My tape weights are falling off too, been on about 2-3yrs?
How should the rim be prepped?
brake clean may work depending on it's composition but is a good start. If one chooses to get really anal do the following.
1. Acetone wipe the area until a white paper towel stays white.
2. Follow with and alcohol wipe down, again until the towel remains white.
3. Scrub the area with a mild abrasive 220 or coarser. The scratches create more surface area for the adhesive.
4. Follow up with another alcohol wipe down until clean.
5. Apply adhesive weight trying not to touch any part of the adhesive.
6. Applying as much pressure as possible roll the top off the weight with a wooden or metal seam roller
A bit over the top but I'll bet that weight will be hell to get off
