Two dialects of Mandarin Chinese, Beijing and Liaoning, display different patterns in r-suffixation, a morphophonological process. This paper investigates the low vowel rhymes: /an/, /a/, /aŋ/ in the two dialects. In Beijing, /an/ and /a/ undergo neutralization with the addition of the diminutive /-r/ suffix (Zhang 2000). But in Liaoning, the two rhymes maintain their contrast in the suffixed forms by each employing a different /r/ allophone for the suffix. /an/ selects for the retroflex rhotic [ɻ], while /a/ opts for the non-retroflex, or bunched, [ɹ] in Liaoning. I present a contrast preservation analysis to account for the difference between the two dialects. The analysis is set in the framework of Flemming’s (1995) Dispersion Theory. It employs MinDist constraints and PreserveContrasts-BD, which is a modified version of Flemming’s MaximizeContrasts, adapted to refer to output-output mapping. I argue that the overarching objective for both dialects is to maintain salient contrasts between the suffixed forms, but they differ in whether they prioritize preserving the three-way contrasts of low vowel rhymes or maintaining enough auditory distance between the suffixed rhymes. Liaoning prioritizes preserving the three-way contrasts, ranking PreserveContrasts-BD alongside MinDist, whereas Beijing is less preoccupied with keeping three suffixed forms, ranking PreserveContrasts-BD below MinDist. This is why the contrast between /an/ and /a/ is preserved in Liaoning via /r/ allophony, but neutralized in Beijing. Acoustic evidence for the two allophones of the r-suffix is provided. Segmental processes involving the low vowel and the nasal coda are also discussed.