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Weight Weenie Question(11 posts)

Weight Weenie QuestionJerBear
Feb 4, 2003 9:07 PM
Not that it'll truly make a difference..but...has anyone ever checked the weight of their tires with different psi levels? I was thinking about this the other day when I was changing out a propane tank for a BBQ...light when empty and heavy when full (I think that it's just gas in there?)
re: Weight Weenie Questionlaffeaux
Feb 4, 2003 10:27 PM
This came up on the mtbr.com board last week:

http://forums13.consumerreview.com/crforum?14@@.ef8ecfd/4
well duhcollinsc
Feb 4, 2003 10:40 PM
welcome to chemistry 101.
well duhkoala
Feb 5, 2003 3:22 AM
Shows ya what I know. Six years of college education and I thought it was physics!
You could always fill it with hydrogen! nmRusty McNasty
Feb 5, 2003 5:09 AM
Don't some racers still use helium today? (nm)joekm
Feb 5, 2003 5:54 AM
non-issueDougSloan
Feb 5, 2003 6:46 AM
The weight difference infinitessimal. I read that some pros use pure nitrogen, though, but not for weight; apparently, it has less rolling resistance.

Doug
What about nitrous oxide? Could come in handy. nmdzrider
Feb 5, 2003 6:49 AM
agree 100%cyclopathic
Feb 5, 2003 7:42 AM
at room temperature/pressure (14.7psi) you need ~6 gallons of air to make up 1oz. With respect to lower rolling resistance helium has been used for TT haven't heard about nitrogen. Is it as good or it's just stays inflated longer to be practical for road races?
propane, nitrogen, helium--what a gasContinental
Feb 5, 2003 8:13 AM
Propane is a liquid at the pressure used in propane tanks. At 70 F propane condenses into a liquid at 125 lb psi. The propane tank is heavy because it is full of liquid. The reason for using nitrogen in tires is that the nitrogen is virtually dry. It contains no water vapor. If you pump humid air into a tire some of the water will condense at the higher pressure. In race cars enough heat is generated in the tires to vaporize some of the condensed water and significantly change the tire pressure. Bike race teams applied this technique from the auto racers, although bike tires don't undergo enough temperature change to vaporize a significant amount of condensed water. Then somebody took it a step farther and thought that helium is lighter than nitrogen. The problem is that helium diffuses through rubber quite quickly, and there is no significant weight advantage, even to the most extreme weight weenie. Air nitrogen, and helium all behave as a practically ideal gas under these conditions, so rolling resistance is not affected. Just pump up your tires with air and ride.
propane, nitrogen, helium--what a gasContinental
Feb 5, 2003 8:15 AM
Propane is a liquid at the pressure used in propane tanks. At 70 F propane condenses into a liquid at 125 lb psi. The propane tank is heavy because it is full of liquid. The reason for using nitrogen in tires is that the nitrogen is virtually dry. It contains almost no water vapor. If you pump humid air into a tire some of the water will condense at the higher pressure. In race cars enough heat is generated in the tires to vaporize some of the condensed water and significantly change the tire pressure, so they use dry nitrogen. Bike race teams applied this technique from the auto racers, although bike tires don't undergo enough temperature change to vaporize a significant amount of condensed water. Then somebody took it a step farther and thought that helium is lighter than nitrogen. The problem is that helium diffuses through rubber quite quickly, and there is no significant weight advantage, even to the most extreme weight weenie. Air nitrogen, and helium all behave as a practically ideal gas under these conditions, so rolling resistance is not affected. Just pump up your tires with air and ride.