Those are Nokian Mount & Ground W160 studded tires. Those Finns know a thing or two about cycling in these conditions!
I installed a sweet 39t 105 chainring purchased just today from the good folks at Monkey Wrench Cycles here in Lincoln, NE. I took the rig for a spin and knew right away this was the correct choice: just big enough, when paired with my 17t freewheel, to not spin out on the flats.
I’ll save the Challenge tires for actual racing season next year. For now, the Kenda Small Block 8’s that came on it will work just fine.