I bought a new Diamondback Trace hybrid bike about a month ago. Rode it twice for about an hour a piece and the last time for about two hours. I had no problems any of the times and inflated the tires to about 70psi each time, well within the range specified. A week after the last ride I loaded my bike into the back of my Honda CRV. I didn't check the pressures at that time but they were obviously not flat. I ended up leaving the bike in the Honda for 4 or 5 days before finally unloading it. It became immediately apparent that both tires were completely flat. I took a look at one of the inner tubes and there was a four inch split at the seam that runs the full side of the tube. it was about 90-95 degrees on the days it was in the car and considerably hotter inside the car I would assume. based on the fact that the tires were aired up when put in the car and completely flat when I pulled it out days later I kinda assume it had to do with the heat. I'm just curious if other people have had this happen to them or if it might be something else I haven't considered. id appreciate any insight you have to offer
I have had a couple of times that an inner tube blew up while the bike was parked in bright sunlight. It seems that high temperatures are a contributing factor, but overpressure? I never pump my tires close to the maximum pressure, mostly the pressure is in the lower half of the min-max range.
The pressure of compressed air increases proportionally to the absolute temperature, i.e. 273+T ; T in degrees centigrade. Hence an increase from 95F (35°C) to, say, 140F (60°C) will result in an increase by only 8%. I don't believe this itself is causing the blow outs.
More likely the blow outs are due to an undersized inner tube in combination with a high temperature. Rubber is a material that behaves elastically in a limited range. Beyond a point it starts a plastic deformation. I guess that this point drops with higher temperatures. Most inner tubes are specified for a certain width range, e.g. 18<-->23C for road bike clinchers. The remedy is to buy an inner tube that matches closely with the tire width.
Tires blowing up in hot cars is a common occurrence, especially for high pressure road tires which are often already inflated to the specified maximum pressure. Heat expands the air inside the inner tube, as the pressure builds eventually something gives resulting in a rupture like you experienced. (Typically the tire bead comes off the rim, the inner tube escapes out, and without the reinforcement of the tire casing it expands until it ruptures.)
Pro tip: if you are storing a bike in a hot car, reduce the pressure in the tires. Carry a floor pump to reinflate the tires before you ride.
I'll take the contrary opinion that high temperatures won't increase tire pressure enough to blow the tire.
Using the Ideal Gas Law PV=nRT and solving for pressure: P=nRT/V. Since n, R, and V are constant, if we increase T by some factor, the pressure increases by that same factor. (ok, the volume may increase a bit as the tire heats up, but not a lot)
So if the tire starts at 60 degrees F (288K) and it increases in temperature to 120F (322K), that's a factor of 322/288=1.12.
So if the starting pressure is 70PSI, it will end up at 78PSI. Which shouldn't be enough to make it blow out since there's a margin of safety in the tire pressure ratings. Even if the sun was beating down on the tire directly and raised it to 180F, that'd still only lead to a 23% rise in pressure, and I'd hope that there's a much better margin of error than 23% in tire pressure ratings. I used to ride with a biking friend that switched from 23mm tires with a high 160psi pressure rating to 25mm tires with a 90psi rating, and he didn't notice the difference and he spent months filling it to 160psi until someone pointed it out to him.
This is pretty close to the rule of thumb of 1 psi of pressure rise for every 10 degrees in temperature rise, which would predict that the 60 degree rise in temperature would lead to a final pressure of 76psi.
Also, tubes don't hold in pressure, tires and rims do, and the original poster said that his tube was split, not that the tire blew or the rim failed. I suspect that it's a bad tube that failed during use, poor installation that damaged the tube and eventually fail, or maybe no (or bad) rim tape that led to the tube being damaged.
I just noticed that Batman gave an almost identical answer to mine in a different answer