The old rubber must be removed before a new tyre can be pulled onto the rim. This first stage is done manually, and the mounting machine is used afterwards.
The garage employee first jacks up the car so that they can remove the wheel from the axle. Then the air must be released from the tyre. This is done by unscrewing the tyre valve.
The mounting machine is next, so the bead breaker can detach the tyre wall from the rim. The garage employee positions the bead breaker on the tyre and the rim and presses down on it. The tyre is then turned once and the process is repeated. This dismantling step ensures that the tyre bead, i.e. the inner ring of the tyre, is pressed completely over the rim hump. The employee then clamps the rim in the mounting machine, removes the balance weights from the rim and then uses the mounting lever to position the tyre bead over the mounting arm. Now it's just a matter of pushing a button. The mounting machine (tyre changer) is made to rotate and the tyre is automatically pulled off of the rim.