Riders assume the engine is the loud thing. It is not. At open-road speed, wind roaring over the helmet edges and visor is far louder than any 110cc engine, and it does not arrive as a one-off blast — it is a continuous low-frequency roar that fatigues hearing for hours after you park. Riders who do long distances without ear protection end the day with muffled hearing and ringing ears, repeated weekend after weekend. That is a hearing-damage pattern, not an annoyance.
Why it is worse in heat
Cracking the visor open for airflow in hot weather — the comfort habit explained in helmet-ventilation-hot-climate — doubles the noise at the ear. A loose helmet fit does the same: air hammering into the gap around the jaw turns the helmet into a drum. A correctly fitted helmet (helmet-fit-guide-vietnam) is quieter at the same speed, which is protection as well as comfort.
What earplugs actually do
Motorcycle earplugs are not meant to make you deaf to the road. They are designed to cut the low-frequency wind roar while letting traffic sounds, horns and voices through. Cheap foam plugs rolled tight and inserted deep do this well enough; filtered plugs shaped for riders do it more evenly across frequencies. What earplugs do not do is block your own horn or an approaching bus — with plugs in you will still hear the things that matter, usually more clearly, because the roar no longer masks them.
Wearing them correctly
Foam plugs only work rolled, inserted and held while they expand; worn half-out they do nothing. Reuse ends when they lose their spring or go grey from Hanoi dust — a box of cheap plugs beats one pair worn for a month. Comfort matters with a helmet pressed on top: choose low-profile plugs that do not stick out of the ear canal, or the helmet padding will push them into an ache. If you use an intercom, know that speakers blasting into a plugged ear partly undoes the point — keep intercom volume at conversation level (helmet-intercoms-bluetooth-vietnam).
The habit
Earplugs are the cheapest piece of rider gear you will ever buy, and unlike a jacket they protect something that does not heal. Long rides, highways and full-day trips are the priority situations; hearing damage is dose-based, so the hours add up. For everything else about riding comfortably through a Hanoi summer, see hot-weather-riding-motorbike-vietnam.