I have had this issue since new. Was told in 05 that the tires had cupped a bit - no worries. In late 07 was told that the cupping required new tires - was do anyway. Still wobble - same speed as yours (60 km/h), not at 55 or 65. Goes in on 18th. Suspecting neck bearings, wheel bearings, swing arm adjustment, weight distribution or alignment.