Tell the bike shop they are full of it. It can't be that hot in NJ yet. By Garden State Exit 135, I'm guessing you are in Bergen County, NJ. Out here in the desert, the roads can get extremely hot, far hotter than the inside of your car. I have never had a tire blow out from the heat inside the car our out. I've taken the same tires to elevations of 10,000 feet where the change in air pressure would have a similar effect on fully inflated tires. Never had a problem. Look for some other reason.