How to cut out tire decals.
Plan "A" I tried cutting out the tire decals with a knife and a circle template. The knife knicks the template and there aren't enough sizes to cut it just right.

Plan "
B".  Make compass cutter out of a cheap plastic compass. Too flimsy and glue won't hold.

Plan "
C" is to use a proper circle cutter as suggested by Graham Mason.
The Olfa cutter. The Larch....
Xacto import that goes by Dafa, Hobbico, AM-tech and other names eleswhere. Has nice metric dimensions for radius and diameter. Looks like a winner to me.
I got this one on eBay Buy it Now $3.95
One more, just because. It's expandable.
And now, something completely different !
The BF Goodrich Scorcher. Model this ! Hmmmm .............