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Felt's AR frameset is very fast and very stiff – perfect for racers and even time triallists. However, as a complete bike the AR4 has some potential shortcomings that you should be aware of before parting with your £2,399.99.
When it comes to creating aero road bikes, Felt has a strong track record thanks to its origins in (whisper it) triathlon, and the 'AR' frame is its latest crack at creating a speed demon machine – a frame that it says forms the foundation of 'best-performing aero road bike in the world'.
Felt also prides itself on using clever carbon frame manufacturing techniques, and with its striking looks taking centre stage when it landed in the road.cc offices, there was a queue of people lining up to take the AR4 for a spin...
The lucky person selected for the task was me, but before swinging my leg over it I got in touch with Felt's PR man Andreas Lieberherr to get the lowdown on the frameset.
He explained that the frame features Felt's third-tier, entry-level carbon – known as UHC Performance Carbon Fibre – which ostensibly differs from the more premium Advanced and Ultimate blends because it doesn't feature TeXtreme, a premium carbon material that allows frames to be laid up in a lighter, stiffer (and more expensive) construction.
The AR4 is about performance value, then, and while Felt doesn't quote numbers, the 56cm test bike in its entirety weighs in at 8.04kg on road.cc's Scales of Truth – not bad for a bike with very clear and obvious aero sections around the head tube, down tube, seat tube and bottom bracket.
The frame is laid up into an aggressive race geometry, with a 392mm reach and 567mm stack height marrying to a 988mm wheelbase that creates a direct-feeling front end and responsive overall ride. What's clever is that the bike is designed to transform into a machine suitable for time trials, with that bladed Varimount seatpost reversible to move you further forward and optimise your position on time trial bars.
Felt calls it 'Variable Geometry Optimised', or VGO for short, and in pure numbers it means the seatpost can be switched around from the standard 72.5-degree position to a steep, time trial-friendly 78.5 degrees.
Elsewhere there are design features aimed at optimising aero performance including rear brake calliper mountings hidden away under the chainstays, a narrow 'Twin Tail' bridgeless seatstay design made possible by the removal of the traditionally mounted rear brake calliper, and a twin-tail fork crown that smooths airflow from the straight Advanced carbon fork and around the down tube.
These relatively complex shapes, including the deep-section aero tubing with squared Kammtail-like rear sections at the down tube, are made possible using Felt's InsideOut carbon moulding technology. According to Felt, this process – using specially designed moulds inside the frames during the lay-up process – creates smoother resin finishes, allowing for more complex shapes to be produced without telltale signs of carbon overlapping or uneven surfaces.
The rear triangle features a tightly fitting cutout (so tight that in reality you can only fit 23mm tyres in the gap without risking tyre rub) to reduce rear wheel turbulence, and that's complemented by the 'Gap Shield', which are specifically designed flares on the seatstays and chainstays to help manage the all-important boundary layer of air as it flows over the area.
Meanwhile, the BSA bottom bracket is shrouded in a serious wedge of carbon fibre to provide structural rigidity when you lay the power down. Like the rest of the bike, it's slim in profile to cut as clean a line as possible through the air, rather than wide-stanced like most carbon all-rounders.
Naturally, we also find internal cable routing, ready for upgrading to Shimano or Campagnolo electronic drivetrains, should you want to.
And, what's the aero bottom line? Well, Felt claims that compared to the next best performing bike in its benchmark wind tunnel testing (300w output over a 40km 'typical' time trial course), the AR frame saves 43 seconds over its next closest rival, the Cervelo S5. Make that 66 seconds over the Specialized Venge, 68 over the Giant Propel and 75 over the Scott Foil.
Certainly the raw stats are impressive, but the question is how those claims translate into real world performance.
There's no question that the Felt AR is designed as a tool for reaching ultimate speeds rather than a more versatile aero all-rounder, the likes of which we see more and more of these days.
It's properly rigid – stiff around the bottom bracket in the extreme – while the bedrock of the bike formed by the BB, the aero profiled down tube and chainstays is well up to the task of transferring any and all lateral force that I can produce.
As a result, acceleration is impressive despite the basic rolling stock, as all the torque produced is funnelled into the drivetrain and wheelset. No doubt a light set of mid-section carbon clincher wheels would set the ride alight, but your options are limited given the lack of tyre clearance on the Felt and the trend towards ever-wider rims, which in turn blow tyres wider.
This means that while the bike is no doubt ultra-slippery in the wind tunnel, and similarly so in the real world despite relatively sharp tube profiles, comfort is at a premium here. The narrow 23mm tyres contribute to a shaky ride given the higher pressures needed, with proven downsides for ultimate rolling resistance too.
