what bit to easily drill 3/8 or 1/2" holes in about 80 tires?

[saltbranch]

I need to drill 2 holes each in about 80 car/light truck tires so I can run some cable thru them to hold 2 lines of tires in place on the back side of my dam that suffered some serious erosion/washouts when the water ran over the dam. Some are steel belted--some not steel belted.
I don't want to use a hole saw because I'd have to punch the core out of the bit after every hole drilled.
Got plenty of spade bits and some helix twist bits. Any other options?

Also, how long will 3/8" galvanized cable last covered with soil?


Not even sure it's going to help much, but at the very least will provide me a legal way to not have to haul tires to the disposal place at $4-$7 fee each. (Texas Environmental Quality Board allows this use as long as the tires are covered with soil) The cables will be anchored off to existing cross tie posts in the fence and to 10" diameter pine trees that runs along the top rear of the dam.

Any thoughts/suggestions on this plan or the bits?

I have no personal experience to verify this yet. Many of the youtube vids I have been watching about making tire water troughs, all recommend speedbore bits to drill through the tire. Never knew those existed but I will be buying some when my project starts.