P1Analysis Study - 2016 Rolex 24 GTLM Corvette Racing #4
This document examines the exciting IMSA 2016 Rolex 24 race at Daytona
International Speedway through
P1Analysis.com reports
for the GTLM class winning #4
Corvette C7.R,
the hero car in this analysis.
P1Analysis.com is a web subscription service providing its IMSA
WeatherTech SportsCar Championship and
Continental Tire SportsCar Challenge race team
customers with a set of clear, insightful, and timely post-session reports
to help with decision making.
P1Analysis currently consists of the following types of reports,
produced for the listed sessions.
Report Type |
Answers these questions ... |
Session |
---|
Session Summary |
How did your car do in your class? |
R, P, Q |
Race Lapchart |
How did the ranks of the cars change from lap to lap during the race? |
R |
Race Gaps to Hero |
How did the time gaps between you and other cars change during the race? |
R |
Lap Time Trends |
How did every car’s lap times change throughout the race? |
R |
Lap Time Box Plots |
How consistent and what was the range of lap times for each driver? |
R, P, Q |
Sector Gaps to Hero |
How much slower or faster than you were the other drivers sector by sector?
Also within the hero's make? |
R, P, Q |
Pits and Stints |
What pit and driver change strategies did each car use? |
R, P, Q |
Pit Lane Times |
How much slower was your pit service? |
R |
This document describes each of the reports for #4 GTLM hero car and then
analyzes the report information.
http://p1analysis.com's
version of this document has clickable links to the actual reports and pointers to
resources.
Session Summary
The official IMSA WeatherTech SportsCar Championship Race Summary
that teams receive,
merges all 54 cars from all four classes, P, PC, GLTM, and GTD creating a
report suitable for seeing the overall results. While this view is
great if you are an official or broadcaster, it is less useful if you are on
a racing team where you are primarily concerned about your class's race.
The Session Summary report allows you to quickly see summary
information on just the 11 cars in the GTLM class. It additionally reveals
per-driver summary statistics.
Note that unlike the official results, all P1Analysis reports are generated
from raw timing and scoring data and therefore cannot take into account
any penalties or other human updates and corrections that may affect a
report.
Race Lapchart
The race lapchart displays the ranks of the cars within your class
during a race. By using overall rank on the y-axis, it possible to
see both overall and class rank. Furthermore, rough clusters
of cars within your class might otherwise be hidden if the y-axis only
plotted class rank.
- The x-axis plots each lap. This chart has lap-level fidelity.
- The y-axis plots the overall position for each car in the class.
- Although the y-axis represents overall position, we can easly see
that within GTLM, #911 has pole position while #4 finishes P1.
- While there is a main grouping of GTLM cars in successive positions,
we can easily see the cars that encounterred problems, as they fall
below the main grouping.
- Crossing lines represent an overtake at that time.
- Pit stops are marked with circles.
- This chart usually has little value during non-race sessions and is not
produced for those sessions.
Race Gaps to Hero
The race gap chart displays the time gaps between your #4 hero
car and the other cars in your class during a race.
- The x-axis plots the session time. All data observations are
for start/finish.
- The y-axis plots the total time gap other cars are ahead or behind
your hero car.
- The hero car is thus represented by horizontal
y = 0 line (green).
- Cars ahead of you, appear above your line.
- Cars behind you, appear below your line.
- Pit (in) stops are marked with circles.
- Caution periods are marked by yellow (there are 21!) or red (0)
vertical bands.
- The legend along the right hand side is ordered by finish position.
- This chart usually has little value during non-race sessions and is not
produced for those sessions.
Analysis
The GTLM race was very close throughout most of the 24 hours, as seen by the
very close lines weaving around the winning #4 hero
(green) above.
Notice the upper right corner of the chart. Just before the last yellow,
#4 (green) was furthest behind
912 (magenta),
#3 (olive),
#68 (blue), and #25
(brown), but still on the lead lap.
