I ride in the woods 25 to 50 miles per session, 20 to 30 sessions a year. No sand, some mud. What is the least expensive chain and sprocket setup to use over the long run ? Does it pay to run an O Ring chain ? When should one replace the sprockets and when should one replace the chain ? Does one have to replace the sprockets when one replaces the chain ? What is the purpose of running an Ironman sprocket if you have to replace it when the chain wears out anyway ? Is there any logic to running a non O Ring chain and aluminum sprockets and replacing them more often ? Thanks !