Cycling Aero Testing: DIY Speed Testing Methods

“Aerodynamics” is a competitive advantage that professional cyclists constantly pursue. In the past, improving aerodynamics required expensive wind tunnel testing, but now there are several practical DIY methods that allow everyday riders to effectively evaluate their riding position and equipment choices without spending a fortune.

Why Is Aerodynamics So Important?

In cycling, the faster you go, the higher the proportion of total resistance that comes from air resistance:

This means that at high cruising speeds, any change that reduces air resistance (position, equipment, clothing) delivers significant benefits.

Method 1: Fixed-Distance Time Trial Testing (Baseline Testing)

Test Setup

Choose a straight section of road 500 meters to 1 kilometer long, ideally meeting the following conditions:

• Flat (gradient within ±0.5%)
• Stable wind (recommended to test when wind speed is below 3 m/s)
• Test at the same time each session (to avoid temperature and wind direction differences)

Test Procedure

1. Establish a baseline: Complete 3 runs in a standard riding position (hands on the hoods) and take the average time
2. Change one variable: For example, switch to a TT position (tucked low) and repeat 3 runs
3. Calculate the data: Convert the time difference into a speed difference

Practical Example

Assume a test distance of 1 km:

• Standard riding position: average 1 minute 30 seconds (40 km/h)
• TT position: average 1 minute 25 seconds (42.4 km/h)

A 5-second difference over 1 km translates to approximately a 2.4 km/h speed advantage.

Method 2: The Chung Method (For Power Meter Users)

If you have a power meter, the Chung Method (also known as the Virtual Elevation Method) is a more precise way to test aerodynamics.

Principle

By recording power output and speed, a mathematical model is used to calculate the CdA value (coefficient of drag × frontal area). This method does not require a wind tunnel, only:

• A power meter
• A GPS device (to record speed and gradient)
• Analysis software (such as Golden Cheetah, which is free)

Test Procedure

1. Choose a flat road section of 1–4 km
2. Complete multiple out-and-back runs at a steady power output
3. Import the data into Golden Cheetah and use the “Aero Lab” feature
4. The system automatically calculates the CdA value

CdA Reference Values

Method 3: Rolldown Test

This method does not require a power meter, only a GPS cycling computer.

Principle

On the same slope, coast freely (without pedaling) from a fixed starting point and record the time or speed at the finish. The longer the coasting distance, the better the aerodynamics.

Steps

1. Find a smooth descent with a gradient of approximately 3–5% and a length of 300–500 m
2. Release your feet at the same starting point and the same initial speed (recommended to start at a fixed speed)
3. Record the speed at the finish or the time to pass a fixed point
4. Repeat 3–5 times for each test position/equipment setup

Notes

• The starting speed must be consistent for every run
• Body position (including hand placement) must be identical each time
• Avoid sections with traffic or traffic lights

Common Aero Improvement Items

Quick Wins (Low Cost)

1. Switch to an aero helmet: CdA improvement of 0.01–0.02 m²
2. Adjust riding position (lower the upper body): CdA improvement of 0.02–0.05 m²
3. Tight-fitting aero jersey: CdA improvement of 0.005–0.015 m²

Moderate Investment

1. Aero wheelset (deep section): CdA improvement of 0.01–0.02 m²
2. TT clip-on aerobars: Brings a road bike position closer to a TT riding position

Conclusion

While DIY aero testing cannot match the precision of a wind tunnel, it is more than sufficient for amateur riders to evaluate the benefits of different positions and equipment choices. The most important thing is to keep test conditions consistent and test one variable at a time, avoiding changes to multiple variables simultaneously that could confuse the results.

Remember, the biggest aero gains often come from adjusting your riding position, not from expensive equipment upgrades.

Related Reading

• DIY Aero Testing in Practice: Optimize Your Riding Position Without a Wind Tunnel
• The Aerodynamics of Cycling: The Science of Drag Reduction from Helmets to Riding Position
• Cycling Aerodynamics Deep Dive: The Science of Wind Tunnel Testing and CdA
• Road Bike Aerodynamics: How to Reduce Drag Without Changing Your Bike