Generally-speaking, there are three types of transmission, including manual, automatic, and continuously-variable (CVT). Interestingly, CVTs are only available on scooters and a very few motorcycles, and the rest of the motorcycle fleet is equipped with manual transmissions. Automatic transmissions are practically unheard-of on motorcycles, but there is a relatively-new transmission, found in racing, which is making waves and winning titles, the seamless-shift gearbox. It’s good to note that this is not a dual-clutch transmission, which is illegal in MotoGP racing.
As in all racing, speed is the name of the game. In motorcycle racing, there is plenty of upshifting and downshifting, and this creates a problem. When races are judged by hundredths-of-a-second difference, between one racer and the next, even the slightest things can be the difference between first- and second-place. Tire pressure, aerodynamics, and even how fast the transmission shifts can add or subtract precious time from a lap.
The manual transmission, on a Ducati Desmosedici racing bike, can shift between gears in a stunning 42 ms (milliseconds) – the typical road bike shifts at a pokey 600 ms, or six-tenths of a second. Even road and track quick shifters, which cut the throttle for an infinitesimal amount of time to reduce shift shock, can only reduce shift time to 65-80 ms.
Even that’s not fast enough, however, and still generates a problem: During the shift, no power is being transmitted to the wheels, which means lost time, but that’s not all. At high speed and high power, power letting off pitches the bike forward, then putting power back on pitches the bike backward. The resulting instability further increases time losses as riders compensate.
Seamless shift gearboxes, first introduced by Honda in 2011, absolutely dominated the track, but not for the reasons you think. By eliminating neutral between gears, engaging the higher gear while the lower was still disengaging, or vice-versa while downshifting, Honda could reduce shift times to around 8 ms. Eight-milliseconds may sound like a great improvement, but it’s not great because it’s fast – it’s great because it’s stable.
Because the Honda, and later Yamaha in 2015, seamless shift gearbox shifts so fast, the shift shock is nearly imperceptible. There is no lurch and shift bump, so the rider is more stable. Because the ignition doesn’t cut out, there’s zero power drop. The end results speak for themselves, because Honda’s introduction of the seamless shift gearbox dominated the track in 2011 and 2012, and Yamaha’s seamless shift gearbox won 11 races and 16 podium finishes, as well as the Triple crown, in 2015.
Though the seamless shift gearbox was developed strictly for racing, we haven’t seen any street bikes with the new technology. Still, there’s hope. If the transmission is approved for use in World Superbike class, then manufacturers would be forced to produce at least 250 road-legal versions of the bike for sale to the public.