This article considers tractors traveling on rough terrain and studies the effects of the road surfaces on their behavior. Clarifying these effects is useful for their stable traveling on rough terrain, which contributes to the automation of tractors. We select the H2 norm as a performance index to quantify the behavior of tractors and attempt to analyze the norm of a system corresponding to a tractor traveling on rough terrain. To improve the accuracy of the analysis, we modify the system by focusing on the relationship between the H2 norm, white noise, and the characteristics of the road surface. Subsequently, the H2 norm of the resulting system is derived as a function of the parameters, including the road roughness. Numerical examples demonstrate that the analysis result based on the modified system accurately captures the behavior of the tractor compared with the result based on the original system.