Introducing the T0, Grand Seiko’s Concept Breakthrough Constant Force Tourbillon

Grand Seiko shared some surprising news last week: the brand has developed a new movement featuring a tourbillon and constant force mechanism. This is a very big deal for the brand, which has never produced a tourbillon enabled wristwatch, much less any movement featuring a remontoire (although Credor, which falls under the Seiko umbrella, produced a tourbillon in 2016). Still, it makes sense for the brand, when you consider certain recent breakthroughs they’ve made in movement tech, and their history of focusing like a laser beam on chronometry.

To understand how this movement came about, it’s best to go back to the introduction of the 9SA5 caliber, which we covered earlier this year. This high beat movement, with an extended power reserve, was introduced in the SLGH002, a solid gold dress watch that’s very much a halo product for Grand Seiko in their 60th anniversary year. Among this movement’s many novel features is a brand new dual impulse escapement, which dramatically improves efficiency in the 9SA5, allowing for the 80 hour power reserve and a high level of accuracy throughout the duration of that 80 hour period. One of the great problems in movement making is compensating for the negative effect on timekeeping as the mainspring loses power. The 9SA5’s escapement, along with some creative MEMS manufacturing techniques that Grand Seiko has pioneered, go a long way to mitigating the issue. 

But there’s another way to combat this problem that involves the use of the constant force principle to deliver power to the escapement at the same rate throughout the span of a movement’s power reserve. Constant force mechanisms are having something of a moment right now – we just discussed two notable new takes on the concept in our Geneva Watch Days roundup. While it’s likely something of a coincidence that the watches by Ferdinand Berthoud and Bernhard Lederer that we highlighted last week are coming to market at the same time, the reveal of Grand Seiko’s remarkable new caliber is directly related to the development of the 9SA5. 

The T0 (that’s “tee-zero”) movement, as it’s called, was developed in parallel to the 9SA5 as a concept, and allowed the team at Grand Seiko to harbor data and design components that ultimately made their way into the production version of the 9SA5. It speaks to Grand Seiko’s commitment to chronometry and pushing boundaries in movement making that their process for creating a new caliber is essentially to create two new calibers. The 9SA5 found its way into a regular production and, it seems likely, will be featured in new watches down the line as the years go by at Grand Seiko, thanks in no small part to what their technicians learned in thinking through the T0. And while this tourbillon movement hasn’t been mated to an actual watch just yet, Grand Seiko has indeed built it, and are claiming that it’s capable of keeping time to 0.5 seconds per day in a controlled environment. That’s quite a breathtaking achievement, even more so when you consider that it came along by way of what was essentially a research project for the development of another movement. 

So how does it all work? The governing idea behind the creation of the T0 is to deliver maximum torque to the balance for the longest possible period. This is the goal of any rementoir, but there’s a natural tradeoff that occurs depending on where a watchmaker places the constant force mechanism within the gear train. When the rementoire is placed closer to the mainspring, it’s easier to control power as it unwinds, but it’s less efficient, and torque is uneven. If the rementoire is placed further down the gear train and away from the mainspring (thus, closer to the balance) it can deliver power in a more stable manner, but the mainspring’s unwinding is less predictable. 

Grand Seiko’s solution was to place the rementoire as close to the balance as possible, but underneath a tourbillon, which reduces the impact of gravity on an unwinding mainspring. Unlike most tourbillons, this one uses two cages. As the outer cage rotates, it powers the rementoir underneath it, and the charged energy in turn powers the inner tourbillon cage as opposed to delivering power directly to the escapement. The distribution of energy from the constant force spring is controlled by a ceramic stop wheel that’s mated to the inner tourbillon cage.

The result, in theory at least, should be stable and predictable power, with torque stored and subsequently released for the purposes of rotating the tourbillon cage, with the balance inside of it. 

Torque is maximized at the start of the gear train through the use of dual mainspring barrels that run in parallel, as opposed to in sequence. Often, when we see movements in dual barrels, one must expire before the other is used. This allows for lengthy power reserves, but the delivery of that power is inherently uneven. With twin barrels running simultaneously, torque is doubled and controlled through the gear train by the rementoir, with the tourbillon acting as a further safeguard against the effects of gravity. 

Amazingly, all of this novel technology, much of which has never been implemented in precisely this manner, is based on the movement architecture of the tried and true Grand Seiko 9S65 caliber, the brand’s most basic, 3-day automatic movement, that runs so many of their watches. This is the Grand Seiko equivalent of a “workhorse” caliber, and is capable of incredible accuracy on its own, but has been turned up a notch or two at the very least with so much new tech downloaded on top of it. Again, this speaks to Grand Seiko’s unique ability to innovate through research, and by pushing what they do everyday to the next logical step, over and over again. 

Right now, because this remains a concept without an actual watch attached to it, we must live with the visuals of the T0 alone. That’s not a problem, because Grand Seiko has gone to the trouble of making the thing incredibly stunning to look at. At the top we have two large mainspring barrels, and can carefully observe the movement of power down the gears to two separate tourbillon cages (three arms each, in blued titanium). The appearance is appropriately dramatic for such a complex and innovative movement. 

As we noted when discussing the SLGH002 earlier this year, the excitement around a new high end innovation from Grand Seiko isn’t necessarily around the specific product it’s attached to. Indeed, with the T0, there is no product, just a one-off movement. The excitement is in the possibilities for the future. Will Grand Seiko put the T0 into production, ringing in a new era of high performance super watches from the brand? Will technology from this caliber trickle down to more affordable watches at the consumer level? A week ago, none of this was on the table, and now it is. And that’s an exciting thing for fans of the brand. 

The T0 is on display at the newly opened Grand Seiko Studio Shizukuishi, on the second floor. Visitors to the studio will be able to view the movement in action, while wondering what kinds of incredible watches Grand Seiko might create in the future that use it. Grand Seiko