The CCR rates obtained from the MD simulations of ubiquitin are compared with the experimental data from Zhang and coworkers 32 in Figure (all data are given in Table in supporting information). Overall, the computational and experimental CCR rates agree well, demonstrating the suitability of the theoretical approach developed in this work. Both force fields, AMBER ff99SB*-ILDN and CHARMM36, accurately describe the side chain dynamics of ubiquitin. When comparing the MD simulations with experiment, it appears that the AMBER force field slightly outperforms CHARMM36, as the correlation coefficient of 0.92 and RMSD of 0.33 s -1 can be considered to be slightly better than for CHARMM (R = 0.82 and RMSD = 0.41 s -1 ). However, the differences between the two force fields are rather modest. Figure furthermore shows that the CCR rates are insensitive to the fitting model used (LS2 or 4P). It is reassuring that the CCR rates are hardly affected even if the simple 2-parameter model is used for all methyl groups, that is, also for those that display slow motional components and are thus better described with the 4P model, such as ILE61-C δ discussed above. Hence, the results are found to be consistent and robust with respect to the details of the fitting model.