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Deflate tires after riding?
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 2009-08-12 12:45 PM |
Veteran  499   El Segundo, CA |  Subject: Deflate tires after riding?Occasionally after races, I've seen people take some air out of their bike tires. Does anyone do this, or know why it might be beneficial? It seems feasible to me that keeping a lower pressure in your tires while not riding might prolong their life due to less stress on the rubber. Of course, it seems that the constant inflating/deflating could wear them down just as fast (or faster). Any thoughts? |
| 2009-08-12 12:50 PM in reply to: #2344157 |
| Subject: RE: Deflate tires after riding? Hot day and the bike's going to go on a car rack? They're flying with the bike and don't want to forget to deflate them? They're going to take the wheel(s) off and that's an easy way to get it through the brake? Those are the only three I can think of offhand. I leave mine alone after getting them to 120 PSI, though. |
| 2009-08-12 12:50 PM in reply to: #2344157 |
Champion 7233  | Subject: RE: Deflate tires after riding? i do after races and anytime i am going to leave my bike in my car for a while, it gets hot in there and tires do pop (90% of the flats i have had were from leaving inflated tires in my car and having htem blow as it heats up. if it ever happens while you ae driving try not to wig out, sounds like a gun going off in your back seat. |
| 2009-08-12 12:51 PM in reply to: #2344157 |
| Subject: RE: Deflate tires after riding? Can't think of why they'd do that..... |
| 2009-08-12 1:00 PM in reply to: #2344157 |
Resident Curmudgeon 25290 The Road Back Gold member | Subject: RE: Deflate tires after riding? During a race, the air loses it's freshness, which increases the tire's rolling resistance significantly. It's best to let this stale air out before you forget and leave it in for the next races. |
| 2009-08-12 1:16 PM in reply to: #2344157 |
Elite 3091 Spokane, WA | Subject: RE: Deflate tires after riding? Why wouldn't you? I deflate my car's tires when I'm not using it--same thing. |
| 2009-08-12 1:19 PM in reply to: #2344157 |
Regular 186 SW VA | Subject: RE: Deflate tires after riding? |
| 2009-08-12 1:58 PM in reply to: #2344200 |
Pro 3932 Irvine, California | Subject: RE: Deflate tires after riding? the bear - 2009-08-12 11:00 AM During a race, the air loses it's freshness, which increases the tire's rolling resistance significantly. It's best to let this stale air out before you forget and leave it in for the next races. I find this hard to believe.... |
| 2009-08-12 2:05 PM in reply to: #2344355 |
Master 2380 Beijing | Subject: RE: Deflate tires after riding? Tripolar - 2009-08-11 2:58 PM the bear - 2009-08-12 11:00 AM During a race, the air loses it's freshness, which increases the tire's rolling resistance significantly. It's best to let this stale air out before you forget and leave it in for the next races. I find this hard to believe.... Then your BS detector is perfectly calibrated. Everyone knows it's to keep your bike from rolling away. After a race the air in the tires has so much momentum that if you don't let any out.... the bike will roll out of the rack while you're on the podium. |
| 2009-08-12 2:45 PM in reply to: #2344157 |
Veteran 237 Buffalo Grove | Subject: RE: Deflate tires after riding? The reason people take air out of tires after a race is to prevent a tire for "blowing up". Some of the posters are correct. When you place a fully inflated tire in a hot car it will burst after just a little while. The air will expand due to the heat and next thing you know, flat. This does not always happen in a car. I have been at races and you just hear the tires "poping". People over inflate, the air temp goes up and then you are SOL. Last year, I was walking from the transition area at the Louisville Ironman and I heard two or three tires burst. You shuld inflate based on the tire presure suggested by the tire maker but also keep in mind the environment. Is it 60 when you pump up your tires but the high for the day is going to be 100? If so you may want to leave some "wiggle room". |
| 2009-08-12 2:51 PM in reply to: #2344355 |
Resident Curmudgeon 25290 The Road Back Gold member | Subject: RE: Deflate tires after riding? Tripolar - 2009-08-12 1:58 PM the bear - 2009-08-12 11:00 AM During a race, the air loses it's freshness, which increases the tire's rolling resistance significantly. It's best to let this stale air out before you forget and leave it in for the next races. I find this hard to believe.... I find it harder to believe that someone would take it seriously enough to comment on it. |
| 2009-08-12 3:28 PM in reply to: #2344157 |
Champion 6503 NOVA - Ironic for an Endurance Athlete | Subject: RE: Deflate tires after riding? Off topic, slightly. I always treat the Maximum Tire Pressure is just that...the max...I always inflate mine to about 5-10 psi less than the max. |
| 2009-08-12 4:17 PM in reply to: #2344157 |
