The Rally Page

Following the Correct Route.

It is not much use trying to stay at the correct speed if you are on the wrong road.

Here are a few tips that may help you to follow the correct route.

Most crews make a mistake very early in the rally because they are not paying attention. You must get in the groove straight away.

Approach every junction with care.

Here in Florida the route will probably be easy because most of the roads are straight and the junctions are 90-degree turns. If you compete in a rally where there are complex roads it is a different matter altogether.

If you get to a junction that could be the one you are searching for, enter the junction slowly and check to see if it is the correct point where you have change direction. The navigator should read out the route instruction again, and both the driver and navigator should check to see if it is right place. If it is not right junction, speed up to get back on to the correct speed. If you try to drive at a constant speed you will go through the junction too fast and be more likely to make a mistake.

When you do get to the correct junction make sure that you cross the instruction off the list, so you know where you are and you don't go looking for one instruction twice.

Immediately (and I mean immediately) after going through the junction the navigator should read out the next instruction and both of the crew should look to make sure they haven't missed the next instruction. Sometimes two instructions can occur within yards of each other. This happened on the Jaguar rally in Lake Wales.

If the distances to each instruction are not given, then make a note of the distance you have traveled to the junction. Later, if you discover you have made a mistake, you can go back and know how far you have gone wrong.

When you get to the bottom of a page of instructions make sure you only turn over one page.

Always make sure that you pay more attention to the route than the timing.

All these tips sound like very obvious things, but we have done all of them more than once at different times.

Achieving a Set Speed.

The speed at which you have to drive will be given by the rally instructions. If, for example, the instructions tell you to drive at 30 miles per hour, then you drive at that speed as closely as you can.

At some point along the route the rally marshals will check you to see if, in fact, you are sticking to the correct speed. Now you may think, that all you need is to keep the speedometer reading the set speed, but in fact that will not be very accurate.

Firstly, you don't know how accurate your speedometer is and secondly, and much more significantly, you will have to make turns, stop at junctions and other things that cause you to have to slow down from your set speed. You won't know how much time you lost, for example, at a traffic light.

In order to measure the average speed that you have traveled at, you use a stopwatch and the trip odometer. When the rally marshal tells you to go, at the start of the rally section, you start your watch.

Improving Speed Accuracy.

In order to know whether you are fast or slow at any point, you need to know two things:

1. the distance traveled

2. the time taken to cover that distance.

Since speed is distance divided by time, if you know the speed you are supposed to travel at and you know the distance you have traveled, you can work out how long it should have taken you to that point.

Example.

 

Suppose you have traveled 6 miles and you should have been traveling at 30 miles per hour. The time you should have taken will be 6÷30 hours or (6÷30)×60 minutes = 12 minutes.

 

If you have measured the distance and time from the start of the route, you will know how long it actually took you to reach say, six miles. If the time when the odometer reads 6.0 is (say) 12 minutes 25 seconds then you know you are 25 seconds late.

The big problem with working out whether you are early or late by this method is you need to do lots of calculations which is very time consuming. Whilst you are doing all these calculations you will probably get lost. This problem is usually overcome by using a speed table.

 

What are they? A speed table is simply a table that gives you a set of figures that relates distance and time for a given speed. A speed table for 30 miles per hour is shown below. Suppose you have driven 5.6 miles, then the time it should have taken you is 11 minutes and 12 seconds.

The speed table is used in the following way:

The driver calls out "I am approaching (say) 5.6 miles". He will call this out a few seconds before he actually reaches that distance. That gives the navigator time to look at the table and see that the time should be 11 minutes and 12 seconds. When the car reaches exactly 5.6 miles, the driver, who is watching the trip odometer, says "now". The navigator then notes whether the time on the stopwatch is less than 11 minutes 12 seconds or more. The navigator then calls out whether you are early or late and by how many seconds. If for example the time at 5.6 miles were actually 11 minutes and 34 seconds the navigator would call out "late 22 seconds". In this example, the driver would then speed up to remove the 22 seconds lateness. It takes a lot of practice to know how fast to drive, and for how long to drive at the higher speed, in order to remove the lateness.

Obviously, it will be necessary to have a speed table for every speed that the rally organizer will be using. Sometimes you will know before hand, which speeds will be used and sometimes you will only find out when you read the route instructions.

Speed tables can be calculated and printed using a spreadsheet or you can buy pre-printed books of speed tables. If anyone wants to produce speed tables using a computer, the author has a suitable Excel spreadsheet. If you want to buy a set of speed tables, they can be purchased from http://www.donbarrow.co.uk/.

Improving Accuracy Further.

When Lauri and I first started driving TSD rallies we were very pleased if we achieved a penalty, for a stage, of less than one minute. Now after six years and maybe 20,000 rally miles we are disappointed if we have a penalty of more than five seconds. We are not especially clever, but with patience and perseverance, it can be done. Like any other sport, as you improve you always want to try to do better. In order to achieve such accuracy you have to drive within a few seconds of the correct speed the whole time, as you don't know where the checkpoint will occur. Sometimes of course, you cannot help being late, say due to a traffic light. This is where you need some luck, to not have a checkpoint occur where you are unavoidably delayed.

