The short answer
A fake Big Pilot IW5105 stands or falls on three things: case thickness, crown shape, and how the dial is built. Photos rarely show any of them. Ask for a straight-on side profile, a macro of the crown, and a running movement shot. If the seller cannot send those, you are buying a guess.
What the IW5105 actually is
The reference sits inside IWC's Big Pilot line, so the design language is fixed: a large case, a big conical crown that sits proud of the case band, a legible black dial, and a long power reserve on most versions. Depending on the exact variant, you are looking at roughly 46mm across and about 15mm thick, with a 7-day Pellaton-wound movement and a power reserve display, or a smaller 43mm body with a 4Hz automatic and no reserve indicator. Confirm which one you are comparing against before you judge any replica. Judging a 43mm copy against 46mm specs is how people talk themselves into a bad watch.
Case and crown
This is where most fakes give themselves away. Replica Big Pilots routinely measure 44 to 45mm and come in a millimeter or two thin, which changes how the watch sits on the wrist more than photos suggest. The crown should be a fat cone with cut flutes, screw down cleanly, and stand off the case band. Cheap copies shrink it, smooth the flutes, or soften the edges until it looks like a generic onion crown. Turn the crown and feel for wobble. A stem that rocks side to side means the tube and gaskets are an afterthought.
Crystal and dial
Genuine Big Pilots use sapphire with anti-reflective coating on both faces, which is why the dial reads almost black from an angle. Single-sided or uncoated crystals glare hard and give the dial a grey wash. On the dial itself, look at the numerals. Genuine applied numerals have polished bevels that catch light differently from the flat top. Many replicas print them or polish them badly, so they look dull. Check the date window position and the font of the date wheel, then check lume. A quick charge under a lamp should give an even, pale green glow. Blotchy or dim lume on a watch at this price is a tell.
Movement
Two families show up in replicas. One is a decorated ETA or Seagull clone with IWC engraving on the rotor and bridges. The other is a custom movement built to look like the real calibre. Pellaton winding uses a pawl system, not a rotor spinning on ball bearings, so a fast, noisy, free-spinning rotor is not what you want to hear. Finishing matters too: genuine bridges have Geneva stripes with clean edges, jewel sinks that are polished, and engraved text that is crisp under magnification. Printed or laser-etched text on a rep movement looks flat. Power reserve is the easiest field test. A 7-day reference should still be running a week later. An ETA clone gives you about 40 hours, and that gap is not something a seller can fake.
Caseback and serials
Engraving depth is the giveaway. Genuine casebacks have lettering cut deep enough to catch a fingernail, with a light polish in the recess. Reps tend to look sandblasted, shallow, or over-polished. Read the text closely: the reference should appear in full, not as a bare four digits, and the spacing of the brand name should be even. Serial numbers on modern IWC watches run to eight digits. A six-digit number, a repeated serial across listings, or a caseback that does not match the case metal are all reasons to walk away.
Strap, buckle, and hardware
OEM straps are supple with tight, even stitching and cleanly finished edges. Replica straps feel stiff, use a coarser thread, and often have stitching that wanders. Check the folding clasp or pin buckle for engraving quality and for sharp edges where the strap meets the metal. On a Big Pilot, the strap is 22mm at the lugs on the 46mm version, so measure it. A 20mm strap squeezed in is a strong sign the case is not what it claims to be.
Price signals and red flags
- Very low prices almost always mean a quartz movement or a 21-jewel automatic, not a copy of a long-reserve calibre.
- Listings with only front-facing photos hide case thickness and caseback quality.
- Claims of a perfect 1:1 copy without a movement video or timing numbers are marketing, not evidence.
- A case that feels hollow or light for its size usually means a thin caseback and a spacer ring.
My ten-minute routine in hand
- Measure the case and the thickness with calipers.
- Wind it, set the date, and check that the crown engages without grinding.
- Angle it under a lamp to judge the crystal coating.
- Charge the lume and check it in a dark room after two minutes.
- Listen to the rotor and time it over 24 hours.
- Read the caseback with a loupe, then compare the serial to any listing photos.
Bottom line
The IW5105 is a hard watch to copy well because the whole design depends on mass, proportion, and finishing. A replica with the right diameter, the correct crown, and a movement that actually runs seven days will fool most people at arm's length. One that is 2mm thin, wears a flat printed dial, and stops after two days will not. Decide what matters to you, then buy the version that gets those things right instead of the one with the nicest sales page.