This paper presents the results of comparative studies of strain modulus from static (PLT) and dynamic (LWD) plate testing. The tests were conducted on 9 sections of forest roads with different surfaces made of unbound aggregates. They produced 140-element sets of results, including values of reloading modulus (E2) and dynamic modulus of deformation determined using 10 and 15 kg drop weights (Evd10 and Evd15). An attempt was made to determine the relationship between the values of the moduli from tests with LWD loads (10 or 15 kg) and PLT, which would allow to determine the values of reloading modulus based on the dynamic modulus values. The analysis of the test results revealed that the values of the dynamic moduli are characterized by lower variability than those obtained from static testing and that from the engineering point of view there is no significant relationship between the sets of results of the subgrade deformability tests made with dynamic and static plates. The analysis of the results confirmed a simple relationship that allows for a qualitative assessment of subgrade deformability defined by the values of reloading modulus PLT tests based on the results of LWD tests with a 10 kg drop weight. The assessment error did not exceed 7% in this case. An analogous relationship was revealed for the results of LWD tests with a 15 kg drop weight. In this case, the assessment error did not exceed 6%. The results of the LWD tests can be used to provide a qualitative assessment of the deformability of subgrade, but the PLT tests are required for its quantitative assessment.