What is the origin of "when the rubber hits (or meets) the road", not meaning, origin?

Question

the meaning is available on numerous internet sites, and in common sense as the "moment of truth" that time when theories or thoughts about something is tested, ie" the wheels are spinning, but when they touch "the road" they should produce action, or results. But from where does it come? Thanks

Answer 1

folk lore

Answer 2

Firestone Tire jingle/add from the sixties

"Where ever wheels are rolling,

No matter what the load,

The name that's known is Firestone

Where the rubber meets the road."

Firestone was the 2nd? largest tire manufacturer -

They were put on new Fords exclusively

handshake deal between Ford and Firestone

some marriages down the line.  Firestones, Fords and Edisons (?) used to vacation together.

Firestone even had TV and radio programs - not to mention the Firestone Country Club (PGA event)

Firestone sponsored Barnie Oldfield - first mile a minute at Indy.

So you can see Firestone did influence mid-twentieth century culture