As cars become increasingly computerized, automatic emotion detection and affective computing provides a promising basis for future-oriented human-computer interaction (HCI) in cars. However, we are still facing severe problems when trying to detect the users' emotional state reliably. This experimental study investigated grip-strength as a new non-invasive method to detect emotions directly in an automobile context. A positive emotion (happiness) and a negative emotion (anger) were examined regarding their influence on grip-strength applied to the steering wheel. Results confirmed and extended preliminary findings: Drivers' grip-strength slightly increased while driving a car when happiness was experienced and especially decreased when anger was experienced. Implications for further research as well as for praxis are outlined.