Hi I think I posted about steelies before on here you can go 14s or 15s.
I only have one 15 but got tyres on the alloys and stuck with those there is a page that shows the wheels for k12 if I posted it up will still be around.
It has all the types that were available on k12
And also includes all the alloy wheel styles should you decide to choose those.
In my opinion the steel wheels are pretty cool and I would run those over the alloys.