Bicycle Mechanics - Do you deflate your tires when your bike is in the sun?

I recently took a 750 mile trip from Kentucky to the Outer Banks of North Carolina. My bike was on a rack in the back. I read somewhere that you should not park your bike in the sun over long periods of time because the heat expansion will blow the tires. So half way through the trip, I deflated both tires, only to find that letting a little air out takes the tire from 110 pounds down to 70 or 80. I stopped at a LBS, and the wrench there said I needn't worry. He said most bike tires are designed to take DOUBLE the recommended maximum inflation pressure. If he's right, my Michelin Axial Carbons could have inflated to 220 pounds from the sun heat, and not been harmed. Is this true? Also, what effect does the air rushing over the bike tire when the car is moving have on pressure expansion? Does this negate the heat from the sun (the temp during my trip was in the low 90's).Thanks for your input.

I've biked with high pressure road tires in areas with temps in the 100+ F. range for 8 hours at a go with no problem. Have also left bikes parked in blazing sun all day with no damage to the tires/tubes. Can't say for certain, but I've never felt a need to let air out due to temp or sun.

Paul

uh, there's no way the heat expansion could blow your tires...

anyone remember charles' law? says that pressure is directly proportional to absolute temperature. heating from 0 C to 35 C will only raise your tire pressure by 13%.

so in a nutshell, no your tires will not blow off their rims

I park my bike in sunlight all summer during the day. It has seen 115 degrees this summer pumped up to 118 and no problems.

The only danger to your bike from solar radiation is that it will cause your tires & brakepads to deteriorate somewhat faster, & also may fade your paint. I park my bike out of the sun whenever possible.

This post is a joke, isn't it?

Dave, I wouldnt call this a joke. When I worked in the buisness custumoers asked us this all the time. More specifically if they should let air out when the bike was in the back of the car. deleriou5 got it right with charles' law. Consider it an informative post. Heck, my car tires only go from 30 to 33.

The question probably gets asked here frequently in different forms. I remember a few months back someone posted and was worried their tires would blow at the top of a mountain if they started at the bottom of the mountain with them at full pressure.

pressure vessels including tires have a 2-3.5 factor of safety depnding on the design pressure and volume..

That's about 100psi more.

Originally posted by deliriou5
uh, there's no way the heat expansion could blow your tires...

so in a nutshell, no your tires will not blow off their rims

Deliriou5, I always like your posts, but I have to advise you and others that the sun/heat CAN blow the tires of your rims. It happened to my friend. We were on a tour and had ridden about four hours. I had inflated our tires in the cool morning. The day grew hotter.

We took a break at noon and leaned our bikes outside against a big window at a resturaunt. The bikes were in the sun and we sat next to the window so we could watch our bikes.

All of a sudden KAWHAMEE!! there was like an explosion against the window. Everybody inside the resturaunt jumped (most of all my friend and me!).

Somebody thought that a pelican must have flown into the window. Further inspection revealed that the rear tire on my friend's bike had exploded. The tire was blown off the rim and the tube was shredded.

Thanks to some kind help from a locals, we bought a replacement at the only hardware store in town (no bike shops in that town AND the hardware store had a couple of tires).

Here are some factors:

1) The tires were 27" with a max inflation of 90 lbs.
2) I filled the tires to 90 lbs - maybe just a pound over:rolleyes:
3) The failed tire was not new (don't know how old).

Mike...repeat, repeat, repeat.....that tire did not blow because of a pressure inrease due to heat!!!!!

Originally posted by miamijim
Mike...repeat, repeat, repeat.....that tire did not blow because of a pressure inrease due to heat!!!!!

So... are you saying a pelican did it?

I'm saying something other than the heat did it.......actually the only way heat could have done it, and its very un-likely it happened is if the gumwall sidewalls melted. That may have contributed to the failure but it DID NOT happen due to an increase in pressure.

Something to keep in mind is that pressure increase due to heat is even regardless of the temperature. In other words if the temp goes from 0 to 100 thats the same as it going from 100 to 200. My car tires are 30 degrees when the temp is 85. After they heat uo to what, 150 degrees? They only go up to 33 degrees. 35C degree change 13% pressure change......see above..

The blowout could also have resulted from a defective/old tube, combined with heating.

