Cervelo R5 Ultegra Di2 Bike

The Cervelo R5 Ultegra Di2 Bike is Cervelo's answer to a simple question: what's the fastest bike on a climb? Where the S5 is built around aerodynamics and flat-terrain speed, the R5 is built around weight, stiffness, and the kind of climbing performance that puts it in the hands of Tour de France riders contesting mountain stages. A 651g frame, 5.97 kg complete bike (Ultegra Di2, size 56), and a Reserve 34|37 SL wheelset developed specifically for this platform — at $10,100, the R5 Ultegra Di2 is Cervelo's lightest production road bike fully built and ready to climb.

The R5 frame uses Squoval Max tube shaping — Cervelo's proprietary cross-section geometry that runs a square profile with ovalized corners and curved sides. The shape is a structural engineering choice: a true square cross-section maximizes stiffness-to-material ratio in both lateral and torsional directions, but square corners concentrate stress. By rounding the corners and curving the faces, Cervelo maintains the structural advantages of the square profile while distributing load more evenly through the tube wall. The downtube specifically is shaped to maximize lateral and torsional stiffness while keeping mass to a minimum — the combination that produces a 651g frame weight and a 5.97 kg complete bike that sits 900 grams under the UCI minimum weight limit. The carbon layup delivers 130 grams less than the previous R5 generation without any reduction in ride feel or stiffness. Cables route fully internally through the frame, reducing aerodynamic drag by an additional 25 grams — a detail that matters when Cervelo is counting every gram. The PF BBright bottom bracket shell (79mm, asymmetrical pressfit) places bearings wider than a standard 68mm shell for a stiffer, more efficient power transfer at the crankset interface. A 298g all-carbon fork completes the front end on 12/100mm thru-axle with a 160mm flat-mount disc interface.

The R5's HB18 is Cervelo's integrated one-piece carbon handlebar and stem — a different unit from the S5's HB19, designed specifically for the R5 platform and compatible with the Aspero-5, Caledonia-5, and Rouvida. The HB18 weighs approximately 134 grams and saves roughly 150 grams compared to an equivalent traditional bar-and-stem setup. It's 2 watts more aerodynamic than the prior R5 bar/stem configuration and runs 7° of flare with 2° of sweep — proportions that work well for riders who move between the hoods and drops frequently on long mountain stages. Bar widths of 36, 38, and 40cm are available in 15 different combinations with stem lengths from the same range, so most riders can find an appropriate fit within the integrated system. All Ultegra Di2 connections route internally through the steerer, leaving the front end clean from handlebar to caliper.

The drivetrain is Shimano Ultegra Di2 R8150 — 12-speed wired electronic shifting with Shimano ST-R8170 dual-control levers for hydraulic disc integration. The Shimano FC-R8100 crankset runs 52/36T chainrings on a BBright-specific pressfit BB. The cassette is Shimano Ultegra CS-R8100 in 11-34T — the climbing-appropriate range that keeps close gear steps through the upper portion of the cassette while providing genuine bailout gearing at the bottom. Shimano Ultegra hydraulic disc brakes with 160mm CL800 Centerlock rotors handle stopping front and rear. The wheelset is Reserve 34|37 SL — a shallow carbon set (34mm front / 37mm rear) at approximately 1,300 grams per pair, co-developed with the R5 in mind. The SL designation reflects the super-light build, with 20 spokes front and 24 rear on DT Swiss 240 hubs, mini-hookless tubeless-ready rims at 22.6mm internal width front and 21.6mm rear on Centerlock disc mounts. For a climbing-focused bike, 34 and 37mm rim depths hit the right balance — light enough to not penalize the rider on extended ascents, with enough structure for confident descending. Vittoria Corsa Pro TLR 26mm tires are fitted tubeless-ready. The Cervelo SP24 carbon seatpost (D-shaped, 0mm or 15mm offset, 370mm) pairs with the R5's seat tube for clean integration.

