It should be “where/when the rubber meets the road.” (Not ‘meet’) It refers to rubber tires on a vehicle which come into contact with the road, making the vehicle move. It means ‘where something real actually happens’, ‘when theory is put to the test.’ I wouldn’t use it. The coach is happy with how the team looks in practice, but the rubber will meet the road in their first game.

The expression started with cars that have rubber tires. You can think about a new kind of car. You can design one. You can make lots of new and different parts. You can put it all together. But does it really work? It is only when you drive it out of the garage and onto the road --- 'when the rubber meets the road' --- that you find out if it works and is a success. The expression is used for many projects. There is a point, in testing or in real use, when you find out if it is a success or it is a failure and you have to go back and do more work.

Hi