Ask a Hanoi rider where people actually fall, and the answer is rarely speed: it is the zebra crossing at the wet intersection, the steel plate across a dug-up lane, the polished tiles in front of a bank. The city is paved with a mix of surfaces, and a few of them are effectively friction-free when wet.
The four slick suspects
Road paint (crossings, arrows, lane lines), steel plates and manhole covers, glazed tiles on sidewalks and shopfront aprons, and polished stone at building entrances. Dry, most are fine; wet or dusty, all of them are treacherous.
Cross them like ice
Upright bike, steady speed, no brakes, no throttle change, no lean. If a slick patch sits mid-corner, hold the lean you have — do not add brake. This is the same logic as emergency-braking: painted lines are exactly where front wheels lock, emergency-braking-motorbike-vietnam explains why.
Place your wheels
You have options: the paint strip is usually only a few tens of centimetres wide. Look for clean asphalt beside it and route around it. Cornering discipline — eyes and line — makes this automatic; cornering-motorbike-vietnam.
After rain, before trust
Wet tiles and steel hold their film long after asphalt dries — after-rain-slippery-roads-motorbike covers the post-rain timing. The first minutes of drizzle are the worst of all.
Standing water hides the slick stuff
Flooded streets cover exactly the surfaces you cannot see: a submerged steel plate or painted arrow gives no warning at all. Keep speed right down through standing water and exit it upright — flooded-streets-riding-motorbike-vietnam is the full guide.