The aerodynamic impact of the time-trial skinsuit: a CdA-based quantification

Among the interventions available to reduce time in an individual time trial, clothing —and specifically the aerodynamic skinsuit— presents one of the most favourable cost-benefit ratios, ahead of deep-section wheels or the frame. This is not a subjective assessment: it is the conclusion obtained when the aerodynamic coefficient is measured and introduced into the power equation.

Physical framework

The power required for forward motion is distributed between aerodynamic drag and rolling resistance. On flat terrain and at racing speed, the aerodynamic term dominates the balance:

P = ½ · ρ · CdA · v³ + Crr · m · g · v

CdA is the aerodynamic drag coefficient multiplied by frontal area, and it quantifies the interaction of the rider-bicycle system with the airflow. An aerodynamic skinsuit modifies neither the athlete's power nor position, yet it reduces CdA: its zoned fabric delays boundary-layer separation over the arms and shoulders. At a lower CdA, the same power yields a higher speed.

Comparative data: CdA of 26 suits

In the AthletePro library, suits are catalogued by their CdA delta relative to a neutral road kit (standard jersey and bibs = 0). A more negative value indicates greater aerodynamic efficiency. The figures derive from public testing (Aerocoach, Rule 28, Nopinz, Drag2Zero/Endura, GCN/BikeRadar) and from reasoned estimation by fabric type and construction. A representative selection:

The difference between categories is substantial: between a triathlon suit (−0.017) and a high-end time-trial suit (−0.040) there is more than 0.02 m² of CdA, a magnitude that in a time trial translates into minutes.

Quantifying the saving

A representative case is taken and solved with the AthletePro physics engine: a 40 km flat time trial at 300 W steady, with a rider-bike mass of 78 kg, a Crr of 0.004, air density of 1.2 kg/m³ and a starting CdA of 0.240 with the neutral kit. The time saved relative to that kit, by suit type, is as follows:

The high-end time-trial suit represents more than three minutes over 40 km with no increase in power. A frequently overlooked nuance is worth noting: the largest gain is obtained when replacing the jersey with a suit (the first 90 s), whereas the additional improvement from a mid-range to a high-end suit is smaller (around 50 s). In events decided by narrow margins, however, that difference can be decisive.

Limitations

• Morphological dependence. The stated values correspond to the typical gain of each garment; on a specific morphology and position they may vary. It is therefore preferable to measure the athlete's real total CdA (via the Chung method, for instance) rather than rely on the catalogue alone.
• Fit is decisive. A high-end garment that wrinkles performs below a correctly fitted mid-range one, since aerodynamic fabric is only effective under tension. The order of preference is: custom construction, optimal size and, lastly, high-end fabric with a loose fit.
• UCI regulation. Competition imposes restrictions on fabrics and seams. A garment admissible in triathlon may not be so in a UCI time trial; the regulations should be verified before purchase.

Conclusion

In the allocation of resources for a time trial, the hierarchy of return is generally: position > helmet > suit > wheels. The suit ranks highly because its cost is comparatively low and its benefit high and reproducible. By entering the suit, helmet and position into AthletePro, the variation in estimated time can be observed, segment by segment, prior to the start.