Argon 18 Sum Pro Force eTap AXS review

The Sum Pro is Argon 18’s all-rounder race bike, blending aerodynamic efficiency with low weight.

Unlike many of its competitors, which have almost unanimously gone down the proprietary or one-piece bar-stem setup route, the bike sticks to a traditional non-integrated cockpit.

This makes customising the Sum Pro easier – good for fettlers with exacting requirements – while the short stack naturally positions the bike towards the aggressive end of racy bike fits.

I’ve been very impressed with the Sum Pro’s turn of speed and predictable-but-sharp handling, and I’m convinced it’s a great platform for racing.

Out of the box, though, the finishing kit leaves plenty of room for improvement in a bike that costs £7,500.

Argon 18 Sum Pro Force eTap AXS frameset

The Argon 18 Sum Pro launched at the beginning of 2022, with claims it matched the aero prowess of the Nitrogen Pro, Argon 18’s dedicated aero road bike.

As with the majority of bikes in the all-rounder race genre, it was also intended to hit a low weight that rivalled the Gallium Pro, the brand’s climbing bike.

It’s worth noting that Argon 18 has since stopped selling those reference-point bikes – perhaps a sign that the Canadian brand felt it could offer the benefits of both of those machines in one package.

The Sum Pro has a high-modulus carbon-fibre frame that’s claimed to weigh 850g in a size medium (54-56cm).

This is competitive with the Ridley Falcn RS (825g, size medium) but is somewhat gazumped by the Specialized Tarmac SL8 (780g, size 56cm).

Argon 18 says the frame features truncated aerofoil tubing throughout, with an optimised down tube said to help shape airflow around a water bottle.

Up front, the fork uses bladed legs with plentiful clearance around the front wheel and tyre, and an hourglass-shaped head tube, which fits a 1.5in headset.

The frame uses FSA’s ACR internal routing system, but this means the two-piece cockpit can be (relatively) easily swapped out for a preferred, compatible option.

At the rear, dropped slender seatstays are designed to stay out of the way of turbulent air, and contribute to the bike’s compliance.

In a similar fashion to the Canyon Ultimate, Scott Addict RC and Ridley Falcn RS, the Sum Pro uses a proprietary D-shaped seatpost for its ride-smoothing properties.

The frame fits a BB86 press-fit bottom bracket.

Argon 18 Sum Pro Force eTap AXS geometry

The Argon 18 Sum Pro’s geometry is right where most racers will want it to be.

The bike features the brand’s 3D fit system, which it says enables the stack height to be adjusted by 25mm without compromising steering stiffness.

I had my size-medium test bike set to the middle of the three settings (15mm), providing a stack of 554mm and reach of 393mm.

I found this nominal size fitted me in a similar fashion to the Ridley Falcn RS – on paper, it’s a size smaller than I’d usually opt for, demonstrating that careful attention should be paid to the geometry chart to get the right Sum Pro for you.

The bike’s standover height is also low, much like the Ridley, at 766mm.

A 72.7-degree head tube angle is 0.8 degrees slacker than a Specialized Tarmac SL8. This might not sound much, but the steering feels quite relaxed as a result. More on that to come.

The 73.5-degree seat angle is designed to pitch the rider forward over the bottom bracket, which can help open up the hip angle for improved power output (in theory).

In my case, knowing where my optimal sitting position should be in relation to the bottom bracket, I was able to fit the saddle in the middle of the 20mm setback range offered by the seatpost (as opposed to pulling the saddle forwards).

Argon 18 Sum Pro Force eTap AXS build

As the same suggests, this Sum Pro comes fitted with a SRAM Force eTap AXS groupset.

At the time of writing, the bike continues to be sold with this previous-generation drivetrain (as opposed to the latest Force AXS groupset). This should get updated as the old groupset sells through and a new model year comes into effect.

Having said that, while the latest groupset features some improvements, this version remains a very good performer – to the point where fellow tech editor Warren Rossiter summated the improvements weren’t enough to justify an immediate upgrade.

Unless you’re the kind of person who needs the latest-generation kit on your bike, you’re not losing out on anything truly meaningful here.

The crankset features 48/35-tooth chainrings, paired with a 10-28t cassette.

I enjoyed using this close-ratio cassette on my local test loops with only relatively short climbs.

That said, if I had been riding the Sum Pro on more mountainous terrain, such as you’ll more likely find in Europe or parts of the US, then I suspect I’d have preferred SRAM’s 10-33t model.

There’s no power meter here, which is unfortunate at this price. In comparison, Canyon’s latest Ultimate CF SLX includes a SRAM Force AXS power meter spider for £6,699.

The bike comes supplied with a Hunt 48 Limitless Aero Disc wheelset, which are alloy-spoked siblings to the wheels I tested in February 2023.

