Onset vs. coda asymmetry in the articulation of English /r/

We describe an asymmetric categorical pattern of onset-coda allophony for English /r/, the post-alveolar rhotic approximant, drawing on published and unpublished information on over 100 child, teenage and adult speakers from prior studies. Around two thirds of the speakers exhibited allophonic variation that was subtle: onset and coda /r/ were typically both bunched (BB), or both tip-raised (RR), with minor within speaker differences. The other third had a more radical categorical allophonic pattern, using both R and B types. Such variable speakers had R onsets and B codas (RB): but the opposite pattern of allophony (BR) was extremely rare. This raises questions as to whether the asymmetry is accidental or motivated by models of syllable structure phonetic implementation