I replaced OEM tires at 8000 miles on my 2010 Goldwing due to severe rear tire cupping on drivers side with Avon Cobras. I watch tire pressures closely running rear tire at 42 which is what Avon said for this application. At just under 4000 miles I'm starting to feel cupping on drivers side. Is this normal on this bike? This never happens on my Venture. Any thoughts.