[Formula 1] #060 - The Secret Story of Seamless Shift Development: The Transmission That Achieved 'Zero Torque Interruption' Through Honda's 2,500km of Testing
When watching F1, you notice that the car does not lose speed while accelerating and shifting gears. Whenever there is a momentary loss of speed during a gear change, it is because there is an instant where engine power is not reaching the wheels. However, in F1 since 2005, that 'moment of disconnection' has become almost zero. The seamless shift, which BAR Honda introduced into competition for the first time in the world, is a technology that fundamentally changed F1 gear shifting.
In this article, we will follow the history of its development, its world-first introduction amidst adversity, and its influence on the new era of 2026.
This article presents the latest trends in technology, selected by the author—an engineer and consultant—in an easy-to-understand format of approximately 3,000 characters. If you found this article helpful, please give it a like and follow.
'The distance to the car in front has closed'—The meaning of the 0.4 seconds Button felt
In 2005, Jenson Button, driving the BAR Honda 007, said he experienced a rare sensation. 'The gear shifts are seamless, with absolutely no feeling of hitting a wall. Every time I shift up, the distance to the car in front closes.'
What Button felt was an average lap time reduction of 0.4 seconds per lap. In a race, 0.4 seconds is a difference large enough to override a pit stop strategy by one level. 0.4 seconds is the cumulative value gained from 15 to 20 gear changes per lap. That is a reduction of about 0.02 to 0.03 seconds per shift. Compared to the 0.05 seconds it takes for a normal F1 gear change, this has been compressed to less than half.
Almost all the F1 gear shifts you see on your screen today are built upon this technology. When you hear the engine sound rising continuously without interruption in onboard footage, that is the moment the seamless shift is working.
The pain points of the old world—An era when torque was interrupted every time you shifted
Until the arrival of the seamless shift, F1 gear changes operated on a simple procedure: disengage the current gear, then engage the next gear. During this two-step process, engine power would inevitably fail to reach the wheels for a split second. This gap was a problem even in 1990s F1. Even in the era of 7-speed and 8-speed multi-gearboxes, this 'power gap' during shifting was physically unavoidable. The gap time was reduced from 50-60 milliseconds to 25-30 milliseconds through the evolution of electronic control. But even if it was reduced, it was still an interruption.
Even more serious was that this gap could trigger a crash. If a gear change occurred the moment the accelerator was fully opened at the exit of a corner, power would suddenly return to the rear wheels, causing skidding or spinning when the tires were near their limit. Honda's engineers tackled this challenge with the idea of 'reversing the sequence of gear changes itself'.
'Engage the next gear first'—The mechanism of reverse thinking and the protest to the FIA
The mechanism of the seamless shift implemented by Honda is as follows: when shifting up, the next gear is moved in advance to a position just before the dogs engage. It waits while the current gear is transmitting torque, and at the moment the accelerator is momentarily eased, the current gear disengages while the next gear slides in simultaneously. Engine power transitions to the next gear without interruption.
The problem is that there is a moment when two gears are in contact at the same time. In a normal gearbox, if two gears engage simultaneously, catastrophic force is concentrated on the entire drivetrain, causing the gears to break. Honda solved this with a mechanism called a one-way clutch. A one-way clutch is a component that transmits force in only one direction. By making it one-way, they created a state where two gears could momentarily coexist.
Honda adopted a single-barrel system that housed all gears in one drum. In contrast, the twin-barrel system later adopted by McLaren and others separated even and odd gears into two separate drums. While both share the principle of 'having the next gear wait in advance,' the mechanical implementation differs.
After the 2005 season-opening Australian GP, Ferrari protested to the FIA, claiming, 'This transmission is equivalent to a CVT and violates the prohibition regulations.' A CVT is a mechanism that changes the gear ratio continuously without switching gears in stages. The then-FIA President Max Mosley judged it to be legal after a review by the Technical Committee. Honda's technology survived.
In the midst of a suspension—The world-first introduction born from adversity
In 2005, the year BAR Honda achieved its world-first introduction, a scandal was simultaneously unfolding that shook the team. After the 2005 San Marino GP, an FIA technical inspection revealed a violation in the fuel tank of the BAR Honda 007. The issue was that a structure was built into the tank to make it appear as fuel, allowing the car to meet the minimum weight requirement. The team was suspended for two races, the 6th and 7th rounds.
After the suspension was lifted, the team returned with the 007 equipped with the seamless shift. Because they were in the midst of a scandal, the gamble on the new technology was significant. The engineers had no choice but to provide answers with results on the track.
The rivals' pursuit was swift. Ferrari and Renault introduced similar technology in 2006, and McLaren entered with a twin-barrel system in 2007. In 2008, the seamless shift became a standard technology under FIA regulations, and all teams were required to use it for four consecutive races. Within three years of BAR Honda's world-first introduction in 2005, it became the standard for all of F1.
Honda was further developing a next-generation 'in-shaft' improved version. The goal was to clear a 2,500km durability test. However, at the end of 2008, Honda announced its withdrawal from F1. Development was interrupted at the 1,300km mark, and the in-shaft type remained in the records as a phantom technology.
2026: MGU-K Output Triples—A New Dimension for Seamless Shift
The 2026 F1 technical regulation changes pose a new problem for seamless shift technology. The electric motor output will increase from the current 120kW to 350kW, roughly tripling. This means three times the power will continue to flow even during the moment of gear shifting.
Seamless shift was designed to fill the torque gap of internal combustion engines, but from now on, it must maintain zero power interruption while including integrated control with the electric motor. How to combine the torque of the internal combustion engine and the electric motor at the exact moment of gear shifting is the challenge that engineers at each team are tackling.
Honda will return to F1 in 2026 by supplying power units to Aston Martin. How will the technical lineage of Honda, which created the seamless shift, answer this new dimension of integrated control with electric motors? Twenty years after its world-first introduction in 2005, the essential technical question remains unchanged: how to keep power from being interrupted during the moment of shifting.
Summary
The history of the seamless shift reflects the typical structure of F1 technological innovation. To address the long-standing problem of torque interruption during every shift, Honda achieved a breakthrough with the idea of 'reversing the sequence.' They overcame Ferrari's protests and the adversity of a fuel scandal to deploy it in competition, and within three years, it became the industry standard.
When you hear the engine sound accelerating without interruption in F1 footage today, that is proof that the seamless shift is working. As you watch, please keep in mind how the next generation of engineers will answer the new challenge of tripling the electric motor output in 2026.
If you would like to continue following F1 technological innovations with us, please follow and like this content.
References
いいなと思ったら応援しよう！
記事がお役に立てば、応援いただけると嬉しいです！いただいたチップは、より良いコンテンツ作りのための活動費に使わせていただきます。