Using Zeeman and quadrupole spin-lattice relaxation rates, timescales of the C3 and C3' reorientation in trimethyl[H-2(9)]ammonium ions are obtained at room temperature. The orientation dependence of the spin-lattice relaxation rates can be expressed in a finite series expansion of Legendre polynomials. The coefficients of this expansion fully describe the spin-lattice relaxation anisotropy and can be obtained from the Zeeman and quadrupole relaxation rates.