Road unevennesses affect the safety and comfort of a vehicle. It is desirable, therefore, to maintain a certain evenness standard on a road. However, this evenness standard should be established in terms of safety and comfort. This thesis provides: (a) definitions of the terms "road holding" (safety) and "ride comfort", (b) survey of literature describing different measuring criteria and methods to determine road holding and ride comfort, (c) how road holding and ride comfort are influenced by vehicle and road parameters. Furthermore, the influences of different wave lengths and amplitudes of the road unevennesses on road holding, ride comfort and impact factor, (the stress imposed upon the road by a vehicle) as a function of vehicle speed, are investigated with the help of a mathematical model of two-axle and two-wheels vehicle with driver. The road holding problems are also studied with the help of one-wheel and one-axle vehicle model. Road sur face, in this investigation, is considered to be a continuous sine wave. This investigation, thus, presents a range of significant wave lengths which ought to me measured by road surface measuring devices. At last, the theories developed in this thesis are compared with some experimental data.