Extreme Veteran 605 | Subject: pV=nRT Warning Science Ahead This is all based on the ideal gas law. pV=nRT. In this case we are going to assume that V, n and R are all constants. I know the tire expands and so V isn’t exactly constant, but I’m going to say it is anyway. So p/T = a constant. As T changes so will p. So: p1/T1 = p2/T2. By the way p is pressure and T is temperature in absolute scales. Now for the fun part Let’s assume a tire rated for 100 psi max that you fill to 100 psi in the morning before the race when it is 60 degrees out. Since we are talking about absolute scales we add atmospheric pressure to the 100 psi to get 114.7 psi and we change 60 degrees F to ~288 K. That is your starting point. Then at the end of the race it’s now 85 degrees F and you go put your tires in the car which has been baking in the sun and it’s 20 degrees warmer, 105 degrees F. 105 degrees F is ~313 K. A little algebra and you get (114.7/288)*313 = 124.7 psi. Wait that’s absolute pressure, so subtract 14.7 psi and get about 110 psi. That is 10% over the tire limit. The analysis 10% over is probably not enough stress to cause every tire to blow, but it is probably (and anecdotal evidence supports) enough stress to pop some tires. I guess that used tires and high performance tires are probably more at risk for this phenomenon. So if you pump your tires to the max and if you have HP tires and if you carry your bike in your hot car then yes this could be a problem. If you ride a MTB like me and your tires are crappy and usually under inflated then I wouldn’t lose too much sleep over it. Just my two cents. PS Does this qualify me as a tri geek or just a geek? |
| 2009-08-12 4:51 PM in reply to: #2344784 |
Veteran 499 El Segundo, CA | Subject: RE: pV=nRT MNGopher - 2009-08-12 2:17 PM Warning Science Ahead This is all based on the ideal gas law. pV=nRT. In this case we are going to assume that V, n and R are all constants. I know the tire expands and so V isn’t exactly constant, but I’m going to say it is anyway. So p/T = a constant. As T changes so will p. So: p1/T1 = p2/T2. By the way p is pressure and T is temperature in absolute scales. Now for the fun part Let’s assume a tire rated for 100 psi max that you fill to 100 psi in the morning before the race when it is 60 degrees out. Since we are talking about absolute scales we add atmospheric pressure to the 100 psi to get 114.7 psi and we change 60 degrees F to ~288 K. That is your starting point. Then at the end of the race it’s now 85 degrees F and you go put your tires in the car which has been baking in the sun and it’s 20 degrees warmer, 105 degrees F. 105 degrees F is ~313 K. A little algebra and you get (114.7/288)*313 = 124.7 psi. Wait that’s absolute pressure, so subtract 14.7 psi and get about 110 psi. That is 10% over the tire limit. The analysis 10% over is probably not enough stress to cause every tire to blow, but it is probably (and anecdotal evidence supports) enough stress to pop some tires. I guess that used tires and high performance tires are probably more at risk for this phenomenon. So if you pump your tires to the max and if you have HP tires and if you carry your bike in your hot car then yes this could be a problem. If you ride a MTB like me and your tires are crappy and usually under inflated then I wouldn’t lose too much sleep over it. Just my two cents. PS Does this qualify me as a tri geek or just a geek?
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| 2009-08-12 4:59 PM in reply to: #2344372 |
Pro 6767 the Alabama part of Pennsylvania | Subject: RE: Deflate tires after riding? moondawg14 - 2009-08-12 3:05 PM Tripolar - 2009-08-11 2:58 PM the bear - 2009-08-12 11:00 AM During a race, the air loses it's freshness, which increases the tire's rolling resistance significantly. It's best to let this stale air out before you forget and leave it in for the next races. I find this hard to believe.... Then your BS detector is perfectly calibrated. Everyone knows it's to keep your bike from rolling away. After a race the air in the tires has so much momentum that if you don't let any out.... the bike will roll out of the rack while you're on the podium. Come on, don't mess with people this way. A bike tire doesn't maintain momentum once it's stopped. The real reason is environmental. When you filled the tires, you were using air from the morning, before all the people started exercising. While everyone is out running, biking, and swimming, they are exherting themselves more, and therefore generating more CO2 that they exhale. CO2 is a greenhouse gas, contributing to global warming. One way to immediately offset this to a small degree is to release back into the enviroment the air from the morning, which logically has a lower CO2 concentration, and helps to dilute the CO2 generated during the race, reducing the carbon footprint of the race. |
| 2009-08-12 5:13 PM in reply to: #2344478 |
Pro 3932 Irvine, California | Subject: RE: Deflate tires after riding? the bear - 2009-08-12 12:51 PM Tripolar - 2009-08-12 1:58 PM the bear - 2009-08-12 11:00 AM During a race, the air loses it's freshness, which increases the tire's rolling resistance significantly. It's best to let this stale air out before you forget and leave it in for the next races. I find this hard to believe.... I find it harder to believe that someone would take it seriously enough to comment on it. Well, granted, I wasn't giving it my undivided attention. I was also busy looking up "gullible" in the dictionary since my coworker said it wasn't a real word... |
| 2009-08-12 8:05 PM in reply to: #2344942 |
