Never had a ball crack yet, but heard stories and seen the effects.

Not sure I have the right extreme ranges (maybe someone else does?), but I leave my stuff in the car as long as the outside temperature is between 20 and 80 degrees Farenheit. If I know it's going to be outside that temperature range, I will bring the balls inside.

When going to the lanes... if the balls have been in the trunk and it's been relatively cold ---- in the 20's-30's----, I'll try to use another ball (I have a locker at both bowling centers also) for the 1st game or so. My theory being that the ball won't crack if I don't subject it to a rapid warmup by rolling it and causing friction, or "blunt trauma" from hitting the pins while in it's ice cube state.

Maybe this is nonsense, but so far have never had a ball crack going back 40 years, but especially going back 10 years with today's coverstocks.

other than travel my equipment is never left in the car. modern bowling balls do not like extremes of temperature.

only time mine arent in my car is during league and tourneys, rest of the time in the trunk no matter the weather, never had a ball crack except the one in my bedroom floor that cracked a few months back before it got real cold
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I leave mine in my trunk all week but my car sits in my garage all week unless I am going to the center to bowl.  I have another vehicle for work.

I live in Michigan, have my whole life, and i leave my balls in the car 60-80% of the time.  And everyone knows the temperature changes here are extrememly abnormal.  Never had a ball crack, nor anyone that I know that does the same thing.  If its really really cold outside, i bring my bag into my office at work on bowling days only, just so i don't get to the lanes and have frozen balls.  Then the grips start sweating after about 15 minutes and i have to use alot of powder.  

No one likes frozen balls.... well except for Kman300