Speed vs fuel consumption
On my recent trip to Perth and back I have kept track of fuel economy. In addition, I was in a hurry to get there for a conference, which meant that on the trip west, we travelled at a target speed of 110kph where this was legal (probably mostly 105-110), but on the way back there was no such imperative, and except for the second last day (I had ideas of making it home that day, but got too tired), I worked on a target speed of 100kph.
Having topped up the tank yesterday (so the distance includes an extra trip to town), I now have the figures, which give us an idea of the effects of that extra 10kph. Travelling 3976km to the outskirts of Perth averaged 11.90 l/100km, and on the return trip, 4152km, including a bit of driving in Perth, averaged 10.80 l/100km.
So it seems that increasing the driving speed by 10% means an increase in consumption of a bit over 10%.
This is with the Isuzu engine, but since the extra drag is almost entirely from the 'aerodynamics' of the vehicle, I expect the results are applicable directly to any 110 wagon, and probably indicative for any 90/110/Defender. Diesel engines operating in the part of the power band would not have any appreciable difference in efficiency for a 10% change in speed, so I expect the relative results to apply equally to any engine - Isuzu, Tdi, Td5, Tdci.
Petrol engines, especially older ones, may have efficiency that varies more, which may make the results less applicable, and more streamlined and lower frontal area vehicles may have a smaller effect.
John
JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol
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