An impact break involves damage to the carcass (the casing of the tyre) inflicted when the tyre is in contact with certain obstacles. Usually an externally visible bulge on the sidewall of the tyre indicates that cords have been destroyed inside the carcass. If such damage is ignored there is the risk of tyre failure at some time in the future, usually delamination of the tread and/or plies or disintegration of the tyre sidewall. Damage of this kind is typically caused by driving over objects – like kerbs or speed bumps – at excessive speed and/or at the wrong angle. This over-stresses the carcass and can cause individual cords to break. The extent of the damage depends on the speed and angle of impact and on the size of the obstacle. Motorists are usually able to prevent this type of damage themselves. It is inevitable only in very exceptional cases - when an obstacle suddenly appears in front of a vehicle, for example.
Tip: Kerbs and similar obstacles should only be driven over at an obtuse angle and at appropriately slow speed.
Please note: In some cases, people mix up sidewall bulge and sidewall indentation.