Name: Tudor Black Bay GMT M79830RB-0001
Brand: Tudor
SKU: M79830RB-0001

The Black Bay GMT (ref. M79830RB-0001) is Tudor's traveler's-GMT, 41mm steel, red/blue 'Pepsi' bezel insert in aluminium, and the in-house MT5652 caliber with an independently-jumping local hour hand. Launched in 2018, it answered the long-standing 'why can't I have a GMT-Master at half the price?' question without compromising on the one specification that matters: the local-hour-jump that makes a GMT useful in actual travel.

What it is

Tudor announced the Black Bay GMT at Baselworld 2018, a year that also saw the Pelagos LHD GMT and a renewed focus on Tudor's in-house movement portfolio. The MT5652 caliber is a chronometer-certified GMT with a 70-hour reserve and a true traveler-GMT layout (jumping local hour hand, not the cheaper office-GMT layout where only the 24-hour hand is independent). Bezel-insert variants ship in red/blue ('Pepsi') and a later black/grey ('Earl Grey') and the 'Opaline' silver dial.

The Coke-style red/black bezel is not a factory Black Bay GMT issue.

Buying notes

Common things to check: bezel insert (aluminium, not ceramic, fading and minor scratching are normal on used examples; severe denting is a service item); crown function (the GMT crown layout has three positions, verify the local hour hand jumps independently in position 2 and the date moves in position 1); bracelet (the riveted-style bracelet is the canonical option; rubber, fabric, and aged-leather straps also ship factory, verify the bracelet against the box contents); the MT5652 caliber is robust, but the GMT module adds wear surfaces that benefit from a service every 7-10 years; a heavily-traveled example with no service history should be priced with a service factored in.

Market read

MSRP is approximately $4,400 on bracelet; the secondary market through 2024-2026 trades clean full-set examples in the $3,800-$4,500 range, close to MSRP and meaningfully below the GMT-Master 126710BLRO (current retail ~$10,900). The 'Pepsi' configuration is the most-traded variant; the 'Earl Grey' bezel has historically traded at a modest discount and is the value buy within the line. Authorized-dealer allocation has loosened since 2023.

Service expectations

Service is performed by Tudor and competent Rolex/Tudor independents, the same service network as the BB58. Service interval is 7-10 years; cost is moderate (low-four-figures via Tudor). The GMT module is the wear point worth watching on examples that have been in regular use; otherwise the watch is as service-tolerant as any modern Tudor.

Editorial copy is AI-drafted from primary sources and reviewed by Grail Atlas before publication. Where the text is uncertain about a fact, it says so. Email corrections@grailatlas.com if something reads wrong. Signals on this page (community, OSINT) are clearly separated from the editorial sections.

GPHG 2018EnteredChallenge category

Entry to the Grand Prix d'Horlogerie de Genève is voluntary and made by the brand. An entry is a watch registered for that year's competition, not a jury verdict, and several large houses including Rolex, Patek Philippe and Omega do not take part at all.

The Black Bay GMT with its bi-directional 24-hour bezel is the most functional Tudor and the strongest secondary market performer in the Black Bay family outside the BB58.

Mass-producedmost sought#2 in familyOfficial press photos

What it was up against

Challenge, GPHG 2018

The Challenge category at GPHG 2018 held 35 entries. These are the other 34.

Filter the full GPHG field for Challenge, 2018

Condition affects price

Pre-owned watches trade across a wide condition spectrum. These ranges are typical for the secondary market.

New Old Stock

Unworn example retaining original packaging, tags, and warranty documentation.

+30–50% vs median

Unpolished

Worn but the case has never been polished; original brushed and polished surfaces are intact.

+15–25% vs median

Polished

Case has been professionally or amateur polished at some point; edge definition is softened.

-15 to -5% vs median

Recently Serviced

Movement has been recently serviced with documented service records; case condition varies.

At median

Project

Needs service, has dial or hand issues, non-original parts, or other remediation before daily wear.

