scuff up the rims a little.
Heres a few more tips
before you mount them flip them inside out and rap a piece of packing tape around them loosely, so they keep their same shape. Now, fill the air holes of the rims with ca. Now, put several small holes in the tires. The rubber is very elastic so the holes will not be gaping or anything. This is so that water and debris will spin out of the tires when ever some gets in them. Now, scuff up your rims. mount them up on the rims. Take a rubberband and put it right over the top of the tire where it goes in the groove. Now, take a tube of thin ca and stick it in the bottom of the rim. Run it around the inside of the rib while ca is going into the rim.