I made several test vehicles to check gasoline usage a bit back:
- A 3x4 780kg roadster with a V6 engine, racing slicks and 20L of gasoline
- A 3x4 1500kg personal tank with also a V6 engine, but heavy frames and armored wheels. Also mounted a set of rams in front for some of the tests (making 3x5)
- A 5x8 7000kg Mobile fortress with a v8, but also tested a v12, an electric engine, rams and front quarterpanels and naked frames
I made a test track consisting of a mixture of road areas and traversable off-road areas and made the cars to a fixed number of laps after topping up.
- Lighter vehicles consume less gasoline than heavier ones. Weight seemed to be the most significant aspect in my tests. Removing the storage batteries and the extra ballast (to make the fortress slim down two tonnes) impacted the fuel consumption significantly.
- Smaller engines consume less gasoline than bigger ones, but also a smaller engine seems to consume more than a bigger engine when pulling big loads. Replacing the V6 of the tank for a V8 did not increment the fuel consumption as much as it did on the roadster. Swapping the V6 of the roadster for an I4 make it so efficient that probably you could traverse the full map back and forth on a single 20L tank. Increasing the engine size in the mobile fortress actually made it run a bit more efficient on roads, IIRC.
- Aerodinamics seem to be also a determining factor: replacing the row of rams for a quarterpanel made the fortress consume a bit less and made the top speed a bit better
- Wheels also seem to affect: replacing the roadster slicks for wide wheels made little difference if I kept to roads, but saved fuel when I started going off-road. Adding a third row of wheels on the fortress improved the speed on off-road, reducing the consumption notably (but slightly increasing it while on roads)
- Speed does seem to affect but to a less degree: the roadster sipped gas at 130km/h while the fortess was gulping it at 80km/h
I did not test for damage, as save for start hitting the parts (and that does not guarantee reproducible results) I did not found a way to spawn a partially damaged engine or wheels.
IIRC you liked to travel light, with small vehicles and little load. Motorcycles and small cars consume very little gasoline and can travel very far without worrying about having to reload. You start feeling the pain at RV size.