I have found a useful tecnique for roughing the roadwheels on armor. It also eliminates the need for scraping off the mold seam usually running around the outside of the circumference of the wheel.

I lay a piece of 300 grit sandpaper on my workbench, hold the wheel on either side and slowly stroke it in one direction, rotating it as I go.

Hope this is helpful!

Attach the road wheel to a Dremel tool or drill on slow speed and it'll go much faster...lightly push the sand paper to the wheel...not too hard...and you will rough up the road wheel and not get any flat spots....and be easier on your fingers.