Preparing And Using A Performance Chart For A Time-Speed Rally

As I get ready to compete in the upcoming 2014 Pumpkin Run rally, I am thinking about preparing a Performance Chart for Harald von Langsdorff’s 1968 Mercedes-Benz 300SEL 6.3 in which I will be the navigator.  The Pumpkin Run rally is a Time-Speed rally where the competitors have to be on time, as measured to the second, all of the time with hidden checkpoints.  This has to be done without the use of any kind of odometer, including the car’s standard odometer.  Many people who might look at this page might not be familiar with Time-Speed rallies or the use of Performance Charts.  As a result, I thought that I would show a simple example of how these work.

Below is an example of a few instructions from the 2008 Pumpkin Run rally.

Pumpkin Run Sample Instruction 2008

Sample Instructions From The 2008 Pumpkin Run Rally

Route Instruction 38 tells the competitors to change their speed to 30 miles per hour at the next road curve sign.  Route Instruction 39 tells the competitors to stop at the stop sign at Hardscrabble Road for 15 seconds and then turn left and go 30 miles per hour.  I have added a hand drawn arrow to remind myself to look at Route Instruction 40 immediately after Route Instruction 39, so that we don’t miss going straight as possible onto Shiloh Church Road.

Route Instruction 39 can be visualized by the following plot of time and speed.

Timing Plot 4

Visual Representation Of Route Instruction 39

However the real world does not work like the above visualization.  A car cannot stop instantly nor instantly accelerate from 0 to 30 miles per hour.  As a result it is necessary to take into account the braking and acceleration characteristics of the car used in the rally.  This is where the Performance Chart comes into play.

In order to determine the effects of stopping and starting, the following method could be used. There are other ways, but this is simple and straightforward.  Find a section of road that does not have a great deal of traffic and mark off the end points of a section of road about 1/2 mile apart.  The distance does not have to be exact, just long enough to establish a stable speed in the car.  Then drive the distance between the two end points, using a rolling start, at a speed of 30 miles per hour and record the length of time to do this.  You may want to do this more than once to get a value that you are comfortable with.   In the example shown below, at a steady speed of 30 miles per hour, it takes 70 seconds to travel the length of the test section.

Timing Plot 1

Base Time Measurement In the Test Section

After this is done, go to one end of the test section and from a standing start accelerate up to 30 miles per hour, travel at a steady 30 miles per hour to the other end of the test section, and measure the time to get to the other end.  In the example shown below, the total time to do this is 74 seconds.  That means that there is a loss of (74 – 70) 4 seconds when accelerating from 0 to 30 miles per hour.

Timing Plot 2

Example Of Measuring Time Lost During Acceleration

Then drive into the test section at a speed of 30 miles per hour, travel the length of the test section, stopping at the marker at the other end of the test section and then record the time.  In the example shown below, the travel time is 72 seconds, therefore the time lost in braking from 30 miles per hour to a complete stop is (72 – 70) 2 seconds.

Timing Plot 3

Example Of Measuring Time Lost Coming To A Stop

This data is used when executing Route Instruction 39, shown previously.  We know that 2 seconds will be lost coming to a stop from 30 miles per hour and 4 seconds will be lost accelerating back up to 30 miles per hour.  In order to account for this lost time, the stop at the Hardscrabble Road stop sign must be less than the 15 seconds stated in Route Instruction 39.  A total of ( 2 + 4) 6 seconds will be lost stopping and starting, so the actual stop time or zero movement time at the stop sign can only be (15 – 6) 9 seconds.  This is illustrated below.

Timing Plot 5

Actual Rally Timing Method To Execute Route Instruction 39 And Stay On Time

The timing measurements to know the car’s performance for a range of speeds and actions will be extensive.  Also during the rally, the driver must drive the car in the same manner as the car was driven when the test measurements were made.  And the driver must be able to drive the car at a steady speed.  That is why a large diameter, highly visible, calibratable speedometer is very important in order to do well in these types of rallies.

I have included the Performance Chart that I prepared for Harald’s Mercedes-Benz 560SL that we used at the Pumpkin Run rally in 2008.  The base data was measured by Harald with Paul Henshall during a long day of testing in Canada.  As Harald & I live about 500 miles apart, I was not able to join Harald for the Performance Chart test day, but I did work with Harald & Paul to establish the testing program and Harald sent me all of the timing data for analysis.

Performance Chart MB 560SL

Sample Performance Chart

This Performance Chart is used by using the initial speed in the left column and the final speed in the top row.  For example, the time lost braking from 45 miles per hour to 0 is 4.8 seconds and the time lost accelerating from 0 to 25 miles per hour is 2.6 seconds.  There is no common format or style for a Performance Chart and each time will have its own data and presentation style.

During the rally, the navigator must be able to provide the route instructions to the driver and to keep track of time lost or gained with each manuever .  In addition, local traffic can slow down or interfere with a planned manuever causing additional losses which must be made up before the next checkpoint is encountered or figure out the extent of the needed Time Allowance.  For example, in the case of Route Instruction 39 shown above, the navigator might know or believe that they were running 2 seconds late, as a result the standing stop time at the Hardscrabble Road stop time should be reduced by 2 seconds, down to (9 – 2) 7 seconds to get the car back on time.

This is by no means an exhaustive explanation of establishing the Performance Chart, but it provides an overview of the timing methods needed for a Time-Speed rally.

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