Quoting: Erathoniel
Vehicles are practically made for combat. What's the use of having a huge tank if you can't use it?
Heh, I once designed a GURPS battlesuit akin to the Bubblegum Crisis hardsuits. Even with playing games with tech levels, it turned out that the capabilities of the suit had to be adjusted every few rounds because it became drastically more mobile as it used up it's fuel

Of course you could figure out the performance each round, if you didn't mind solving a quadratic equation (or solving a differential equation up front).