Targets for reducing emissions and improving energy efficiency present the automotive industry with many challenges. Passenger cars are by far the most common means of personal transport in the developed part of the world, and energy consumption related to personal transportation is predicted to increase significantly in the coming decades. Improved aerodynamic performance of passenger cars will be one of many important areas which will occupy engineers and researchers for the foreseeable future.The significance of wheels and wheel housings is well known today, but the relative importance of the different components has still not been fully investigated. A number of investigations highlighting the importance of proper ground simulation have been published, and recently a number of studies on improved aerodynamic design of the wheel have been presented as well.This study is an investigation of aerodynamic influences of different tires. Two different tire models were investigated in combination with three different wheel designs using the Volvo Aerodynamic Wind Tunnel; including moving ground and rotating wheels. In addition to force measurements, flow field investigations were also performed using both surface pressure probes and 12-hole pressure probes. The tire sizes investigated in this study were 215/50R17 and 215/55R16. An investigation of changes to the tire geometry for 215/55/R16 tires was also performed using two high speed cameras in the wind tunnel.Results show that different tire types have a significant effect on not only aerodynamic drag, but also on lift to some extent. Drag differences between 5 - 10 drag counts were measured depending on wheel and vehicle configuration. It was also concluded that the drag difference between tire types was dependent on wheel design. The flow field investigations showed noticeable changes to the front wheel wake structures as well as significant changes in the rear wheel and base wake structures. Investigations of the tire deformations showed changes in wheel lift, as well as radial expansion and axial compression correlating with the observed drag changes.