Jaguar Clubs of North America

Guide to JCNA Club Rallying & Program Rules
    Chapter 4 - Average Speed and Calculations

(TSD) Rally
Instructions and Terms
Route Instructions
Avg. Speed and Calc.
Odometer and Tires
Rally Equipment
Your First Rally
Rules and Techniques
Variations to the Rally
JCNA Rally Rules
Rallymaster Guide
Appendix A
Appendix B

Being in the right place at the right time on a rally means staying on course, never letting attention wander so that you miss a route instruction. But that is only part of the battle. To be in the winners circle you must be on time, and stay as close as possible to the average speeds required in the Route Instructions. Several times each mile you should check the distance you have traveled against time elapsed since the start so that you know how much you are early or late. The driver can then adjust his speed accordingly.

There are several ways this can be done, some easier than others. Some methods require nothing more than pencil and paper, while some demand specialized equipment. You will, of course, need a means of measuring distance. That is the odometer. It comes with your car, and it will be discussed in the next Chapter. And you will need a means of keeping time, which will also be be covered separately in Chapter 7.

At this point we will assume that you do possess means of measuring distance and time accurately, and we will take up the methods of applying one against the other to obtain average speed.

The simple example of a 30 mph average speed will show how different winning rallyists work out this problem. Driving steadily at 30 mph, in 60 minutes you would cover exactly 30 miles, one-half mile per minute, or two minutes per mile. You could make up a little chart, or table, showing time and distance for tenths of a mile and for integral miles up to 30 or 40 miles. It would look in part like this:

MILES TIME (minutes)
  0.1 0:12
  0.2 0:24
  0.3 0:36
  0.4 0:48
  0.5 1:00
  0.6 1:12
  0.7 1:24
  0.8 1:36
  0.9 1:48
  1.0 2:00
  2.0 4:00
  3.0 6:00

It is so easy you could do it in your head.

No rally is going to be that simple. There will be average speeds of 24.37 mph, or 31.24 mph or anyone of thousands selected by the Rallymaster. Obviously you will need a table for each average speed. If you have a friendly rally master he might even include basic tables in his General Instructions. You should obtain a set of your own tables if you plan to run rallies regularly. Larry Reid's "Rally Tables", first published in 1959, is an old standby. Try to get a newer set in decimal minutes. Older versions gave time in seconds, but are still useful. Another type of table is Cone's Factors, which not only gives you minutes per mile at an indicated average speed, but also takes into account odometer error. Some of these materials are still readily available today. Try your local library, other rallyists, or the classified section of automotive magazines. See our bibliography for sources.

Not all navigators like to work with tables. Some like to work with circular rally indicators like the Stevens Model 25 or the Blackwell Rally Indicators which have scales for time, speed and distance. Using movable pointers, theseindicators show graphically the time and distance combinations for an infinite number of average speeds. Some even have the added refinement of accommodating odometer error. Other methods utilize slide rules, pocket calculators or computers, onboard original equipment tripcomputers, and even the old mechanical Curta "pepper mill" calculator that works by turning a crank. It is expensive and difficult to find as it is no longer manufactured, but has been the favorite of serious rallyists for many years. The Curta was manufactured in Liechtenstein. JCNA Rally Program rules permit all of the aforementioned devices except for portable or aftermarket electronic computers and aftermarket electronic, electro-mechanical or mechanical odometers. NONE OF THESE DEVICES WILL THINK FOR YOU & THEY WON'T KEEP YOU FROM GETTING LOST!

Here are some basic TSD equations that can be used to keep you on time:

Distance = Speed(mph) x Time Sample: 1 hour =  30 miles/30mph
Time = Distance/Speed Sample: 30 mi = 30 mph X 1 hr
Speed = Distance/Time Sample: 30mph=30 miles/1 hour

Previous: Chapter 3 - Route Instructions
Next: Chapter 5 - The Odometer and Tires