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FiftyOne Bikes Assassin review

Adaptable lightweight gravel bike designed in Dublin

Our rating 
4.0 out of 5 star rating 4.0
GBP £5,450.00 RRP | USD $6,923.00 | EUR €6,499.00
FiftyOne Bikes Assassin gravel bike

Our review

A fast, fun ride that’s as at home racing as it is touring
Pros: Balanced yet quick handling; adaptable geometry; versatile
Cons: Some build quirks; Ekar has operational issues
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FiftyOne Bikes built its reputation manufacturing custom carbon bikes at its Dublin headquarters.

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The Assassin is the Irish bike builder’s first full production model, with frames built to FiftyOne’s exacting specification in Asia and assembled in the Emerald Isle.

Versatility is a big plus when it comes to gravel bikes, but it can result in a ‘safe’ option that’s more about haulage than high jinx. However, the Assassin manages to mix practicality and performance, both in terms of speed and flickable ride response, to brilliant effect.

FiftyOne Bikes Assassin frame

FiftyOne Bikes Assassin gravel bike
FiftyOne’s finishing is superb.
Russell Burton / Our Media

At the heart of the Assassin is its adaptable geometry, realised by using flip-chip dropouts in both the fork and rear stays.

This enables the bike to switch between three positions at the rear. Adjusting the wheelbase in 5mm increments, shorter settings are intended to bring more agility, while longer settings improve ride stability.

At the front, the two-position dropout can be switched to a lower position, which gives a longer trail and slacker head angle. This serves to make the bike more adept when it comes to technical terrain and twisty trails.

FiftyOne Bikes Assassin gravel bike
Proper mounts make the Assassin a versatile off-road option.
Russell Burton / Our Media

Conversely, the higher position steepens the head angle and shortens the trail, which speeds up the steering.

FiftyOne says tyre clearance is equal across both 700c and 650b wheel sizes, at 47mm.

The versatility extends beyond geometry and into the bike’s fittings. There are front and rear mudguard mounts, rack mounts, and routing for both Di2 cables and a dropper post.

FiftyOne Bikes Assassin gravel bike
The Assassin keeps things simple up-front.
Russell Burton / Our Media

It even has internal routing for a dynamo lighting system through the fork. Additional top-tube bosses and multiple bottle mounts add up to a bike that should be able to handle everything from fast gravel riding to transcontinental adventures.

The Assassin isn’t limited on drivetrain options, being able to run 1x and 2x drivetrains and even up to a 50/34-tooth compact road crankset.

The crankset turns on a threaded T47 bottom bracket.

FiftyOne Bikes Assassin geometry

FiftyOne Bikes Assassin gravel bike
The substantial head tube keeps the front end stiff and direct.
Russell Burton / Our Media

The Assassin leans more towards the sort of long front-centre geometry we’ve seen on the likes of the BMC URS in recent times.

It’s not quite as extreme as some gravel bikes, however, so the FiftyOne is very much an off-road champion rather than an all-road hybrid.

My size-large test bike has a 415mm reach, combined with a 590mm stack. That’s significantly longer and lower than most gravel bikes.

Here, though it’s combined with a short 90mm stem, which brings the reach towards the rider somewhat.

FiftyOne Bikes Assassin gravel bike
The fork’s flip chip switches between 53mm and 45mm offsets.
Russell Burton / Our Media

The adjustable wheelbase makes a huge difference to how the bike feels. The mid-point setting on the rear dropout gives a 430mm chainstay length, which can be shortened or lengthened by 5mm.

Up-front, the two-position chip switches between a short 45mm and longer 53mm offset. Combined with the resulting 69.5- or 70-degree head angle, this makes for a trail of either 75.95mm or 87.49mm, respectively, with a 40mm tyre in place.

Seat angle (degrees)73.573.573.573.5
Head angle (degrees)69.569.569.569.5
Rear center (mm)430430430430
Seat tube (mm)465490510530
Top tube (mm)534.96562.1589.77613.65
Head tube (mm)116141170202
Fork offset – Low / Hi axle (mm)53/4553/4553/4553/45
Trail – Low / Hi axle (mm)87.49/75.9587.49/75.9587.49/75.9587.49/75.95
Bottom bracket drop (mm)70707070
Wheelbase (mm)1,023.031,052.121,081.731,107.94
Stack (mm)540565590620
Reach (mm)375395415430

FiftyOne Bikes Assassin build

FiftyOne Bikes Assassin gravel bike
The highlight of Campagnolo’s 13-speed Ekar groupset is the carbon crankset.
Russell Burton / Our Media

This stock build combines Campagnolo’s 1x 13-speed Ekar groupset with the brand’s tubeless Shamal carbon wheelset.

The shifting is positive and well-controlled, although occasionally the upshift lever can catch on the brake lever, which leaves the chain hanging in a ‘no-man’s land’ between gears, unless you flick it again with your finger.

Downshifts are much more positive with the curly trigger that’s accessed easily from the hoods or the drops.

