowledgeable, so we adopt a simpler empirical approach to modeling performance based on past race results. The PAX system was built upon a large national database of SCCA autocross results. But since Porsches are not very well represented in the SCCA, we wanted to compile a P-car database using results from our own events. With help from Tom Tweed and Chris Benbow, we have collected results from PCA-SDR events for the past four years. In compiling this database, we focused on the winning times for each class, rather than using the average time of all the cars in the class. We reasoned that the winner’s time is more representative of the performance capabilities of a well-prepared and well-driven car of that class. With this approach, we make no distinction between the different Porsche models running within a particular class; so a 356, a 912, and a 914 running in AS/S will all have the same index this year.

Over the past several years, many of our best drivers have jumped from one class to another as they bought different cars or made modifications to their old cars. There have even been rumors of drivers who may have changed classes looking for a greater (or lesser) level of competition. Being naively optimistic, we had hoped that with so many drivers shifting classes, averaging 4 years worth of race results would tend to even out the drivers’ contributions and we’d be able to identify the performance characteristics of the cars in each class. But real world data is rarely as clean as one might wish and we’re still left with obvious inconsistencies, such as classes in which drivers on street tires were faster than drivers using sticky tires.

Since a handicapping system based strictly on past performance data can lead to unacceptable results; it is necessary to apply some subjective judgements when creating a model that fits the data in some approximate manner. So we attempted to follow a couple of some simple guidelines consistent with the Zone 8 rule permitting a competitor to run in a higher class:
(1) As cars move up in class, the index should reflect increasing levels of performance (FS/S should be faster than CS/S, which should be faster than AS/S, etc.),
(2) As cars within a given class become more modified, the index should reflect an increase in performance potential (prepared should be faster than stock, which should be faster than street stock).
In general, past race results are consistent with these trends, but there are some notable exceptions. We then attempted to fit a simple smoothed surface through the data consistent with these 2 rules. The resulting index is given in Table 1.

All of these numbers are considerably higher than those used in 2002; due simply to the manner in which the race results were normalized. The PAX system creates a ratio relative to the TTOD. We found that the data become more consistent if we use the average winning time for all the classes on that particular day to normalized the data. An index greater than 1 corresponds to a class that’s faster than average and an index that’s less than 1 corresponds to a slower than average class. As before, your corrected time will be simply your actual time multiplied by your class index.

As a sanity check, the 2003 index has been applied to the 2002 autocross and time-trial results. No single model or class dominated the results. Individual events would have been won by everything from a 1965 356 to a 2000 Boxster-S, and from AS/S to AR. Of course we hope that the current BRI is better that its precursor, but it seems certain that we will discover flaws in the new system as the years go along. We’ll certainly try to improve upon it again as we add more years worth of results to to the database. But a certain number of flaws are actually desirable in that they provide us with a ready-made excuse when comparing our correct times with others. Have fun with it, but try to remember that it’s just about bench racing.

Bench Racer's Index Table
Class Autocross Time Trial
ASS 0.961 0.961
ASSL 0.961 0.961
AS 0.986 0.996
ASL 0.986 0.996
AP 1.011 1.021
APL 1.011 1.021
AI 1.042 1.051
AIL 1.042 1.051
AM 1.095 1.095
AML 1.095 1.095
AR1 1.130 1.182
AR1L 1.130 1.182
AR2 1.155 1.222
AR2L 1.155 1.222
CSS 0.975 0.977
CSSL 0.975 0.977
CS 1.000 1.012
CSL 1.000 1.012
CP 1.025 1.037
CPL 1.025 1.037
FSS 0.984 0.986
FSSL 0.984 0.986
FS 1.009 1.021
FSL 1.009 1.021
FP 1.034 1.046
FPL 1.034 1.046
FI 1.059 1.076
FIL 1.059 1.076
GSS 0.990 0.993
GSSL 0.990 0.993
GS 1.015 1.028
GSL 1.015 1.028
GP 1.040 1.053
GPL 1.040 1.053
HSS 0.991 0.996
HSSL 0.991 0.996
HS 1.016 1.031
HSL 1.016 1.031
HP 1.041 1.056
HPL 1.041 1.056
HI 1.066 1.086
HIL 1.066 1.086
ISS 0.992 0.998
ISSL 0.992 0.998
IS 1.017 1.033
ISL 1.017 1.033
IP 1.042 1.058
IPL 1.042 1.058
II 1.067 1.088
IIL 1.067 1.088
IM 1.105 1.130
IML 1.105 1.130
JSS 1.008 1.010
JSSL 1.008 1.010
JS 1.033 1.045
JSL 1.033 1.045
JP 1.058 1.070
JPL 1.058 1.070
KSS 1.011 1.022
KSSL 1.011 1.022
KS 1.036 1.057
KSL 1.036 1.057
KP 1.061 1.082
KPL 1.061 1.082
KI 1.086 1.112
KIL 1.086 1.112
KM 1.125 1.152
KML 1.125 1.152
LSS 1.020 1.016
LSSL 1.020 1.016
LS 1.045 1.051
LSL 1.045 1.051
LP 1.070 1.076
LPL 1.070 1.076
MSS 1.030 1.032
MSSL 1.030 1.032
MS 1.055 1.067
MSL 1.055 1.067
MP 1.080 1.092
MPL 1.080 1.092
MI 1.115 1.122
MIL 1.115 1.122
NSS 1.030 1.044
NSSL 1.030 1.044
NS 1.055 1.079
NSL 1.055 1.079
NP 1.080 1.104
NPL 1.080 1.104
OSS 1.035 1.052
OSSL 1.035 1.052
OS 1.060 1.087
OSL 1.060 1.087
OP 1.085 1.112
OPL 1.085 1.112
OI 1.120 1.147
OIL 1.120 1.147
PSS 1.065 1.084
PSSL 1.065 1.084
PS 1.090 1.119
PSL 1.090 1.119
PP 1.115 1.144
PPL 1.115 1.144
QSS 1.090 1.109
QSSL 1.090 1.109
QS 1.115 1.142
QSL 1.115 1.142
QP 1.140 1.167
QPL 1.140 1.167
QI 1.185 1.202
QIL 1.185 1.202
X 3.000 3.000
944 Spec 1.040 1.040
944 Cup 1.065 1.065
944 Super Cup 1.110 1.110
Boxster Spec 1.040 1.040
Boxster SpecX 1.065 1.065
Cayenne 1.000 1.000