well the first set I replaced this year i could see my hand throught the other side, not wore through yet! But I was worried so the whole ay home after a ride on hard pack I would tip it up and have someone make sure i wasnt in aluminum yet lol. That is probly the not so recomended way... second set was dangerously thin tooo, but Im on my third set this season (2000 miles tonight) and this last set has lasted 200 miles and is right up on the wear line, or where the slides wied out. I added an extra set of wheels and it cured my slide life problems, but remember i got a mountain with a 1 1/2" track and im trail riding it!
Joe