A bicyclist was fatally struck by a truck early Thursday in Brooklyn, two hours before a speeding car killed another bike rider in the borough, authorities said.In the first crash, Craig Murphy, 26, was crossing Ten Eyck St. in Williamsburg when the truck turned from Union Ave. and into the bicyclist, cops said.Murphy was a member of Right Rides, a free volunteer service that offers rides home at night in North Brooklyn and in other city neighborhoods, according to Transportation Alternatives, a bicycle advocacy group.He was pronounced dead at the scene of the 4:15 a.m. crash.Less than three miles away at 6:20 a.m., a 25-year-old man was mowed down as he biked across Fulton St. in Bedford Stuyvesesant, cops said.Alfred Taylor, 41, of Williamsburg was speeding east on Fulton St. near Utica Ave. when he struck the victim, whose name was not released pending family notification.Taylor was charged with criminally negligent homicide, cops said.