Aerodynamics plays a critical hole in open wheels race cars. The work here presented shows a comparative study of different undertrays design and their influence over the drag coefficient measured on an open wheel prototype race car, using CFD simulations in a virtual wind tunnel. For all cases, velocity was 60 km/h and it was considered both moving ground and rotating wheels to look for a more realist representation of the real interaction between car and racetrack. One model without any aero-part was taken as baseline and three different undertrays proposals were evaluated looking for an aerodynamic improvement. As final results, the drag coefficient of the proposals were ranked and compared with baseline results. Also pressure, velocity and wake images help to illustrate the improvements on the drag coefficient by using an undertray in this vehicle.