The standard set of tires are 35 inch Goodyear Wrangler All-Territory tires. But during the reveal GMC also showed the Hummer with 35 inch BF Goodrich Mud-Terrain Tires.
For those that want more ground clearance and off-road capability the Hummer is ready to accommodate 37 inch tires right from the factory. The speedometer can adjust to the larger tires and there won't be an issue with clearance.
Unfortunately it does not have air lines connected to each tire you you won't be able to inflate or deflate the tires like in the H1. But you can set the horn to honk at a certain tire pressure while you're airing down so you don't have to check.
Goodyear Wrangler All-Territory
BF Goodrich Mud-Terrain Tires