stephen1254

I seem to remember reading that if you use a CO2 inflation device, once you get home you should replace the CO2 with air because the CO2 leaks out faster than air. Is that true or did I make it up?

furiousferret

Never heard that one before.

uspspro

It is true.

airosen

I have absolutely no scientific evidence, but I believe it's true that CO2 will tend to leak slightly faster than regular air, though it shouldn't be an issue if you top off your tires before each ride.

wfrogge

"air" and CO2 will both seep out (CO2 a little faster.. Pump your tires when they get low..... No need to replace anything.

/end thread

Nate552

Or you could air up/check your tires before every ride and not sweat it.

PhilaRider

You can knock CO2, but Ferrari uses it in their F1 tires.
McClaren which (as most race teams) used Nitrogen but was considering CO2 because of a secret communique (part of a big scandal)
Though for bike purposes, CO2 is probably lost. The benefit was F1 tires run cooler on CO2 than Nitrogen.
Anyway if I could do so with no inconvenience, I would run Nitrogen in my bike tires. (larger molecule than plain air which is "mostly" Nitrogen)

DieselDan

It is true and I have somewhat scientific data to support that conculsion. My son did his science fair experiment on ambient air vs CO2 in a bicycle tire. In five days, the CO2 filled tire, starting at 45 psi, was completely flat, while the ambient air filled tire, starting at the same 45 psi, lost 12 psi in the same amount of time. We used a 26" x 1.5" tire with Scharder valves.

Tequila Joe

FACT : CO2 seeps out faster than O2.

127.0.0.1

it's true

for a while, your tires will get soggy in days until you pump them up a few times

127.0.0.1

ftfy

one co2 molecule is larger than an o2 molecule.

air is mostly nitrogen. nitrogen doesn't leak out as much

AEO

Components of dry air (volume)
Nitrogen 78.0842%
Oxygen 20.9463%
Argon 0.9342%
Carbon dioxide 0.0384%
Other 0.0020%

by that logic, I already am pumping a high concentration of N2 into my tyres.

StanSeven

I sometimes wonder if people here have brains. You add air when you tires get low pressure.

travkat

Yes the CO2 leaks out of the inner tubes on bicycle tires relatively faster than air. (especially at higher PSIs). So just top off with your pump before your next ride and you should be fine. All of the chem nuts out there (my wife is a chemist and physicist) no one needs to know the percentage of these molecules in our atmosphere. The OP just wanted to know if the damn tires leak CO2.

AEO

you want to know why CO2 leaks out faster than just regular air?

A: Molecular Diffusion. Carbon dioxide at 0.0384% concentration in air diffuses quicker through the rubber.

rollin

I sometimes wonder if people here read the original post before answering.

monk

I must be losing it . . . when I first read your post I thought you meant that you should "refill" the CO2 cartridge with air . . . It's gettin' late, I guess I should go to bed . . .

DesnaePhoto

This confuses me. CO2 is a much larger molecule than that of Nitrogen or Oxygen. Nitrogen and Oxygen are both diatomic in the air, meaning 2 of each are bonded together. CO2 is larger still. Slight polarity in the bonding.

Diffusion occurs as molecules smaller than the pores in the container (like the inner tube). DieselDan, I'm curious about the procedures used. Did your son use more than one tube to test? Did you reverse the situation (change the control to the variable and vice versa)?

Someone explain the chemistry behind these "Facts", please.

Thanks
David

robdac

My favorite is people who are willing to pay extra to have their car tires filled up with Nitrogen. Having never passed a high school science class they don't understand that they're getting 78% N from the free pump at the gas station.

msincredible

Almost never.

Shimagnolo

I read a news article about some fools at PD that were using taxpayer dollars to fill the patrol cars tires with nitrogen at about $50/tire. Then they were extolling about how it made the cars:

1. Ride smoother.
2. Handle better.
3. Get better gas mileage.

Now to ride smoother, the tire would need to be flexing more. To get getter mileage, the tire would need to flexing less. So which it it???

blacksquid

Whaddya expect? This is BF!

ridethecliche

It's along the lines of what AEO was saying. A bicycle tube is made of porous material. When you have concentration of CO2 inside much greater than it is outside the semi permeable membrane, the CO2 is going to flow down the 'gradient' and out of the tube. The fact that the tube is pressurized adds to this equation.

In a tube filled with dry air, I believe pressure is the main thing causing the 'leak' since the concentration inside and outside are pretty much the same.

bikeride

CO2 is also heavier than air. For you weight weenies out there.

Retro Grouch 

True, but it's one of those problems that solves itself. Assuming that you top up your tires before you ride you don't have to do anything extra.