In inertially-reacted road test simulations, spindle accelerations that are acquired in the field can be replicated precisely and their replication improves the accuracy of the simulations versus simulations in which spindle accelerations are not replicated. In fixed-reacted road test simulations, on the other hand, spindle accelerations are often not replicated due to the belief that doing so will introduce unrealistic loads into the test specimen. Although this is true with regards to the lower frequency range of the control band, it is shown in this paper that replicating spindle accelerations in the upper frequency range of the control band can improve the accuracy of fixed-reacted road test simulations. In order to analyze the effects of spindle vertical acceleration control on suspension loads, models were created for a half vehicle on the road and on a fixed-reacted road test simulator. Differences in spindle loads and in sprung and unsprung mass motions between the two models are discussed. Theoretical and experimental analyses presented in this paper point to the detrimental effects of replicating spindle accelerations at lower frequencies and the beneficial effects of replicating spindle accelerations at higher frequencies.