Most real-world drum parts don't politely stay in one subdivision for a whole bar. A fill rolls in with 8ths, snaps into 16ths, and lands on a triplet. To read music like that — and to play it cleanly — you have to do something that sounds simple but is genuinely hard: change the subdivision in your head while keeping the underlying pulse rock-steady.
The pulse is the quarter note. That doesn't move. What changes is how many strokes you fit inside each pulse: two for 8ths, three for triplets, four for 16ths. The skill is gear-shifting — switching counts mid-bar without the metronome drifting. The trick is to keep counting the quarter notes underneath at all times. The triplet count 1-trip-let sits inside the same beat as the 16th count 1 e & a; the 1 in both lands at the same place.
Take these slowly. The metronomes here look low because the test isn't speed — it's accuracy through the density change. Speed is something you only earn after the gear shift becomes invisible. Count audibly, and switch counts between beats, not during them.