Automobile hydroplaning speed is affected by both the vehicle load on the tire and its inflation pressure, yet only inflation pressure is used in Horne's (1968) equation. He later (1984) made modifications to include a vehicle's tire footprint characteristics. Dunlap et al. (1974) studied the influence of water depth and tread depth on an automibile's hydroplaning speed. Empirical studies by Gallaway et al (1979) produced more conclusive hydroplaning speeds for both automobiles and Ivey et al (1984) for trucks.This paper uses an influence diagram to show how all the models are related. Using the model the author pursues a few vehicle design parameters that may be combined to make vehicles more prone to hydroplaning. Also, a set of rules is suggested that may be used during accident reconstruction to determine if a vehicle has in fact hydroplaned and the potential source.