Well if cars are replacing animals, (assume the cars have their own kids for a min) animals don’t get faster with every generation unless natural selection is pushing it, so if cars Are the animals, they wouldn’t necessarily get faster with every generation, some would be faster than others by genetics. Look at the Olympics, the fastest of the fast in the human world, and they had to have the right genetics plus lots of hard work, why can’t racing be the same? genetics gives them the speed (like makes them a Porsche, Corvette, etc) and hard work gets them a sponsor. The way to make cars overall faster would be for the slower cars not to reproduce and the faster cars to reproduce with other faster cars. For example, we saw Francesco’s mom in Cars 2, she looked like an older race car build, if his dad was also a race car, then he had the genetics to be a race car, and his parents probably pushed him in that direction (“Talk about a home court advantage, Francesco grew up racing on these streets”). Jeff Corvette is a Corvette, so (assuming “pure blood” lineages) that would make both of his parents Corvettes, which have speed, so that would get passed down. Lightning, on the other hand, doesn’t have a specific make/model for us to analyze, and there is no mention of his family (since we now have proof there are family units in the cars world) which makes this a guessing game, but maybe his lack of specific car brands makes him a “hybrid” of two car types, and if both his parents had speed (like they were a Corvette and a stock-car for example) that would give him the speed, whether that would give him the speed to rival pure-blooded racing (assuming Francesco’s dad is a racecar) would be up to chance of genetics, how much work is put in, and determination (much like anything)
on a related, though random note: in my head, I like to think Doc is Lightning’s grandfather (on his mom’s side, we’ll call her Mrs. McQueen) but maybe Doc never knew he had a kid (like maybe thats when he had his accident and it was over a year before he was put back together or something, I haven’t figured that part out yet) and Mrs. McQueen didn’t grow up with Hudson as her last name. I like to think That’s where Lightning gets his racing genes (and the blue eyes… after all, they say everyone with blue eyes is descended from a common ancestor, though a lot of Pixar characters have blue eyes). I also like to think that Lightning’s family (mom, her mom, Lightning’s dad, any siblings) came to visit him in RS, and Lightning and Doc learned the whole story before Doc’s death. (That’s how it is in my head, and I’m sticking to it!)
Using the stork/factory theory of car creation: Why do cars in our world get faster year by year? because humans want to be able to drive fast (even if they never do, they want to be able to say “my car can go 250 mph”) If there aren’t any people in their world, what would the motivation be to make certain cars faster than others? especially if they can upgrade their own engines (and we know they can, look at Dusty, even if he’s not a car, or Pixar, its supposed to be the same universe, and thus the same rules should apply) why would they need to be made able to go 400 mph if they can decide how fast they want to go later, if they want to go faster they have that choice.
And to me, this doesn’t complicate the racing, because there are probably regulations on it, like there are in real life (that’s why they are called “stock cars” at least it was at first) like maybe they can’t mechanically up their speed or horsepower after entering a racing league (like after Lightning starts racing for the piston cup, he can no longer add horsepower by adding to his engine) and theres probably regulations on how much horsepower you can add and how before you enter. That would even racing out between the various circuits.
Ok, 
wow, that was a lot of words… did I miss anything? does that make any sense? Do I sound like a crazy person?
