Tire sidewall cracking is a condition caused by oxidation in the rubber compounds used in a tire's construction. Though modern manufacturers use a number of additives to prevent it, this cracking condition can affect any tire no matter how new.
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.
