Tyres in the Sun Warning

[Lozz360]

I've been thinking about this, probably due to the recent hot weather we have been having. When I was in my early teens, in the early 1970s, it was quite common for random elderly men (it was always elderly men) advising us kids to beware of leaving our bikes in direct sun. The reason being is that the tyres would deflate. This advice seems really strange nowadays, and I would never offer such advice to anyone as it seems totally pointless. I assume the logic of it was that the sun would warm the tyres and therefore the air inside would expand and leak out. The point of this post is that I was wondering whether there was ever any truth in it. Has anyone else been offered such advice? Bearing in mind that an elderly man in the early '70s would have life experience from approaching 100-years now (albeit you only have my word for it). It's very possible that tyre valves have improved a lot over all those decades, but I still can't help wondering that the valves are under more pressure during normal use than when the tyres are stationary but left in the sun.

 

[Randy Butternubs]

Once on a hot day in France (30 degrees or more IIRC) I left a bike in direct sun while having a drink at a cafe and had one tyre deflate. On inspection the tube had failed in a really odd way with a sort of rippled, or saw tooth, radial split in it. My best guess is that the heat had weakened the rubber, allowing the tension of the expanded tube to pull it apart.

 

[oldfatfool]

Once on a hot day in France (30 degrees or more IIRC) I left a bike in direct sun while having a drink at a cafe and had one tyre deflate. On inspection the tube had failed in a really odd way with a sort of rippled, or saw tooth, radial split in it. My best guess is that the heat had weakened the rubber, allowing the tension of the expanded tube to pull it apart.

I would imagine that will have been at the join made when the tube was made.

 

[rrarider]

I can vouch for the fact that the sun does have an effect on tyres. Back in the 1980s on a hot summer day, a young technician at work addressed me with "Oi Nick, your bike's just exploded". Going out to the bike rack which had a corrugated iron roof to investigate, I found the back tyre off the rim on one side and the inner tube in pieces.

 

[nickyboy]

[QUOTE 5359355, member: 9609"]when heat goes up pressure will go up, and it could be enough to do damage

THESE FIGURES NEED CHECKED by someone who does science stuff

tyre left in the sun, goes up from 20c to 100c
therefore
(273+100) / (273+20) = 27% increase

so tyre with 100psi could go up to 127psi ?[/QUOTE]

Yeah your maths is correct. 100C (so the boiling point of water) sounds rather warm for a tyre however. I suspect tyre pressure would be the least of your concerns at that temperature

 

[IBarrett]

I've witnessed a tyre explode when the bike was left in direct sunlight. I couldn't tell you much more about it as it was on a sportive and I was sat with a load of people and their bikes.

 

[Drago]

Ah these the same old men that told us to leave the bike for half an hour after pumping the tyres to allow the air to settle?

 

[Smokin Joe]

Ah these the same old men that told us to leave the bike for half an hour after pumping the tyres to allow the air to settle?

Don't be silly, you have to spin the tyre for a couple of minutes to distribute the air evenly.

 

[Globalti]

Old wives' tales, eh?

The tyre damage story probably dates from when tyres were rubber without additives and hot sun and prolonged exposure to UV light would damage them. I remember seeing people shading their car tyres in French campsites in the 60s.

This is probably mostly the sort of homespun belief that made people rev the nuts off car engines before switching off to distribute the oil. My wife has a particularly illogical one of patting drinks cans before opening them to prevent them from spraying.

But yes, tyres can explode in the sun especially inside hot cars if the pressure rises enough.

 

[User169]

Had one explode this earlier this year when I left my bike in the sun.

 

[Drago]

The thermal coefficient of air is 0.0034k at 25C. A rise of 100C would bring an increase of about 0.3of a Psi, assuming pure air with no water vapour. A tyre may explode in the sun, but not because of the sun.

 

[nickyboy]

The thermal coefficient of air is 0.0034k at 25C. A rise of 100C would bring an increase of about 0.3of a Psi, assuming pure air with no water vapour. A tyre may explode in the sun, but not because of the sun.

You've misunderstood what thermal coefficient is measuring. It is 0.0034/k. So it expands by 0.0034 (so 0.34%) per 1k increase in temperature.
Increase it from 20c to 100c is 80k increase. So the expansion is 80 x 0.0034 = 0.272=27.2%

 

[rrarider]

The thermal coefficient of air is 0.0034k at 25C. A rise of 100C would bring an increase of about 0.3of a Psi, assuming pure air with no water vapour. A tyre may explode in the sun, but not because of the sun.

That's rubbish, the pressure will be proportional to the absolute temperature (Gay-Lussac's law)

 

[confusedcyclist]

The thermal coefficient of air is 0.0034k at 25C. A rise of 100C would bring an increase of about 0.3of a Psi, assuming pure air with no water vapour. A tyre may explode in the sun, but not because of the sun.

Sir, I think you'll find if you left your tyre inside a nearly perfect sphere of hot hydrogen plasma, it certainly would get... crispy.

 

[ColinJ]

I was thinking it needed Boyle's Law***, but I just checked and was the Combined Gas Law - P1V1/T1 = P2V2/T2. Assuming that the tyre doesn't stretch or shrink much with the change of temperature then V1=V2 and it reduces to P1/T1 = P2/T2 or P1/P2 =T1/T2, which is what @User9609 was getting at. (T1, T2 being absolute temperatures, which is where the 273s come in.)


*** It is half a century since I studied this at school, so please cut me some slack!