where the rubber meets the road

US /wɛr ðə ˈrʌbər miːts ðə roʊd/
UK /wɛr ðə ˈrʌbər miːts ðə roʊd/
"where the rubber meets the road" picture
1.

いよいよ本番, 正念場

the point at which a theory or idea is put to a practical test; the crucial point of a situation

:
All the planning is done, now we're at where the rubber meets the road.
計画はすべて終わった。さあ、いよいよ本番だ
When it comes to actually implementing the changes, that's where the rubber meets the road.
実際に変更を実施するとなると、それがいよいよ本番だ