£7,500 Rapid performance shines through, but not without flaw
Weight 7.6kg (M, 54-56cm) Frame High-modulus carbon Fork Carbon Gears SRAM Force eTap AXS 12-speed (48/35t, 10-28t) Brakes SRAM Force eTap AXS hydraulic disc Wheels Hunt 48 Limitless Aero Disc Finishing kit FSA SL-K SCR Compact carbon bar, FSA ACR ST-OS-160 alloy stem, Argon 18 Sum Pro carbon seatpost, Repente Prime 3.0 saddle, Vittoria Corsa TLR G2.0 700x25c tubeless-ready tyres
LAUNCHED IN EARLY 2022, THE SUM Pro is Argon 18’s all-rounder race bike, blending aerodynamic efficiency with a low weight. Its frame features truncated aerofoil tubing throughout and weighs a claimed 850g (Medium). An optimised down-tube is said to shape airflow around a water bottle. Bucking the trend for one-piece bar/stems, the Sum Pro sticks to a traditional non-integrated cockpit, which makes customising it easier. Up front, the fork has bladed legs with plentiful clearance around the front wheel, while at the rear dropped slender seatstays contribute to the bike’s compliance, as does the D-shaped seatpost which offers a 20mm setback range.
The geometry is spot-on for most racers. The Sum Pro features the Canadian brand’s 3D fit system, which enables you to adjust the stack height by 25mm without compromising steering stiffness. I had my Medium test bike set to the middle of the three settings (15mm), providing a stack of 554mm and reach of 393mm. 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 choose the right bike. The bike’s standover height is also low, at 766mm. A 72.7° head angle means the steering feels quite relaxed, and the 73.5° seat angle is designed to pitch the rider over the bottom bracket for improved power output.
Out with the old
At the time of review, the bike is sold with the previous generation Force eTap AXS drivetrain; this will get updated to the latest Force AXS as the old groupset sells through. However, this version remains a very good performer so you won’t miss out too much on the few recent improvements. I enjoyed using the close-ratio 10-28t cassette on relatively short climbs, but if I regularly rode more mountainous terrain I’d prefer SRAM’s 10-33t model. There’s no power meter here, which is unfortunate at this price.
The Hunt 48 wheels have a progressively wide 35mm external rim and are shod in Vittoria Corsa 700x25c tyres – narrow compared to today’s standards – which seems a shame given the bike’s purported clearance
