Originally Posted by
FBinNY
yes, not to worry. As noted the rubber dries and develops this check cracking over time, because of tire flex as you roll. It's meaningless as long as the tire's fabric plies are intact, as evidenced by even width without lumps or bumps when full.
Minor comment, the tube doesn't stretch the tire. The air inside does, pushing on the tube and tire wall together. The fabric has some give the same way a rope or even a steel cable will stretcha bit when tensioned, which is why the cracks are more visible when the tire id pumped up hard.
You are mostly correct with two minor(ish) nitpicks. First, rubber doesn't "dry out". There is nothing in the isoprene polymer that is liquid and can be removed by evaporation. Tires can weather check but that's not the same as "drying out". That is oxidation of the rubber causing it to lose its elasticity. The lower elasticity combined with the hysteresis of loading and unloading the tire constantly leads to cracking.
Second, the difference in dimensions between a tire that is inflated and a tire that isn't is really small as long as both are unloaded. The tire will stretch a little under pressure but it is a minor change. Certainly not enough to cause the rubber to crack. The cracking is all due to ozone induced oxidation and sidewall flexing.