Felt F1x Di2 review

Fantastic carbon frame and lots of clever spec work make for a race ready machine

This article originally appeared on BikeRadar

The revamped Felt F1x cyclocross racer is all-new for 2016, featuring an ultra light carbon frameset, a disc brake-only configuration, and tubeless carbon wheels that can hold their own against many tubulars but without the hassles of glue. Felt has even reprogrammed the stock Shimano Dura-Ace Di2 transmission to create its own custom 1x electronic drivetrain. All in all, it's a slick package and unquestionably speedy – but it's not without its quirks.

  • Highs: Ultra-light and efficient frame, surprisingly smooth ride, great handling, slick custom drivetrain and wheels
  • Lows: Clutchless rear derailleur yields so-so chain security, sketchy tires, curiously wide handlebar spec
  • Buy if: You want a top-end 'cross bike that's race ready out of the box and don't plan on using it much off the race course

A fantastic new chassis…

Whereas some 'cross bikes proudly tout their versatility and practicality for a wide range of uses, the F1x is singularly focused on going fast – preferably on a race course. The new frame's oversized tubes yield an incredibly efficient chassis that rockets forward under power, matching the best full-on road frames in terms of responsiveness.

Felt's new carbon 'cross frameset is absolutely superb

There's no wag detectable through the bars when sprinting out of the saddle, for example, and not the slightest iota of side-to-side movement through the rear triangle when you're really on the gas. Fork rigidity is impressive, too, with no twist even in hard, high-speed corners with excellent traction.

Helping that matter even further is the F1x Di2's exceptionally low weight: just 7.44kg (16.40lb) for my 53cm test sample (without pedals) with a claimed frame weight of just 950g. Even the rotational weight is kept to a minimum with custom shallow-profile carbon tubeless DT Swiss wheels and matching Schwalbe X-One tubeless tires, which rival many deep-section carbon tubulars I've used in terms of acceleration out of tight corners.

The disc-only format yields heaps of clearance

Despite appearances, Felt has done a great job of tempering the F1x's ride quality. Although the huge tubes obviously don't move much, the chassis is superbly adept at squelching smaller-amplitude vibration, subtly (but effectively) filtering out the buzz of hardpacked trails and even taking the edge off of sharper rocks and roots. Plush and soft the F1x is most certainly not, but it's nevertheless surprisingly calm and composed.

When it comes to 'cross, mud clearance is also a key performance metric and the F1x has it in spades all around. The disc-specific format leaves heaps of space around the seatstays and fork legs but it's down below where it's most impressive. Felt has moved away from its usual narrow-format BB30 bottom bracket shell in favour of the wider BB386EVO system, which allows for much wider chainstay spacing and better clearance in that critical area without sacrificing cross-sectional area.

The wide-format bottom bracket shell allows the chainstays to be pushed further apart for better clearance but without sacrificing rear-end stiffness

There's still a bit of a shelf behind the bottom bracket shell for mud and debris to accumulate, however.

Handling is spot-on though, with a quick turn-in, excellent high-speed stability, and just enough bottom bracket height – BB drop is a middle-of-the-road 65mm – to allow pedaling through most corners without feeling tippy. Just be mindful when choosing a size, though, as the F1x runs a bit big.

...and a clever build kit to go with it

Felt has long been no stranger to creatively assembled spec sheets, and this F1x Di2 flagship perhaps embodies that talent best of all. Currently, off-the-shelf single-chainring drivetrain options are limited to SRAM, SRAM, and SRAM but road product manager Dave Koesel is a big fan of electronic shifting and wanted to provide a Di2 option as well.

Shimano doesn't offer a single-ring Di2 transmission so Felt went ahead and made its own

Since Shimano doesn't offer a left-hand lever without shifter internals, Felt has gone ahead and reprogrammed the controls itself. Tap either right-hand button for an upshift and either left-hand one for a downshift, effectively creating a sequential transmission perfectly suited for the rigors of 'cross. Whereas I usually have reservations about using Di2 in cyclocross given the lack of tactile button feedback and the small targets, that simply wasn't an issue here – you can literally just smack the side of the lever and you get the desired shift, even when wearing heavy winter gloves.

Unfortunately, the range of gears at your disposal is frustratingly limited as Felt has opted for a curiously narrow 11-28t cassette – enough for flatter courses but not for ones with more demanding climbs, and certainly not enough for everyday training. And while the gear ratio ‘window' can be moved relatively inexpensively on SRAM Force 1 by swapping chainrings, expanding the range on Felt's custom 1x setup will require buying a more expensive cassette.

