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Does freewheeling improve fuel consumption?

Does freewheeling improve fuel consumption?

Believe it or not, but the answer is “no”.

Here is a very simple explanation

  1. An idling car needs fuel to be sprayed into the combustion chamber by the injectors to keep the car running or else the engine will die.
  2. In contrast a vehicle in motion and in gear, without any accelerator inputs is running against the compression of the engine and thus need no fuel injected to keep the engine running.
  3. Therefore a vehicle driven in a high gear down a hill with no accelerator inputs will actually consume less fuel than a vehicle freewheeling.

We recently put this theory to the test

  • Our test vehicle was an Audi A1 1.2T FSI
  • Our road section was the same 2.5Km downhill section of road.
  • We drove at roughly the same speed, although the average in neutral gear freewheeling was actually a bit lower than our in-gear average speed we achieved.
  • Herewith our results as per GPS unit and the vehicle’s on-board trip computer:

Freewheeling Fuel Consumption Test Results

Neutral Freewheeling In top gear with no or very little throttle inputs
Distance 2.5Km 2.5Km
Time taken to complete section 2-minutes and 25 seconds 2-minutes and 4 seconds
Average Speed 61.2 Km/h 72.2 Km/h
Maximum Speed 91 Km/h 99 Km/h
Descent Meters 139 Meters 139 Meters
Fuel Used as per vehicle’s trip computer 1.4-Litres per 100Km 0.9-Litres per 100Km