Still, it's the lack of compliance that tells over longer distances when using this road bike for its primary purpose. Sure, the bladed, cut-out seatpost with 3T mountings provides a reasonable amount of flex so your rear isn't totally ruined after a 100km ride, but the alloy Devox cockpit is less impressive. It's noticeable how much more vibration rumbled through my hands and forearms compared to the Rose X-Lite 6 Disc I reviewed a few weeks back – and that wasn't exactly the most cushioning of rides.
Nevertheless, as a performance tool there's lots of fun to be had from the AR4. Once you've grown used to the stiffness of the ride in all areas, confidence in the handling through the racy position and 23mm rubber starts to build, and you can begin to throw it into corners and descents with vigour.
The front end, perched atop the bladed fork, produces a direct response when picking a line into a corner, and the shortish wheelbase keeps the rear end tucked in behind you. It results in a bike that handles sharply and efficiently in pretty much any scenario – climbing, descending, flat or rolling terrain, at slow or high speeds – and it's predictable to boot.
While I've spoken already about the lack of compliance from the narrow tyre width restriction and limited deflection in the frame itself, it's the Devox 30 wheelset that really lets the side down here. This should be a bike that can mix it the best aero bikes in the world, but with shallow rims like these, it's like trying to run with wellies on, or swim with a parachute attached – and yes, I've tried both.
You could argue that Felt is really selling you a frame here and expects you to own or buy a set of shiny wheels to put on it, but with the bike costing £2,399.99, you'd be justified in expecting something a little more sprightly than these.
To play to the AR4's obvious racing potential, a Shimano Ultegra drivetrain provides the propulsion, but as is often the case where the frame is seen as the centrepiece of the bike, there have been shortcuts made to minimise the cost.
The chainset is Shimano's stock RS500 model which, although perfectly serviceable, is an eyesore when a standard Ultegra chainset would probably add a greater air of quality, plus additional stiffness and less weight. If you want one from the get go, you'll need to spend a further £1,200 on the deep-section-wheeled AR3, or ask your bike shop very nicely if they wouldn't mind installing one at a discounted rate. Well, you never know...
The AR3 also demonstrates that the chainstay-mounted brake callipers need not be limited to the numb and weak TRP T851 models found on the AR4 either. Shimano's excellent Ultegra direct mount rear calliper can do the job just as well, while the front calliper on the AR4 is a single-bolt Tektro Quartz T741, which, for the record, feels 105-level in terms of feel and ultimate power. Felt clearly doesn't subscribe to the purported benefits of more integrated direct-mount callipers when it comes to the front of the bike.
The fact is that the AR4 features a groupset that is ostensibly a bag of bits in order to reduce ultimate cost, aside from the essentials of Ultegra-spec front and rear derailleurs. Alongside the wheelset, it's likely that you'll want to upgrade at least the brake callipers before long.
Speaking of the Devox 30 wheelset, at its core is a Devox ARH2 sealed bearing cartridge hub, which spins smoothly enough for an entry-level wheelset, laced to alloy Devox rims that are 27mm deep at the front and 30mm deep at the rear.
Who is Devox, I hear you ask. Well, it's Felt's in-house component brand, and in the case of the 30s at least, it has created a wheel that effectively gives the AR frame something to perch on, and that's about it.
In fact, ultimate build quality is questionable too – a front spoke nipple worked its way loose after a mere 150km of normal riding (in total), requiring a trip to a mechanic to get it fixed and the rim re-trued. Of course, it could be a one-off, but add that to the general lack of stiffness or aero performance, and it suggests they're intended as placeholders rather than hoops to use in anger on the road. Even if you do already own a set of premium hoops to throw at the AR4, it's still a shame in a bike that costs the best part of two and a half grand.
The rest of the finishing kit is solid enough for a bike of this price, including the bladed seatpost complete with aero profiling, split cutout and 3T Difflock comfort zone. Given the relative harshness of the 23mm Continental Grand Sport tyres, it does a fair job of damping road buzz, although it's certainly no magic carpet ride when you hit the odd small pothole.
That's a fundamental trait of the AR4, though, and was always going to be hard to overcome. Nevertheless, the flexibility of being able to switch the seatpost round to give a time trial-friendly 78.5-degree angle will appeal if you can't have or don't want both a dedicated road and time trial bike.
Tying it off is a decently shaped Devox Aero Road handlebar with a 130mm drop, Devox alloy stem and FSA sealed bearing headset, while the saddle – in a rare flourish of mainstream brand – is a suitably aggressive Fizik Arione R5 model.
In a conclusion of two parts, I'll address the frame first. It's stiff, it's light, it's very aerodynamically capable, and it looks the part, and the inclusion of the reversible seatpost gives it a USP as an all-in-one aero road and time trial-capable machine. For that, it deserves kudos, even if the ride isn't the most well rounded.