Since the chart is a PDF and not a bitmap, you can zoom in on any
section.
- Hero #4 pits 4 times in the end race, including a
"second" stop during the last yellow, while #3 does not
pit under last yellow.
- We can see that #3 sister car has faster pace by its
positive (upward) sloping gap line relative to the hero.
- #3 is P3 after his last pit stop, but shortly passes
912 and battles with #4 until the
finish.
Lap Time Trends
During the course of an endurance race, a car's lap times fluctuates due to
different drivers, pit stops, caution periods, track conditions, degradation,
and conservation.
The lap time trend chart
scatterplots
each car's lap times over the course of the session, excluding pit-in,
pit-out, and caution laps. To make sense of the ten thousand or so
individual lap times,
(LOESS)
smoothing lines are created for each car, clearly revealing their lap
time trends. Practice and qualifying sessions may not have enough data
points for smoothing.
Analysis
Notice the closing stages of the race at the lower right corner of the graph.
- The #3 sister car (olive) at the
bottom has a better, lower, lap time trend line than the winning
#4 hero (green) immediately above it.
We already knew this from the earlier gap chart.
- If you follow say the #3 and #4 lines back in time in the full graph
above, towards mid- and early- race, you can perhaps see that the car
was being conserved (slower lap times) earlier in the race.
- We see that most cars have faster lap times towards the finish.
Degradation would be exhibited as rising trend lines.
Lap Time Box Plots
In the IMSA WeatherTech and Continental Tires series, each car has more than
one driver during a race. Each has different capabilities, particularly in
Pro-Am classes like WeatherTech PC and GTD.
Box and whisker plots allow you to quickly visualize each driver's
lap times.
The lap times used in each driver's plot again excludes pit-in, pit-out, and
caution laps. Plots are ordered by each driver's fastest lap time
(lowest point on plot, either whisker or outlier) which is labeled.
Details on the math behind how box and whisker plots are created can be
found at P1TS's
Understanding Box and Whisker Plots.
- Roughly, the colored rectangular box represents the "meat" of the
lap times considered. The colored box consists of 25% of the lap times
faster (lower portion of the box) and 25% slower (upper) than the
driver's median lap time.
- The driver's
median
lap time is indicated by the colored horizontal line inside the box
while mean (average) is marked by the black diamond.
- The colored whisker lines extending above and below the box, show
the lap times lying within a certain distance from the colored box.
- Those lap times falling outside the whiskers are known as statistical
outliers
and are marked by gray circles.
Slow outliers usually indicate typical slow laps during a session.
Fast outliers occur less frequently and depending upon the conditions,
may possibly suggest
sandbagging.
Analysis
- #3 Antonio Garcia's plots stands out as it is noticeably
faster (lower) than all the other drivers by a wider margin.
- Not only was #3 Antonio Garcia's fastest lap 0.279 sec faster
than the next fastest driver, #67 Ryan Briscoe, this was
also true for the majority of their laps - their box and whiskers
closely resemble each others, just displaced by about 0.2 sec.
- #4 hero car's Oliver Gavin has one of the shortest boxes
and whiskers suggesting a high degree of consistent fast
laps. We see 4 slow outliers between 107.0 - 107.5
seconds.
Sector Gaps to Hero
By comparing each driver's
sector
times, we can see how much slower or faster than the hero car's drivers,
others are, sector by sector.
Each panel in the chart represents a driver, ordered by best 1-lap (not
pictured) or best 5-lap lap time average (pictured above). The fastest
10 drivers are shown on the top row with the fastest driver on the left.
This report is for Oliver Gavin's fastest 5-lap averages.
Since the #4 hero car has 3 drivers, there are altogether 6 individual
charts.
- The hero driver's panel is highlighted in bright gold while
co-drivers are in light yellow. The hero driver's panel is
always boring and since the difference is always zero.
