Two flat tires.car was in the sun,no tinted glass.is this normal?bike shop said the heat did it.

You're bike was in the car, right. Would not surprise me too much. In the summer if my bike is left in the back seat, I tend to leave my tires a little soft and the bike covered.

Yea bike was in car,oops

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.

What was the tire pressure originally ?

I have seen postings with formulas that described the increase in pressure as a factor of temperature, and I don't recall the formulas, but as I recall even doubling the temperature wouldn't increase the pressure more than a few PSI.

I do wonder if there could be an issue with a tire that weakens as it heats... but as someone mentioned, people ride on some pretty hot roads without blowouts... but then again, they are also moving, which could provide some assistance in moderating the temperature.

So, even though I started this post thinking I could provide some insight... I don't know!

Basically, pressure is proportional to temperature starting from absolute zero. Convert to Kelvin or Rankine. e.g. 72F = 532R. 125F = 585R. (585-532)/532 = ~.1 So a tires inflated to 100 psi at 72F would be ~110 psi at 125F...or ~120 psi at 180F.

Actually it was my sons bike in Pennsylvania,we had some days in the eighties in this area.His tire is rated 95psi max and he inflates to 90psi.He keeps it in the car because he lives in an apt and it's awkward bringing it in and out of the building.I didn't believe the sun,heat, greenhouse theory either.Ill have him mark the rim,tube,tire and see if it's happening in the same place.Ill explain the purpose of rim tape and have him check the tire pressure gage against another.

If the tire is only rated for 95, and maybe on a non-hooked rim, and maybe the bead not settled down properly, maybe that was enough to push it over the edge.

Whenever this happens you need to check the bead on the tire for being bent. Sometimes when a tire lifts off the rim it bends the wire bead that holds it in place. That makes it much more likely to happen again when you put in a new tube and inflate the tire. Whenever you install a new tube (did it yesterday on a 700C tire) slightly inflate to tube before putting it inside the tire casing. Then re-seat the tire on the rim and check along the entire tire to make sure that no part of the tube is caught between the tire bead and the rim. The last thing I do before inflating the tire is to push the valve in toward the tire and pull it back out before I install the nut on a presta valve. Then you know the valve is properly seated. I learned this the hard way while working in a bike shop. I was fixing a flat for a customer when POW the tire blew up on me. Not only did I have to give the customer a new tube but we replaced the tire for free as I had indeed bent the bead where it lifted off the rim.

P2 = P1*(T2/T1)

Temperatures should be in absolute, Kelvin or Rankine

Otherwise known as the Law of Gay-Lussac. I will also add the proviso that the pressure that a tire can withstand is dependent on the tire and is highly variable from tire to tire. Calculating the pressures from Gay-Lussac's Law, you find that the pressure increase with temperature is a rather shallow line at relatively low temperatures in question. At 120 F, the pressure has only increased from 90 psig to 98 psig. There are some tires that can stand up to pressure much higher than the rated pressure and some can't.