It's not really clear how it caught fire, but it was a section about a foot square inside the wheel rim with yellow flames coming out.
What is clear is that the four idiots should probably not have;
a) All stood within 1 metre of it jumping up and down and panicking
b) Open the boot and try to unpack their gear, and
c) Run into the nearest building and grabbed a water bottle and crawl right next to the fire flicking bits of water at it.
(Eventually one of them blew it out with breath.)
Not the sharpest tools in the shed.
If a man speaks in the middle of the forest and there is no woman around to hear him, is he still wrong?