RAGBRAI riders Carl Antczak and Glenn Dorn, both from Cleveland, Ohio, locked horns during a mid-morning break in Rembrandt yesterday. Riders weren't butting heads over the weather - after temperatures in the high 90s and uncomfortable humidity Sunday, it was perfect riding weather on Monday. The Register's Annual Great Bike Ride Across Iowa rolled through Rembrandt and Marathon before reaching Emmetsburg for an overnight stay last night. Bicyclists stayed in Cherokee Sunday night. Buena Vista County Sheriff's officials reported a few biker spills and traffic situations, but no serious problems as the throngs of riders made their way through the area.