FiftyOne Assassin gravel bike review: Not to be pigeonholed

A production gravel bike from the Irish company best known for its custom road bikes.

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Based in Dublin, Ireland, FiftyOne is a name growing in familiarity within the high-end, handmade and custom bike scene. Launched in 2016, the company has built a reputation for creating custom carbon fibre road bikes with classic tube profiles, uninterrupted seatstays, and wild, one-off paint schemes unique to each handmade frame. 

And while FiftyOne has previously teased made-in-house custom carbon gravel bikes, its official entry into the space is a surprising one. The new FiftyOne Assassin isn’t made in Ireland, there is no custom geometry, and even the monocoque construction method is different to the company’s usual tube-to-tube approach.

Instead, the Assassin spells FiftyOne’s entry into the production frame world. And as a small company, FiftyOne sought to design a single model that could cover a broad usage range that a few larger brands now do with two or three different gravel models. The Assassin is a fairly progressive gravel bike ready to be tailored to individual needs. 

I’ve had a pre-production sample on test for a couple of months, long enough to provide a detailed opinion of this new gravel bike. 

Story Highlights

  • What: A truly versatile carbon fibre gravel machine with highly adjustable geometry, plenty of mounting points, and somewhat progressive geometry.
  • Key features: Geometry flip chips at both wheels, ready for any drivetrain of your choosing, clearance for up to 700 x 47 mm rubber, T47 bottom bracket, regular seatpost and stem, many mounts.
  • Weight: 1,245 grams (medium painted frame with hardware), 540 g (fork), 8.7 kg as tested (without pedals).
  • Price: €3,500 / US$3,500 (frameset), €6,499 / US$6,500 (complete bike, as tested).
  • Highs: Highly tuneable and well-considered off-handling handling with easy-to-switch flip-chips that offer noticeable changes, unhindered component compatibility, a useful mix of accessory mounting points.
  • Lows: Rides on the stiff side (but plenty of room to add comfort), polarising model name, price.

An intro to the Assassin

The ability to tailor the Assassin to individual needs is seen through the extensive feature list. There are flip chips at both front and rear dropouts to let you adjust the handling and stability of the bike (more on this later).

With low slung chainstays there’s room for 47 mm tyres, whether they’re 650B or 700C. And that’s while allowing for 1x or 2x shifting, mechanical or electronic. And yep, it can even fit a compact (50/34T) double crank on the front if you’re seeking more road-going gearing. 

Meanwhile, the use of a regular stem and 27.2 mm round seatpost allow you to dial in the fit or add comfort-inducing features to the bike as you please.

Cable routing is run internally through the frame but not through the stem or headset, and the design is intended to be highly modular based on your cable routing preferences. The bike even has a few added cabling tricks, such as a Di2 battery hatch beneath the rubber cover on the down tube, something that means you can run the bike with both a dropper seatpost and Shimano electronic shifting if you please.

Meanwhile, the use of a 68 mm-wide T47 threaded bottom bracket shell will be music to the ears of many home (and professional) mechanics, and it also means you can run just about any crankset you wish. This bottom bracket shell also provides a large opening into the frame for assistance with internal cable and hose routing. 

And then there are the many mounting points for carrying both old and new styles of luggage. Of course, there are the usual bottle cage mounts within the main triangle and underneath the down tube. And there are bolts for a Bento-style bag on the top tube. However, there are also provisions for regular full-length fenders front and rear. And you can also fit racks above each wheel (15 kg max rear, 5 kg max front). And then FiftyOne’s own matching carbon fork, named the Trident, has carry-anything-type mounting points running along its blades (5 kg max per fork leg), and internal routing for a dynamo hub. 

My sample came fitted with Prototipo bolts. FiftyOne offers this as a €100 upcharge (there’s a lot of them, including the grub-screw style along the fork blades).
There’s a removable fender bridge for the otherwise-uninterrupted and curvy seatstays. It’s a nice touch, and one somewhat like the Marin Headlands and Chapter2 AO previously reviewed.

With all the hardware, a medium-size painted frame weighs 1,245 grams, while the matching fork is 540 g. My sample, as tested with Campagnolo’s 1×13 speed Ekar groupset, sits at 8.7 kg without pedals. Certainly, this isn’t the lightest thing around, but that’s clearly not the intent, either.  

Despite being a company known for its custom paint, FiftyOne is launching the Assassin with just two stock paint options – there’s the Rothmans Racing Blue as tested, or a British Racing Green. Neither are boring, and the option to pay extra for custom paint is in the works. FiftyOne’s in-house-made custom bikes typically cost about €7,000 / US$7,000, while the made-in-China Assassin frameset is half that at €3,500 / US$3,500. It’s available now and carries a lifetime warranty.

British Racing Green is the alternative stock colour option.

The bike as tested retails for approximately €6,499 / US$6,500 (subject to specific component availability). “Complete build options are a moving target currently due to price increases and unknown delivery dates but our aspiration is to have an entry build around €4,500,” said FiftyOne’s founder Aidan Duff of the current industry supply issues. 

