Ventum, Dimond, Cervelo – Why do these triathlon bikes look so weird?

Aerodynamics vs. Weight

• Modern high-end bikes prioritize aerodynamics over weight; aero dominates performance except on steep climbs.
• WorldTour road bikes are reportedly all above the UCI’s minimum weight, accepting extra grams for better aero.
• Some argue tiny weight savings (e.g., 150 g) are lost in the noise of rider weight and water carried; others note that lighter is still lighter, even if the gain is very small.

Non-Double-Diamond (NDD) Tri Bikes

• NDD frames aim to reduce frontal area rather than literal surface area, improving wind-facing profile.
• Skepticism exists that real-world aero gains are overstated; top pros winning on more “normal” TT frames is cited.
• Stiffness and handling over long distances at 25–27 mph are concerns; extra carbon can make them stiff but may reduce their relative advantage.
• Integrated storage and hydration are now central to tri bike design; article’s “weird” bikes are seen as already several years old, not bleeding-edge.

UCI Rules and Design Constraints

• UCI bans NDD frames and mandates a traditional main triangle, tightly constraining shapes, weight, and equipment.
• This makes NDD designs commercially unattractive for road/TT because they can’t be used in UCI events or easily resold.
• Rules are driven by safety, tradition, cost control, and aesthetics, not just engineering.

Tires, Wheels, and Rotating Mass

• Trend toward wider tires (≈28–32 mm) for lower rolling resistance and better aero when matched to wider rims.
• Wider tires increase rotating mass; debate over how significant this is. Some claim effect is small; others say it’s noticeable, especially on climbs and during accelerations.
• High-quality, supple casings and pressure tuning are emphasized as more important than pure weight.
• Disc wheels are viewed as more impactful for aero than frames but are very expensive.

Rider Position and Human Factors

• Most drag comes from the rider, not the frame. Position, comfort, and the ability to hold an aero posture over time are crucial.
• Significant effort goes into fit, aero testing (wind tunnels, velodromes, on-road), sensors, and real-time drag measurement.
• Gains from bar/hand position, helmets, skinsuits, overshoes, and even shaving or 3D-printed body “fairings” are highlighted.
• Commenters stress that for many riders, fitness and body weight overshadow marginal equipment gains.

Materials, Durability, and Use Cases

• Extreme tri/TT frames can be “not generally roadworthy” and may fail after hard use or impacts; occasional catastrophic cracks are reported.
• Carbon is strong in designed directions but vulnerable to lateral impacts; post-crash x-ray/inspection is common.
• Steel is praised for ductility and lower embodied energy; aluminum for cost and ease; carbon for performance and repairability in some cases.
• Concern is raised about people using fragile, expensive tri bikes for commuting or touring.

Discipline-Specific Design Tradeoffs

• Triathlon: no drafting, long relatively flat courses, and a run afterward push designs toward pure aero and energy conservation.
• Road racing: drafting dominates, handling and descending skills matter; being able to ride close in a peloton is more important than extreme solo aero.
• Mountain biking: control, grip, rolling resistance, and robustness trump aero; speeds are lower and terrain technical.

Terminology and Miscellaneous Points

• Confusion exists around “double diamond” terminology; some interpret it as two triangles making one diamond, others as left/right or extra bracing.
• “Eliminating surface area” is criticized as imprecise; commenters clarify distinctions between surface area (skin friction) and cross-section (form drag).
• Wheel size (e.g., 650c) can’t simply be shrunk indefinitely due to pedal clearance and handling constraints.