Re: Can You Get More than 90 PSI from a 12 Gram C02?
David L. Johnson 5 April 2005 09:13:52
On Mon, 04 Apr 2005 21:46:00 -0700, Jay K wrote:
While it is usually accepted that the 12g C02 will only reach 90 psi> regardless if the tube is partially full of air or empty
By whom?
-there are> always a few people on the ride that claim that prefilling the tube> does matter--thus can get to 110psi with a 12g C02. Is there any> truth to this?
Of course there is truth to this. The only way that 90psi would be an upper limit would be if the CO2 were only at 90psi in the cartridge, which is certainly far from the case. The "observation" that a 12g cartridge only fills a tire to 90psi would have to be based on starting from empty. I have, in the past, filled a tire with one cartridge, then started another to top it off, hoping to save the remainder for the next flat. It doesn't usually last, since the release trigger gets pressed by jamming the inflator in my seat bag, but even using 2 12g threadless cartridges is far cheaper than one 16g threaded one.
--
David L. Johnson
__o | And though I have the gift of prophecy, and understand all _`\(,_ | mysteries, and all knowledge; and though I have all faith, so (_)/ (_) | that I could remove mountains, and have not charity, I am nothing. [1 Corinth. 13:2]
Jay K wrote:> When I change a flat I sit the tire with a mini (semi useless)> pump-then take some air out, and finish the job with a C02. I've been> using a 16g C02 instead of the 12g as I want to ride on a little more> than 90 psi. So I put up with the 16g taking up a little more room,> weighing a little more, and most importantly having to control the> tire inflation so it doesn't blow off the rim.
If you have CO2 along why do you bring an extra minipump also? I always set my tire carefully with the CO2, massage it a little and check that it's set properly before I attach the CO2 again and go to full pressure, carefully. It still only takes a few seconds. I use threadless 16g cartridges for this and always reach a pressure above 100 this way.
-- Perre I gave up on SPAM and redirected it to hotmail instead.
David L. Johnson 5 April 2005 20:54:29 [ permanent link ]
On Tue, 05 Apr 2005 12:44:14 +0000, Per Elmsäter wrote:
David L. Johnson wrote:>> but even using 2 12g threadless cartridges is far cheaper than one>> 16g threaded one.>
But not cheaper than one 16g threadless cartridge, I presume.
I donno, but I also don't know whether or not 16g threadless are available. The 12g kind are easily found in any x-mart, since they are used by nasty little boys to shoot cats with b-b guns.
--
David L. Johnson
__o | What is objectionable, and what is dangerous about extremists is _`\(,_ | not that they are extreme, but that they are intolerant. (_)/ (_) | --Robert F. Kennedy
"You're lazy, not to steal the article and paste on the web !" or - "French muscles don't pump like American ones !"
But .....
In a test of 19 pumps, the best pressure achieved, without hernias, was the Topeak Master Blaster DX, giving 8 bars pressure, , and the rest of them reached between 3.5 bars and 7.3 bars, though most were below 5 bars.
Some variance from manufacturers' claims were really large, such as the SKS Matrix Zoom, where the publicity reads 8 bars, and the actual pressure achieved was 4 bars. Even the (above) Topeak is marketed to put 11 bars in your chambers.
From Top Velo, April 2005, pp 97-100. Available from lots of your local (depends on what your locality is) kiosks. -- Bonne route,
"You're lazy, not to steal the article and paste on the web !" or -> "French muscles don't pump like American ones !">
But .....>
In a test of 19 pumps, the best pressure achieved, without hernias, was > the Topeak Master Blaster DX, giving 8 bars pressure, , and the rest of > them reached between 3.5 bars and 7.3 bars, though most were below 5 bars.>
Some variance from manufacturers' claims were really large, such as the > SKS Matrix Zoom, where the publicity reads 8 bars, and the actual > pressure achieved was 4 bars. Even the (above) Topeak is marketed to > put 11 bars in your chambers.>
From Top Velo, April 2005, pp 97-100. Available from lots of your > local (depends on what your locality is) kiosks.
I agree. There are very few good pumps, and the good pump always interfere with my second waterbottle I don't want to give up. So the very few flats I get I fix with CO2. I stored 2 CO2 16 gr cartridges in my saddlebag last season. I never had to use them because I had no flats for 7500 km.
I agree.>> I realize the first replies will be :>> "You're lazy, not to steal the article and paste on the web !" or ->> "French muscles don't pump like American ones !">> But .....>> In a test of 19 pumps, the best pressure achieved, without hernias,>> was the Topeak Master Blaster DX, giving 8 bars pressure, , and the>> rest of them reached between 3.5 bars and 7.3 bars, though most were>> below 5 bars.>> Some variance from manufacturers' claims were really large, such as>> the SKS Matrix Zoom, where the publicity reads 8 bars, and the>> actual pressure achieved was 4 bars. Even the (above) Topeak is>> marketed to put 11 bars in your chambers.>> From Top Velo, April 2005, pp 97-100. Available from lots of your>> local (depends on what your locality is) kiosks.>
I agree. There are very few good pumps, and the good pump always> interfere with my second waterbottle I don't want to give up. So the> very few flats I get I fix with CO2. I stored 2 CO2 16 gr cartridges> in my saddlebag last season. I never had to use them because I had no> flats for 7500 km.
