Issue link: http://read.dmtmag.com/i/34501
COMMON TIRE DAMAGES No tire, regardless of its quality, is indestructible. Certain conditions of use and abuse can stress a tire beyond reasonable operating limits, causing it to come out of service even when considerable tread remains. Such conditions are clearly indicated by the damage they leave on the tire itself. Listed below are some common damages and the signs they leave behind. Please understand that this list is by no means exhaustive and is intended only as a general guide. UNDERINFLATION This condition is often referred to as a “run-flat” tire. It is caused by operating a tire at very low or zero air pressure. When a tire is run at normal highway speeds, underinflated, it flexes too much and builds up heat. This heat damages the inner liner, casing, and outer sidewall of the tire. If not remedied quickly, the tire will be irreparably damaged. In extreme cases, the sidewall of the tire is destroyed, from the excessive heat and the weight of the vehicle crushing/cutting the tire against the wheel as it rolls on the uninflated sidewall. According to guidelines put out by the Rubber Manufacturers Association (RMA), any tire that has been run at less than 80% of recommended air pressure for the load it is carrying should be inspected for possible damage. When one tire in a dual configuration comes out of service due to under-inflation/run-flat damage, the other tire in the dual configuration should be inspected immediately. If the unserviceable tire was underinflated, that means the serviceable tire was carrying more and more of the load for that wheel position. Consequently, it too may have suffered some casing damage. Fatigue Rupture or “Zipper” Underinflation FATIGUE RUPTURE This type of damage is sometimes called a “zipper rip” because of the zipper-like effect it creates in the steel casing cords of the damaged tire. When a casing cord is damaged or repeatedly and excessively bent due to over- load and/or underinflation, it will eventually break and DUAL KISSING While somewhat romantic in name only, this type of damage refers to what happens when two tires in dual configuration make contact with each other while in operation. The heat generated by the friction between the two tires severely weakens the casing material of the dual tires. This is easily seen on the sidewalls of the tires where the duals came in contact. The condition may be caused by several factors: - improper mounting - incorrect wheel width or offset - underinflation - “casing growth” In this last case, the fabric casing cords of the tire actually stretch and expand, causing the tire to touch or kiss, under load at the contact patch. Section Five: MICHELIN RV Tires 79 ® subject the cords on either side to even more stress. When enough strength has been lost due to additional cord breakage, a rupture occurs and can progress rapidly along the path of least resistance in the upper sidewall. This can happen hours, days, or even months after the initial damage event when all evidence or memory of the initial damage or overload/underinflation is gone. Casing cords in the MICHELIN ® truck tires used on motorhomes are very strong twisted steel cables. Extreme over-deflection of a tire, that can occur during improper blocking of tires or high energy impacts, may weaken the structure of the cable so as to make it less tolerant of the repeated bending stress encountered in normal use. If in addition, the integrity of the steel cords is degraded by corrosion from moisture reaching the cords through cuts or tears in the rubber, their tolerance of these conditions will be even further reduced. This corrosion may result from mounting damage, foreign objects left inside the tire, road hazards, tire mishandling, or even improper repair of a nail hole.