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Old 02-01-2008, 09:16 AM   #51
wmtire
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Quote:
Originally Posted by mtnguy View Post
Maybe Bobby (wmtire) will chime in here to explain how the sun damages tires.......all I know is, that you should keep them covered while in storage.

Chap
Chap, here is a good an explanation in easy to understand terms. Although some things have changed in the industry (which I emboldened) since the article was published, it still holds true for the most part

Tire Tech Facts

The sidewalls of tires which are parked for extended periods, dry check and eventually crack and split. Annually, tire "dry-rot" is a multimillion dollar problem for RVers, trailer boaters and owners of classic cars. This engineering memorandum is a scientific examination of the whys of this process.

Tire manufacturers blend into the tire polymer certain chemical ingredients which inhibit damage from ozone and ultraviolet light, the main environmental degradants of tires and all other types of synthetic and natural rubbers. Ozone is an odorless gas, but is commonly thought of as the "electric train smell". Though more severe in cities and manufacturing centers, ozone is part of the air we breathe everywhere on earth. Hastened by the hazardous effects of UV light, ozone eventually causes rubber to dry and become brittle no matter the locale.

Ultraviolet Light
The need to protect rubber against UV damage is why tires are black. For this purpose, a common type of UV stabilizer called a "competitive absorber" is used. Competitive absorbers work by capturing and absorbing harmful UV light wave energy (instead of the adjacent molecule of tire polymer..that's why it's called "competitive"). Competitive absorbers have the added ability to convert harmful UV light wave energy into heat so it can dissipate harmlessly. All tire manufacturers use the same competitive absorber, carbon black...an extremely inexpensive compound. All other UV stabilizers are prohibitvley expensive. This is why tires are black and why tires are not available in designer colors. All UV stabilizers are sacrificial, meaning they are gradually "used up" to where they can no longer protect against UV damage. As carbon black loses the ability to do its job, it turns gray. This is why rubber grays as it ages.

Ozone
Tire manufacturers use waxes to protect against ozone. When tires are in use (regularly running up and down the road for example) they flex. Flexing causes the protective waxes to migrate to the surface where they form a physical barrier between the air (ozone and oxygen) and the tire polymer. This process...the waxes migrating to the surface of the tire during flexing..is called "blooming". When tires are not regularly used ( a parked RV, boat trailer, or classic car, etc), blooming does not occur. Ozone begins eating away the protective wax and before long reaches the tire polymer. Often by this time, the surface carbon black has lost its ability to protect against UV. With UV light and ozone working in concert, degradation starts. The tire dries, checks, and will eventually crack.

Other Degradants
Petrochemicals and silicone oils can remove the protective waxes and increase the rate of degradation. Common automotive "protectants" and "tire dressings" are typically devoid of UV stabilizers of any type and contain petrochemicals and/or silicone oils which dissolve away the protective waxes and can actually aggress the sidewall. In the event of warranty sidewall failure, one of the first things tire manufacturers look for is evidence of the use of these types of products. When found, this is often cause for not warranting the sidewall failure.

This is why I have preached in other forums, not to use Armor-All on your tire sidewalls.
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