What's Round, Rubber, And Black All Over?

You guessed it, it's tires. John and his daughter went to San Antonio to buy new tires for his old work pick-up. The ones he drives over cactus and mesquite bushes with sharp thorns. I heard him say the one he just had fixed was about to blow and we had hauled a heavy load of feed just last week. Every since they got home he keeps wanting me to go look at his new tires. I say are they black, he says yes. I say are they round, he says yes. I say are they made of rubber, he says yes. I say well I've seen those before. A question to me just like as if I insisted on him coming to the kitchen to see my new mop and broom.