One of my bikes has a pair of Schwalbe Marathon XR tires 700x37 (Schwalbe discontinued this model in 2010). They're 5 years old and have about 20,000 km. I've ridden them on all kinds of mixed surfaces and never had a flat. When new, the tires were 570g each. The tires now weigh 485g for the front and 470g rear. The tread is is a little worn, but there's plenty of life in them still.