Uploaded August 2025 | Updated September 2026, 2 weeks ago
The FiftyOne Assassin is a gravel bike born from the skills of this Irish 🇮🇪 custom frame builder. They harvested all that direct rider feedback and geometry knowledge and applied it to a production frame. The result is a gravel bike that is feature rich, but still light weight, exceptionally well made and an utter joy to build, ride and own.
The frame features
• Variable Geometry +5, 0, or -5mm chainstay length to adjust overall wheelbase and stability.
43
• Variable fork offset to adjust trail length at the front wheel. Producing a stable or agile feel.
• Cable ports for gears, brakes, dropper posts, and dynamo lighting front and back.
• Massive load carry capacity with mounts for rear racks, fork panniers, bottles.
• Mudguard mounts front and rear
• 1x or 2x gear set ups with chainrings up to a compact 34/50!
• 47mm (1.85") tyre clearance in either 700c or 650c wheel sizes.
... and then some beautifully standard features for useability.
• T47 external BB
• 27.2mm seatpost
• Standard steerer tube and FSA headset
• Flat mount brake mounts
• 12mm Thru axles
00:00 Intro
00:10 Build Spec
01:10 Build Quality inspection
06:00 Frame Features
07:40 Variable Geometry
10:32 Build Choices
12:00 Ride Review
Our build spec:
FiftyOne Assassin Size Large @fiftyonebikes4568 @fiftyonebikes7589
Industry Nine AR40 Wheels, reviewed previously @industryninecomponentry
Enduro Bearings Stainless 440c Bottom Bracket and headset bearings @endurobearings
Ergon Saddle, Bar tape and soon, Flex seatpost @ErgonBike
Pirelli Cinturato Medium Tyres in 45c x 700c @Pirelli
Vecnum Stem @Vecnum-GmbH
Learn more about the FiftyOne Assassin at Mapdec
mapdec.com/products/fiftyone-assassin?variant=55248671048056
Learn more about a custom build
mapdec.com/pages/custom-bike-builds
This frameset is on loan to us and you can come and ride it!
mapdec.com/pages/bike-demo-rental-fleet
We paid for all the other components ourselves.
The FiftyOne Assassin is a gravel bike born from the skills of this Irish 🇮🇪 custom frame builder. They harvested all that direct rider feedback and geometry knowledge and applied it to a production frame. The result is a gravel bike that is feature rich, but still light weight, exceptionally well made and an utter joy to build, ride and own.
The frame features
• Variable Geometry +5, 0, or -5mm chainstay length to adjust overall wheelbase and stability.
43
• Variable fork offset to adjust trail length at the front wheel. Producing a stable or agile feel.
• Cable ports for gears, brakes, dropper posts, and dynamo lighting front and back.
• Massive load carry capacity with mounts for rear racks, fork panniers, bottles.
• Mudguard mounts front and rear
• 1x or 2x gear set ups with chainrings up to a compact 34/50!
• 47mm (1.85") tyre clearance in either 700c or 650c wheel sizes.
... and then some beautifully standard features for useability.
• T47 external BB
• 27.2mm seatpost
• Standard steerer tube and FSA headset
• Flat mount brake mounts
• 12mm Thru axles
00:00 Intro
00:10 Build Spec
01:10 Build Quality inspection
06:00 Frame Features
07:40 Variable Geometry
10:32 Build Choices
12:00 Ride Review
Our build spec:
FiftyOne Assassin Size Large @fiftyonebikes4568 @fiftyonebikes7589
Industry Nine AR40 Wheels, reviewed previously @industryninecomponentry
Enduro Bearings Stainless 440c Bottom Bracket and headset bearings @endurobearings
Ergon Saddle, Bar tape and soon, Flex seatpost @ErgonBike
Pirelli Cinturato Medium Tyres in 45c x 700c @Pirelli
Vecnum Stem @Vecnum-GmbH
Learn more about the FiftyOne Assassin at Mapdec
mapdec.com/products/fiftyone-assassin?variant=55248671048056
Learn more about a custom build
mapdec.com/pages/custom-bike-builds
This frameset is on loan to us and you can come and ride it!
mapdec.com/pages/bike-demo-rental-fleet
We paid for all the other components ourselves.
