The Black Bay Chrono has been a one-size proposition since Tudor launched it in 2017: 41mm of stainless steel, 14.4mm thick, 49.9mm lug-to-lug. A serious watch by any measure — the MT5813 manufacture movement inside is COSC-certified and represents Tudor's most capable chronograph engineering — but one that some wrists have always regarded with a certain caution. The M79310N-0001 changes that. Announced in June 2026, the new Black Bay Chrono 39 is the first time Tudor has brought the manufacture chronograph down to a 39mm case. It arrives in a matte yellow dial with black sub-counters that has already earned it a name: the Bumblebee.
Why 39mm Matters for a Chronograph
Chronographs tend to run large. The functional logic is understandable — sub-counters, pushers, and a bidirectional rotor system require real estate — and the category has historically tolerated 41mm, 42mm, and above as a result. Tudor's original Black Bay Chrono fit comfortably in that tradition. What it could not do was fit comfortably under a shirt cuff, or sit without presence on wrists below about 17cm.
The move to 39mm is not cosmetic. The case is genuinely smaller: 2mm less in diameter, and — more meaningfully — 1.3mm thinner at 13.1mm versus the 41mm's 14.4mm stack height. On a chronograph, that 1.3mm difference is the gap between a watch that catches on a shirt cuff and one that disappears under it. The lug-to-lug drops to 47mm from 49.9mm, reducing overhang on smaller wrists by nearly 3mm.
Together these numbers represent a meaningful recalibration rather than a minor update. Tudor has not simply shrunk the dial — it has reengineered the proportions for a different kind of daily use.
The Yellow Dial
The choice of yellow as the launch colorway for the 39mm is not accidental. The matte yellow field with contrasting black sub-counters occupies a visual register that Tudor has explored deliberately over the past few years — the same bold use of color that characterizes the broader Daring Watches collection of which the M79310N is a part. The result is a high-contrast, purposefully legible layout: yellow ground, black registers at 3, 6, and 9 o'clock, blackened snowflake hands, applied markers filled with white Super-LumiNova.
The tachymeter bezel uses a black anodized aluminum insert with silver markings — functional, readable, resistant to fading in the way aluminum has always been — paired with the fixed steel case construction that keeps the bezel proportionally tight on the smaller diameter. The three-link stainless steel bracelet carries alternating polished and satin-brushed surfaces, with Tudor's T-Fit micro-adjustment system in the folding clasp. The Daring Watches family also includes Pink and Flamingo dial variants; the yellow is the boldest read of the three and the one most people will call the Bumblebee from the first glance.
The Movement: MT5813
Both the 39mm and the 41mm Black Bay Chrono run the same calibre: the MT5813, a column-wheel automatic chronograph co-developed with Breitling and architecturally derived from the B01. It is COSC-certified, beats at 4Hz, delivers 70 hours of power reserve, and uses a silicon balance spring for antimagnetic resistance without the fragility of traditional hairsprings.
The column-wheel architecture ensures smooth pusher engagement. The vertical coupling clutch eliminates the hand jump that plagues less refined chronograph mechanisms. At this price point, the MT5813 sits among the more credible manufacture chronograph calibres available — and Tudor carries it across both case sizes unchanged. Buyers of the 39mm get the same mechanical substance as the 41mm with no concession to the more compact format.
39mm vs. 41mm: Side by Side
The numbers below illustrate exactly how much the new case format changes the on-wrist proposition.
| Black Bay Chrono 39 | Black Bay Chrono 41 | |
|---|---|---|
| Reference | M79310N-0001 | M79360N |
| Case diameter | 39 mm | 41 mm |
| Thickness | 13.1 mm | 14.4 mm |
| Lug-to-lug | 47 mm | 49.9 mm |
| Movement | MT5813 (COSC) | MT5813 (COSC) |
| Power reserve | 70 h | 70 h |
| Water resistance | 200 m | 200 m |
| Price (EUR) | 6,200 | from ~5,350 |
| Price (USD) | $6,725 | from ~$6,650 |
The 1.3mm reduction in thickness and the 2.9mm drop in lug-to-lug are the figures that will determine fit on most wrists. The diameter difference of 2mm is noticeable in person but secondary to those two measurements when judging whether a watch clears a cuff or lies flat on a smaller wrist.
Who It's For
The Black Bay Chrono 39 is not a replacement for the 41mm — both remain in Tudor's catalog, and the larger watch continues to serve wrists and preferences that work well with it. What the 39mm adds is a version of the same manufacture chronograph that a broader range of proportions can wear without compromise.
At 47mm lug-to-lug and 13.1mm thick, the M79310N is scaled for wrists in the 16–18cm range where the 41mm has always overhung slightly. It is a dress-adjacent chronograph in a way the 41mm was never designed to be — something that works at dinner as credibly as it works at a weekend market. The yellow dial signals that Tudor intends the Bumblebee to be noticed; the 39mm case means it can actually be worn more often.
How It Sits Against the TAG Heuer Carrera Glassbox 39
The Carrera Glassbox is the other 39mm chronograph that comes up most often in the same conversation as the Black Bay Chrono 39. Both are steel, both are 39mm, both use manufacture-derived column-wheel movements. On paper, they occupy the same category. The specs tell a different story.
| BB Chrono 39 Bumblebee | Carrera Glassbox 39 | |
|---|---|---|
| Reference | M79310N-0001 | CBS2216 / CBS2210 |
| Case diameter | 39 mm | 39 mm |
| Thickness | 13.1 mm | 13.9–14.1 mm |
| Lug-to-lug | 47 mm | ~46 mm |
| Movement | MT5813 (COSC) | TH20-00 |
| Power reserve | 70 h | 80 h |
| Water resistance | 200 m | 100 m |
| Price (USD) | $6,725 | from ~$4,700 |
The most striking number is thickness. At 13.1mm, the Black Bay Chrono 39 is meaningfully slimmer than the Carrera Glassbox — between 0.8mm and 1.0mm depending on which Glassbox reference you measure. That gap is felt more than it appears on a spec sheet; it is what separates a watch that sits flush against the wrist from one that carries just a little more height.
The Glassbox has advantages of its own: 10 more hours of power reserve, a lower price of entry, and the distinctive dome of its namesake sapphire crystal, which gives the Carrera a visual softness the Tudor doesn't pursue. But if the priority is wearing a 39mm manufacture chronograph as low-profile as possible, the Bumblebee wins on stack height by a margin that wrist use will confirm.
Official page: tudorwatch.com — Black Bay Chrono 39