Streamlining the time trial apparel of cyclists: The Nike swift spin project

Abstract

This paper documents the development of aerodynamic apparel for the Tour de France individual time trial (TT), the Olympic TT, and track cycling races. A wind tunnel and metric balance were used to measure the drag force (Fd) and wind tunnel air velocity on cylinders, limb models, and live cyclists clad in samples or suits sewn with one or more of 200 stretch fabrics. A concurrent measurement of model dimensions and frontal areas provided the non‐dimensional drag coefficient (C_d) and Reynolds Numbers (Re) that characterized the ability of the various fabrics and suits to reduce frictional drag and induce a drag crisis (DC) or premature flow transition. DC defines a critical air velocity over the body segments at which the airflow transitions from laminar to turbulent, yielding a smaller wake behind the body segment and a corresponding decrease in Fd. A number of fabrics triggered DC on cylinders and limb segments, reducing cylinder and limb Cd by over 40 per cent. Several methods of lowering the Fd of cycling apparel proved effective, including custom fitting, aligning seams with the airflow, and matching fabric textures to body segments. Repeated drag measurements of the same cycling suit provided a mean drag of approximately 3200 g with a standard error of ± 29g. The final 2005 individual TT suit design, worn by a pedaling cyclist, had a measured drag at 53kph, which was 125 g less than typical 2001 TT cycling suits worn by competitors (F_d reduction 5 3.9 per cent). A mathematical model predicts that a drag difference of this magnitude would provide a time saving of approximately 44 s in a 55‐km Tour de France TT. In 2002–2005 and 2007, the production version of the ‘Swift Spin’ TT suit was worn by the winner of the Tour de France; by the women's hour record holder and by road; TT and track cyclists who set four world records, six Olympic records, and won seven medals in individual cycling races at the 2004 Athens Olympics.

Keywords:

• aerodynamic drag
• TT suit
• NIKE Swift Spin
• flow transition
• zoned fabrics

Notes

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