The Specialized Aethos wins on paper. The S-Works Aethos 2 frame is a claimed 595 g (painted, size 56), and complete bikes have been weighed as low as 5.98 kg with SRAM Red AXS. The Factor O2 VAM frame is a claimed 700 g, with complete bikes around 6.3–6.7 kg in tested trim.

In practice, both are below the UCI 6.8 kg weight limit in their flagship builds — the difference is meaningful on a stopwatch (roughly 5–10 seconds on a 30-minute climb at 70 kg system weight) but won't be the deciding factor for most riders.

The Factor O2 VAM, by a margin that depends on what you're comparing to. Factor's published numbers put the O2 VAM only ~5 watts behind the full-aero Ostro VAM at 48 km/h, thanks to truncated airfoil tube shapes and a one-piece integrated cockpit. The Aethos, with round tubes and a shallow 33 mm Alpinist wheelset, has no aero optimization to speak of and loses momentum quickly on flats and into headwinds.

This is the deliberate trade Specialized made. If most of your riding is rolling or flat, the O2 VAM is the more honest choice.

Both are excellent. They share an identical 72.5° head tube angle at size 54, but the Factor runs 405 mm chainstays vs the Aethos's 410 mm, and a 985 mm wheelbase vs 992 mm — tighter, more eager out of the saddle.

The Aethos sits 7 mm taller in stack and 3 mm longer in reach, putting the rider in a slightly more upright position better suited to long sustained climbs. The O2 VAM also uses four different fork offsets across its size range to keep trail consistent at 57–58 mm, so handling character doesn't change with frame size — a thoughtful detail for smaller and larger riders.

Factor O2 VAM: 32 mm. Enough for chunky road tires and the occasional hardpack detour.

Specialized Aethos 2: 35 mm — a notable jump from the previous generation, and Specialized engineers explicitly say the frame has "no solidity problems" with light all-road use. Reviewers consistently call out that the Aethos ships with 28 mm tires despite the clearance, and unanimously recommend swapping to 30–32 mm for comfort or 35 mm for genuine all-road capability.

Neither is a gravel bike. For real off-road, look at the Specialized Crux or a dedicated gravel platform.

The Factor O2 VAM has no entry-level builds. The cheapest complete bike is the Shimano Ultegra Di2 at $11,299 — and that's already more than the Aethos's mid-tier 2 Pro at $8,499. Specialized sells the same Aethos frame design (in FACT 10r carbon rather than 12r) all the way down to a $6,599 Expert build.

Factor is a smaller brand with a single carbon grade and limited production volume; the price reflects that. Whether the extra spend is justified depends on whether the climbing-focused geometry and aero touches matter to your riding.

Both bikes use a one-piece bar/stem with internal hose routing, so swapping bar width or stem length means buying a new unit on either platform.

The Factor's Black Inc Integrated Barstem has a notable advantage at point of purchase: Factor lets you spec bar width and stem length individually as a no-cost option. Get it right the first time and you may never need to touch it.

The Aethos's Roval Alpinist Cockpit II ships in 13 size combinations, a wide range that should cover most riders, but Specialized doesn't typically allow free spec-time swaps. Some Aethos buyers have had to negotiate cockpit width with their dealer separately — a documented headache in early reviews.

Aethos — yes, on most builds. The S-Works Dura-Ace ships with a 4iiii Precision Pro dual-sided meter, the S-Works Red AXS has SRAM's integrated meter, and even the 2 Pro Ultegra Di2 includes a 4iiii Precision 3+ single-sided unit.

Factor O2 VAM — only on the SRAM builds. The SRAM Red and SRAM Force builds include Quarq spider-based meters. Both Shimano builds (Ultegra Di2 at $11,299 and Dura-Ace Di2 at $13,199) ship without one, an odd omission at this price point that adds another $300–$400 to your total if you want it.

Of course you can — and Specialized's Quick-Step pros have done it. But the 2026 Aethos is explicitly designed around "ride feel" rather than race performance. It's measurably slower than the Tarmac SL8 on flats (Specialized's own marketing makes this point) and the new taller geometry sits you slightly less aggressively.

For crits, fast group rides, or rolling road races, the Tarmac SL8 is Specialized's better answer. The Aethos is for the rider who wants the lightest, most compliant bike they can buy and considers race results a bonus.