I've read that rated bike tire pressures are determined by inflating the tire until it blows off the rim. The rating is then marked at half of that pressure.

I seem to recall that there was some discussion of
tire pressure and heat around Hotter Than Hell. I've been
looking for the reference but can't find it.
The premise was that due to high heat on the road (up to
140 degrees at surface) there are more blow outs due to
the changes in pressure. The writer mentioned dropping
tire pressure by about 5 - 10 psi for the ride.
All I know is I saw more blow outs
on HHH (both last year and this year) than one would expect
to see for a ride of that size.
Interesting topic tho, and no I don't think this question is
a troll.
I'll continue to search for the article and if I find it I'll post it
(if soft copy).

Marty

Well, I don't know about the physics or what, but I *have* had bike tires blow, twice, when the bike was stored in the back of a station wagon, windows mostly closed, parked in the sun, during a Virginia summer. Say what you will, it wasn't pelicans! I didn't believe it would be possible either, but was told by a local shop monkey that it happens all the time.

Due to the greenhouse effect, the inside of a vehicle can get much hotter than the
ambient air outside. Failure might be due more to weakening of the rubber than to pressure increase.

Granted. I think the heat inside the closed vehicle was the kicker in my case.

It's not the rubber that is holding the tire in one piece under high pressure but the thread.

I had seen my tire blew up right in front of my eyes while I was at roadside watching a parade. I knew my tire had a cut on the side wall but I had it for long time, I didn't think it was going blow up. I could see the tube came out like a balloon slowly then finally blew up. I was so embarrassed to see people looking at my way as if I shot a gun in the public. I just told everybody around me that my tire blew up.

Someone here said the normal tires hold twice the maximum pressure it states and I believe that. Once you get flat tire, it's not only the tube that got damaged but also the tire covers over it. Once it gets damaged that spot will be the weakest part. It'll take a great effort to tear a piece of cloth by hands but once you cut the edge by scissors, you can tear it all the way across effortlessly. The same thing applies to tires. Once foreign object pierce through the tire and break a thread or two, the neighboring thread will get greater stress than the rest, then eventually breaks thread by thread. You can patch a tire from inside but it's not nearly strong as a threaded tire wall.

So, my answer to the original question is to keep a spare tire if you use a tire that already had a flat, or if you can afford it, replace it once you get a flat, instead of keep repeating inflate then de-flate the tire.

Miamijim: The reference by Mike to 27" tires makes me wonder if they were
older, non hook bead tire/rims. These were more sensitive to pressure than the hook beads we all use now.

On another thought: after watching the horror show of Beloki's crash and the suggestion that heat rolled his tire. So I felt my rims after braking from 25mph to 5mph on a downhill over ~200yds. The rims felt like 120F, you could touch and grip them but after 5-10sec it was too hot for comfort. Makes me wonder what the rims would do on a long curvy hilly descent (ala TDF). The upside risk is certainly more than a hot car in July. I have read threads about hydraulic brakes on tandems locking up on hilly descents from heat induced expansion of the fluid. Steve

Originally posted by sch
Miamijim: The reference by Mike to 27" tires makes me wonder if they were
older, non hook bead tire/rims. These were more sensitive to pressure than the hook beads we all use now. Steve

Yes, in my case, the tire was old. I don't know how old, but let's say that a woman born the same year as the tires could probably bear children today.

For the record, the tire was a hook/bead tire, but 'ya', I know what Steve means about the really old rims that were not hook/bead. Those blew tires especially easily.

Ok, since (P1*T2)/T1= P2, and these #'s are in absolute (rankine or absolute temperatures, not common farenheit or celsius), lets see what the difference of a hot day over, say, a cold basement would be, shall we?

Temp basement: 50 degrees F, or 510 degrees R

Temp in hot, hot sun: 120 F, or 580 R

P2 = P1*(580/510) = 1.13P1, or 13% rise in pressure. So, 100 psig cold = 113 psig hot. Big deal.

More than likely this was an isolated blow-out that would have happened regardless of where the bike was.

sch, good thought on the non-hook bead rims. If they were, a 20 p.s.i. change could have been the culprit.

Twice I have seen tires(actually heard them) blow because they were in the sun. Both times they were tubular type tires. Once was in Atlanta, middle of summer at the Mayors Cup race. A few riders had their bikes leaning against a building in the sun. We all heard them blow. Sounded like a gun.

