(where/when) the rubber meets the road:

1. at the point in a process where there are challenges, issues, or problems.

2. when something is about to begin, get serious, or be put to test.

解释：

这个短语通常和where, when合用，意思是：

1. 当实际问题或挑战出现的时候

2. 当某件事要付诸于行动的时候

造句：

1. We need to try our best to help our customers when the rubber meets the road for them.

2. The plan sounds great, but we cannot be sure if it works unless when the rubber meets the road.