Ok you made me work. I used this
http://reflectivelyyours.com/generic141.html
3/8" x 22 inch, it takes about 3 per rim side as I recall. It might only be 2 and some change. You'd have to figure out the circumference and figure out what you need. Or, just do as I did, price break at units of 3, so get 6. I had a tad extra that I used to highlight helmet black shade.

The black is not quite as bright as the 3M diamond, but that is to be expected. It still gives a good reflective flash back.