What is a "Grown Tire"?

Bruce H. wrote:
........I see in a table in Barrystiretech from the Tire and Rim Association that a "grown tire" in the 215/75R14 class will increase its diameter by 0.55". Perhaps that is also a contributor to the problem, but I really don't know what a "grown tire" is. Does it refer to a tire temporarily increasing in diameter due to centrifugal force? Does it refer to an aging tire losing elasticity and just "growing" larger?

Just trying to figure this out.

Thanks,

Bruce

If you were to measure a tire immediately after inflating it, then measure it 24 hours later, you will find the tire has grown. In fact, many tire manufacturers label their tire dimensions as "24 hour measurements".

While most of the growth takes place in the first 24 hours, the tire will continue to grow very slightly over time. It is barely measureable, but it does happen.

But be careful here. "Maximum Grown" dimensions is just a way of indicating what the tire could potentially become, and NOT what it is actually going to achieve.

Further, the "Design New Tire" dimensions listed on that chart are a guideline and not a requirement. Tires can be built smaller or larger than that (BTW, it is the "New Design" dimensions that is measured at the 24 hour mark.)

Plus, the "Maximum Grown" is a kind of warning for both the tire manufacturer and the vehicle manufacturer. A tire does not necessarily grow into that dimension.

Those dimensions are static, freestanding. Deflected tires (tires under load) do NOT conform to those dimensions.

- AND -

Tires get distorted in maneuvers. Do a you tube search for tire testing and see how much movement there can be.