We use a couple concrete blocks made for moorings, forget the weight but they're at least a few hundred pounds each and hold fine. Rolled down to waters edge and floated them out on foam dock floats. We had one failure from the chain rusting to be weak enough to break in a storm, inspect the chain and hardware regularly and replace before it gets sketchy. One concrete filled tire will not hold in any wind or current. Concrete blocks are cheap enough to not cheap out doing tires and such. Only exception would be if you foresee needing to move the mooring ever, then maybe a pair of very large anchors would be suitable.