Hi Wolfepack,
I all tire fires that I have seen (don’t ask me why have seen so many) the tires were removed from the rims and sprayed with gasoline.
If you do not add an accelerant it would be very difficult to light the tire. Unless you just dump one in an actual fire, as you have previously suggested.
It will produce black fumes and a bright and hot flame almost immediately.
The burning time is fairly long, probably from 2 to 3 hours depending on the tire size, and it is very, very, very (have I stressed this enough) difficult to put out. When I was in college, during a Industrial Safety class I used the full content of a 25lbs ABC extinguisher and could not put a tire completely off.
Hope this helps