The Tarmac SL8, by a small margin. Specialized's published wind-tunnel numbers put the SL8 at 209 W to hold 45 km/h — within 4 W of the Cervélo S5 (205 W). The Soloist sits between the S5 and the lighter R5 in Cervélo's range, and reviewers (Granfondo, Velo) note it lags the S5 by ~190 g of equivalent drag.

In practical terms, on a flat 40 km TT effort the Tarmac is probably worth 15–25 seconds over the Soloist for a 250 W rider. At social-ride pace below 30 km/h, the gap collapses to nothing you'll feel.

The Tarmac SL8, on weight alone. The S-Works frame claims 685 g (size 56), and complete bikes come in around 6.67 kg in top trim. Reviewed Soloist builds typically weigh 7.5–8.1 kg depending on spec.

For a 70 kg rider that's roughly 1% of system weight, which translates to ~10–15 seconds on a 30-minute climb. The Soloist isn't a bad climber — Cyclist's tester praised its power transfer in the Austrian Alps — but reviewers (Granfondo, Cyclonline) consistently note it can't quite match dedicated lightweights like the Tarmac S-Works on sustained ascents.

Cervélo Soloist: 34 mm officially. The Reserve wheels run 23 mm internal width, so a 28–30 mm tire often measures 30–31 mm on-bike.

Specialized Tarmac SL8: 32 mm officially. Stock builds ship with 26 or 28 mm S-Works Turbo tires that most reviewers immediately swap for 28–30 mm rubber.

Neither is a gravel bike, but the Soloist's 2 mm extra clearance is meaningful if you ride chip-seal or want occasional dirt-road exploration.

Yes. Cervélo confirms the same carbon layup is used on every Soloist build, from the $3,900 mechanical 105 model to the $7,600 Force AXS 1. Road.cc and BikeRadar both highlight this as a value standout — "even your entry-level bike has a WorldTour quality frameset," per road.cc — and it's a deliberate contrast to how Specialized splits the Tarmac into two carbon grades (FACT 12r on S-Works, FACT 10r on Pro and Expert).

The Soloist uses a semi-integrated system: hoses run under the stem rather than through the steerer. Swapping stem length or bar width is a roughly 30-minute job that doesn't require a brake bleed. Multiple reviewers (Velo, Cyclist UK, BikeRadar) call this out as a major ownership advantage.

The Tarmac SL8 Pro and S-Works use a one-piece Roval Rapide integrated cockpit. Stem length is fixed at purchase; changing it later means buying a new unit (~$600) plus labor. The SL8 Expert gets a two-piece cockpit, which is less aero but standard-fit and easy to swap.

Yes — the Soloist does. Cervélo specifically engineered it to retain compatibility with mechanical drivetrains, and the $3,900 entry build ships with mechanical Shimano 105.

The Tarmac SL8 is electronic-only in its current builds — the cheapest spec is the $4,699 SL8 Comp with SRAM Rival eTap AXS. The frame's clean internal routing isn't designed for mechanical cable runs.

On the Soloist, multiple reviewers (Velo, Cyclist UK, Granfondo) report creaks from the BBRight T47 bottom bracket and headset. Other long-term testers (In The Know Cycling, ~3,000 miles) report no issues, suggesting it's setup-dependent rather than universal.

On the Tarmac SL8, the most common gripe is the stock 26 mm S-Works Turbo tires being extremely tight on the rims — multiple reviewers (David Arthur, Chris Horner) flag roadside-puncture difficulty. Specialized addressed an SL7-era fork-steerer compression-ring issue on the SL8.

At the same out-the-door spend, the Soloist usually comes with a tier-better groupset or a tier-better wheelset. The Soloist Ultegra Di2 at $7,350 is the closest match to the Tarmac SL8 Pro Ultegra Di2 at $8,499 — same drivetrain, same shifting, $1,150 cheaper. For that delta you're paying for the Tarmac's sharper handling, lower frame weight, and the integrated Roval cockpit. Whether that's worth $1,150 depends on whether you actually race.