The other time was after descending Brasstown Bald. We stopped at the bottom waiting on the uphill time trial. I think it was the heat from all the braking going down hill and then letting them sit in the sun.

Apollo ;)

Twice I have seen tires(actually heard them) blow because they were in the sun. Both times they were tubular type tires. Once was in Atlanta, middle of summer at the Mayors Cup race. A few riders had their bikes leaning against a building in the sun. We all heard them blow. Sounded like a gun.

The other time was after descending Brasstown Bald. We stopped at the bottom waiting on the uphill time trial. I think it was the heat from all the braking going down hill and then letting them sit in the sun.

Apollo ;)

Welcome to the forums Apollo. Let's not make a habit of digging up 3 year old threads.
;)

Sounds like the 27" tires were old. They really don't make very high quality 27" tires any more as the industry went to 700c a long time ago. Old tires are dangerous and could conceivable have blown. Scrap the 27" rims and have the hubs laced with the current rim size.

Not a problem - my bike has stayed in my car parked in the Houston sun for hours, no issue with the tires. The only place you probably have a concern is when flying with your bike - tire deflation is a good idea then...

I'm gonna throw in one more thing that is a factor.

I fix bikes at Burning Man every year. It's up in the Black Rock Desert in Nevada, I think the elevation is 4000ft. Every year we get dozens of folks in the shop who aired up to max pressure at sea level in the cool of night. Then when they get to 4000 ft and desert sun, their tires blow. The heat plus the elevation is only part of the cause however. Not all tire/rim combinations are good to 2X the published pressure. Some are good past 2X, some are nowhere near as good. One thing that seems to be left out of some folks' answers here is the color of tires. Folks, dull black absorbs sunlight like nobody's business. There is no possible way that the temperature of the air inside a tire sitting in the sun will be the same as the ambient air temperature. Then take into effect a possibly slight defect in a section of the bead, or in the casing, and the effect of the higher temp on the materials of the tire, let alone the increased pressure.

Anyway, I guess all I'm trying to say is that it is quite possible, and like most things that go wrong has to do with a combination of factors. I bet those who say it "can't happen" have simply not yet had it happen to them :)

Excessive heat could conceivable blow a tire; usually there are other causes/reasons.
However, living in the desert, have ridden 1000s of miles through the years in 100+ degree temps (as hot as 117). Blacktop is at least 40+ degrees hotter from the sun. No blowoffs ever from heat.

I think that elevated ambient temperatures have the potential to cause a previously damaged tire catastrophically fail. In such instances, I think that the temperature merely serves as the proverbial straw that broke the camel's back.

Well, I don't know about the physics or what, but I *have* had bike tires blow, twice, when the bike was stored in the back of a station wagon, windows mostly closed, parked in the sun, during a Virginia summer. Say what you will, it wasn't pelicans! I didn't believe it would be possible either, but was told by a local shop monkey that it happens all the time.

Well, you can believe the "shop monkey's" myth or you can believe in the laws of physics. Yes tires come off all the time due to deterioratiion of the rubber/casing, mechanical damage and cuts or improper installation. they do NOT come off due to the small pressure increase from getting hot in a car.

Another myth is that you should deflate the tires if you are going to ship your bike by air since the cargo holds of aircraft aren't pressurized. Nonsense. If the hold was under a perfect vacuum, the pressure change would total 15 psi.

Well, you can believe the "shop monkey's" myth or you can believe in the laws of physics. Yes tires come off all the time due to deterioratiion of the rubber/casing, mechanical damage and cuts or improper installation. they do NOT come off due to the small pressure increase from getting hot in a car. As we've seen posted a thousand times here, people get their tubes pinched between the tyre and rim ALL THE TIME! Some blow right as they're pumping it up, others blow days later. But there's a difference between cause and effect! The cause is a pinched tube, the effect is a blow-out (playing basketball does not make one taller). So yes, hot temperatures and high-altitubes will increase tyre-pressures by +15-20% max. That is just a contributor to an existing problem like pinched tube, weak-tyre casings, straight-wall rims, etc. That last bit of extra pressure may push a marginal configuration over the edge, but there was already a pre-existing problem to begin with.

....but there was already a pre-existing problem to begin with.

This is the heart of the answer right here!