There are a number of factors that affect the accuracy of speed that is achieved during the rally.

Odometer Calibration

The odometer in the car will not give the same measurement of distance as the rally organizer. In a professional rally, the organizer will measure the route using an electronic distance recorder with an accuracy of about two feet per mile. However, whether the organizer uses such an electronic device or only a normal car instrument, your odometer will undoubtedly have a different reading to the organizer. To reduce this error, it is necessary to calibrate your odometer.

To enable you to carry out the calibration the organizer will give you a known distance, which you drive and note the reading of your odometer. This may be a separate calibration route to be driven before the rally or alternatively the first part of the rally route will be used for calibration purposes.

Suppose the correct distance given by the organizer is 10.35 miles, and the reading on your odometer at the distance is 10.6 miles. The error factor for your odometer is then 10.6 ÷ 10.35 = 1.024. To allow for this error you need to use a corrected speed table. That is a speed table, which is modified by this factor.

If the rally instructions tell you to drive at 30 mph, the table you would use (in the above example) would be 30 × 1.024, which is 30.7.miles per hour.

If the speedometer in the above example read 10.1, then the error factor would be 10.1 ÷ 10.35 that gives an error factor of 0.976. The speed table to use would then be 29.3 miles per hour.

Odometer Lag

This is a further refinement if you are trying to remove the last few seconds of error. Most odometers, of older cars, do not start to read immediately the car starts to move. In order to find out how much this error is, proceed as follows:

Set the trip odometer to zero. Drive a circular course of about one mile or so. Stop at exactly the same point in the road that you started. Note the reading of the odometer. Try to estimate the reading to the nearest 1/100 of a mile. (For example half way between 1.2 and 1.3 would be 1.25) Do not reset the odometer. Drive one more lap of the route. Note the reading again.

Work out the distance for the second lap by subtracting the value for the first lap from the total for the two laps. The second lap will usually be bigger than the reading for the first lap.

To make this clear I will give you an example.

The first lap odometer reading is 1.65 miles. The reading after two laps is 3.34 miles. Distance for second lap is 3.34 - 1.65 = 1.69. The difference between the two laps is 1.69 - 1.65 = 0.04

 

This value of 0.04 miles is the distance the car has traveled down the road before the odometer starts to read. (Since you did not reset the odometer at the end of the first lap there was no lag in starting the second lap.)

 

You could correct this error if you could set the odometer to read 0.04 before you started to drive. Unfortunately, you can't do that on most cars. So the alternative is adjust the time on your stopwatch. In the above example with an error of 0.04 miles, you would adjust the time as follows.

If rally speed is 35 miles per hour it would take (0.04÷35) × 3600 seconds = 4.1 seconds.

To adjust your timing proceed as follows, when the rally marshal counts to zero and says go, wait a further four seconds before you press your stopwatch button. This has the effect of making your watch run late by four seconds, which at 35 miles per hour will have the effect of correcting your distance, by 0.04 miles. You will have to use different time delays for different rally speeds.

Navigation Errors and the Effect on Timing.

Sometime during any rally, you may turn onto the wrong road. As soon as you realize you are wrong, you need to turn round. This is rather obvious, but the problem is then to know how much you are out on the timing.

Proceed as follows:

When you turn round, make a note of the distance reading on the odometer.

Drive back to a point on the route where you know you were on the correct road. Note the distance again.

Calculate the correct mileage to that point. That will be the speedometer reading less twice the distance traveled from the point at which you turned round. This may sound very complicated so I will give you an example to try to make it clear.

Point at which you turn back, distance (say) 23.5.

Reading when you get back to the original route (say) 25.6

Distance that you traveled on the wrong route is (25.6 - 23.5) × 2 = 4.2. (You will have traveled 2.1 out and 2.1 back. So you will have traveled 4.2 further than you should have done, so the correct reading at that point should be 25.6 - 4.2 = 21.4.

At the point where you went wrong, the distance would have been 21.4. If the rally speed is 35 mph then the correct time at that point should have been 36 minutes 41 seconds.

If you drove out and back from the point where you went wrong at 35 miles per hour (and not allowing any time for the turn round) you would arrive back at the junction at 43 minutes 53 seconds. In other words, by the time you get back on the correct route you would be 7 minutes 12 seconds late. This is very difficult to make up. For example, if you then averaged 60 miles per hour (meaning you would probably be driving at well above 60, to average 60) it would take you just over 10 miles to make up the 7 minutes and 12 seconds.

This reinforces the view that it is vital to stay on the correct road.

It is not impossible to catch up the time lost by navigation errors. We made a mistake on a rally in France last year and drove almost five miles too far. By driving very fast (in pouring rain as well) and luckily there being no control for ten miles, we made up the deficit and in fact came in 9 seconds early.

These few pointers hopefully will give you some idea what TSD rallies are about. I am sure that many members probably think we are mad to go to all this trouble to stay on time within a few seconds. However as with any sport, once you get hooked it becomes addictive.

The article was written by Robert Frost. Reprinted with permission from the South Florida Jaguar Club. This version has been edited from the original document.