This idiom originated from racing - when the rubber hits the road is when the automobile starts moving forward.
It means: "when you get to the action", or "when you get busy", "when it gets serious", or it might mean something like "the last word or final outcome of something"... something along those lines, depending on context.
"Where the rubber meets the road" is a phrase referring to vehicles -- when the rubber of their tires meets the road, you have movement. This idiom means "where the action is going to take place," and is generally used to mean some sort of decisive action.
Firestone.
The Academy - 2007 Where the Rubber Meets the Road 1-6 was released on: USA: 28 June 2007
The pattern of the rubber part that meets the road.
Static Shock - 2000 Where the Rubber Meets the Road 4-9 was released on: USA: 27 March 2004
Rodney - 2004 Where the Rubber Meets the Road 2-14 was released on: USA: 28 February 2006 Germany: 6 June 2008
Wherever wheels are rolling,No matter what the load,The name that's known is FirestoneWhere the rubber meets the road
It is referring to the tires on your car. It can also be a metaphor for a defining moment.
The Weather Channel Weekend View - 2006 Where the Rubber Meets the Road Winter Tire Safety was released on: USA: 23 November 2013
the rubber meets the sky
Perhaps you mean NBR (acrylonitrile butadiene rubber) an oil and fuel resistant rubber which is does not distorted with heat and resists abrasion.If you do mean NBR (National Building Standards) it is a rubber that meets those standards in defined applications.
It means to actually start whatever it is you're about to begin. "Rubber" refers to your vehicle's tires -- if you put the rubber onto the road, you are rolling your vehicle along the highway and moving along.