Aerodynamic testing protocols

Estimated reading: 3 minutes

Overview

Aerodynamic testing is inherently difficult. There are many variables involved and the final CdA values are only as accurate as the least accurate measurement.
For this is reason it is important to use dual-sided power meters, and magnet-based speed sensors.

Terminology

A baseline is the first and last test you perform to determine data confidence levels, likely in a standard position or with standard equipment.

The baseline confidence delta is the % difference between the baseline and repeat baseline CdA – this determines data confidence levels.

A configuration is your bike setup with a change that you’d like to test, say a new helmet, new wheel etc

A run is one interval using a configuration (e.g. one lap on velodrome, or one out and back on the road)

A test is made up of multiple runs which are then averaged to give the overall measurement data for the tested configuration (e.g. multiple laps on velodrome or multiple out and backs on road)

A session is comprised of a baseline, one or more tests, and ideally a final baseline.

For velodrome testing we recommend doing at least 6 laps for a test.

For road testing we recommend at least 3 out and back runs for a test.  The distance over which you should ride for each individual out or back should be between 600 and 1000m.

Remember the more runs you do, the more accurate the data.

Baseline control

You should start and end each test session with a baseline repeat.
Example
For helmet testing, start with your usual helmet (baseline), then do one test for each helmet.  Finally do a one more test with your baseline helmet.  The variation in CdA between the first and last tests tells you what your repeatability is.  If this difference is 0.0015 then you know that any measured difference greater than this is a reliable result.

Equipment

Keeping track of the variables in your control isn’t just limited to your aerodynamic testing plan or your body position – it includes your bike.
It is worth getting into the habit of logging your clothing, shoes, bike geometry, wheels etc when aero testing – we would recommend photos of your configurations too to add to your post processed data. You can never have too much information in a diary – we recommend using Aerotune’s web platform for this.
In addition make sure your bike is routinely maintained, including a clean and well-lubed drivetrain, and that you have correctly inflated tyres.
We can’t stress enough that aerodynamic testing is made accessible with Aerosensor, but there the data will only be as reliable as the testing. Think about everything you do to make sure you are being as consistent as possible between each test.
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