Specs at a Glance

• Frame: Squoval Max carbon, 651g (size 56), 130g lighter than previous R5; BBright PF 79mm BB; internal cable routing
• Fork: All-carbon R5 fork, 298g, tapered steerer, 12x100mm, 160mm flat-mount disc
• Groupset: Shimano Ultegra Di2 R8150, 12-speed electronic
• Shifters: Shimano ST-R8170 Di2 dual-control hydraulic disc levers
• Cranks: Shimano FC-R8100, 52/36T, BBright pressfit
• Cassette: Shimano Ultegra CS-R8100, 11-34T, 12-speed
• Chain: Shimano, 12-speed
• Brakes: Shimano Ultegra R8170 hydraulic disc; 160mm CL800 Centerlock rotors front and rear
• Wheels: Reserve 34|37 SL (34mm front / 37mm rear), mini-hookless tubeless, DT Swiss 240 hubs (Centerlock), 20h front / 24h rear, ~1,300g pair
• Rim internal width: 22.6mm (front) / 21.6mm (rear)
• Tires: Vittoria Corsa Pro TLR, 26mm, tubeless ready
• Cockpit: Cervelo HB18 one-piece integrated carbon, 7° flare, 2° sweep; 36/38/40cm widths; 15 bar/stem combinations
• Seatpost: Cervelo SP24 carbon, D-shaped, 0mm or 15mm offset, 370mm
• Geometry (size 56): Reach 389mm | Stack 565mm | HTA 73° | STA 73° | Chainstay 410mm
• Complete bike weight: 5.97 kg (size 56) — 900g under UCI minimum
• Sizes: 48, 51, 54, 56, 58, 61cm
• Colors: Five Black / Bronze, Five Black / Silver

Design Benefits

1. Squoval Max tube shaping. The square-with-rounded-corners cross-section extracts maximum stiffness per gram from the carbon layup — lateral stiffness for power transfer, torsional stiffness for precise handling — while distributing stress evenly to avoid the concentration points of a true square profile. It's the structural geometry that makes a 651g frame weight achievable without compromising ride quality.
2. 5.97 kg complete bike, 900g under UCI limit. The R5 Ultegra Di2 in size 56 weighs 5.97 kg without pedals. At an event where every gram on a long climb matters, arriving 900 grams under the UCI minimum is a meaningful performance margin.
3. Reserve 34|37 SL co-developed wheelset. Purpose-built for the R5 at approximately 1,300 grams per pair — shallow enough to stay honest on long ascents, structured enough for aggressive descending. The asymmetric depth (34mm front / 37mm rear) mirrors the logic of the bike: every detail is calibrated for climbing performance, not just overall speed.
4. HB18 integrated cockpit at 134g. Saves roughly 150 grams over a comparable traditional bar-and-stem setup, routes all cables internally, and adds 2 watts of aerodynamic benefit over the prior R5 bar. On a bike where weight is the primary objective, a 150g savings at the cockpit is substantial.
5. 11-34T climbing cassette. The Ultegra Di2 build ships with genuine climbing range — 11-34T gives you close gear steps in the mid-range for sustained tempo efforts and real bailout gearing for the steepest pitches.
6. Internal cable routing throughout. All Ultegra Di2 wiring and hydraulic lines run inside the frame and fork, contributing 25 grams of aerodynamic drag reduction and keeping the bike visually and mechanically clean.
7. BBright bottom bracket advantage. The 79mm asymmetrical pressfit shell places bearings further apart than a standard 68mm BB, increasing the stiffness triangle at the crankset without adding frame weight — an important efficiency gain on a bike that will be asked to transfer power at high outputs on long climbs.

Final Take

The Cervelo R5 Ultegra Di2 is the right bike for riders who want maximum climbing performance from a production road frame. At 5.97 kg with Shimano Ultegra Di2 and Reserve 34|37 SL wheels, it delivers the platform that WorldTour climbers reach for on mountain stages — at a price point that makes it accessible to the serious amateur who takes long alpine days as seriously as race results.