The R4 was a transformation of the factory Attack race cars into something much lighter. By basing the car on Radical wheels, suspension and chassis, and putting a reworked "silhouette" body, Juraj engineered a car that shaved significant weight from Chris' original Attack Biturbo FIA chassis, which was based on the cheaper and heavier production car chassis. This car proved very competitive, except for the failure of various RPE V8 engines.