These have a 22.5mm internal rim width and measure a progressive 35mm-wide externally.

Although one might argue wheels costing £1,249 aftermarket might not seem as premium as other larger-brand wheels, I can’t fault their performance or (on-paper) aero credentials.

The tyres are Vittoria Corsa TLR G2.0, in a 700x25c size.

These leave the external edges of the rims clearly visible when mounted, but more importantly don’t maximise the volume and comfort a larger set would provide.

This is a shame, given the bike’s purported clearance for 32c rubber. The wide Hunt rims also seem a better match to larger 28c rubber, and the potential ride quality and rolling resistance gains that accompany them.

The tyres come set up with tubes, which is a small pain for those wanting a tubeless setup right out of the box.

That said, the tubes are then spare, which is always handy should the worst happen on the road.

Up front, Argon 18 specs a carbon FSA SL-K SCR Compact handlebar and ACR ST-OS-160 alloy stem.

The overall shape of the bar is well-considered and it’s easy to move from the hoods to the drops, but I found the bar diameter to be overly narrow for my large (but not huge) hands, especially when riding on the tops.

This can be partly remedied aftermarket by double wrapping bar tape, but a more aerodynamically shaped bar (perhaps with flattened tops) would have been a more fitting choice given the Sum Pro’s purpose.

The Repente Prime 3.0 saddle has a suitably racy shape with some supporting curvature and a pressure-relieving cutout. It matches the intentions of the bike, but saddle comfort is very subjective.

Of course, you can switch this and the cockpit yourself given the standards used here, but it’s a pity to need to do that having spent £7,500 already.

To that end, the Sum Pro is challenged when it comes to comparative pricing.

You can buy a Pinarello F7 Ultegra Di2 and have £500 left over, or a Canyon Ultimate CF SLX 8 Di2 for £6,199 (which includes a single-sided power meter) – a £1,300 saving.

That said, a Ridley Falcn RS Ultegra Di2 is £8,599, while a Specialized Tarmac SL8 Pro (with either Shimano Ultegra Di2 R8100 or SRAM Force AXS, albeit both power-meter equipped) costs £8,000.

Territory-specific prices vary between brands, and are dependent on many factors, but the Sum Pro certainly doesn’t stand out in this regard.

For the record, the Sum Pro Force eTap AXS tipped the scales at 7.6kg.

Argon 18 Sum Pro Force eTap AXS ride impressions

While testing affirmed my reservations about some of the finishing kit, the Sum Pro is undoubtedly a quick and able race bike.

It feels efficient when accelerating and holding a constant speed of around 35-40kph, and is also notably stable when the wind picks up.

The wide Hunt wheels certainly play their part here, while I suspect the truncated frame tubes help to minimise buffeting too.

Married to very predictable handling, I found the Sum Pro to be a very easy bike to ride at speed with confidence.

Although I prefer a slightly sharper front end, the steady nature of the steering pays dividends when cornering at speed. I could be slightly ham-fisted with my inputs and the bike would respond with an air of calm.

I’ve found the opposite on other pin-sharp race bikes in recent times, such as the Colnago V4RS and Pinarello F7, which can punish when you take liberties.

In a group situation, where riders can be elbow to elbow, such easy steering can also be a positive, given twitchy reactions can lead to disastrous consequences. Nevertheless, personal preferences will dictate if it’s right for you.

As previously mentioned, the Sum Pro has a relatively low stack.

For some, the position might be a little too aggressive if you want to use the bike for longer summer rides as well as racing – it feels very ‘business-like’ and purposeful.

Naturally, this could be ideal if your idea of fun is riding as fast as you can in an aerodynamic position, but if you’re after a racy bike that has a steadier side to its character for longer rides, then there are road bikes with more balanced geometries available.

The Sum Pro also feels relatively rigid. Not bone-shakingly so, but firm enough that the Canyon Ultimate SLX 8 Di2 and Scott Addict 40 (which I tested alongside the Sum Pro) felt notably more comfortable.

Lighter riders are unlikely to feel this as keenly as me – I weigh more than 80kg. We cyclists come in all shapes and sizes.

All things being equal, fitting some wider tyres and running lower pressures, would go some way to remedying this.

Argon 18 Sum Pro Force eTap AXS bottom line

The Argon 18 Sum Pro Force eTap AXS is a mixed bag.

It has many plus points, including its obvious speed, easy handling, lack of proprietary cockpit system and progressive wheels.

That said, the handlebar choice doesn’t feel like a good fit for the bike and the tyres are narrow by today’s standards.

The ride position is relatively aggressive – I suspect too focused for some – and there are cheaper alternatives with better all-round builds.

Fundamentally, the Argon 18 Sum Pro is a capable all-round race bike, but best described as a qualified purchase rather than a slam-dunk winner.