Methods and systems for improving the uniformity of a tire are provided. More specifically, one or more characteristics of a composite uniformity parameter can be determined from harmonic magnitudes associated with a plurality of harmonics of the composite uniformity parameter. For instance, a range of a composite uniformity parameter and/or a distribution of amplitudes of a composite uniformity parameter for a set of tires can be determined from harmonic magnitudes associated with selected harmonics of the composite uniformity parameter. According to example aspects of the present disclosure, the one or more characteristics of the composite uniformity parameter can be determined using Weibull distributions of the harmonic magnitudes. Once identified, the one or more characteristics can be used to modify tire manufacture to improve tire uniformity.