-50 to -25% vs median

Full condition grading guide →

Market price

$3,200–$4,500

steel·2026 Q2

Price trend chart coming soon

The Black Bay GMT is Tudor's most technically complete reference and commands the highest secondary prices in the Black Bay lineup outside the limited editions; demand from GMT-function buyers is consistently strong.

Editorial estimate, 2026 Q2. Actual prices vary by condition, date, and box/papers status.

Movement tier: unclassified · caliber Tudor MT5652: in-house automatic GMT, 28,800bph, 70h PR, 26j; COSC-certified, bidirectional winding; used in Black Bay GMT · 70h power reserve (2.9 days)

Medium-large: suits wrists 6.5 in+ (16.5 cm+)

41 mm case. Wears confidently on average to larger wrists. May overhang on slender builds.

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Authentication

MT5652 in-house movement with bi-directional 24-hour bezel and correct two-tone color split authenticate the Black Bay GMT

Known issues in the market

Red/blue "Pepsi" and grey/blue "Facel" bezel variants have different desirability profiles; verify the bezel color matches the claimed reference
ETA-free from launch; any claimed Black Bay GMT with ETA movement is incorrect or a parts watch
Bezel color accuracy on fakes is the most common shortfall; red should be true red, not orange-red

Area	What to check	What is correct	Red flag
movement	MT5652 in-house automatic	"Tudor MT5652" engraved; manufacture movement (not ETA); exhibition caseback standard; 70-hour power reserve; "Tudor" signed; COSC certification optional per variant	ETA 2893 base (incorrect for Black Bay GMT); movement unsigned; power reserve inconsistent with MT5652 specification; no exhibition caseback
case	Snowflake hands and GMT-specific 41mm case	41mm diameter; snowflake hour hand with luminous fill; red or aluminum GMT hand reaching 24-hour scale; "TUDOR" on signed crown; screw-down crown; 200m water resistance	Non-snowflake hour hand; GMT hand not reaching outer bezel scale; incorrect case diameter; crown without Tudor signing
crystal	Two-tone rotating bezel	Bi-directional 24-hour bezel (both directions, unlike dive watches); correct color split at 12/24 position; "AM/PM" or numerical 24-hour scale; aluminum or ceramic insert per variant	Uni-directional bezel (dive watch, not GMT); color split at wrong position; incorrect hue on red or grey sector; scale numerals inconsistent with documented variant

Common legitimate replacements

Riveted Rouleaux bracelet is desirable original option; leather strap also OEM; aftermarket replacement common.
GMT hand tip luminous material can fade; verify it reaches the outer bezel and is correctly proportioned.

Expert resources: Tudor authorised dealers authenticate via serial. Fratello Watches Black Bay GMT review documents calibre and bezel color in detail.

Authentication guide

Last reviewed June 2026

The Black Bay GMT is powered by the MT5652, Tudor's in-house bidirectional GMT caliber. The bicolor aluminum bezel (red and blue "Pepsi" or black and blue "Batman") is the signature visual, and the GMT hand is independently settable via the crown. The snowflake hands are the house signature across all Black Bay models; hand proportion is the first thing to check on any suspected non-original example.

Known reproduction risks

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HIGH RISK

Replicas targeting the Black Bay GMT, often using ETA or Sellita GMT base movements that lack the bidirectional independent GMT function.

Snowflake hand proportions off: too narrow, too tapered, or with wrong lume plot shape -- this is the easiest single check
GMT hand that moves with the local hour hand rather than advancing independently at crown position 1
Bicolor bezel with a color join that is not sharp at the 6/18 division
Tudor caseback markings with incorrect text layout or the wrong Tudor shield proportion

MEDIUM

Genuine Black Bay GMT cases fitted with non-MT5652 movements from other Tudor references or third-party GMT calibers.

