# Pressure rise due to heat in a tire

1. Sep 30, 2011

### I am stupid

I am not smart enough to know the answer to this question. My son is being accused of touching a bike yes touching on the seat a bike on a bike rack which the school is claiming made both tires pop. The only way i see this as possible is if the bike owner aired the tires up in the morning around 7:30 am with the out side temp at 67 degrees and by 3:45 the temp outside was 101 degrees . Is it possible that the air expanded enough from say 40psi at 67 degrees at 7:30 am to cause both tire to pop when a small amount of weight was applied . How much would the air in a tire expand with a 33 degree rise in temp at a starting point of 40psi at 67 degrees. Sorry so long winded . Thanks for any help .

2. Sep 30, 2011

### Mapes

Hi, uh, I am stupid! Welcome to PF! (I hope you choose your user name with tongue in cheek; after all, we are all here to learn more about physics.)

It is plausible that a higher temperature played some part in the tires popping. Gases that aren't confined do expand with increasing temperature, and this tendency would increase the stress on the tire material. However, it's impossible to say how close this extra load brought the tires to failure, since failure could also be promoted by nicks in or wear on the tube material -- along with someone possibly pushing down on the seat.

3. Sep 30, 2011

### I am stupid

Yes it was tongue and cheek. I do not know a lot about Physics. I agree that the tire and other factors had to have played a part. Two tires do not just pop because some one touched a seat not going to happen. I think the tires where aired up past the normal operating pressure range in the morning so that they could get to school and by the after noon the extra pressure, the heat with my son was the straw that popped the tires.
No big deal the whole thing just does not feel right and that's why i ask poeple who know more about this stuff than i do. Now if you need your plumbing repaired I am your Master Plumber .
Thanks for your reply and help

4. Sep 30, 2011

### HallsofIvy

Staff Emeritus
"PV= nRT" where T is measured in "kelvins" (degree size the same as Celcius but "0" is absolute 0"). 67 degrees farenheit is 293 degrees kelvins and 101 degrees is 311 kelvins. So,initially, you have PV= (nR)293 and then P'V= (nR)311 (I am using P and P' for the different pressures but V, n, and R stay the same). So
$$\frac{P'V}{PV}= \frac{P'}{P}= \frac{(nr)311}{(nr)293}= \frac{311}{293}= 1.06$$/.

That is, the pressure in the tire, because of the increased heat, increases about 6%. No, that is not going to pop the tire.

5. Sep 30, 2011

### I am stupid

Thank you very much . I am going to see the video myself monday. I Just don't get 2 tires popping because the seat was touched. Is that not what you are supposed to do to a bike seat is apply pressure while riding which should far exceed the pressure my son could apply with his hand. How ever i do see the math and your point and that is what i ask for Thank you for your time . Have a great Night.

6. Oct 1, 2011

### AlephZero

Applying a force to the bike seat will not increase the pressure of the tires by any significant amount. What it does is deform the shape of the tires to increase the area in contact with the ground (force = pressure x area). The only change in pressure would come from the change in volume of the tire as it is deformed, and that is very small.

FWIW you son could easily apply more than his body weight to the seat with his hands, assuming he can push down hard enough lift himself off the ground.

7. Oct 1, 2011

### mrspeedybob

I guess the moral of the story is...
If it's not yours, don't touch it.

8. Oct 1, 2011

### I am stupid

I ask for an answer. Not a smart a#\$ statement.

9. Oct 1, 2011

### I am stupid

I thank all the people who gave answers to the question. To all the ones with opinions. Opinions are like butt holes we all have them and they all stink.
Please close the thread.

10. Oct 2, 2011

### BobG

You're not going to pop a bicycle tire simply by touching the seat, nor by putting a lot of weight on the seat.

What will pop an innertube is the tire or the rims. If the innertube got pinched between the tire and the rim while uninflated (which usually happens because the innertube is the wrong size for the tire), then you have a pinched spot where the tire rim could easily puncture the innertube. Or, if there is debris inside the tire, inflating the innertube against the debris provides a point where the innertube could puncture. Or, if there is no rim tape between the innertube and the rim and the rim is damaged, the spokes can unseat from the rim and puncture the tube (of course, the punctured inner tube is the least of the problems, since innertubes are much cheaper than a new wheel).

Still, the chances of this happening on both tires at the same time is pretty remote. Wrong size innertubes would increase the chances (just based on the probability the owner installed the same size innertubes on both tires), but I still wouldn't expect both to pop at the same time. The video should be very interesting.

11. Oct 2, 2011

### Naty1

I would ask the school what their inspection of the tires and rims revealed about the failure.

No inspection...
no fact based conclusions??
No cause and effect established?
Is that how they teach???

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