500 is a large racing event held annually in Sault Sainte Marie, Michigan. It is a race on a track, with the current purse being in excess of $40,000. It has been running since February 1969. Drag racing is common with snowmobiles year-round, with summer and fall often with grass or closed-course (asphalt or concrete) drag strips. The largest event is Hay Days in North Branch, Minnesota, on the first weekend following Labor Day. The World Championship Watercross or snowmobile skipping races are held in Grantsburg, Wisconsin, in July. The snowmobiles are raced on a marked course, similar to motocross courses, without the ramps and on water. The Snocross racing series are snowmobile races on a motocross-like course. The races are held during the winter season in Northern United States and Canada. One of the largest in New York is the Northeast SnoX Challenge in early January in Malone, New York, and run by Rock Maple Racing and sponsored by the Malone Chamber of Commerce. Snowmobiles are used for ice racing. The racing is held on an "Ice Oval" track. The World Championship Snowmobile Derby is held each winter in Eagle River, Wisconsin. Alaska's "Iron Dog" is the longest snowmachine race in the world. It is long and runs from Big Lake to Nome to Fairbanks. The name refers to dog mushing, long popular in Alaska. Vintage Snowmobile Racing is the racing of vintage snowmobiles and has grown in popularity as a sporting event on the Canadian prairie and in America. The World Championship Hill Climb competition is held in Jackson, Wyoming, at the Snow King Mountain resort each year in March. 2019 was the 43rd year of the four-day event and drew around 10,000 in attendance. Snow bike A snow bike takes a typical dirt bike and replaces the rear wheel with a single tread system similar to a snowmobile and the front wheel with a large ski. It is much smaller and nimbler than a snowmobile, and it has a tighter turning radius, which lets the rider go where many snowmobiles cannot. The first prototype of motorcycles with a rear tread date to the 1920s, with subsequent failed attempts to bring them to market. Many motorcycles made after the 1990s can be fitted with kits that transform them into snow bikes. In 2017, Winter X-Games introduced the first snow bike event in the form of a SnowBikeCross race.