My research shows a wide range of usage. A passage in Quora.com said the phrase's rise in popularity did coincide with the first airings of the Firestone commercials, that Avon Tyres in Britain used a similar passage, "Where the tyre meets the road," in its ads dating back to the 1940s.
Many online sites weigh in on the origin and meaning. Even the Urban Dictionary has two definitions. One calls it "the moment of truth for something," and the second "where the action is most immediate."
And KnowYourPhrase.com chimes in with "when a theory or idea is put to the test to see if it actually works," or "when things become serious."
There also are other musical uses of the phrase besides the commercial. Meat Loaf had a song titled "Where the Rubber Meets the Road," on his "Welcome to the Neighborhood" CD. Yes, I admit to being a fan of the singer of "Bat Out of Hell" fame.
But that doesn't mean I have to like all of these other references. So that's why I'm going to leave you with a few tidbits about the Firestone jingle.
It was sung on the original commercials by Don Rondo, who sang ballads during the mid-1950s. He first became popular for his rendition of "Two Different Worlds." He apparently also was famous for singing the "It's Us or Rust" commercial for Ziebart.
But now I want you to go listen to one of those early Firestone commercials, and see that this is where the phrase is rightly used. And as an added bonus, there's a good chance you'll have the tune stuck in your head for the next couple of days.
Bruce Meyer is editor of Rubber & Plastics News and he sees rubber-related stories nearly everywhere he goes. Follow him on Twitter @bmeyerRPN.