The subject of carbon black in tires and it's effect on the "rubber" insulating machine from ground is much discussed here but little believed.

Almost done with wheat harvest here and before I put the combine away, I'm going to run one of the drive tires onto a sheet of copper. With the machine parked on the sheet, I intend to hook an ohmmeter between the sheet and rim. It will at least quantify just how much Resistance there is between ground and rim.

When all is said and done, however; I expect we will still hear about just how great an insulator a black rubber tire is