I don't know. We just pump ours up until they feel semi-hard. Someone in this office is guessing 10-12 lbs.
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Okay, I just called the manufacturer, Danny Brooks at Florida Sailcraft, and he says 10 lbs. But he says the best way is what I said -- pump up to semi-hard -- and that most tire gauges won't even register as low as 10 lbs anyway.