Master 2380 Beijing | Subject: RE: Deflate tires after riding? Tripolar - 2009-08-11 6:13 PM the bear - 2009-08-12 12:51 PM Tripolar - 2009-08-12 1:58 PM the bear - 2009-08-12 11:00 AM During a race, the air loses it's freshness, which increases the tire's rolling resistance significantly. It's best to let this stale air out before you forget and leave it in for the next races. I find this hard to believe.... I find it harder to believe that someone would take it seriously enough to comment on it. Well, granted, I wasn't giving it my undivided attention. I was also busy looking up "gullible" in the dictionary since my coworker said it wasn't a real word... sigh. I had such high hopes for you. It obviously *IS* a real word.... they just don't put it in the dictionary. At least, no dictionary worth its salt. |
| 2009-08-12 8:25 PM in reply to: #2344157 |
Master 1848 Canandaigua | Subject: RE: Deflate tires after riding? I think I;m partial to the CO2 effect, but I believe it's like taking you boat from one lake to another. To cut down on invasive species one should drain the bilge and wash the boat. So purging the air out of the tire save on cross contamination of the local air masses. |
| 2009-08-12 11:27 PM in reply to: #2344912 |
Master 2665 The Whites, New Hampshire | Subject: RE: Deflate tires after riding? gearboy - 2009-08-12 5:59 PM Come on, don't mess with people this way. A bike tire doesn't maintain momentum once it's stopped. The real reason is environmental. When you filled the tires, you were using air from the morning, before all the people started exercising. While everyone is out running, biking, and swimming, they are exherting themselves more, and therefore generating more CO2 that they exhale. CO2 is a greenhouse gas, contributing to global warming. One way to immediately offset this to a small degree is to release back into the enviroment the air from the morning, which logically has a lower CO2 concentration, and helps to dilute the CO2 generated during the race, reducing the carbon footprint of the race. I went to this race once that had a discount if you reduced your carbon emissions and they said this exact same thing and you couldn't get your money back until you showed your deflated tires at the end. Well, it wasn't my race, but my friend's brother and his friends did it and they got first in their AG out of like 500 people, so they totally know what they are talking about. Oh, and it was that race in Hawaii, I bet you saw them on TV. hOw cOoL!!11!!!! |
| 2009-08-13 4:37 PM in reply to: #2344157 |
Champion 6503 NOVA - Ironic for an Endurance Athlete | Subject: RE: Deflate tires after riding? Everyone knows that you should fill your tires with Hydrogen. It is extremely light, and stable too! |
| 2009-08-13 5:13 PM in reply to: #2347241 |
Pro 6767 the Alabama part of Pennsylvania | Subject: RE: Deflate tires after riding? pga_mike - 2009-08-13 5:37 PM Everyone knows that you should fill your tires with Hydrogen. It is extremely light, and stable too! Again with the silly answers! Hydrogen gas is flammable, and hard to get. There are two schools of thought on the alternative gas approaches. Helium for producing a lower overall bike weight. You can get helium tanks at most party stores for filling balloons. However, the tires will need to be filled right before use, as the gas escapes more readily. Or argon (available from your local dive shops), which is heavier than air, and produces an effect like disc wheels adding to the momentum and speed of the bike. Also being a denser gas, it will last longer in the tube, so you don't need to fill as often. |
| 2009-08-13 6:13 PM in reply to: #2344784 |
Member 381 | Subject: RE: pV=nRT MNGopher - 2009-08-12 3:17 PM Warning Science Ahead This is all based on the ideal gas law. pV=nRT. In this case we are going to assume that V, n and R are all constants. I know the tire expands and so V isn’t exactly constant, but I’m going to say it is anyway. So p/T = a constant. As T changes so will p. So: p1/T1 = p2/T2. By the way p is pressure and T is temperature in absolute scales. Now for the fun part Let’s assume a tire rated for 100 psi max that you fill to 100 psi in the morning before the race when it is 60 degrees out. Since we are talking about absolute scales we add atmospheric pressure to the 100 psi to get 114.7 psi and we change 60 degrees F to ~288 K. That is your starting point. Then at the end of the race it’s now 85 degrees F and you go put your tires in the car which has been baking in the sun and it’s 20 degrees warmer, 105 degrees F. 105 degrees F is ~313 K. A little algebra and you get (114.7/288)*313 = 124.7 psi. Wait that’s absolute pressure, so subtract 14.7 psi and get about 110 psi. That is 10% over the tire limit. The analysis 10% over is probably not enough stress to cause every tire to blow, but it is probably (and anecdotal evidence supports) enough stress to pop some tires. I guess that used tires and high performance tires are probably more at risk for this phenomenon. So if you pump your tires to the max and if you have HP tires and if you carry your bike in your hot car then yes this could be a problem. If you ride a MTB like me and your tires are crappy and usually under inflated then I wouldn’t lose too much sleep over it. Just my two cents. PS Does this qualify me as a tri geek or just a geek? damn science is killing creativity here.  btw - i'll cautiously add that, because the tire is black and has a pretty high emissivity, it can be hotter than the car if in direct sunlight. so if the car is 105F maybe the tire is 110F or whatever. you get the point. |
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