Effects of venting geometry on thermal comfort and aerodynamic efficiency of bicycle helmets

Bicycle helmets are mandatory for recreational or professional bicycle riders in many countries including Australia. Over the past decade the designers and manufacturers have been engaged in helmet development that can comply with the safety standards. The regulations set the standards for impact protection to reduce head injury during serious accidents. In light of this, there is no standard concerning helmet ventilation or the effects associated with thermal stress and aerodynamic efficiency. It has only been recently that attention of such areas in helmet design has been implemented mainly pursued in the professional arena. In the pursuit for greater thermal comfort there is a trend to increase the number of ventilation openings. Unfortunately increasing the ventilation of a helmet not only degrades the structural integrity of the helmet but also increase the aerodynamic drag. Today most helmets are constructed from an external plastic liner with a foam (polystyrene) liner to protect the user from repeated impacts over the entire helmet area. Currently designed foam helmet is an excellent insulator and helps to thermal buildup within the helmet. The main proponents of ventilation from a helmet are through cooling by convection and evaporation. Airflow around the helmet will remove heat buildup and also moisture (sweat) from the surface of the rider’s head. This can be very critical in humid environments. According to a survey conducted by the US Consumer Product Safety Commission in 1999, 95% of people who regularly use the helmets said that comfort or fit was an important factor. On the other hand, 18% those who do not use helmet at all said that comfort was the main reason not to wearing the helmets. Therefore, a bicycle helmet needs to be designed such a way that it can provide both thermal comfort as well as aerodynamic efficiency. Although several studies by Alam et al. (2005, 2006), Bruhwiler (2003) and Reid & Wang (2000) were conducted to measure the aerodynamic drag and temperature measurement techniques for bicycle helmets, these studies are not comprehensive and most studies except Alam et al. (2005, 2006) did not consider the aerodynamic efficiency at all. Therefore, the primary objective of this work as a part of a larger project is to study the aerodynamic and thermal efficiency (comfort) of a series of current production bicycle helmets available in Australia for recreational use under a range of wind conditions and speeds.