My mother-in-law has a boat/trailer that she's trying to sell. Several people have reviewed it and mentioned the nice quality/condition but haven't yet had any tangible offers. My thoughts are that the trailer it's resting is a real eye-sore and needs help. I've added safety chains at the hitch and winch areas (yup, they were missing!) and pulled the right side wheels to repack the wheel bearings. The tires are extremely weather checked/cracked and sized 5.8/5.0 - 8.0 (can't read the name brand). The boat is an 18ft, 80" beam, aluminum, deep V-hull with 80hp Mercury 2-stroke and 4.5hp Mercury kicker. The trailer is a tandom but I cannot find any brand name. Are these tire sizes adequate for hauling this boat? I want to buy new tires but don't want to get anything undersized.