I seem to recall that there was some discussion of
tire pressure and heat around Hotter Than Hell. I've been
looking for the reference but can't find it.
The premise was that due to high heat on the road (up to
140 degrees at surface) there are more blow outs due to
the changes in pressure. The writer mentioned dropping
tire pressure by about 5 - 10 psi for the ride.
All I know is I saw more blow outs
on HHH (both last year and this year) than one would expect
to see for a ride of that size.

Marty

No way. I've ridden in the last 7 Hotter'n Hell Hundreds. There are many flats on this ride but not from the heat, they're from sand burrs or goatheads picked up at the rest stops. For the last two years the air temperature never even got to 100 F.

Al

The blowout could also have resulted from a defective/old tube, combined with heating.

I've read that rated bike tire pressures are determined by inflating the tire until it blows off the rim. The rating is then marked at half of that pressure.

That is what happened to me a number of years ago. It was heat coupled with poor rim tape. Two days in a row. The bike was inside the car for a day for a bike commute home. The first time I just thought it was a bad tire or an older pinhole. But on the second day, I noticed an embossed circle at the puncture - it was the image of the spoke nipple's inside. Looking at that location my rim tape was thin at that location and allowed the inside of the spoke to poke when the tire expanded from the heat.

Excessive heat could conceivable blow a tire; usually there are other causes/reasons.
However, living in the desert, have ridden 1000s of miles through the years in 100+ degree temps (as hot as 117). Blacktop is at least 40+ degrees hotter from the sun. No blowoffs ever from heat.

I will agree with you, in part, in that my tires never have blown off in the heat. (I also rarely get flats while many others get them cosntantly.) But just because we haven't had it happen it can't happen to others? I'm not sure I get that mindset around here. Being part of the Black Rock City Bike Guild puts me in direct contact with literally thousands of bikes every year in the desert. The vast majority of them have no problems at all, but a number of them have heat related blowouts...it's just the way it is.

Another myth is that you should deflate the tires if you are going to ship your bike by air since the cargo holds of aircraft aren't pressurized. Nonsense. If the hold was under a perfect vacuum, the pressure change would total 15 psi.

Well, let's do some math. The net atmospheric pressure on the outside of an average MTB tire is about 3000 pounds. The only reason we can have pressurized tires at all is because of atmospheric pressure holding it all together. Heck, it's what holds us all together too :D Look up how much net pressure you have on you right now. It's a big number considering you have a couple of square meters of skin (some of a little more) ;)

PSI is a misleading unit because we tend to think of the, say, "15 pounds" of atmospheric pressure. But we are very rarely dealing with a single square inch. Multiply it out over the surface area of the object.

Ever seen a crushed tank car? 7/16" steel, crushed like a pop can by atmospheric pressure alone. Very impressive, and actually quite scary.
http://www.delta.edu/slime/cancrush.html

BTW - we don't need to deflate our tires in the cargo holds of airplanes because cargo holds are heated and presurized.

I'll add to the "I've had it happen to me" list. And this was on a mountain bike - not a high pressure road bike. Went for a ride in the morning - temps probably in the mid-upper 60's. Had the pressure pumped up to the rec'ed max for the tire. Put the bike away in an outdoor storage shed (sheet metal) where the outside temps probably reached 100, inside the shed probably more like 150+. When I came back to the bike the next morning for another ride I found the tire blown OFF the rim and the tube had a 3-4" slit ripped in it. Perhaps it was a defective tube, or a bad install that weakened it. But the pressure change DID blow that tube one way or another.

Another myth is that you should deflate the tires if you are going to ship your bike by air since the cargo holds of aircraft aren't pressurized. Nonsense. If the hold was under a perfect vacuum, the pressure change would total 15 psi.

And not only that, they *do* pressurize the cargo hold. If they didn't, there'd be lot of dead pets at the destination :o

Well, let's do some math. The net atmospheric pressure on the outside of an average MTB tire is about 3000 pounds. The only reason we can have pressurized tires at all is because of atmospheric pressure holding it all together. Heck, it's what holds us all together too :D Look up how much net pressure you have on you right now. It's a big number considering you have a couple of square meters of skin (some of a little more) ;)

PSI is a misleading unit because we tend to think of the, say, "15 pounds" of atmospheric pressure. But we are very rarely dealing with a single square inch. Multiply it out over the surface area of the object.

