Tudor Black Bay 58 vs Casio G-Shock GA-B2100 CasiOak
Two divers compared — $2,500–$5,000 vs $100–$150
Quick Verdict
The Casio G-Shock GA-B2100 CasiOak ($100–$150) delivers Casio Quartz (Solar-Powered) technology in the tier below the Tudor Black Bay 58 ($2,500–$5,000). The G-Shock GA-B2100 CasiOak measures 45.4mm (48.5mm lug-to-lug, 11.9mm thick) and is rated 200m (20 ATM). The Black Bay 58 justifies its premium with Swiss Made heritage and Automatic Manufacture Calibre MT5402. Both represent excellent choices in the diver category.
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Specifications Compared
| Feature | Tudor Black Bay 58 | Casio G-Shock GA-B2100 CasiOak |
|---|---|---|
| Price | $2,500–$5,000 | $100–$150 |
| Case Size | 39mm | 45.4mm (48.5mm lug-to-lug, 11.9mm thick) |
| Movement | Automatic Manufacture Calibre MT5402 | Quartz Module 5689 (Tough Solar + Bluetooth) |
| Caliber Type | In-House Automatic Manufacture (Kenissi) | Casio Quartz (Solar-Powered) |
| Power Reserve | 70 Hours | About 7 months on a full charge without light; about 18 months in power-saving (Casio) |
| Water Resistance | 200m (20 ATM) | 200m (20 ATM) |
| Crystal | Domed Sapphire | Mineral Glass |
| Case Material | 316L Stainless Steel | Carbon Core Guard Resin |
| Origin | Swiss Made | Made in Japan |
Category-by-Category Analysis
Design & Aesthetics
Tudor's design language vs Casio's approach
The Tudor Black Bay 58 features a 316L Stainless Steel case at 39mm with Domed Sapphire protection. The Casio G-Shock GA-B2100 CasiOak offers Carbon Core Guard Resin construction at 45.4mm (48.5mm lug-to-lug, 11.9mm thick) with Mineral Glass. Both represent their brand's distinct design philosophy and heritage.
Movement & Performance
Automatic Manufacture Calibre MT5402 vs Quartz Module 5689 (Tough Solar + Bluetooth)
The Black Bay 58 runs the Automatic Manufacture Calibre MT5402 (In-House Automatic Manufacture (Kenissi), 70 Hours power reserve) at 28,800 vph (4 Hz) frequency. The G-Shock GA-B2100 CasiOak uses the Quartz Module 5689 (Tough Solar + Bluetooth) (Casio Quartz (Solar-Powered), About 7 months on a full charge without light; about 18 months in power-saving (Casio) reserve) at standard. The Black Bay 58 edges ahead on power reserve.
Wearability & Fit
39mm vs 45.4mm (48.5mm lug-to-lug, 11.9mm thick) — different wrist presence
At 39mm, the Black Bay 58 wears more compactly on smaller wrists compared to the G-Shock GA-B2100 CasiOak at 45.4mm (48.5mm lug-to-lug, 11.9mm thick). Water resistance differs: 200m (20 ATM) vs 200m (20 ATM).
Value & Cost of Ownership
Casio sits in the lower tier
The Tudor Black Bay 58 sits at $2,500–$5,000 and the Casio G-Shock GA-B2100 CasiOak at $100–$150. On the specs that outlast any price: the Black Bay 58 uses Domed Sapphire with 70 Hours, against Mineral Glass and About 7 months on a full charge without light; about 18 months in power-saving (Casio) on the G-Shock GA-B2100 CasiOak. Service intervals are typically 5-7 years for both.
Water Resistance
200m (20 ATM) vs 200m (20 ATM)
The Black Bay 58 is rated to 200m (20 ATM) while the G-Shock GA-B2100 CasiOak handles 200m (20 ATM). Both offer identical water resistance ratings.
