Argon 18 SumvsCervelo Soloist

Argon 18 and Cervelo have arrived at a similar conclusion: the era of owning two separate bikes for climbing and aero is mostly over for non-pros. The Sum merges the legacy of the aero Nitrogen and the lightweight Gallium into a single 850g frame that handles both roles with a surprising amount of suppleness. Cervelo’s Soloist does something nearly identical, slotting between the pro-tour S5 and R5 to provide a package that is not quite as extreme as either but remains "just right" for the amateur circuit. Maintenance and longevity highlight the biggest philosophical gap between these machines. The Soloist uses a threaded T47 BBRight bottom bracket and cables that tuck under the stem rather than through it, a move clearly intended to keep the bike out of the shop and on the road. The Sum sticks to a BB86 press-fit system and uses the FSA ACR internal routing, which remains adjustable but lacks the same degree of mechanical simplicity found on the Cervelo.

Steering on the Sum feels impressively joined up, offering a level of road damping that many pure race bikes lack. It mutes road buzz effectively, with reviewers noting it can pedal over rough stretches that usually require bracing. On the other hand, the Soloist is a stiff, punchy beast that rewards every watt you put into the pedals, though it can feel chattery on broken tarmac. The front end of the Cervelo is particularly firm; unless you swap the stock alloy bars for carbon, prepare for some hand sting on unkempt lanes. Handling is where the two bikes diverge slightly in personality. The Soloist's geometry is lifted from the R5 climber, giving it a poised, stable feel that comes alive on winding descents without the twitchiness of a pure aero rig. The Sum is equally confident at high speeds—Mark Beaumont famously took it past 80kph without a hint of wobble—but it feels more playful and nimble in tight corners. While the Soloist is a precise tool for holding a line, the Sum is a fun, supple machine that encourages you to push harder on twisty terrain. Performance at high speed is a strong suit for both, but the Sum earns extra credit for its high-speed stability on the descents. Road.cc rated the Sum a 9/10 for stability, noting it never feels skittish even when the wind picks up. The Soloist matches this confidence through technical switchbacks, though its "experiential road" focus means it is less sensitive to crosswinds than deep-section pro bikes. If you spend most of your time on hilly, wind-blown routes, both bikes provide a planted feel that doesn't punish the rider. Efficiency is the name of the game for the Soloist, which manages to feel stiff throughout the entire frame spine. Every pedal stroke results in immediate forward motion, whereas the Sum has been described as having a more "poised and connected" sensation that emphasizes rhythm over raw snap. The Soloist struggles slightly on the hardest, steepest climbs where its 8kg-plus weight becomes noticeable, but it redeems itself on punchy, rolling terrain.