Power reserve shorter than 60 hours from full wind
GMT hand that cannot be independently set
Movement sounds or beat rate inconsistent with 28,800bph

Dial variants by era

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Era	Description	Identifiers
2018 to present (red and blue "Pepsi" bezel)	Black dial with snowflake hands and applied dot indices. The bicolor red and blue bezel with 24-hour scale is the defining configuration. The MT5652 is Tudor's first bidirectional in-house GMT caliber.	Snowflake hands: flat, wide hands with rectangular lume plots -- not the sword or Mercedes hands of other sport watches Bicolor aluminum bezel with red (nighttime) and blue (daytime) halves, 24-hour scale GMT hand with a distinct arrow tip; sets independently via the crown at position 1 Applied dot indices at each hour position 41mm case with a screw-down crown and 200m water resistance
2018 to present (black and blue "Batman" bezel)	Same specification with a black and blue bicolor bezel instead of the red and blue "Pepsi."	Snowflake hands consistent across all Black Bay GMT variants Black (nighttime) and blue (daytime) bicolor bezel Same MT5652 movement and 41mm case as the Pepsi variant

Service part flags

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Snowflake hands

Original: Tudor's snowflake hands are wide and flat with a square lume plot inset near the tip. The profile is distinctive: the hour hand is broader relative to its length than most sport watch hands. Reproductions frequently get the proportions wrong -- either too narrow, too pointed, or with incorrectly shaped lume plots.

Replacement tells

Hour hand with a tapered or pointed profile rather than the flat wide rectangle of the genuine snowflake
Lume plots that are round rather than rectangular, or that do not extend to the correct proportion of the hand width
Seconds hand that does not match the lighter, thinner snowflake profile -- the seconds hand is also wider-than-normal but distinct from the hour and minute hands
Hands with polished surfaces rather than the correct matte finishing of the genuine snowflake hands

MT5652 GMT movement

Original: Tudor MT5652 is an in-house automatic GMT, 28,800bph, 70-hour power reserve, 26 jewels. METAS-certified. The GMT hand advances independently via the crown at position 1 in one-hour increments without stopping the seconds hand.

Replacement tells

GMT hand that cannot be set independently at crown position 1 -- if the GMT hand only moves with the local hour, the movement does not have a proper GMT function
Power reserve depleting in under 48 hours from full wind -- the MT5652 is rated 70 hours; under 50 hours suggests a different movement or a worn mainspring
Caseback showing a movement without Tudor hallmarks: the MT5652 caseback has Tudor branding and the MT designation visible through the caseback if exhibition; solid caseback has Tudor markings on the outside
Seconds hand that stops during local hour adjustment -- on the MT5652, the local hour hand adjusts without stopping the seconds hand

Bicolor aluminum bezel

Original: Aluminum bicolor bezel with a 24-hour scale. Aluminum is softer than ceramic; genuine Tudor aluminum bezels will show normal wear marks from use, but should not have scratches inconsistent with the watch's overall condition. The color join is clean and sharp at the 6/18 position.

Replacement tells

Color join between the two halves that is not sharp or is offset from the 6/18 position on the 24-hour scale
Bezel insert with a sheen or color inconsistent with Tudor's aluminum specification
Single-color bezel on a stated Black Bay GMT -- the bicolor bezel is standard for this reference

Case back markings

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2018 to present

Solid caseback with Tudor shield and rose hallmark at center
"TUDOR BLACK BAY GMT" on the outer ring
"MANUFACTURE MOVEMENT" designation on later examples
"200M / 660FT" water resistance rating
Reference M79830RB and serial number on the case midband between the lugs
METAS certification mark on movement-facing side (visible if caseback removed)

Movement tells

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MT5652, 28,800bph, 70-hour power reserve. A fully wound Black Bay GMT should run 65 to 70 hours before stopping.
The local-hour quick-set function: crown position 1 advances the local hour hand in one-hour jumps without stopping the seconds hand. This is the key functional test for genuine MT5652 operation.
METAS certification requires the movement to maintain rate within specified tolerances in multiple positions; a timegrapher check across dial-up and crown-up positions should show low variation.
Silicon hairspring on the MT5652: immune to magnetic interference. Placing a strong magnet near the case should not affect rate if the movement is genuine.

Sources: Fratello -- Tudor Black Bay GMT review; Tudor -- MT5652 movement specification.