Bad balance on bike (wrong frame size or rubbish rider)
I started trying to get back into cycling last year, and was mooching about on a mountain bike and enjoying it, but it hurt my knees (long running problem) and wasn't too fast so picked up a road bike (Carerra TdF from Halfords). When I bought it they let me try both sizes sat on frame in store and the large felt best for my knees, but I always feel unbalanced when I ride it and when I try to indicate that I want to turn i wobble a fair bit, which makes me a bit of a risk so I've not been out as much as I'd like. So could it be the frame is a bit too large for me (5'10") and my centre of gravity is off, or am I being a bit rubbish? And if I am being rubbish where should I start?