You don't need atmospheric pressure for a pneumatic tire to work. And 3000 pounds is not a pressure. It is a force. The air pressure at sea level is about 15psi and the air pressure in space is 0psi and if you bring a bicycle tire from sea level to space, the air pressure inside the tire will increase by about 15psi.

You don't need atmospheric pressure for a pneumatic tire to work. And 3000 pounds is not a pressure. It is a force.

Okay - I'll give you that one. IANAP (I am not a physicist) :D

Ever put something inflated into a vacuum chamber? A balloon, a ziplock bag, a bike tire? In a previous life I was an R&D engineer for a geophysical tool manufacturer. It's fun putting things into the vacuum chamer and seeing them pop. And they do pop...well BANG in some cases. Don't tell my old boss I said so though.

Yeah, you can add up the surface-area of the tyre and calculate how much force there is on the casing. Add +10% when taking the tyre into a vacuum. Not much of a change compared to the +100% testing done to determine blow-off point in coming up with a max-pressure rating of 1/2 that.

Tyres have strong casings relative to a balloon or zip-lock bag. They do not change internal volume by much when internal pressures are increased by 800% over atmospheric, whereas an balloon's internal pressure is barely higher than atmospheric, not more than 5%, yet it has stretched over 1000% of its original volume. Add some more, like 10% in a vacuum and yes, it will push a balloon over the edge. Not a bike-tyre though... To make the comparison fair, take a balloon, zip-lock bag and tire. Grab each at the ends and yank apart. How many people can rip a tyre in half with their bare hands?

Ok, here's some more cause-and-effect relationship. On my New Years Day ride, it started out drizzling and was about 65-degrees or so. By the end of the ride, it was a constant rain; people said California got 2" of rain during my ride. :) Anyway, the cold weather caused the pressure to drop during my ride. Then when I came back, I put the bike into my heated garage and cleaned it off. Wiped off the tight spots with Q-tips and used a hair-dryer to get the last bits of water out. In the middle of the night, the tyre BLEW! Obviously the heated garage and hair-dryer raised temperatures over the limit for the tyre:

http://www.gururacing.com/cycling/equipment/blowntyre1.jpg
http://www.gururacing.com/cycling/equipment/blowntyre2.jpg
http://www.gururacing.com/cycling/equipment/blowntyre3.jpg
http://www.gururacing.com/cycling/equipment/blowntyre4.jpg

Ever put something inflated into a vacuum chamber? A balloon, a ziplock bag, a bike tire?

A bicycle inner tube (one not inside a tire) might pop inside a vacuum. Actually, you don't even need a vacuum to test. Just try pumping one up to over 15psi. I've never tried this since it takes only a couple psi (if even that) to get them inflated enough to find the hole or see if they hold air.

Well, let's do some math. The net atmospheric pressure on the outside of an average MTB tire is about 3000 pounds. The only reason we can have pressurized tires at all is because of atmospheric pressure holding it all together. Heck, it's what holds us all together too :D Look up how much net pressure you have on you right now. It's a big number considering you have a couple of square meters of skin (some of a little more) ;)

PSI is a misleading unit because we tend to think of the, say, "15 pounds" of atmospheric pressure. But we are very rarely dealing with a single square inch. Multiply it out over the surface area of the object.

Ever seen a crushed tank car? 7/16" steel, crushed like a pop can by atmospheric pressure alone. Very impressive, and actually quite scary.
http://www.delta.edu/slime/cancrush.html

BTW - we don't need to deflate our tires in the cargo holds of airplanes because cargo holds are heated and presurized.

Your entire line of reasoning is wrong.

Well, Dr. Hunter S. Thompson claimed to have pumped up the tires on a Caddy to 100psi, all so that he could more easily burn rubber and break 'em loose around corners. So I think bike tires should not be harmed by slightly-higher than recommended air pressures.

Your entire line of reasoning is wrong.

Well okay. I just thought I'd throw it out there and see if it floated.

Well okay. I just thought I'd throw it out there and see if it floated.

Whew, you had me worried for a minute there. :eek:

Welcome to the forums Apollo. Let's not make a habit of digging up 3 year old threads.
;)


Shows what you know Urban. There might be something useful to add to an old thread. Mind your own business next time. :p ;)