I averaged 3200 miles on a 28mm Gatorskin in the rear. After that, I'd start getting bits of glass and rocks causing slow leakers.
The compound tends to pick up a lot of stuff when it's wet, too. On a pair with only 2000 miles on them I got 3 flats in 10 miles during a rain soaked 200k. (That's when I switched to Pasela TG 32mm folding bead).
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"I feel like my world was classier before I found cyclocross."
- Mandi M.