[Lynn Eades]

Robert. Bead spreaders or bead locks keep the bead of the tyre in firm contact with the rim. This means that a runflat tyre that has been holed by a bullet or shrapnel will still drive. Otherwise, the wheel will turn inside the tyre with no forward movement. Even without the runflat tyres it still affords movement which might allow movement away from an otherwise dire situation.
Kelsey Hayes combat rims fitted Jeeps and trailers. In a rubber shortage the bead spreader was also the flap that insulated the tube from the "pinchy" joining of the two rim halves.