The Cervélo S5, by a meaningful margin. Cycling News ran the new S5 in a wind tunnel and recorded a 27.57 W saving over their baseline at 40 km/h with a rider on board. Cervélo's own claim is that the 2025 S5 is 6.3 watts faster than the outgoing model.

The Cervélo R5 picked up some aero work — the new HB18 cockpit is worth roughly 2 watts versus the prior R5 — but it makes no pretense of competing with a bayonet-fork aero frame on the flats. Reviewers consistently note the R5 'doesn't retain speed in the same way' as a dedicated aero bike.

The Cervélo R5, by a clear margin. Independent measurements put the SRAM Red AXS R5 at 5.97 kg complete (Granfondo) — well under the UCI's 6.8 kg minimum and roughly 1.2 kg lighter than the equivalent S5, which Granfondo measured in the 7.17–7.44 kg range.

On a 30-minute climb at threshold for a 70 kg rider, that's somewhere in the neighborhood of 30–60 seconds, depending on gradient. The R5 also gets a claimed 13% stiffer bottom bracket, which reviewers describe as 'instantaneous' under power.

Both frames are officially rated to 34 mm. In practice the Cervelo R5 ships with 26 mm Vittoria Corsa Pro Speed tires (a deliberate weight choice, and one most reviewers recommend immediately upgrading to 28 or 30 mm). The Cervelo S5 ships 29 mm Vittoria Corsa Pro on wider Reserve 57|64 rims, which actually measure closer to 30 mm on-bike.

Neither is a gravel bike. For anything rougher than chip seal, look at the Áspero-5 or a true endurance frame.

Within a few millimeters, yes. At size 54 the R5 has a stack of 544.6 mm and reach of 383.3 mm; the S5 is 542 mm stack and 384 mm reach. Head tube angle is 73° on both. That's a deliberate Cervélo decision so that a pro on Visma-Lease a Bike can swap from the S5 on a flat stage to the R5 in the mountains without re-fitting.

Where the bikes diverge is underneath the rider: the S5 has 5 mm shorter chainstays (405 vs 410), 1.7 mm less trail (55.6 vs 57.3), and a 3 mm shorter wheelbase. Same cockpit position; sharper handling on the S5.

Yes — every complete R5 and every complete S5 ships with a dual-sided power meter stock. Shimano builds get a 4iiii Precision Pro on both crank arms; SRAM builds get a Quarq spider-based meter. That's a value worth roughly $1,000 you'd otherwise spend after the fact, and it's consistent across both ranges from the Ultegra Di2 builds up through Red AXS.

The R5 uses the HB18 one-piece carbon cockpit; the S5 uses the HB19. Both are one-piece bar/stem units that limit post-purchase fit changes. Cervélo mitigates this with a 30-day no-charge cockpit exchange on the R5 and a 60-day exchange on the S5 — useful if your initial guess on bar width or stem length turns out wrong.

Day-to-day maintenance favors the S5: reviewers note its front-end is 'considerably simpler to maintain than its predecessor' thanks to easier headset access. The S5's BBright press-fit bottom bracket, however, also houses the Di2 battery — and reviewers consistently call it a hassle for home mechanics.

Because at WorldTour speeds, the S5's aero advantage often pays back its weight penalty even on climbs that aren't extreme. A pro holding 380+ watts on a 6% gradient is already moving fast enough that drag matters.

When the gradient gets truly steep — high-mountain summit finishes, sustained 8–10% — the team switches to the R5. That's exactly the line: at a typical amateur climbing pace below 20 km/h, weight wins easily, which is why the R5 is the better choice for most non-pro riders who climb regularly.

Yes — both top out with a SRAM Red XPLR AXS 1x build at $14,400 (R5) and $14,500 (S5). Cervélo claims roughly 2 watts of aero saving from removing the front derailleur on the S5. The 10–46T XPLR cassette gives wide range, but reviewers note the gear jumps at the top end can feel gappy for fine-cadence work — a real consideration if you're a cadence-sensitive rider on rolling terrain.

For anyone who's never run 1x on the road, neither of these is the place to start. The 2x Force AXS or Ultegra Di2 builds are the safer pick.