Automobiles are very unnatural. Nothing in the evolution of animals really prepares any animal for it, or gives any animal a context in which to make sense of it. Instead, aeons of deep-seated instinct tell every animal that certain sensations, as of motion, mean certain things, and should be responded to in certain ways, because those ways lead to survival. The normal reaction to something as unnatural as an automobile ought to be instinctual reactions that make transporting an animal by automobile a difficult proposition at best.
There is, of course, one exception that is provided for by the nature of automobiles: mankind. It is easy, if one makes an effort of imagination, to conceive of forms of locomotion that mankind might have tried to invent, but which he could not have put up with because they were too disorienting, ran too counter to his survival instincts, and so which he never bothered to invent, or to try to invent. Actually, that's not true: it's not that easy, because we are conditioned not to think of those possibilities. You have to find the preconceptions we don't usually question (such as the fact that we look forward and down, but rarely up) and then question them. But it's certainly possible. The point remains: the methods of locomotion we invent are those which are suited to us, or we wouldn't've invented them.
So when you think about it, isn't it really a handy coincidence that the vast majority of dogs, one of mankind's most domesticated animal companions, not only tolerate but actively enjoy riding in a car? They stick a head out, loll their tongues, and savor the wind blowing through their ears. Very few dogs have any problem with it, and most of them seem to delight in it.
There's nothing about the circumstances of how dogs got to be one of mankind's first and best domesticated animals that really selected for this. Nothing mankind was doing with early dogs had any correlation to the form of locomotion that humans would invent tens of thousands of years later. In fact, most of the other animals that humans domesticated don't like car travel, with reactions ranging from displeasure to an actual need for blinders or sedation, even when their involvement in it is nothing more than sitting on the back seat and not really having to see it happening. Even in those circumstances, where the awareness that the animal even is in a car seems remote, there's enough frisson between instincts and situation to make cats howl, and most animals get at least nervous, if not panicky. But dogs revel in it.
One can't help wonder what odd little juxtaposition of instincts is playing out in their heads. Their simple joy makes you think they're thinking, "I'm running so fast, and I don't even feel tired!" That's a glib and amusing thought, but no animal dumb enough to not be able to tell what running feels like could last very long, particularly one whose primary method of getting food is running it down. It's just too vital a process to be affected by that big a disconnect.
The more you think about it, the more impressive a happy coincidence it is that dogs are comfortable in, and even happy in, cars. Then again, if they weren't, it wouldn't change much. We take our cats to the vet in cars even though they, guided by quite sensible instincts, hate it, and say so repeatedly and volubly. If our dogs disliked it similarly, we could just keep them on short leashes, only take them out when we had to (as we do with cats), use operant condition to train them to tolerate it quietly, and at worst, use a sedative. But every time my dog is loving the heck out of being in the car, I'm glad for her sake that the wild coincidence, that the thing we invented for ourselves also happens in some completely different way to suit them too, just worked out.