Materials Face-Off
| Component | Tudor Black Bay 58 | Casio G-Shock GA-B2100 CasiOak |
|---|---|---|
| In-House MT5402 Caliber | Fully in-house manufacture at Kenissi (Le Locle). 26mm × 4.99mm, 27 jewels, free-sprung balance with variable inertia regulation | Casio's proprietary monocoque case technology integrating carbon fibers into fine resin. The carbon fibers dramatically raise the tensile strength and modulus of elasticity of the case structure, allowing the GA-2100 to achieve an 11.8mm thickness — the thinnest analog G-Shock at launch — while maintaining full 10m drop impact resistance. Total case weight: 51g. |
| Silicon Balance Spring | Si hairspring providing antimagnetic protection and superior isochronism | Flat mineral glass with Mohs hardness ~6. Thermally tempered for impact resistance — flexes under force rather than shattering like sapphire. Not scratch-proof, but replacement crystals cost ~$10. |
| Domed Sapphire Crystal | Synthetic corundum (Al₂O₃) grown via Verneuil process, anti-reflective coating on inner surface Mohs 9 | Durable urethane polymer resistant to sweat, saltwater, UV radiation, and skin oils. Features quick-release spring bars. Known to last 5–10 years with daily wear before degradation. |
| Anodized Aluminum Bezel | Anodized aluminum insert with engraved 60-minute dive scale — deliberately not ceramic | Secured by 4 Phillips screws for 200m (20 ATM) water resistance. The GA-B2100 is Tough Solar: a rechargeable cell topped up by any light, so there is no coin cell to swap. Casio rates a full charge at about seven months of normal use without light, and about eighteen months in power-saving. |
| 316L Stainless Steel | Medical-grade 316L (Cr 16–18%, Ni 10–14%, Mo 2–3%). Satin-brushed tops, polished bevels | The luxury MRG-B2100 variant ($3,500+), hand-assembled at Yamagata Casio's Premium Production Line (PPL) by certified "Medalist" craftsmen, uses Cobarion® (cobalt-chromium alloy, 4× harder than pure titanium) bezels and DAT55G titanium (3× harder than pure titanium) bracelet links. |
Cost of Ownership Compared
Who Should Pick Which
Pick the Tudor Black Bay 58 if…
- True in-house COSC-certified manufacture movement at sub-$4,000
- 39mm "perfect proportions" — fits virtually any wrist from 6" to 8"
- Heritage collectors — direct lineage to the 1958 Tudor Submariner Reference 7924
- Wilsdorf Foundation (Rolex sister) pedigree without the waitlist or pricing
- 10-year service interval — longest in Swiss watchmaking, an explicit confidence statement
Pick the Casio G-Shock GA-B2100 CasiOak if…
- Anyone wanting an indestructible daily beater under $100 with serious design credibility
- Water sports enthusiasts — 200m WR with G-Shock shockproofing
- Watch modding enthusiasts — massive aftermarket ecosystem of metal conversion kits
- High-end collectors needing a dedicated beater alongside their luxury pieces
Tudor Black Bay 58
- No date complication — a feature for purists, but a limitation for daily-wearer buyers who want at-a-glance date
- 316L not 904L — Tudor uses standard steel, not Rolex's "Oystersteel" (practically irrelevant for the wearer)
- Aluminum bezel insert scratches more easily than ceramic — heritage-correct, but less daily-wear robust
- Bracelet endlinks are proprietary — limits aftermarket bracelet options (straps still work via drilled lug holes)
Casio G-Shock GA-B2100 CasiOak
- Stealth-black legibility deficit: The GA2100-1A1 has absolutely no Neobrite luminescent paint on hands or indices. Low-light readability is poor — you must rely entirely on the Double LED Super Illuminator.
- Mineral glass scratches: Not sapphire. Daily beater use will accumulate minor scuffs over time. Replacement crystals are cheap (~$10) but require caseback removal.
- Tiny digital subdisplay: The LCD window at 4:30 is small and genuinely difficult to read for anyone with less than perfect vision. The Hand-Shift feature (sweeps hands to 7:35 position to clear the LCD) helps but isn't a substitute for a full digital display.
- Module 5689 is quartz: For mechanical-watch purists, this is a non-starter. For everyone else, it's a feature — better accuracy (±15 sec/month), no winding, no expensive servicing, and solar charging that never needs a battery change.
Our Verdict
Tudor
Black Bay 58
Choose the Tudor Black Bay 58 if you prioritize In-House Automatic Manufacture (Kenissi) engineering, Swiss Made craftsmanship, and 200m (20 ATM) water resistance. At $2,500–$5,000, it delivers Automatic Manufacture Calibre MT5402 with 70 Hours power reserve.
Check Price on AmazonCasio
G-Shock GA-B2100 CasiOak
Choose the Casio G-Shock GA-B2100 CasiOak if you value Casio Quartz (Solar-Powered) technology, Made in Japan heritage, and 45.4mm (48.5mm lug-to-lug, 11.9mm thick) proportions. At $100–$150, the Quartz Module 5689 (Tough Solar + Bluetooth) with About 7 months on a full charge without light; about 18 months in power-saving (Casio) power reserve makes it a compelling choice.
Check Price on AmazonThe Bottom Line
The Tudor Black Bay 58 and Casio G-Shock GA-B2100 CasiOak represent two distinct approaches to the diver category — the Tudor bringing Swiss Made tradition while Casio delivers Made in Japan engineering.
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Our comparisons are generated from a hand-maintained specification database and reviewed under our editorial standards. We use AI tools to assemble pages from that data. We don’t invent specs: every number traces back to the database, and when we correct an entry, the fix is applied site-wide. As an Amazon Associate, The Horologist earns from qualifying purchases.