The finished build to complete the AR4, though, is truly a mixed bag, from the relatively numb rear brake and obvious shortcuts made at the chainset and wheelset, to the fundamental (and excellent) Shimano Ultegra R8000 drivetrain that props up the bike on the spec sheet.
For £2,399.99 I would expect a little more to describe it as good value – and the underlining point is this: so should you.
There are highlights when it comes to stiffness and aero performance in the frame, but it's a mixed bag elsewhere
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road.cc test report
Make and model: Felt AR4
Size tested: 56cm
About the bike
State the frame and fork material and method of construction. List the components used to build up the bike.
Felt says: The AR4 features all of the aerodynamic benefits as the rest of the cutting-edge AR line, with a frame kit developed through computational fluid dynamics software and extensive wind tunnel testing. It's crafted from UHC Performance carbon fiber, which delivers an efficient platform with an impeccable ride quality.
Felt Aero Road UHC Performance carbon fiber, MMC with InsideOut construction, BSA threaded bottom bracket shell, carbon fiber dropouts, replaceable rear derailleur hanger, internal mechanical or internal electronic cable routing
Felt Aero Road UHC Advanced carbon fiber monocoque construction, AeroTaper 1.125" - 1.25" carbon fiber steerer tube, integrated crown race, crown, blades and dropouts
FSA integrated sealed cartridge bearing with Felt VariableHeight Cone Spacers (20mm PC, 4.5mm aluminum), No. 382/DJ, 1.125" - 1.25"
Devox, +/-7° rise, Ø31.8mm, 51cm: 90mm --- 54 - 56cm: 100mm --- 58cm: 110mm --- 61cm: 120mm
Devox Aero Road VariableShape, 80mm reach, 130mm drop, Ø31.8mm, 51 - 54cm: 400mm --- 56 - 61cm: 420mm
Felt VelvetGel tape with 3M reflective base with reflective Felt Bubble-Tech F-Wing bar end plugs
Shimano Ultegra R8000 11-speed
Shimano Ultegra R8000 braze-on
Shimano Ultegra R8000 11-speed short cage
Shimano RS500, 52/36T, 51cm: 170mm --- 54 - 56cm: 172.5mm --- 58 - 61cm: 175mm
Shimano Hollowtech BSA threaded
KMC X-11, 11-speed
Freewheel / Cassette:
Shimano 11-speed, 11-28T
Shimano Ultegra R8000
Tektro Quartz T741 dual pivot caliper
TRP T851 direct mount caliper
Fizik Arione R5
Felt Vibration Reducing Aero Road flip position UHC Advanced carbon fiber with 3T DiffLock Comfort Module internals, 51cm: 280mm length, 5mm offset --- 54 - 61cm: 350mm length, 25mm offset
Seat Post Clamp:
Felt Internaloc integrated with titanium bolts
Rims / Wheelset:
Devox 30; front: 17mm inner width, 27mm depth, --- rear: 17mm inner width, 30mm depth
Devox ARH2, sealed cartridge bearing, 100mm QR, 24H
Devox ARH2, sealed cartridge bearing, 11-speed, 130mm QR, 28H
2.0 / 1.5 x 2.3mm butted aero stainless steel with aluminum nipples
Grand Sport Race folding, 700 x 23c
Carbon assembly paste, chain plate protector, valve extenders, aero seat post slot covers
Tell us what the bike is for
"Combined with an ever-dependable Shimano Ultegra drivetrain, the AR4 will help you gain speed and save precious energy whether you're sprinting to the finish line, completing a century or dropping your friends on the club ride."
Frame and fork
Tell us about the build quality and finish of the frame and fork?
The carbon weave stands out on the Felt thanks to the matt lacquer finish, and it looks very smart indeed. The InsideOut mould technology ensures a smooth resin finish internally too.
Tell us about the materials used in the frame and fork?
This bike has entry-level UHC Performance carbon fibre in the frame, while the fork features an 'Advanced' blend.
Tell us about the geometry of the frame and fork?
The geometry is racy, and can be tweaked to run a time-trial position via the reversible seatpost.
How was the bike in terms of height and reach? How did it compare to other bikes of the same stated size?
As road bikes go, it matches up with sizes I've ridden before – it sizes normally with no real outlying foibles.
Riding the bike
Was the bike comfortable to ride? Tell us how you felt about the ride quality.
Not especially. The limitations of 23mm tyres are mainly to blame here, while the frame itself isn't that compliant either, playing to its racy/time trial credentials.
Did the bike feel stiff in the right places? Did any part of the bike feel too stiff or too flexible?
The AR4 frame excels in this area. However, a higher spec wheelset will certainly take it to the next level.
How did the bike transfer power? Did it feel efficient?
