Here's some info from ehow.com
"Dry Rot" vs. Sidewall Cracking
# The term "dry rot" applies only to old cotton-based bias-ply tires that haven't seen production for the street in 30 years. The condition as it applies to modern tires is called "sidewall cracking."
# There's about a 50/50 chance your cracking tires will begin to lose air pressure in a slow leak before catastrophic failure occurs.
# These small cracks can open rapidly, releasing the tire's air pressure in a severe blow-out with no warning whatsoever.
# Sidewall cracks can lead to sudden and massive rips in the sidewall severe enough to separate the tire from the rim.
# Since a sidewall's job is to absorb road variations, sudden failures will usually occur while traveling at high speed on imperfect roads.
Read more: Are Dry Rotted Tires Dangerous? | eHow.com http://www.ehow.com/facts_5696057_dr...#ixzz19kwomJza
ceb added comment: While water based lubricants can slow the development of dry rot by keeping a tire from losing the additives that are part of the tire when manufactured, once dry rot sets in you can't "fix" it by using 303 (a product I thoroughly love.) All you can really do is replace the tires.