- Each panel plots the percent difference in sector times between the
labeled driver relative to the hero driver (y = 0 line). For a
Best 5-Lap chart, like the one pictured above, each driver's fastest 5
laps are used.
- Times from each sector are averaged and plotted on the
y-axis as percent differences to the hero. This allows for
better comparison between short sectors, like speed traps, and longer
sectors.
- The markers though, are labeled with the absolute
sector time differences in seconds.
- The colored horizontal line shows the percent difference in 1-lap
or 5-lap average (pictured) of lap times relative to the hero driver.
Within Make
Some WeatherTech and Continental car classes have several cars of the
same make. To more easily compare the intra-make race, there are
additional reports for the hero's car make.
Analysis
- Since GTLM is a pro-only class, driver's best 5-lap average lap
times (colored horizontal lines) are all fairly close, with the
majority within +1% of the 4-OG hero.
- The 4th panel reveals that the #100 BMW M6 driven by
Lucas Luhr, is almost 2% faster in
S07
(red circle), the bus stop chicane. We
again see this in the 12th and 14th panels, for the sister
#25 BMW M6 by Dirk Werner and Augusto Farfus.
- It's then interesting to then see that the BMW's speed from
S07 is not carried as well (relative to #4
Corvette) into S08
(blue circle) and beyond - likely due to
the Corvette's torque.
There is a also companion hero driver
table that contains the same
information, with sector time gaps are represented in a
heat
map. Faster sectors for other drivers are colored in
green, where gradient shows how much faster.
Pits and Stints
Managing pit stops and drivers changes are important part of endurance race
strategy. The pits and stints chart not only makes it easy
to review your own strategy, but also study competitor strategies.
This is useful not only during a race, but also during practice sessions to
quickly see how competitors chose to make use of their practice session.
- The x-axis plots the session time. Caution periods are marked by
yellow or red vertical bands.
- Each row represents a car, ordered by race finish position. Practice
and qualifying sessions are ordered by best lap time.
- Each row is divided in time by pit-in and pit-out.
Sections therefore depict either driver stints or time in pit lane.
- Driver stints are color-coded and number of laps and stint times are
shown.
There is also a numeric companion
table where each row represents a driving stint
and information about the pit stop ending that stint.
Information includes when (in both time and laps)
a driver's stint started and ended, and also pit lane duration as
well as what the flag was when the car crossed pit-in.
Pit Lane Times
Many times, a car wins by only a scant few seconds over their
competitors. For this particular case, the winning margin was a mere 34
milliseconds. Faster pit service may give a team a winning advantage, so it
is useful to examine pit service times.
This chart zooms in on the pit portion of the Pits and Stints data above.
Data is grouped by stop number, allowing you to more easily
compare your 1st, 2nd, etc. stop sequences with your competitors's.
For longer races like this one, there can be quite a bit of time "drift"
between cars as the race progresses.
- Timing and scoring data does not provide us with
the time the car was standing still in the pits, but instead we again
use the time spent between pit-in and pit-out timing
loops. For convenience, I'll just call this "a pit stop".
- Rather than compare the total pit stop times, separate panels are
created for each of the stops.
- The cars are ordered on the y-axis in race finish order, matching
the race's Pits and Stints chart. The x-axis represents pit lane time.
- The best pit time for each stop number is printed, rounded to the
nearest 0.1 second along with a dashed vertical reference line.
All other cars are labeled with how many seconds slower they are
than the fastest stop.
- The pit stop bars are drawn in colors corresponding to the race
flag during pit-in (green, yellow,
red). In the "Stop 1" panel we see that all cars took their
first pit stop under yellow, except for car 67 who drove only 9 laps
and pitted under green (only his first 2 minutes are plotted).
- The left end of each bar is annotated with the number of laps
in the driving stint immediately before the pit stop.
In the "Stop 1" panel we see that all cars pitted after 14 laps,
except for car 67.