My 06 Dyna Low Rider seems to through rear tires like crazy; I keep the air pressure at proper levels and 99% of my riding is on the highway. I have tried the Dunlop K591 (OEM), Michelin MACDAM 50, and most recently a Metzeler; the most I have ever gotten is 5,000 miles from any tire. Every dealer I take the bike to says there is nothing wrong but 6 tires in 25,000 miles seems excessive. Any ideas????