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Know Your Phrase - The Meanings For Common Phrases and Idioms > W-Letter Sayings
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Phrases and Idioms
knowyourphrase.com - The Meanings and Origins For Many Common Idioms and Phrases
When something is about to begin, get serious, or be put to the test.
What drives on the road? Cars, of course! Well, there's also trucks, motorcycles, and bikes too. All of these vehicles have one thing in common: they have wheels, wheels made out of rubber. So this phrase is likely referencing a car's rubber wheels making contact with the road.

The earliest I could find of this phrase being used in a figurative way is in the mid-20th century. For example, in 1956, Mt. Vernon Register News uses the phrase with the meaning of 'getting serious.' In an article the writer explains that in order to be succesful in advertising for radio and TV, one has to speak their language, and then goes on to list a "collection of stylized phrases" that advertising men might use:

"How much is it going to cost?:
'Let's get down to where the rubber meets the road."

If you noticed, the expression above is written with 'meets' instead of 'hits.' That's just another way in which this phrase is said. An early recording of its other form, where the rubber hits the road rather than meeting it, appears in The Modern American Usage: A Guide by Wilson Follet, first published in 1966:

"Lately, speakers of weak imagination have taken to saying 'where the rubber hits the road', evoking an
image of cars falling or bouncing."
* I've been training my body for years so that I could win the upcoming marathon, but tomorrow, when the race actually begins, that is when the rubber hits the road and I find out how conditioned I really am.
Note: The origins for many phrases are so unclear, it's like trying to find needle in a haystack! However, while it's not the case for every saying, what you'll often see are the more popular theories that are around that try discerning how a phrase came about. Keep in mind, though, that these are merely theories, and are not a 100% confirmation!

Additionally, the quotes you see coming from old books, plays, newspapers, and so on, are there to give you, the reader, an idea on how far back in time some of these idioms go. Consider this also: If you see a quote from William Shakespeare, and he's using some popular expression, it doesn't necessarily mean he's the one that came up with it. Maybe he heard it from a friend, who really knows! Anyways, I do try to list the oldest recorded forms of a phrase that I can find, but it's always a possibility that I missed something.
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