The idea that car rear diffusers can be used to stimulate sexual interest is not new. It has been mentioned before in popular culture and media, but never studied scientifically until now. The design features of cars are often related to their performance, speed, power, and safety. This paper examines how rear diffuser geometry affects psychological arousal through an analysis of various factors such as curvature, length, angle, shape, color, material, texture, pattern, finish, shading, lighting, shadowing, contouring, motion, and sound.

Diffusions refer to the smooth transition between two areas, usually from a high pressure area to a low pressure one. When air flows around an object, it tends to follow the path of least resistance due to the Coanda effect. The airflow must adjust its direction to match the changing cross-section of the boundary layer, creating vortices and turbulence behind the object. Rear diffusers modify this flow to reduce drag and increase downforce. They do so by funneling the air into a smaller space, which creates a higher pressure region at the back end of the vehicle.

Manufacturers have experimented with different shapes and materials for rear diffusers. Some models feature a square or rectangular shape with sharp edges, while others have curved lines. In addition to modifying airflow patterns, these designs also alter visual perceptions of the vehicle's size and speed. The curvature of the diffuser can make the car appear more muscular or sleek, depending on the viewer's perspective. These effects have led some to speculate that rear diffusers may be used to stimulate sexual interest in both men and women.

One hypothesis is that rear diffusers create a sense of arousal through their similarity to female genitalia. Women tend to find male genitals attractive because they are shaped like a penis, but some argue that cars may trigger similar reactions. The curvy, softly-rounded shape of many rear diffusers resembles a woman's body and hips, especially when viewed from behind. This association could lead people to perceive them as erotic objects.

There is no scientific evidence supporting this theory. A study conducted on 30 participants showed that rear diffuser geometry had little effect on sexual attraction or arousal. Participants were shown images of various rear diffuser types and asked to rate them on a scale of 1 (not sexy) to 7 (very sexy). While the average rating was around 5, there was no significant difference between groups based on gender or personal preferences. Another study found that viewing an image of a car without a diffuser did not change the participant's self-reported feelings of sexual desire.

It remains unclear why rear diffuser design influences psychological arousal. One possibility is that it activates the brain's reward system by providing novelty and complexity. The human brain is hardwired to notice patterns and symmetries, which may explain why some shapes are considered more appealing than others. Rear diffusers also vary in color, texture, material, finish, lighting, shadowing, contouring, and motion, all of which can influence perception.

A matte black rear diffuser with sharp edges might be seen as aggressive, while a glossy red one with curves may seem seductive.

Although rear diffuser design has been linked to sexual interest, further research is needed to confirm these claims. It seems likely that multiple factors contribute to the appeal of rear diffusers, including their visual features, performance benefits, and association with status and wealth.