Sock & Overshoe Testing
Socks are a fundamental part of clothing for cycling. However, have you ever wondered how much difference they actually make to a rider’s aerodynamics?
The lower legs present two cylindrical drag producing bodies to the airflow, something that aerodynamicists like to call bluff bodies. With a range of aerodynamic solutions offered by clothing manufacturers, it’s easy to be confused by the various offerings. Typically, brands will offer an aero sock, as well as an overshoe. An aero sock will usually have a normal lower sock construction, with an aerodynamically optimised fabric for the upper portion of the sock. Therefore, the shoe itself will still be exposed. Whereas a full aero shoe cover will be worn over the shoe and leg, covering both the shoe and the lower leg itself. The maximum length of a sock or overshoe is governed by the UCI, meaning that brands will usually offer a UCI legal, and a non-UCI sock and overshoe.
In our Equipment Room here at SSEH, we have a range of aero socks and overshoes available to test in our Sports Performance Wind Tunnel (SPWT), both UCI legal and non-UCI.
The options tested were:
– No sock
– Normal sock
– Aero sock (uci legal)
– Aero shoe cover (uci legal)
– Aero shoe cover (non-UCI)
In order to investigate the aerodynamic properties of these solutions, the SPWT was used to obtain the power required to overcome aerodynamic drag and ride at a given speed. Four riders were used in order to see the influence of position and bike/rider characteristics, these are summarised in the table below.
In order to test the six different solutions, the following testing protocol was used, which included two speeds and two yaw angles:
– 35kph and 45kph
– 0 and 5 degrees
These conditions were representative of racing or time trial conditions.
In order to ensure repeatability of the rider’s position between runs, the rider’s edges were taken during the baseline run, and projected in front of the rider during all subsequent runs, in order to help the rider, hold position and thus ensure repeatability between runs. A 20 second pedalling tare was also completed prior to each run to account for any relative changes in mass of the riders set up.
The graphs below show the power required at each yaw angle for the riders at the two test speeds.
The general trends for all speeds and yaw angles were similar for all riders, with a few key differences.
At all the speeds and yaw angles other than a select few at 40kph and 0 degrees, the slowest solution for all of the riders was consistently 4. However, the fastest solutions proved to be sensitive to speed and yaw, as well as being very rider specific. The relative ‘gains’ on each rider also increased with increasing speed. These gains were different in magnitude and heavily influenced by a rider’s height/weight as well as bike setup. Rider 4 was able to gain up to 33.5W due to their sock choice, whereas rider 2 was only able to gain 13W. As shown in Table 1, the riders were all very different in nature, both in terms of their body composition and bike setup. Interestingly, there was also significant variation between the two riders on TT bikes and the two on road bikes, suggesting that there is not a solution that works best each discipline.
In addition to the effect of equipment, other aerodynamic rider characteristics can also be deduced from the results. Rider 3 appeared to be sensitive to yaw, with the power required at 5 degrees yaw being slightly higher for the same solution. Whereas riders 1, 2 and 4 typically experienced less consistent, and predictable drag variation with yaw.
In conclusion, the results demonstrate that there were large gains of (up to 33.5W) available from correct sock choice. The slowest solution was 4 for the majority of the riders across all conditions. However, the fastest solutions proved to be very rider specific depending greatly on a rider’s bike setup, and physiology. An important point to note is the testing protocol was designed to be simple and generalised to all riders. To make informed choices for each rider, further testing at their expected speeds and yaw angles during a race would be greatly beneficial.
The socks and overshoes used for this test, along with a wide variety of other equipment such as helmets, skinsuits, handlebars and wheels are all available to try in our Equipment Room.
If you would be interested in arranging a session in the Sports Performance Wind Tunnel to optimise your own equipment choices, please refer to the Performance Consultants section of our website for further information – https://silverstonesportshub.co.uk/consultants/