Here's what I got straight off of Michelins web site:
May 15, 2006
Service Life for RV/Motorhome Tires
The following recommendation applies to RV/Motorhome tires. Tires are composed of
various types of material and rubber compounds, having performance properties essential
to the proper functioning of the tire itself. These component properties evolve over time.
For each tire, this evolution depends upon many factors such as weather, storage conditions,
and conditions of use (load, speed, inflation pressure, maintenance, etc.) to which the tire is
subjected throughout its life. This service-related evolution varies widely so that accurately
predicting the serviceable life of any specific tire in advance is not possible.
That is why, in addition to regular inspections and inflation pressure maintenance by
consumers, it is recommended to have RV/Motorhome tires, including spare tires, inspected
regularly by a qualified tire specialist, such as a tire dealer, who will assess the tire’s
suitability for continued service. Tires that have been in use for 5 years or more should
continue to be inspected by a specialist at least annually.
Consumers are strongly encouraged to be aware not only of their tires’ visual condition and
inflation pressure, but also of any change in dynamic performance such as increased air
loss, noise or vibration, which could be an indication that the tires need to be removed from
service to prevent tire failure.
It is impossible to predict when tires should be replaced based on their calendar age alone.
However, the older a tire the greater the chance that it will need to be replaced due to the
service-related evolution or other conditions found upon inspection or detected during use.
While most tires will need replacement before they achieve 10 years, it is recommended that
any tires in service 10 years or more from the date of manufacture, including spare tires, be
replaced with new tires as a simple precaution even if such tires appear serviceable and even
if they have not reached the legal wear limit.
For tires that were on an original equipment vehicle (i.e., acquired by the consumer on a
new vehicle), follow the vehicle manufacturer’s tire replacement recommendations, when
specified (but not to exceed 10 years).
The date when a tire was manufactured is located on the sidewall of each tire. Consumers
should locate the Department of Transportation or DOT code on the tire that begins with
DOT and ends with the week and year of manufacture. For example, a DOT code ending
with “0304” indicates a tire made in the 3rd week (Jan) of 2004.
Clearly even the great Michelin says that 10 years is the max.