Can anyone explain to me the benefit to grinding tires and how to go about it? Does the "new" surface create more grip? Do you need the tire to be driven or can you do it on a kart axle without the motor running?
It's refinishing ( sanding ) I cringe when I hear grinding, it's best to use a tire machine to turn them, mix 50/50 simple green and methanol in a spray bottle, keep tire wet to sand 7" variable speed sander / polisher works great, 150 grit paper first finish with 240 grit, yes it helps tire to grip better because it keeps tire surface on fresh rubber.
Removes dry old rubber .
Yes you can do it on the kart.
Its a easy does it . Deal
If your tires outta ballance it will show.
Belt sander is best a angle grinder will work . With a flap wheel or rubber fingers
Assuming your question is regarding pavement oval racing:
Pavement racing builds a lot of heat in the tires, and when they cool the rubber will seal over.
You'll also want to scrape your tires with a heat gun and putty knife to get the clag (dead rubber, gravel, track debris) off of the tires after a run. This will help get the tire back to a clean surface with less "scrubbing" the kart back and forth as much to clean them on warm up / parade laps.
Some guys will sand/refinish their pavement tires from one run, or one race day, to the next. I definitely recommend that.
Now, if you're going to hotlap/practice on that same set of tires, you will obviously scrub the tires in then anyway so there's no need to refinish them prior to a practice. Try to start your competition laps on freshly refinished tires.