Felt repurposed some older DT Swiss carbon mountain bike wheels into tubeless 'cross wheels

I also wish that Felt had used a short-cage XTR Di2 rear derailleur instead of a Dura-Ace Di2 one. In addition to reprogramming the lever buttons, Felt has also increased the pulley cage tension to help boost chain security but without the aid of a proper clutch, the drivetrain is still noisier on bumpy terrain than SRAM's essentially silent Force 1 setup – nor is chain security as reliably solid. What Felt has done here is undoubtedly impressive but I'd recommend a supplemental seat tube-mounted guide to be safe.

There's nothing to complain about with the brakes, however, with Shimano's hydraulic calipers providing their usual superb power and bite plus excellent control in all weather conditions – plus pads that self-adjust for wear for more consistent lever feel. Thru-axle hub interfaces at both ends keep the rotors from rubbing even under hard cornering or sprinting loads, too.

The Shimano Di2 levers are awesome; the bars, not so much

Unfortunately, other spec items also feel a little off-kilter.

In particular, the 3T Ergoterra handlebars are inexplicably wide with my 53cm tester coming with a somewhat reasonable 44cm center-to-center measurement at the hoods but a whopping 47cm at the flared drops. While you could perhaps argue that the extra width might add some control and stability in slippery conditions, I mostly just found it awkward.

Likewise, the firm Prologo X-Zero saddle is fine for shorter stints but I still would have appreciated a bit more padding for remounts. And while the elastomeric insert in the seatpost head seems to be effective at further attenuating vibration on top of the frame itself, the splined head is a nightmare to adjust. Riders who prefer a more forward position will undoubtedly take issue with the generous 25mm offset, too.

The elastomeric insert in the 3T seatpost seems to work at damping vibration but the 25mm setback is a bit much and the head is a nightmare to adjust

Finally, I had a few issues with the tires. They're quite light, roll very quickly, and are very reliable even at low pressures (I easily ran down into the mid-20s in terms of psi), but they just don't provide much grip. The small knobs fold over at the slightest hint of cornering load and feedback through the contact patch is disconcertingly vague.

Great bones to build on

Felt has nailed the fundamentals on its revamped 'cross platform with excellent efficiency, solid handling, and a remarkably smooth and composed ride quality. Most of the associated componentry reveals some impressively clever thinking, too, but a few key missteps hamper what would otherwise be a really stellar total package. 

Full Specifications

Complete specifications as tested:
Name: F1x Di2
Built by: Felt
Price: £N/A / US$6,999.00 / AU$N/A

Frame: Felt Cyclocross UHC Advanced + TeXtreme carbon
Fork: Felt Cyclocross UHC Ultimate + TeXtreme carbon, 1 1/8-to-1 1/2in tapered
Headset: FSA NO.38/42
Stem: 3T ARX II Team Stealth
Handlebar: 3T Ergoterra Team Stealth
Tape: Felt CxGel
Front brake: Shimano BR-R785 hydraulic disc w/ Shimano SM-RT99-SS 140mm rotor
Rear brake: Shimano BR-R785 hydraulic disc w/ Shimano SM-RT99-SS 140mm rotor
Brake levers: Shimano Di2 STI Dual Control ST-R785
Front derailleur: n/a
Rear derailleur: Shimano Dura-Ace Di2 RD-9070
Shift levers: Shimano Di2 STI Dual Control ST-R785
Cassette: CS-5600, 11-28T
Chain: Shimano CN-HG600
Crankset: Rotor 3D+ CX1 w/ 40T Rotor XC1 Q-Ring and 40T Rotor XC1 NoQ-Ring
Bottom bracket: Rotor BB386
Pedals: n/a
Rims: DT Swiss XCR1300 Carbon db, 28h
Hubs: DT Swiss 350 Centerlock, 28h
Spokes: DT Swiss Competition w/ ProLock alloy nipples
Front tire: Schwalbe X-One Evo tubeless, 700x33c
Rear tire: Schwalbe X-One Evo tubeless, 700x33c
Saddle: Prologo X-Zero TiRox
Seatpost: 3T Ionic VR 25 Team Stealth
Total weight: 7.44kg (16.40lb, 53cm, without pedals)

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