FiftyOne Bikes Assassin gravel bike
The rear dropouts are also adjustable, making the Assassin a bike you can really experiment with.
Russell Burton / Our Media

The Campagnolo Shamal wheels are the Italian brand’s all-rounder option and an excellent wheelset for the road, but I can’t help thinking the brand’s gravel-specific Levante wheelset would make a better option thanks to an even greater 25mm internal width (as opposed to the Shamal’s 21mm diameter).

The finishing kit comprises a matching stem and seatpost from Zipp’s Service Course range, and an Easton EA50 AX aluminium gravel bar. This is subtly shaped, with a compact drop and 16-degree flare.

This makes for a lightweight bike at 9.18kg (size XL), complete with 45mm-wide WTB Riddler tyres, bottle cage and FiftyOne saddle pack in place.

FiftyOne Bikes Assassin ride impressions

FiftyOne Bikes Assassin gravel bike
The Assassin is a versatile gravel bike that’s fun to ride fast.
Russell Burton / Our Media

The Assassin’s different configurations can make the bike feel flat-out fast, or speedy but stable. I found the middle ground to be my favoured setup.

With 430mm chainstays and the fork in the 53mm trail setting, I’ve found the FiftyOne to have a brilliant balance between speed on rough roads and flickable control on wooded singletrack or hillside-traversing sheep tracks.

The bike relies heavily on the 45mm WTB tyres for comfort, while the frame and fork both major on stiffness.

I’d have liked to see a carbon seatpost at the rear to add a bit of extra compliance (or, perhaps even better, a dropper post with a bit of suspension travel to give comfort and add to the bike’s handling prowess when things get testing).

FiftyOne Bikes Assassin gravel bike
Double-dropped chainstays give maximum tyre clearance without compromising the frame’s construction.
Russell Burton / Our Media

Up-front, the Assassin’s stiffness adds to the responsive handling, and the Easton bar – along with quality bar tape – nullifies most vibrations. However, it still feels more of a race-like than a recreational ride experience.

The WTB Riddler gravel tyres are superb in the dry and roll fast on hard-packed surfaces.

Like all lower-profile gravel treads, mud clogging can be a challenge. But, being tubeless and large in volume, you can experiment with lower tyre pressures to eke out more grip if the going underfoot is a little sloppy.

FiftyOne Bikes Assassin gravel bike
WTB’s Riddler tyres in a 45mm width are a classic gravel option.
Russell Burton / Our Media

The gear range with a 38/9-tooth biggest gear means plenty of pace for fast descending, and a lightest 38/42t combination is very off-road climb friendly.

Campagnolo should also be applauded for keeping the gear progression nicely balanced across the cassette.

Aside from the occasional catching of the upshift lever I’ve already mentioned, Ekar performed well. The brake feel is very consistent, with great progressive action at the lever.

FiftyOne Bikes Assassin bottom line

FiftyOne Bikes Assassin gravel bike
Get the settings optimised for you and the Assassin is a superb companion over all types of gravel.
Russell Burton / Our Media

Overall, the FiftyOne Bikes Assassin is a wonderful off-road companion.

It can dance its way through the twists and turns of tight singletrack and maintain control on choppy rutted roads, while on smoother ‘princess gravel’ trails it’s near-enough road bike rapid. It’s also practical.

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The taut frameset excels when climbing and the ride position afforded by the smart geometry makes descending balance on the tightrope between confident stability and on-the-edge excitement.

Product Specifications


Price br_price, 5, 3, Price, EUR €6499.00GBP £5450.00USD $6923.00
Weight br_weight, 5, 6, Weight, 9.18kg (XL), Array, kg
Brand br_brand, 5, 10, Brand, Fiftyone bikes


Features br_Features, 11, 0, Features, Extras: FiftyOne carbon bottle cage, FiftyOne saddle pack
Available sizes br_availableSizes, 11, 0, Available sizes, S, M, L, XL
Brakes br_brakes, 11, 0, Brakes, Campagnolo Ekar hydraulic disc with 160mm rotors
Cassette br_cassette, 11, 0, Cassette, Campagnolo Ekar 13 speed 9-42
Chain br_chain, 11, 0, Chain, Campagnolo Ekar 13 speed
Cranks br_cranks, 11, 0, Cranks, Campagnolo Ekar Carbon 38 tooth chainring
Fork br_fork, 11, 0, Fork, Carbon
Frame br_frame, 11, 0, Frame, Carbon
Handlebar br_handlebar, 11, 0, Handlebar, Easton EA50ax 16-degree flare bar
Saddle br_saddle, 11, 0, Saddle, WTB SL8 saddle
Seatpost br_seatpost, 11, 0, Seatpost, Zipp Service course 27.2mm seatpost
Shifter br_shifter, 11, 0, Shifter, Campagnolo Ekar 13s
Stem br_stem, 11, 0, Stem, Zipp Service course 90mm stem
Tyres br_tyres, 11, 0, Tyres, WTB Riddler 45mm tyres
Wheels br_wheels, 11, 0, Wheels, Campagnolo Shamal carbon disc