Two gearboxes dominate Vietnam’s underbones: the rotary four-speed of the workhorse class and the manual six-speed of the sport class. They change more than the number of gears - they change who can ride the bike.
The rotary four-speed
Honda publishes “four-speed rotary” for the Wave Alpha, Blade, Wave RSX and Future 125 FI; Yamaha lists a four-speed rotary with a wet multi-plate centrifugal clutch for the Sirius RC. Rotary means the shift pattern cycles: 1-2-3-4-neutral-in-1… so you can always reach first by continuing to click down. A centrifugal clutch engages automatically with revs - no lever, no stalling in the classic sense. Full mechanics in our semi-automatic gearbox explainer.
The manual six-speed
Yamaha’s Exciter 155 VVA runs six speeds with an Assist and Slipper clutch (dedicated explainer). Honda’s Winner R and CBR150R pages list manual clutches without publishing gear-count detail. Six closely spaced ratios let the engine stay near its power peak - the Exciter makes its 13.2 kW at 9,500 rpm - at the cost of constant clutch work in traffic.
The practical difference in Hanoi
In stop-start flow the rotary four-speed wins decisively: shift when you like, never feather a clutch. On the open road the six-speed wins: real overtaking acceleration and engine-braking control. This is why the rental default here is the rotary class - our price-published Wave and Sirius classes (150,000 VND/day) both use it. Contact us to confirm current availability of either format.