The new limit will only allow for 20mg of alcohol per 100 millilitres of blood, equivalent to about a half pint of beer. This lowering reflects the “greater vulnerability of bikers if involved in a collision and the greater potential for even the most minor error to result in a motorcyclist losing control with catastrophic consequences.”

For the full article http://www.crash.net/motoring/roadbikes/news/article/20491-0/lower_alcohol_limit_for_bikers.html