Joe, I've been getting the same issue with OEM 219s and my 19" RG63s. Perfectly balanced, no issues there, but will get shimmy at 80mph or so. Same comments about turning impacting whether it stays or goes away. I don't get it...
08 E90 | Jet Black / Black | 6MT
Mods: RAC RG63 w/ Pirelli Corsa 255F/285R | Akrapovic Evo Exhaust | OEM Blacklines
Winter Setup: OEM 18s w/ Nokian Hakkapeliita R 245/40-18