The transmission is one of the most complex technical components on a motorcycle, and the Seamless system is the Rolex of the gearbox. A true work of watchmaking, it is very exclusive and complex… Now let's tackle the technical side of it.
It is possible to have access to the various patents of Honda, Yamaha, Ducati or even ZeroShift (which equips Aprilia) on the internet. According to Honda's patents, the input shaft and gears are essentially a single piece, rotating at the same speed at all times. On the secondary shaft, all the gears rotate freely, but inside each gear is a set of four dog rings which therefore allow the gear to be locked onto the shaft to transmit power. These are moved on axles which extend outwards from the center of the shaft by a set of internal springs. The clutches only transmit torque in one direction of rotation. Thus, two of the clutches lock for the higher gear (acceleration), while two others lock for the lower gear (deceleration).
This diagram, present in numerous documentation on the Honda gearbox, shows the locking finger system (red arrows) which engages each gear with the output shaft to transmit power.
When the rider upshifts, the springs retract, but as long as power is still applied, the original gear's dogs remain locked in place and that gear will transmit the power. Once the next gear is engaged and takes the load, the shaft begins to rotate faster than the original gear and the clutches disengage. Everything is reversed if the motorcycle decelerates and the rider downshifts.
Since there is no torque interruption, the gear change is without transition for the pilot.
Here we see the forks, the clutches on the rings and the gears
The video explanation below is less painful to the head (the company ZeroShift equips Aprilias in MotoGP):
It brings a lot to the pilot!
When it first appeared in 2011 at Honda, everyone thought about the potential time savings by eliminating the neutral between gears. If there are, for example, 40 gear changes per revolution and the shifter cut-off time is 20ms, a gearbox seamless pattern should bring a gain of 0.8s, which should have been reflected in the lap time.
HRC was the first team to develop this technology
But that’s not how the pilots felt. Valentino Rossi underlined this when speaking of his Yamaha, equipped in 2015 with a gearbox similar to that of the Honda: “However, there is no big difference on a single lap,” he said. “We tried to make comparisons. I think the most significant progress will be seen over 20 or 30 laps because the bike becomes easier to ride, it is more stable when accelerating and braking. »
Valentino Rossi's M1 has been equipped with a Seamless gearbox since 2015
Highlighting the benefits of the box seamless pattern on the behavior of the M1, Red continued : “We can use the gears more to drive. I mean if you need to change while you're on the angle, you can do it! There is also less stress on the tires and this is therefore very good for the riders because when the bike is easier to ride, you can push it to the limit without making mistakes as easily. So I think it will be something very important over the race distance, more than over a single lap. » Indeed, rather than entering a curve at under or over revs, they have the possibility of shifting gears in a curve without adverse influence on the trajectory.
And the cost?
Another problem is cost. A typical six-speed gearbox has about 80 parts, including gears, shafts, forks, shims, circlips, etc. A box seamless pattern as described in the Honda patents appears to have around 300 parts, with 16 individual parts per report related to the ratchet mechanism alone. Some of these parts are very small and subject to very high load. Transmissions seamless pattern in MotoGP would need daily maintenance on the track by a dedicated technician.
Such a meticulous gearbox is very expensive
When will there be a “Seamless” gearbox on the road?
It is very unlikely that you will see this type of transmission seamless pattern anytime soon on your motorcycle, even if you're on the track. One reason is that, given the construction described previously, neutral is difficult to integrate. And obviously, the astronomical cost of this technology would put off more than one biker!
