"From the reconstructible words it is clear the Proto-Indo-European community were familiar with wheeled vehicles and had the necessary terminology for wheels, axles, shafts, and yokes. It may be significant that the words we can reconstruct for this semantic field are both semantically and morphologically transparent, e.g. *k^wek^wlo- 'wheel' (< *'turner, roller') or *róth₂os 'wheel' (< *'runner'). That may suggest that, while well established in late Proto-Indo-European, this terminology (and the objects they represent?) was not particularly ancient in the language." ~ Mallory & Adams, The Oxford Introduction to Proto-Indo-European and the Proto-Indo-European World (2006)