This study evaluated the effect of drum diameter on radial force variation (RFV) by comparing laboratory development equipment with a drum diameter of 240 mm and commercial equipment with 1707 mm. When measuring RFV, a large drum is suitable for imitating the flatness of the actual road surface, but it is economically advantageous to utilize a small drum. The results of the RFV measurement depend on the drum diameter and tire stiffness. Therefore, several tests have been performed to evaluate the effect of measurement conditions such as drum diameter, air pressure, and static load on RFV. The main factors of RFV are runout and tire radial stiffness; therefore, wheel samples were made by imitating wheel runout. The RFV of the same tire was measured on two different diameter equipment, and the results for the larger diameter equipment were estimated to be approximately 13.8 % greater.