T&D Primer

How to run and win this year’s Nacimiento Rallye Revival


The traditional format for P.B.S.C.C.’s Nacimiento Rallye was always Time, Speed & Distance, sometimes referred to as TSD or simply T&D. The route was straightforward with no “course-following traps” because the original organizers felt the route itself was challenge enough.

In a basic T&D rally, each team is given a set of route instructions that include assigned average speeds that are to be maintained during the run of the course. The rallymaster chooses speeds that consider local traffic conditions and legal speed limits.

Along the course participants encounter checkpoints at unidentified locations where their time is taken. Penalty points are awarded for either early or late arrival.

This type of event puts pressure on navigators because they need to keep the driver on course while continually calculating whether or not they are running on-time.

This year:

The Nacimiento Rallye will be run as a T&D but without manned checkpoints. Checkpoint locations will be clearly identified in the route instructions with  

Teams are to calculate what the elapsed time should be for each leg. Scoring will be based on how accurately each Team follows the course and calculates the elapsed time for each leg based on the assigned average speeds.

This eliminates the pressure of running on-time, all the time. How fast or slow you drive the course is irrelevant.

Odometer Adjustment:

In order to be competitive, you’ll need to do a little math. It’s unlikely that the odometer in your car will match that of the rallymaster since the course has been measured using a calibrated electronic odometer with precision to .001 miles. To help you match the rallymaster’s odometer the rally begins with a 10-mile odometer check. After running the odometer check your odometer reading needs to be compared to the official mileage. This simple formula gives you a correction factor:

Official mileage ÷ your odometer reading = mileage correction factor

Multiplying your odometer reading by this factor should then match the odometer reading of the rallymaster.

For example, at the end of the odometer check your odometer reads 9.3 miles. By the formula, 10 ÷ 9.3 = 1.075. Keep this 1.075 factor handy.

Using the odometer adjustment:

Leg starts are identified in the route instructions with a 

As an example, you start the first leg with an assigned average speed of 35 mph. You follow the course to the next speed change and note you have traveled 8.5 miles by your odometer. Multiply that 8.5 by 1.075 (your factor) and you’ll see the official mileage is 9.14 miles for that section.

Time Calculation:

Next you need to know how long a mile takes at the assigned speed. By the formula:

60 ÷ Avg. Speed = Minutes per Mile

At 35 mph you’d travel 1.714 miles per minute (60 ÷ 35). So, 9.14 miles at 35 would take 15.67 minutes (1.714 * 9.14) or 15:40 (15 minutes 40 seconds).

If the leg has additional average speed assignments simply repeat the above process for each speed section then add those results together at the end of the leg. That result is the elapsed time for the leg (by your calculation) and should be filled in on your score card.

As an example, a Leg may be broken into 3 sections run at 45 mph, 60 mph and 40 mph respectively. You note the following mileages for each speed section:

Speed Miles (your odo) Miles (corrected) Min./mile Time
45    6.5 miles                6.99 miles              1.333       9.32
60   5.0 miles                5.38 miles              1.000       5.38
40 25.4 miles                27.31miles            1.500       40.97
                                                                                    Total leg time 55.67 min or 55:40

If you’re using a trip odometer you can simply reset to zero at each instructed speed change but be sure to record the mileage to that point first.

You record the elapsed time for each leg on your score card in minutes like 55.67 in the above example. You could also convert the .67 minute to seconds if you wish (.67 * 60 = 40). The rallymaster will accept either but you’ll need to indicate which method you are using on the score card.

Alternative to an odometer correction factor:

Some rallyists prefer to adjust the average speeds instead of an odometer adjustment. In that case you’d use the formula:

Your odometer reading ÷ official mileage = speed correction factor

Then multiply the assigned average speeds by that factor to adjust for your odometer’s error. One advantage of this method is that it allows you to adjust all the speeds for the entire rally after the odometer check and odometer readings need no modification.

Using the example above:

Your speed correction factor would be 0.93 (9.3 ÷ 10), so the assigned speeds would be corrected as follows:

Speed Speed(corrected) Miles(your odo)|Min./Mile Time

45      41.85                   6.5                        1.434         9.32

60         55.80                   5.0                        1.075    5.38

40         37.20                  25.4                      1.613     4.97

                                                                                                                Total leg time     55.67 minutes

As you can see the total leg time result is the same.


Remember only the Rallye Class will be eligible for awards and the winning member’s name will be forever engraved on the Ed Leslie Perpetual Trophy.

If you have any questions, feel free to contact me at tim@singmaster.com.

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