I personally believe it is a humidity issue.  Why.....because here in Florida, we keep our house at a constant 78 degrees during the hot months which is most of the time, yet on certain days the house feels warmer than other days.  I check and it always states 78 degrees.
As a result I have 17 balls crack all the way around the ball since 2013.  I keep them in plastic bags and rotate them every 30 days.  Frankly, based on my experience I don't think any of that effort amounts to a hill of beans but if you believe otherwise, I respect your beliefs.
Nine 900 Global/AMF, Six Storm/Roto, One Columbia 300, and One Motiv.
I was completely surprised when I found my Chronic Paranoia drilled in March 2017 completely cracked in July 2017 as I have never personally heard of a Motiv ball cracking outside of the original Tag. Motiv honored under the 1 year warranty.
The real kicker for me was a AMF "Unreal" purchased on closeout & drilled in May 2017, yet I was not in a position to throw it until August 2017 when I discovered it was completely cracked from thumb all the way around to the ring finger.
Damn, I will always wonder what that ball might have been, but I'll never know.
I always believed a ball increased in diameter from humidity until the pressure cracked the cover stock.  Yet, my PSO tells me it is the opposite.  Balls actually
shrink which results in a ball cracking.  He showed me a number of balls which he put his Pro Sect on and they were smaller & out of round. I'm not an expert, so I can't dispute.
Either way, the modern bowling ball is costing me much more than I would prefer.  But as the old saying goes, life is to be enjoyed and you can't take the money with you.

Had my Hustle Pro crack on me while I was bowling with it. It hadn't been hot or cold for several days. Ball had been in the house before I took it to get some practice. Had bowled with it the week before and at least every other week during league seasons.

The crack went from the thumb a quarter of the way around away from the fingers.

My son had two crack on him that he didn't use that much, old Shout and his Sky Rocket. Storm products don't do well in our house for some unknown reason. Unfortunately, it's what both my son and I throw. Really sucks.

There are other reasons besides rapid changes in temperature and humidity, that can cause balls to crack, including bad pours and bad curing at the factory. There are mistakes that the driller does, like drilling with dull drill bits, drilling too fast, putting the pin too close to holes, not beveling all holes, using too much crazy glue, among others.

Quote from: HackJandy on October 01, 2017, 09:01:32 PM

Anybody ever seen a urethane ball especially 2 piece crack except perhaps around the fingers?

Unfortunately yes.  I had a Storm Thunderflash crack around the entire circumference while sitting on my ball rack.  I think it is more rare, but it can happen.

I doubt it has anything to with the actual coverstock's make-up, but more to do with their being 3 different materials, subject to expansion and contraction, at different rates: core, filler and coverstock.

I know one thing for certain! You NEVER place a ball on a concrete floor without some kind of cup or pad underneath it.

I know one thing for certain! You NEVER place a ball on a concrete floor without some kind of cup or pad underneath it.

I have been placing several balls on used rug on the concrete floor of my basement for 20+ years now. I guess the rug insulates them from the effects/influence of the concrete.

Is that so Jeff? That's good information to know,  you learn something new every day.

The fact of their sitting there, yes; the guess, as to why, is a sheer guess.
FYI I do have a dehumidifier running almost constantly in the basement; it keeps the humidity within a range of 50 - 65%, rather narrow as things go theses days. That might mitigate the balls sitting on the rug. They do sit there for months at a time.

Switch to 2 piece Lane Masters , I have balls that are 10 years + old no cracking !