I have bicycled on and off for awhile, never wore a helmet. Now I am considering picking one up mostly because of the speeds I attain on my new road bike, my current size 330lbs, and the thought of losing control at a high rate of speed scares the doody out of me. I have hit my head skateboarding a couple of times going pretty fast, but not at this weight, or this fast. I realize my thinking has been flawed, so I am surrendering, and want a helmet. Is my size something to consider when picking out a helmet? Recommendations please.