Somebody check my logic please!

[BaltimoreGS]

Math was never my best subject so I don't know about calculating volume, pressure etc. so somebody please tell me if my logic is sound.

Short background:  Taking a long trip this week.  I made up a nice tool kit recently with some input from you guys (thanks Jared!) for emergency use.  I have a plug kit in their but no air source. 

The question:  I picked up a CO2 powered bicycle pump today.  As a test I tried one CO2 cartridge out on a car tire (old Toyota 13 incher if that matters).  The tire started at 36 PSI and the C02 cartridge brought it up to 40psi before it was exhausted, a 4 PSI increase.  So by my crude logic I'm guessing that I should carry nine CO2 cartridges in my emergency tool kit.  That sound right??

Thanks for any input!

-Jessie

[cboling]

Something to keep in mind. CO2 expands under heat. Be careful carrying those around with you near a hot surface or if you plan on leaving them in the Sun for very long. They can explode / pop.

[dread_au]

I would say your maths is wrong. In the tyre kits you buy you only need 1 or 2 to inflate a motorcycle tyre. You should of tried to inflate a deflated tyre. It might Have been more accurate. Better yet deflate a bike tyre

[dohabee]

I think a car tire has alot more internal volume than a motorcycle tire. If 1 cartridge increased your car tire by 4psi it might increase a motorcycle tire by 10psi (just guessing)

If you want to be sure then let all the air out of your back tire and see how many cartridges it takes to fill it up.

I'm guessing that it will take at least 2 but less than 9

[Alphamazing]

So, it's pretty safe to assume that the car tire has a lot more volume within the tire. Therefore, it takes a lot more air (from inside the CO2 canister) to increase the pressure.

As an extreme example...

Take a very very very large balloon, we're talkin' hot-air baloon sized. Now if you put one CO2 canister of air into it it does pretty much nothing. Now, if you take that same CO2 canister and fill a regular size balloon, the size increases dramatically.

Same thing with tires. Car tires can hold more air, and therefore it takes more air to increase the pressure.

That's a pretty crappy explanation, but I'm tired. If you want a better one let me know.

[kml.krk]

first of all: how did you come to conclusion of 9 cartridges?? by multiplying 4*9=36?? 
if so then that's very weird because as you mentioned the car tire is only 13 inches in diameter and moto tire is 17 inches. to make it really precise you would also have to measure the width of a car tire to find how many cubic inches or cubic centimeters of air it holds. then compare it to the volume of air moto tire can hold, but then compression also kicks in and those numbers change dramatically and therefore things get complicated. in other words math is quite useless here or just too complicated to even waste time trying to figure out how to calculate that.

anyways, you will be much better of if you just deflate your moto tire and see how many cartridges it will take to bring it back to 35psi
cheers

[KasbeKZ]

ever notice how when filling a tire, the pressure starts to increase more and more slowly as it gets higher.... i'm pretty sure one cartrige maybe two would have been enough to get that tire from flat to driveable

[qwertydude]

Or better yet scrap that co2 inflator and get a small 12v air compressor. One of the guys I ride with actually has one that's been stripped of it's bulky plastic case and it's really compact. Just a small motor, pump and hose not much bigger than your fist.

[BaltimoreGS]

first of all: how did you come to conclusion of 9 cartridges?? by multiplying 4*9=36?? 
if so then that's very weird because as you mentioned the car tire is only 13 inches in diameter and moto tire is 17 inches. to make it really precise you would also have to measure the width of a car tire to find how many cubic inches or cubic centimeters of air it holds. then compare it to the volume of air moto tire can hold, but then compression also kicks in and those numbers change dramatically and therefore things get complicated. in other words math is quite useless here or just too complicated to even waste time trying to figure out how to calculate that.

anyways, you will be much better of if you just deflate your moto tire and see how many cartridges it will take to bring it back to 35psi
cheers

Like I said, my math skills are weak      Thanks for your input though.  I was trying to avoid wasting cartridges but that will probably be the best route to find an answer.  I had looked at electric pumps but the battery on the SV is not easily accessible like it is on the GS and I don't feel like running extra wires.  Thanks again all!

-Jessie

[bassmechanicsz]

I would say without going into all the calculations you would be safe carrying 3 or 4 cartridges and even if it doesn't get you up to the full 35 psi which i am predicting it probably would you will atleast have enough tire pressure to ride it safely to a gas station with air for the tires.

[kml.krk]

I would say without going into all the calculations you would be safe carrying 3 or 4 cartridges and even if it doesn't get you up to the full 35 psi which i am predicting it probably would you will atleast have enough tire pressure to ride it safely to a gas station with air for the tires.

big +1

[BaltimoreGS]

Something to keep in mind. CO2 expands under heat. Be careful carrying those around with you near a hot surface or if you plan on leaving them in the Sun for very long. They can explode / pop.

Never thought about that, would you be concerned with indirect sun light like being left inside a saddle bag?

-Jessie

[jp]

I found this site to use for reference.

http://www.genuineinnovations.com/co2-refills/45-gram-threaded-cartridges-box-of-2.html

For what it's worth, I vote for getting a small 12V pump. Yeah, it'd be a PITA to get to the battery to use it, but if you need it you've already got a flat, which is an even bigger PITA.

[08GSSteve]

keep in mind these CO2 and nitrogen canisters are for emergency use only so pressure is not critical to the exact PSI.  12psi will get you to next servo no worries at all.

If you want to carry these then fine but ignore all the maths and do it the trial and error way and fill your tyre from flat.

OR

+1 jp

buy a cheap air compressor that has a pressure guage and runs off your battery.  They are small compact and CHEAP these days and no problems with possible explosions from over heated CO2 or nitrogen canisters.


Regardless of what you do make sure to post pix of trip.  Have fun

[BaltimoreGS]

keep in mind these CO2 and nitrogen canisters are for emergency use only so pressure is not critical to the exact PSI.  12psi will get you to next servo no worries at all.

If you want to carry these then fine but ignore all the maths and do it the trial and error way and fill your tyre from flat.

OR

+1 jp

buy a cheap air compressor that has a pressure guage and runs off your battery.  They are small compact and CHEAP these days and no problems with possible explosions from over heated CO2 or nitrogen canisters.


Regardless of what you do make sure to post pix of trip.  Have fun

Thanks, I'm looking forward to seeing more of West Virginia. 

Ever get excited for the wrong reasons??  Kay had a screw in her tire so I thought I'd have a chance to try out the CO2 inflator.  Unfortunately (fortunately) the screw didn't go all the way through so I didn't get my chance.  Though she's glad not to have to buy a new tire     Later

-Jessie