This article is from the Bicycles FAQ, by Mike Iglesias with numerous contributions by others.
From: Jobst Brandt <email@example.com>
Date: Mon, 27 Jan 2003 20:38:07 -0800 (PST)
> Why is it better to deflate tubulars between rides or is this just a
> silly rumor?
Yes and no. The "rumor" arises from a misunderstanding. Track tires,
that are most often still tubulars, are generally inflated to more
than 10 bar and are dangerous if they were to explode. Good track
tires, unlike road tires, are often made of silk with fine and thin
strands that are not coated or otherwise protected.
I have seen these tires get touched by another rider's pedal and
explode, or even when carelessly laid on any angular object, they can
burst because only breaking a few cords is enough to start a burst.
For this reason track tires are best deflated to less than half their
running pressure when not in use. I can still vividly hear the sound
of a tire exploding in an indoor track although I heard it only a few
times years ago. It is not something you would like to have happen in
your car or room.
The reasons people give for deflating tubulars are generally false and
are given for lack of understanding. This is what makes it sound like
an old wive's tale. Most people do it just to be doing what they
think is "professional" when in fact the protected sidewalls and
pressure of most road tubulars makes deflation as meaningless for them
as it is for clinchers.
> What advantage is there in aging tubulars?
None! The aging concept arose from the same source as the "steel
frames need to be replaced because they get soft with age" concept.
Both were intended to improve sales during the off (winter) season by
bike shops with too much inventory on their shelves. Tires oxidize,
outgas, and polymerize from ultraviolet light. The concept of a tire
manufacturer making a tire that cannot be used until ripened for six
months from the date of purchase is ridiculous. Tires can be made to
any specification at the factory. Tires are most flexible and durable
when they are new. They don't improve with time and exposure to heat,
light, and oxygen or ozone.
"Over-aged" tubular tires, have crumbling hard brown latex on their
sidewalls that exposes separating cords directly to weather and wear
and they have treads crack when flexed. Considering that this is a
continuous process, it is hard to explain where, in the time from
manufacture to the crumbly condition, the optimum age lies. The claim
that tires are lighter after aging is true. Their elastomers have
evaporated making the tire brittle and weak.
Purchasing tubular tires in advance to age them is unwise, although if
there is a supply problem, tubular tires bought in advance should be
sealed tightly in airtight bags and kept in the dark, optimally in a
freezer. For best results, use new tires because aged tires are only
as good as how little they have aged.