The ratio of the transverse diffusion coefficient to the mobility (D-T/K) for Rb+ ions drifting in Kr and Xe gases at about 303 K has been measured at electric field to neutral gas density ratio (E/N) values ranging from 5 to 500 Td. Calculations of the reduced mobility (K-0) and the ratios of the longitudinal and transverse diffusion coefficients to mobility (D-L/K and D-T/K, respectively) for both Rb+-Kr and Rb+-Xe systems were made using a Monte Carlo simulation (MCS) technique and the interaction potential of Koutselos, Mason, and Viehland [J. Chem. Phys. 93, 7125 (1990)]. Furthermore, D-L/K and D-T/K values were derived from K-0 values obtained from the present MCS calculations and from experimental results reported in the literature, using the generalized Einstein relations which are based on the three-temperature theory. For the Rb+-Kr system, the experimental values of D-T/K were found to be 2%-4% higher than those from MCS calculations for E/N values above 120 Td. For the Rb+-Xe system, the experimental D-T/K values were similarly higher than the MCS values in the range 90-220 Td. Given that the standard error of the experimental measurements of D-T/K is estimated to be better than 3% and that of the MCS calculations is better than 2.5%, the agreement between the present experimental D-T/K data and those from MCS calculations can be considered to be fairly good. The interaction potential of Koutselos, Mason, and Viehland therefore appears to represent well the actual potential for both Rb+-Kr and Rb+-Xe systems.