Felt AR4

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.

• Pros: Aero frameset, time trial adaptability, stiffness
• Cons: Basic wheels, tyre clearance, poor brakes, stiffness

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...

Frame and fork

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.

Ride and handling

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.

Groupset

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.

Finishing kit

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.

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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.

Conclusion

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.

Verdict

There are highlights when it comes to stiffness and aero performance in the frame, but it's a mixed bag elsewhere