OpenRC Tractor modern rear tires

Update 2019: Made a new version of these tires here: https://www.thingiverse.com/thing:3825765

I wanted rear tires for the OpenRC tractor that looks a bit more modern so I designed these. I didn't use support so the treads on the "top" of the tire when printing required some cleaning up as they start to print in mid air. Design can be improved there, but I'm happy with how they turned out even thou they required some work with the soldering to fix the looks.