News Article about Tire Age Limits

burlmart wrote:
Does anybody know whether it is simply exposure to elements that causes RV tires to sidewall cracking, or is it more that they are not 'flexed' by everyday use?

The main reason for asking is I seem to recall someone telling me it was all about squishing all the oil in the rubber through all the pores by daily usage that kept tires happy longer than the rare use case of RVs. If not, I need to learn what explanation to give in the future.

Tire "aging" is complex as it is not just the time on the clock. Rubber is an Organic Compound and as such the chemical reaction (aging) never stops but it can be slowed down with cooler temperatures or sped up with hotter temperatures. If we were talking about steel and could provide protection that prevented rusting, the strength of steel does not change with time. This is why steel frame structures are good for hundreds of years.

The temperature of the rubber is one of the main, but not the only driver of the rate of the chemical reaction.

Basically the rate doubles with every increase of temp of 18°F. While the rate is not zero when the temperature is below 32°F we could use that point as the rate of 1 with 50° being 2 and 68 being 4, 86 = 8, 104 being 16 times etc and 176° being 256 times faster aging than when the tire is at 32°F. Please don't try and do the math to justify using tires longer that the tire company guidelines as temperature is not 100% of the driver of aging. I did the math just to show you the importance of keeping tires properly inflated which means they run cooler. Also the advantage of using white covers to help keep them cooler when in Sunshine.

Now the other things that affect rubber age are Ozone & UV but these only affect the surface as UV does not penetrate the rubber of a tire more than a few thousandths of an inch and same for Ozone. Heat on the other hand affects the internal components and structural strength.

The chemicals, various "waxes and oils" do need to be on the surface to provide protection. These chemicals provide protection by being "consumed" through chemical reaction. Driving (flexing ) the tire helps these chemicals migrate to the surface.

The sidewall cracking is caused by a combination of UV, Ozone and heat so minimizing the exposure to all three will extend a tire's life. Scrubbing the tire sidewall with an SOS pad not only removes the protectant chemicals it also removes the thin layer of oxidized rubber and makes scratches in the surface and provides more area for UV & Ozone to attack. This is why you should be gentle when washing tires. I suggest that you use the same soap and cloth you would use to wash a painted surface of your car or coach.

All the above is a simplification of a complex topic but I didn't think you wanted a College level lecture on Organic Chemistry.