i've ridden mixed 3/32 and 1/8 for years, and never had a problem. it's the cog and lockring for sure. you can't hand tighten that ****. if you want to get it tighter, either google rotafix or find the tallest hill near you and stomp up it with all your might. that will get it pretty tight. DO NOT fool around on it with the cog and lockring loose. you will strip your hub after a while.