Holes in truck wheels

What’s the function of the holes in the front and back wheels of big trucks and buses? I’ve seen as few as two holes or as many as six or eight holes.
Most of the time, the holes look big enough to pass one’s fist through, while at other times they’re just small ovals that one could maybe pass a thumb through.

I believe they are to lighten the wheel, and to aid in cooling the brakes.

Don’t you also need those holes for filling the tires. I believe the valve stems usually poke thorugh those. (But I could be wrong).

      • Has to do with air stems, mostly:
  • (on US trucks) With front tires you usually see at least two holes. The air stem is inside one hole, and then they made a cutout on the other side of the wheel to balance the wheel out.
  • With rear tires it has to do with many rear tires being dual-mounted, so you have to be able to mount two tires on each other, and still reach the air stems of each. So you need more holes, arranged to that they fall “on top” of each other. The number of holes you have is always related to the number of bolts holding the wheel on, but you don’t see “as many holes as bolts” because the holes need to be large enough so that you can reach through the hole in the outer wheel to check air in the inner tire.
  • The holes certainly aren’t for cooling the brakes because the brakes of large-frame trucks are mounted inboard of the axles, on the rear of cabs and trailers (cab front ends I have not seen). Big truck breaks don’t get much out of air-cooling, they overheat very easily, far faster than any car brakes normally would. Truck drivers try to use engine braking as much as possible, especially going down big hills.

I stand corrected. Thanks, DougC.

They’re called hand holes. They’re used to access the air valve on the inside wheels of a dual setup, but I think they are still used to move the wheel around when changing tires.