How close is the fire? Assuming it's not right on top of you, you often have to only travel a couple miles to exit the danger area. If your vehicle is downwind and not that far, that could be the better bet to escape the path of the fire.

If the wind shifts, "upwind" could suddenly be downwind for the fire, especially if you haven't that far upwind, say, in rugged terrain. Like here in California, you can have an onshore breeze during the day as the ground heats up, but then the wind shifts to the opposite direction as the sun goes down.

I guess it all depends on the situation.