I use a Zefal HPX under the top tube. Doesn't interfere with the second water bottle that way. I get more flats than you. I haven't kept track, but the ones I remember best were the result of bits of glass while commuting in the rain. Seems like I have had a lot of those.
In the interest of answering the OP's question and> assuming that you boys have got this right, now,> this means 6.48 atmospheres (14.7 psi @S.L.)> giving 95.25 psi absolute, right?
the 6.48 was liters of CO2 at 1 atmospheres and room temperature, I think. If one assumes a racing tire of 700ml capacity (0.7 liters, ore a tube about 2cm across and 2 meters long) that would be a pressure of 6.48/0.7 = 9.23 atmospheres, or 136 psi. Assuming I didn't screw up too badly, yeah, that is greater than 90 psi for the purpose of winning bar bets.
On Tue, 05 Apr 2005 12:54:29 -0400, "David L. Johnson" <david.johnson@lehigh-nospam.edu> wrote:
On Tue, 05 Apr 2005 12:44:14 +0000, Per Elmsäter wrote:>
David L. Johnson wrote:>>> but even using 2 12g threadless cartridges is far cheaper than one>>> 16g threaded one.>>
But not cheaper than one 16g threadless cartridge, I presume.>
I donno, but I also don't know whether or not 16g threadless are>available. The 12g kind are easily found in any x-mart, since they are>used by nasty little boys to shoot cats with b-b guns.
Sadly, very few cats around here have bb guns.
-- Typoes are a feature, not a bug. Some gardening required to reply via email. Words processed in a facility that contains nuts.
On Tue, 05 Apr 2005 20:05:11 -0700, Mark Janeba <mandPLEASEmljDONT@comSPAMcast.net> wrote:
jtaylor wrote:>
A racing tube has a volume in the neighbourhood of 700cc.>
So that's where "700C" comes from! (It's a joke, son.)>
After three sloppy tries, I did the calculation carefully and verified >this is a good rough figure for a 700x23 tire; it'll be hard to forget, now!>
Mark
Dear Mark,
The 700 cc volume is a reasonable apporximation and fairly easy to estimate.
Typical rollout figures for 700c x 23 tires are somewhere around 2100 mm, or 210 cm.
A tire with a nominal 23 mm width is probably around 23 mm, but it's reasonable to assume that the sidewall and tube on each side reduce the inner tube's roughly cylindrical diameter to about 1.9-2.1 cm.
For a cylinder, pi x radius x radius x length = volume.
3.141 x 0.95 cm x 0.95 cm x 210 cm = 595 cc
3.141 x 1.00 cm x 1.00 cm x 210 cm = 660 cc
3.141 x 1.05 cm x 1.05 cm x 210 cm = 727 cc
These figures are a little lower than 700 cc's, but the tube isn't a perfect cylinder, particularly where it bulges down down into the well and its deformity is hidden.
Of course, even a tiny increase in width has impressive results because it's squared. If we shave the same 2-4 mm off my nominally 26 mm tires, we get an inner diameter of 2.2-2.4 cm on the same 210 cm cylinder:
3.141 x 1.10 cm x 1.10 cm x 210 cm = 798 cc
3.141 x 1.15 cm x 1.15 cm x 210 cm = 872 cc
3.141 x 1.20 cm x 1.20 cm x 210 cm = 950 cc
At first, you might pity the poor motorcyclist with a flat 4 x 18 rear tire. The inner tube is easily a 4-inch (10 cm) circle and unrolls into a a cylinder about 70 inches (178 cm) long.
3.141 x 5 x 5 x 178 ~ 14,000 cc
But the motorcycle tire's comparatively vast volume only needs to be pumped up to about 2 bar or 30 psi--it takes a long time with a small pump, but this low pressure scarcely resists even the feeblest arm. (Motorcycle trials riders are happy with as little as 4 to 6 soggy psi, not a lot more than a child's balloon.)
Meanwhile, the bicycle tire has to be pumped up to about 6 bar or 90 psi, which is where many miniature telescoping pumps give up the battle after arm-wrestling the rider to a standstill. That's why bicyclists fuss about CO2 cartridges and argue about pumps.
carlfogel@comcast.net wrote:> Dear Mark, [...]> For a cylinder, pi x radius x radius x length = volume.>
3.141 x 0.95 cm x 0.95 cm x 210 cm = 595 cc>
3.141 x 1.00 cm x 1.00 cm x 210 cm = 660 cc>
3.141 x 1.05 cm x 1.05 cm x 210 cm = 727 cc
This is pretty much what I did, but a bit more accurately: Use length of the "cylinder"/tire as circumference of a circle running *through the center* of the tire. I used a wheel "diameter" of 65 cm (radius measured from hub to middle of tire, not to inner face of rim, not to tread of tire).
This follows from Pappus' theorem for volumes of rotated solids, or you can look up the volume for a torus.
