Bicycle Tutor

Do tires have a shelf life? My mountain bike tires are 10 + years old and have some wear but not enough to think about replacing. I don't have issues like slipping when riding. I was just curious, since a read of car tires losing grip well before the tread has worn down. I have a small split in the sidewall of my rear tire anyway so I'm expecting a blowout someday as it is. Also... any recommendations on a half mountain bike tire, half road tire for commuting. I'll probably stick to knobby tires since I ride over so much glass.

People usually replace tires when either the tread wears out or when the cracks start to spread to the point that it is getting likely they'll blow out. But tire rubber will harden over time and lose some traction. 10 years is pretty old for a tire. If they're starting to crack, I'd so go ahead and swap them out. You've gotten excellent life out of them and it'd suck to go down or get stranded because of an old tire.
If you not really doing any off-road, I'd suggest an inverted tread tire rather than knobbies for the street. Something like Continental Town and Country Tires or Schwalbe Marathon Plus. They still have thicker tread and a puncture resistant belt, but will roll a lot smoother on pavement. They'll be faster and corner better than knobbies.
I'd change your tubes out at the same time if they are as old as the tires. Old tubes lose air faster and puncture easier. Especially after you remove them from a tire they've been inside for years.