I carry an extra tire on every ride. There's nothing special about a long ride other than that its miles are the same as the sum of many shorter rides. So yeah, I carry a ~220g tire. Also 2 tubes. A rando buddy of mine carries 4 tubes, probably better for rando. Another buddy once had 8 flats from different causes on one pass climb. And yes, I've used the spare tire, but more often have loaned it to other riders. A really cool thing about carrying the spare is that if I flat, I put a spare tube in the spare tire. I don't have to lose time fussing around trying to find the source of the flat. - and maybe missing it. I started carrying the spare tire the day after borrowing one from a fellow rider. You want to carry the smallest tire you'd use, say a 23. That way you can loan it to the widest group of other riders. No point in carrying a big tire that won't fit some bikes.
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