David L. Johnson 6 April 2005 09:34:38 [ permanent link ]
On Tue, 05 Apr 2005 22:15:38 -0700, Mark Janeba wrote:
This follows from Pappus' theorem for volumes of rotated solids, or you > can look up the volume for a torus.
Hard to imagine someone quoting Pappus' theorem in a cycling forum. BTW, that says that the volume is the area of the cross section times the distance traveled by the centroid of the cross-section around the axis of revolution.
--
David L. Johnson
__o | Let's not escape into mathematics. Let's stay with reality. -- _`\(,_ | Michael Crichton (_)/ (_) |
On Tue, 05 Apr 2005 22:15:38 -0700, Mark Janeba <mandPLEASEmljDONT@comSPAMcast.net> wrote:
carlfogel@comcast.net wrote:>> Dear Mark,>[...]>> For a cylinder, pi x radius x radius x length = volume.>>
3.141 x 0.95 cm x 0.95 cm x 210 cm = 595 cc>>
3.141 x 1.00 cm x 1.00 cm x 210 cm = 660 cc>>
3.141 x 1.05 cm x 1.05 cm x 210 cm = 727 cc>
This is pretty much what I did, but a bit more accurately: Use length >of the "cylinder"/tire as circumference of a circle running *through the >center* of the tire. I used a wheel "diameter" of 65 cm (radius >measured from hub to middle of tire, not to inner face of rim, not to >tread of tire).>
This follows from Pappus' theorem for volumes of rotated solids, or you >can look up the volume for a torus.>
Mark
Dear Mark,
Bet they don't include the volume of the Presta valve!
I have a Topeak Mountain Morph for my road bike, and it gets the full > 120psi with a bit of labor. I would never even try a full frame pump, > because I'm way too weak to not use a mini floor pump.>
Clearly a case of American muscle and suspect French testing by an unknown mag. -- Bonne route,
Squid-in-Training Phil 6 April 2005 17:36:06 [ permanent link ]
Sandy wrote:> "Phil, Squid-in-Training" <phil_leeIHEARTBASHGUARDS@hotmail.com> a> écrit dans le message de :> news:SWL4e.4046$Kr2.1496@fe07.usenetserver.com...>
I have a Topeak Mountain Morph for my road bike, and it gets the full>> 120psi with a bit of labor. I would never even try a full frame>> pump, because I'm way too weak to not use a mini floor pump.>>
Clearly a case of American muscle and suspect French testing by an> unknown mag.
With its onboard 4" air hose, I don't even have a chance to snap off my valve locknut, whereas the locknut would snap itself off before I even attempted to pump if I tried to use a frame pump. -- Phil, Squid-in-Training
David L. Johnson wrote:> On Tue, 05 Apr 2005 21:06:11 -0700, Jay K wrote:>
90 psi info comes from packaging that cartridges comes from. I've>> gotten the cheep 12g paintball catridges before--only trouble is that>> C02 inflator for threadless takes up more room than inflator for>> threaded cartridges.>
?? Put cartridge inside threadless inflator, but don't tighten it.> Then the volume is nearly identical to a loose cartridge + threaded> inflator.
Better still. Put cartridge inside threadless inflator backwards and tighten. This will not puncture the cartridge. My 16 g threadless inflator fits very nicely at the side of a water bottle. I carry a couple of spares in my saddle bag. This allows for three flats and so far I've never had more than one on the same ride
-- Perre I gave up on SPAM and redirected it to hotmail instead.
I use 12 gram non-threaded cheap CO2 on both mountain and road. I also have a combination mini-pump and CO2 inflator which works great because I seat beads with manual pump, safely and then hit it with CO2. It beats any frame pump in speed and inflation pressure.
On 700c 23's, I put about 15 PSI with the pump, then dump a 12 gram in for 120+ PSI. I don't have any leaks from either the inflator or chuck.
On the mountain bike, I get well over 65 PSI. Its not free air but its a time saver. Buying them in bulk and not at the bike store makes a BIG difference at only $0.38 each.
carlfogel@comcast.net Wrote: > On Tue, 05 Apr 2005 22:15:38 -0700, Mark Janeba> <mandPLEASEmljDONT@comSPAMcast.net> wrote:>
carlfogel@comcast.net wrote:> >> Dear Mark,> >[...]> >> For a cylinder, pi x radius x radius x length = volume.> >>
3.141 x 0.95 cm x 0.95 cm x 210 cm = 595 cc> >>
3.141 x 1.00 cm x 1.00 cm x 210 cm = 660 cc> >>
3.141 x 1.05 cm x 1.05 cm x 210 cm = 727 cc> >
This is pretty much what I did, but a bit more accurately: Use> length> >of the "cylinder"/tire as circumference of a circle running> *through the> >center* of the tire. I used a wheel "diameter" of 65 cm (radius> >measured from hub to middle of tire, not to inner face of rim, not> to> >tread of tire).> >
This follows from Pappus' theorem for volumes of rotated solids, or> you> >can look up the volume for a torus.> >
Mark>
Dear Mark,>
Bet they don't include the volume of the Presta valve!>
Carl Fogel This is why it is so critical to know in advance whether you are going
to be using a 36mm or 60mm valvestem length when selecting the appropriate CO2 cartridge size. LOL
