After this year's harsh winter, the roads are worse than ever. I've not only seen many stranded motorists parked next to potholes they've hit, but single replacement tire requests have been more frequent lately. While a bubble can be caused by a handful of scenarios, the most common is impact damage such as hitting a pothole.
Tires are made of specialized rubber compounds reinforced by plies of fabric cords and wires. The underlying fabric cords and wires actually define the tire's shape by limiting stretching. In order to bond these dissimilar materials, the cords and wires are coated with adhesives and/or rubber before the other components are bonded to them during curing. This bond can be compromised by contamination during assembly, damage by underinflation or being overloaded and finally by blunt force trauma or impact from potholes, curbs or other road hazards. Any one of these scenarios can cause a sidewall bubble.
Typically, incomplete bonding caused by contamination during assembly will appear within the first six months of service. These types of bubbles are small in size and usually appear before the tire's strength is significantly compromised. However, since typical tires roll about 800 times every mile and the air pressure inside the tire is greater than outside, tire separations/bubbles that are unseen or ignored will continue to grow in size and further reduce strength, while generating noise and vibration. This ultimately leads to tire failure as the tire stretches under load. If a sidewall bubble appears six months after service, prolonged driving on overloaded/underinflated tires or a road hazard impact are the most likely causes. It can sometimes take weeks or even months after an impact for a separation or bubble to appear. The varieties of possible causes make it necessary to inspect the tire while mounted on the wheel, as well as dismounting it to inspect the inner liner for damage.
While taller profile tires can be damaged by more severe impacts with deeper potholes and sharper curbs, low profile tires mounted on large diameter wheels are the most susceptible to this type of damage. The driver of vehicles equipped with low profile tires should make special efforts to avoid potholes, curbs or other road hazards.