A polarising name

So what’s with the name? Is it because this bike is killer on all types of terrain? Is it just an excuse to use the world “ass” twice? Thankfully there’s more of a story to it. It builds on FiftyOne’s own brand name that’s based on the lucky number 51 Eddy Merckx wore to his debut Tour win and a number that was then worn by others to many more wins.

According to FiftyOne, the Assassin naming stems from the 1910 Tour de France that navigated through the high mountains for the first time, including the Col du Tourmalet. Back then every road was gravel, and the stages were far longer than they are today. 

As Duff explains, on the summit of the Col d’Aubisque on a monster 320 km stage, the leading rider and eventual race winner, Octave Lapize, was furious at the stage’s excesses and screamed at the race’s deputy director, Alphonse Steinès, “Vous êtes des assassins! Oui, des assassins!” Translation: “You are assassins! Yes, assassins!” 

Alright, back to the review.

Some brands make it difficult to read the model name. This isn’t one of those.

Flip chips to change how the whip dips

Despite the freedom in how you can build this bike, the Irish company doesn’t intend for the Assassin to be a road bike killer, and that’s reflected in the rather off-road-centric geometry. 

As seen with the likes of BMC’s URS, the Devinci Hatchet, and Canyon’s Grizl, there is a growing list of versatile gravel bikes borrowing the combination of a long front-centre and a short stem, common in mountain bikes. Not only does this fix the issue of toe overlap with larger-volume tyres, it also helps with keeping your mass behind the front wheel, creates a more balanced weight distribution, and produces more stable handling – all good things when tyre traction is limited and the descents are steep.

The Assassin isn’t the most extreme example of this long front-centre trend – bikes like the BMC URS and Evil Chamois Hagar still lead the way there, and by some margin. My medium size sample Assassin features a reach of 395 mm which is accompanied by an 80 mm-long stem. By comparison, a more road-going gravel bike in my size would typically offer about a 380 mm reach with a 100 mm stem (I’m about 170 cm tall with a saddle height of 735 mm to BB centre). 

FiftyOne has launched this bike with just four frame sizes, and an extra-small and double XL will accompany the range in about six months from now. 

On the handling side, those clever flip chips at both ends of the bike provide a whole lot of handling customisation – more than any other adjustable geometry gravel bike I’ve reviewed. There are three chainstay length positions offered: a 430 mm length in the middle, and room to move 5 mm in either direction from there. Making this adjustment involves swapping out the outward-facing aluminium plates (two versions are supplied with the bike) and re-adjusting the brake – a process that takes just a few minutes if you’re comfortable with taking out the rear wheel and aligning a disc brake. 

The chainstay length can be adjusted to 425, 430 or 435 mm. It’s your choice. And yep, a 700 x 45 mm tyre fits just fine in the shortest setting.
There are two chainstay plates provided with the bike. The two shown at the bottom are for the centre 430 mm position, while the two at the top can be flipped to provide either the 425 or 435 mm setting.

Meanwhile, FiftyOne’s own fork design offers a two-position flip-chip that’s even quicker to adjust, doesn’t require different parts to be swapped in, and produces a more obvious change to the bike’s handling. 

Here the fork offset can be switched between 45 or 53 mm, and combined with the approximate 69.5º head angle of my medium sample, the trail figure can be adjusted between approximately 75 and 87 mm (with 700 x 45 mm tyres). I say approximately because that front flip-chip also changes the effective fork height, which in turn, adjusts the head angle, the bottom bracket height, and even the effective fit of the bike. And then those numbers change again (but to a lesser extent) if you adjust the rear flip-chip. 

In its more stable 45 mm rake and longer trail figure, the fork sits higher, producing a slacker head angle and higher bottom bracket. Meanwhile, the reverse is true in the faster-handling 53 mm setting. 

And what makes this design all the more clever is that the brake doesn’t need adjusting between the two settings. In my testing, the rotor height within the brake calliper does change marginally, but according to FiftyOne, it’s within the tolerance of the brake system. It may be within tolerance but it’s likely you’ll get a small lip of unworn disc brake pad material if using the bike in the quicker 53 mm setting. 

Here’s a chart to get lost in. This shows how all the numbers change for each flip chip setting. This chart is just for the medium-size frame.

Riding the Assassin 

Typically it doesn’t take all that long to learn the personality and the positives and negatives associated with an off-the-shelf gravel bike. However, that’s not the case here, and there’s no easy way to summarise the handling or ride quality of a bike that can be configured in so many different ways. The reality is that the Assassin can wear multiple disguises and it does so impressively well. 

For my testing, I mostly kept to 700 x 45 mm tyres and played with front and rear flip chips, but of course, fitting road tyres or 650B off-road tyres will present another impact on the handling again. 

In the long trail fork setting the bike feels eager for you to push the boundaries of where a rigid gravel bike should perhaps go. The long centre and short stem provide control when things get steep and sketchy, and along with the fork that sits a tad higher, it’s easy to get your weight over the rear wheel. Similarly, the front wheel feels secure pushing into loose turns.

