I've had a couple of VINs pm'd to me, let's see what results we get. Thanks to everyone!
Weight in a vehicle is an issue when accelerating or overcoming gravity (going up hill). At most other times it's meaningless - having 10Kg here or 300Kg there doesn't make a meaningful difference cruising along at 95km/h.
What does make an extraordinary difference is the cruise speed. There are TWO factors at play.
First, aerodynamics. Our brick-shaped utes are ... well, brick-shaped. You'll never see one loading passengers ready to depart from Runway 29. As the vehicle speed increases, aerodynamic drag increases at a faster rate (exponential). This means the required energy input increases at a faster rate than the vehicle's speed.
Second, engine performance. Our YD25 motors (standard, unchipped) develop their peak torque at around 2,000rpm. Below 2,000rpm, the engine is using small amounts of fuel but not gaining a lot in torque, however the amount of torque rises rapidly approaching 2,000rpm. At 2,000rpm the torque curve begins to flatten out - so RPM increases a fair bit more (which is directly proportional to fuel input) but the torque doesn't increase anywhere near as much. It basically means you're pumping in much more fuel for little more gain.
Chips change the equation and could vary it wildly. I think there's a reason why the vehicle's drive train (gearbox, diffs and tyre sizes) were designed at the ratios they were - because at the optimum torque point (2,000rpm) the vehicle is just below cruise speed.
Proof? In my car, at 95km/h over a 1,000km trip, I used just over 10LPHK. At 110km/h on the return trip, I used 12LPHK.
