the rubber meets the road

A metaphor derived from the point of contact between automobile tires and pavement.

• the rubber hits the road
• the tackies hit the tar (South Africa)

the rubber meets the road

1. Used other than with a figurative or idiomatic meaning: see rubber,‎ meet,‎ road.
   • 1928, How to avoid automobile accidents, page 30:

     Even 500 feet probably wouldn't allow you to brake to a stop, because it's "where the rubber meets the road" that counts.

2. (idiomatic, with "where" etc.) A place or circumstance at which the implementation of a plan or intent is to be achieved.
   • 1957, Max Shulman, Rally 'Round the Flag, Boys!:

     Now we're getting down to where the rubber meets the road.

   • 2002, F. Stevens Redburn, Public policies for distressed communities revisited, page 159:

     It can only be judged "when the rubber meets the road"; when its implementation does or does not produce results.

   • 2007, Dan Miller, 48 Days to the Work You Love, page 85:

     It is in the interview that the rubber meets the road.

• almost always used with "that", "when", or "where".