If I had to pick a cliche to describe the handling, without a doubt I’d say it’s “playful”. 

No fun was had in the testing of this bike.

When the terrain points skyward it’s evident that while the Assassin lacks the nippy over-the-front feel of racier models, it still does an admirable job of efficiently getting you to the next reprieve. Overall FiftyOne has done a great job of opening up the descending ability without tipping things too far into the realm of floppy handling or wandering climbing. 

I’m typically a fan of lower bottom bracket heights for a sense of glued-to-the-ground cornering. The Assassin’s 70 mm bottom bracket drop is on the taller side of things given most will ride this bike with 40-45 mm rubber and there’s obviously a trade-off here. The positive is plenty of pedal clearance through rocks, and the Assassin seems to have struck a good balance given I didn’t notice any top-heavy handling that is sometimes present with a bike that sits too tall. 

With a 2.5 mm hex key and a spare minute to flip the fork dropout, the handling transforms into something far more lively and sporty-feeling. You feel your weight a little more over the front wheel as the whole bike tips into a direction change with more urgency. In this setting (and even more so with the chainstays in the 425 mm position) the Assassin felt far more like a race-focused gravel machine and would be a better match for faster rides with long tarmac stretches. It’s also what I’d want to use if pinning on a race number (assuming the course terrain wasn’t savage). 

The front flip chip is impressively easy to use.
Here you can see the aluminium flip-chip insert in place. A single hex bolt holds the chip in place.

Meanwhile, the previous long-trail fork setting is obviously what I’d want if going on an epic off-road adventure or just doing short underbiking laps like I often do. One setting isn’t necessarily better than the other; it’ll just come down to personal preference and the terrain you ride. The same applies to the rear-centre length. The nicest part of it all is that it’s relatively quick and easy to experiment with the handling options.   

There is clearly some give to those thin, curvy and uninterrupted seatstays, but upfront the deep-bladed and 1.5″ tapered fork doesn’t do a whole lot to calm the trail.

Due to limited supply, my test sample arrived with Campagnolo Shamal Carbon wheels (21 mm rim width) and an alloy seatpost – both of which I wouldn’t personally choose for unleashing this bike’s off-road capability and all-day comfort. As supplied, the bike had a firmer ride feel than I’d ideally want in an off-road-focussed gravel bike, but thankfully it’s all solvable.

And while the bike may lack the built-in comfort features seen on comparably high-end options, it instead offers plenty of open component compatibility that makes this slightly stiff ride feel a non-issue. You can equip just about any comfort-focused seatpost, stem or handlebar you please, and similarly, there’s a reasonable amount of tyre clearance.

Personally, my solution was a pair of 25 mm internal width rims, some Cushcore tyre inserts, and low tyre pressures to match – exactly the wheel combination that I believe benefits all confident-descending gravel bikes.  

The Assassin is ready to accept any flexible or pivoting seatpost/stem if more comfort is a priority.

Speaking of wider tyres, there is an emerging trend toward running 700×50 or even bigger tyres on gravel bikes. While I personally prefer to grab a lightweight XC hardtail at that point, it is worth noting that this demand is just beyond the Assassin’s limits and is perhaps the only weak point in this bike’s ability to change identity. And while it may not offer room for where gravel bikes may be headed, at least for now the available tyre clearance is inline with current market expectations and any wider would likely have forced FiftyOne to make concessions over chainstay length, front derailleur compatibility, and/or chainring clearance.

Living with this bike should prove rather easy and there aren’t any areas of major concern. Perhaps the only exception is with the lower headset bearing that offers no extra sealing beyond what the cartridge itself provides. And given the off-road intent I’d love to see an additional seal supplied here.

Now, this issue is extremely normal on many bikes running an Integrated Standard (IS) headset with an integrated crown race on the fork, and at least in this case, it’s super easy to occasionally drop the fork out of the frame and clean the headset bearing. 

The headset isn’t exactly exposed, but over time grit will find its way to the lower bearing.

Similarly, I’d have liked to see a little more frame protection given to that lovely gloss paint and the carbon that hides beneath it. FiftyOne does offer a short rubber bumper for the down tube which should help ward off the most common damage, but I’d also like to see some protection on the dropped chainstay (driveside) and perhaps a protective sticker above the down tube bumper. For now, these protective measures will need to be added by the customer. 

Wrap up 

It’s clear that FiftyOne has put some serious thought and effort into its first entry into both gravel and mass production bikes. The result is a bike that really does rival the leaders of the market and even offers a few features that may inspire others.

With such wildly different geometry options available in this one model, the young brand has created a well-refined machine that feels ready to grow and change as your approach to gravel does. And given gravel is a discipline in constant flux, I find that adaptability quite appealing. 

But, beyond the unique flip chips, there’s not much on this frame that screams out for such a high asking price. And based on that the price remains my biggest sticking point. But I guess that also goes with the territory of buying something unique and from a niche brand.

But while it may not be the cheapest thing out, it’s at least very good and ahead of the curve for where highly versatile gravel bikes seem to be going. 

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