WHAT WE DID

We evaluated six apparently plausible (or at least widely touted) fuel saving strategies, plus two consequential issues:

CITY

• Easy versus aggressive driving

• Peak versus off-peak travel

• Switching engine off when stopped in traffic (a Green Vehicle Guide recommendation)

We also quantified the impact of a 25 per cent reduction in tyre pressures (simulated poor maintenance) and evaluated toll roads versus pre-existing arterial road routes from a cost- and fuel-saving standpoint.

HIGHWAY

• Cruise control versus driver throttle control

• 90km/h versus 110km/h on the freeway

• Windows open versus air conditioning ‘on’

HOW WE DID IT
We took one Calais V V6 and one chaotic Sydney road system, and tried to play pseudo-science with it. We generally succeeded – after boning several runs where time and traffic militated against us.

A balance was struck between our requirement for experimental control and the slings and arrows imposed by the real world. We used the same pieces of road for the same tests, drove the same direction (to negate the impact of a net gain or loss in elevation), at the same times of day and in the same basic traffic density, and as far as possible varied only the condition under the microscope.

The VE Calais V V6 boasts the most popular drivetrain in Australia’s most popular car, but the main reason we chose it was the trip computer. Its ‘fuel used’ function goes off and asks the engine control computer how much fuel the injectors are consuming – a precisely known quantity.

It meant we could test accurately and directly how much fuel was being drunk without resorting to the inherent inaccuracy of parking at the same bowser at the same filling station, going to the second click at the pump nozzle, and hoping for the best. Filling a fuel tank repeatably is a very inexact process in the real world. With the Calais we didn’t have to drive tens of thousands of kilometres to derive meaningful results, and we were able to isolate and assess only the driving conditions under evaluation, and not the transit to and from the filling station. The Calais presents its readout in increments of 10ml, meaning measurement accuracy better than one per cent provided each test consumed more than one paltry litre.