Importance of Travel Speed in Sprayer calibration

Often we speak with operators that have an opinion of the speed they spray at but are not certain. While it’s good to have an idea, it’s far better to know 100%. Really it’s critical to the whole operations success and to your wallet. Let me explain, to assume the sprayer is moving at 8 KPH when it’s really doing 6 KPH that’s 25% wrong straight up. Imagine putting 25% to much chemical on an area, it happens. Imagine paying 25% to much at the supermarket or petrol station. Similarly its just as important to be certain you’re not going faster than calibrated.

So how can you ensure you’re speed is accurate?

Relying on vehicle speedometer is one thing, but is it accurate? Tractors have many wheel size options, digital speedometers are better but has it been calculated for the tractors tyre size and at what tyre pressure? I’m sure you get the idea.

There’s a simple manual formula that you can use to calculate speed, its as useful in farming to calculate speed as it is at Bathurst on Conrod straight.

All you need is:

1. A specific measured distance (any distance the longer the better) with the measurement in metres.
2. A stop watch (time is measured in seconds)

So lets consider you’ve measured out a distance of 150 metres, the next thing is to travel over the 150 metres driving at a constant speed and engine revs in a single gear. This means set your Vehicle up with the sprayer if its PTO drive have the engine revving at the speed you expect to spray at and select the gear in which you wish to use when spraying.

Ok, so given the above paragraph is done you will have traveled past the 150m start point at the operating speed and started the stop watch then continued past the end point still traveling at the same given speed, when passing the end of the 150m stop the watch then stop your vehicle, if doing this on a hill side maybe you could perform the same test moving up the hill then also the reverse so an average time can be calculated.

Lets say we’ve done the above and recorded the time taken, for the sample we will use the info below;

Time - 1 minute 5 seconds that’s 65 seconds

And the distance was 150 metres.

That’s the hard work done. Now the mathematics, ready for this? The formula is;

Speed (Kph) = (Distance (metres) x 3.6) / Time (seconds))

Speed (Kph)  = 150 (m) x 3.6 / 65 (seconds)

                                = 540 / 65

                  Answer  = 8.31 KPH (rounded)

Just like back in school perform the multiplication before the division, remember BOMDAS (don't remember maybe you weren't listening) if you don’t perform the multiplication first you’ll get the wrong answer.

Just for interest.

In the case of Bathurst 1000 the track is 6213 metres long and Bathurst’s best lap time is 123.481 seconds (Since Conrod got a bend in it) this translates to an average speed of 181.1355 KPH.

The fastest ever lap is McLaughlin’s 2:03.481s set in Practice 5 in 2019 (more detail Click Here)

Hope this is of help, Happy spraying.

Written by Steve Wells, www.theco-op.com.au