Aerodynamics in Cycling: The Benefits of a Low Position, Helmets, and Clothing

When riding on flat ground at 40 km/h, air resistance accounts for more than 90% of total resistance. This means that at the same power output, optimizing aerodynamics can bring a significant increase in speed. This article analyzes the practical benefits of various aerodynamic improvements from a scientific perspective.

Basic Concepts of Air Resistance

CdA: The Core Metric of Aerodynamics

CdA (Drag Area) = Cd (drag coefficient) × A (frontal area)

The lower the CdA, the lower the air resistance, and the faster the speed at the same power output.

Typical CdA values for different riding positions:

The Effect of Air Resistance on Speed

At the same power output (e.g., 250W), speed varies with CdA as follows:

At the same power, lowering CdA from 0.40 to 0.28 can increase speed by about 6 km/h!

Position Optimization: The Most Effective Aerodynamic Improvement

Low Road Bike Position

Position improvement offers the greatest benefit of all aerodynamic measures. Key adjustments include:

Lowering the Upper Body (Head and Torso Position):

• Hands on the drops rather than the tops of the bars
• Lean the torso forward so the spine is more parallel to the ground
• Drop the head, looking forward from beneath the eyebrows

Reducing Frontal Area:

• Knees tucked in
• Elbows narrowed
• Relax the back muscles and round the spine (avoid arching the back, which creates a “sail” effect)

Estimated benefits:

• Switching from the tops to the drops: saves about 20–30W (at the same speed)
• Leaning the torso forward 5 degrees: saves about 5–10W

Time Trial (TT) Position

For riders with time trial or triathlon needs, the TT position can further reduce CdA:

• Using TT bars (aero bars) or bull horn bars
• Forearms horizontal, elbows close together (the “Superman position”)
• Upper body nearly parallel to the ground
• Benefit: saves an additional 15–25W compared to a regular road bike drop position

The Trade-off Between Position and Power

A lower position requires stronger core strength and flexibility to support it. If an overly low position causes core fatigue and the drop in power output exceeds the air resistance saved, the trade-off backfires. Finding “your own optimal aerodynamic position” requires training combined with a proper bike fitting.

Helmet Selection

Comparison of Helmet Types

Practical Benefits of Aero Helmets

Research shows that using an aero helmet (vs. a traditional helmet):

• Saves about 10–20 seconds per hour (on flat roads at 40km/h)
• Equivalent to about 3–8W of power savings

Notes on TT helmets:

• Head angle is very important: the tail of the helmet must align with the spine; a head position that is too high or too low will “break the streamline”
• Poor ventilation: not recommended for climbing in Taiwan’s summer heat
• Limited field of vision: allow adequate time to adjust before use

Helmet Recommendations for Taiwanese Riders

Taiwan’s climate is hot, so ventilation should be a priority:

• Daily training: traditional road helmet (with many vents)
• Flat-road races / time trials: aero road helmet
• TT races / triathlon: TT helmet (verify head angle)
• Climbing races such as Wuling: climbing helmet (lightweight + ventilated)

Cycling Apparel (Skinsuits & Jerseys)

The Aerodynamics of Cycling Apparel Fabric

Loose clothing “catches” airflow, increasing drag. The benefit gap between form-fitting cycling apparel and loose clothing:

• Form-fitting jersey vs. a regular T-shirt: saves about 15–25W
• Skinsuit (one-piece) vs. separate jersey and shorts: saves about 5–10W (avoiding turbulence at the seam)

Skinsuit (One-Piece Cycling Apparel)

A one-piece garment commonly used by professional riders in races, combining the jersey and shorts into a single unit:

Advantages:

• No waist seam, eliminating one point of turbulence
• Usually uses aerodynamic fabric (surface texture optimization)
• Most significant benefit in time trials

Disadvantages:

• Inconvenient for bathroom breaks
• Poorer ventilation than a two-piece kit in Taiwan’s summer
• Higher price

Cycling Gloves and Shoe Covers (Overshoes)

• Fingerless gloves: slightly better aerodynamically than full-finger gloves, but the difference is minimal
• Aero overshoes: cover the shoe laces/buckles, can save 3–5W (moderate benefit)
• Aero leg covers: some research shows they can optimize leg streamline, but the benefit varies by individual

Bike Aerodynamics

Wheelset Selection

Recommendation for Taiwan: Taiwan has many mountainous routes, so high-profile wheelsets of 60mm or more may not be worthwhile on climbs due to the weight disadvantage. For mixed-terrain routes, 40–50mm is recommended.

Frame

Compared to traditional lightweight frames, modern aero frames (such as the Cervélo S5, Trek Madone) can save about 30–60 seconds per hour (on flat ground at 40km/h).

Practical Recommendations for Taiwan

Priority order for aerodynamic improvements (by benefit/cost ratio):

1. Position optimization (free): Learn the correct low position — the greatest benefit
2. Form-fitting cycling jersey (NT$2,000–5,000): Replace loose clothing
3. Aero helmet (NT$5,000–15,000): Upgrade your helmet
4. Mid-profile wheelset (NT$15,000–40,000): Upgrade your wheels
5. Aero frame (NT$50,000+): Consider this last

Conclusion

Aerodynamics isn’t just for professional riders — amateur cyclists can also achieve faster speeds at the same power output through position optimization and appropriate equipment. Start with the most important factor, position, and gradually invest in other aerodynamic equipment so that not a single watt goes to waste.

Related Topics

• 自行車的空氣動力學：從頭盔到騎姿的風阻優化科學
• 自行車騎乘姿勢的生物力學：降低空氣阻力的科學
• 空氣動力學騎姿的生物力學代價：速度與身體的妥協
• 自行車空氣動力學進階：如何量化並改善你的 CdA