Couple of times while riding home today, I felt the back wheel snake about underneath me. Conditions were dry, appeared to be no oil or grit on the road. No real bumpy lines, or mended cracks on roadsurface, no white lines. It happened once while I was doing a turn once after I straightened up after a turn. Back tyre at right pressure. Back tyre appears to have plenty of tread. Don't appear to be getting on the gas too early (only a CB250) Wheel doesn't look out of round or out of alignment. Can anyone shed some light on what problem could be and where to look, not just the bike, could it be my riding skills and if so how do I improve?