Very much so – in fact, the only bike that sticks in the mind in terms of stiffness like this is the Bianchi Oltre XR4.
Was there any toe-clip overlap with the front wheel? If so
A little, but I have long feet which accounts for a fair amount of it. Nothing disturbed my riding.
How would you describe the steering? Was it lively Direct and predictable, but lacking some feeling.
Tell us some more about the handling. How did the bike feel overall? Did it do particular things well or badly?
The handling is sharp yet predictable – once you're used to the 23mm rubber, it's very good indeed, and balanced.
Which components had the most effect (good or bad) on the bike's comfort? would you recommend any changes?
The wheels could use an upgrade for multiple reasons, and the cockpit isn't great at absorbing shocks either. The seatpost is surprisingly good though.
Which components had the most effect (good or bad) on the bike's stiffness? would you recommend any changes?
The wheels are below the standard set by the frame.
Which components had the most effect (good or bad) on the bike's efficiency? would you recommend any changes?
The wheels need changing, but the Shimano Ultegra drivetrain is very good. I think the Ultegra-issue chains would be a decent upgrade, though.
The shortcomings in finishing kit knock a couple of points off – otherwise we'd be looking at a 10 for the frame.
Despite the rolling stock, the AR4 picks up speed with ease.
Much like the acceleration, it's fully capable of letting me attack out of the saddle. However, the combination of narrow tyres, sub-standard wheels and a lack of feel through the handlebar don't always inspire confidence to lean over the front end.
Can't really complain here, especially as the wheels are so shallow. The frame seems very able to brush off crosswinds.
Stability all round is very good.
Stability all round is very good.
Very good, although the 23mm tyres can limit confidence.
The wheel/tyre combo and slight judder in the cockpit mean that although fairly predictable, the feel through the front end is never brilliant. Just adequate-to-good-at-times.
The stiffness of the frame means that it's surprisingly good at climbing for an aero bike.
Can't complain with Shimano Ultegra, although the RS500 chainset is a bit of a downer.
Nothing too much to say – the RS500 chainset should prove to be sturdy.
Ultegra has always been competitive in this department.
Tell us some more about the drivetrain. Anything you particularly did or didn't like? Any components which didn't work well together?
I don't like the non-series RS500 chainset, but other than that there's not much to complain about.
Wheels and tyres
The hubs seem to roll smoothly, but other than that they're uninspiring and not fast at all.
We're assured that our failure was an isolated incident, but it doesn't bode well.
Simply entry-level in terms of weight, while the rims are quite weighty too.
Not especially absorbing of road buzz.
In the context of a £2,400 bike, these wheels are well below par.
Tell us some more about the wheels.Did they work well in the conditions you encountered? Would you change the wheels? If so
They roll smoothly, but that's the only thing I can be truly positive about. Otherwise, stiffness, stability, reliability and weight are all questionable.
Despite being 23mm models, Continental Grand Sport tyres are a good, grippy compound.
No issues to note.
In a world of 25mm (or wider) tyres, they are disappointing in this regard.
Tell us some more about the tyres. Did they work well in the conditions you encountered? Would you change the tyres? If so
They work well, but 23mm rubber is now looking very outdated in the real world for numerous reasons.
Ultegra is excellent, but the cockpit is a little basic and shaky when rolling over poor surfaces.
No real complaints here.
The Devox bar and stem setup isn't especially remarkable but it's fine.
Solid performance, although the cost of the bike pulls this back a bit.
Tell us some more about the controls. Any particularly good or bad components? How would the controls work for larger or smaller riders?
A standard setup: the drops are easy to reach, and the bar is 42cm in width.
Anything else you want to say about the componentry? Comment on any other components (good or bad)
The TRP/Tektro brakes aren't to Shimano Ultegra standard, especially the direct mount calliper on the chainstays.
Did you enjoy riding the bike? In parts, yes. I can't help but the think that the AR4s spec sheet lets the obviously fast frameset down.
Would you consider buying the bike? No – in my opinion a carbon bike that can only reasonably run 23mm rubber should be (by now) consigned to the history books.
Would you recommend the bike to a friend? If they wanted a pure aero bike that could be run as a TT bike, then yes. The frame has potential, so I'd probably point them to the AR3 or higher despite the extra cost.
Use this box to explain your overall score
If this was a review of the Felt AR4's frame, we'd be looking at a higher score despite the lack of clear space for 25mm tyres. It's fast, stiff, and quite light even in this entry-level format. It lacks compliance though, while the build could (and maybe should) be better for the money.
About the tester
I usually ride: Canyon Ultimate CF SL 9.0 SL (2016) My best bike is:
I've been riding for: 5-10 years I ride: Most days I would class myself as: Expert
I regularly do the following types of riding: time trialling, club rides, sportives, general fitness riding