Well,as a few of you know,I just acquired a nice Kawasaki bicycle with a 1.2 HP friction roller drive for my 11 yr.old son.Anybody out there that would suggest what type of helmet,reasonably priced,that would be light enough for him and yet protect him at 20mph?I'm putting a smaller drive roller on it which will slow it down for him.He'll be riding along with me on city streets and back alleys.Would a regular bicycle helmet be sufficient?Opinions are much valued here.THANKS!