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I have a road bike (Cannondale Synapse Alloy 6). I bought it this past March. In addition, I purchased an inflator. It came with, I presume, a 16g cartridge. I haven't had the need to use this yet. I understand that one of these can put 130lb of pressure in a 27" tire. My tires are designed to hold 105-110lb. I don't want to overinflate my tire. How do I know when I've put 110lb of air in my tire? With my floor pump, this is no problem. I set the pump to 110 and I can't put more in when I reach this amount. I don't want to blow my tire out with one of these cartridges.

Thanks for your help.

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  • Remember that the width of the tire has more effect on the total volume than the wheel diameter. (Unfortunately, I can't find a table anywhere of tire size vs pressure for CO2 inflators, but there must be one somewhere on the net.) – Daniel R Hicks May 27 '12 at 20:15
  • (And keep in mind that CO2 is heavier than air and will make you ride slower. ;)) – Daniel R Hicks May 27 '12 at 20:15
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    @DanielRHicks - I wish I was a good enough rider to be concerned about the difference in weight between the two. – Randy Minder May 27 '12 at 20:17
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    Related: bicycles.stackexchange.com/q/4858/1584 – Daniel R Hicks May 27 '12 at 20:20
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    With these cartridges, care must be taken to assure the tire is fully seated in the rim, otherwise the sudden inflation might cause the tube to snap out and blow off. – heltonbiker May 28 '12 at 0:25
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These cartridges are intended to inflate a tire in an emergency situation, like during a race, or for example during a ride on the country-side, far away from gas stations ;o)

(or, by the way, just to save your arm muscles from inflating a skinny tire up to a very high pressure)

When they say "up to 130 PSI", I think the manufacturers want the potential customers to be sure that the product actually might achieve 130 PSI if needed. For, say, 700x20 tires (very skinny ones), that would be a very reasonable pressure.

To use the cartridge, it must be attached to an inflator, which allows you to control how much pressure you desire. The key issue is: since there is not a pressure gauge, the only way to know the right point is to know beforehand what the right pressure "feels like" with your current tire, and then trying to replicate that after you fix the tire, for example:

  • Thumb-checking the tire so that it is "hard enough";
  • Grabbing the seat or the handlebars and hitting the wheel against the floor so that it is "hard enough";
  • Riding the bike while looking at the bulge around the ground-contact area, so that it "looks right";
  • Riding the bike while hitting small irregularities on the ground, so that it "feels right".

(unfortunately the gauge from my floor pump broke, and I am becoming expert on "sensitive" tire inflation methods :o(

As a bottom line, if your tire is designed for 110 PSI max., that doesn't mean (at all!) that it will instantly explode as soon as it reaches anything beyond that pressure, because that is the maximum pressure recommended to BE RIDDEN. If you get, say, 130 PSI with the cartridge, you'll probably feel it is too much, so you can deflate it a bit before riding. In the end, between too hard and too soft, there is a lot of room for personal taste, specially if you just want to go on riding, after a flat.

Just as an example: I had (have?) a lot of friends who ride mountain bikes with knobby tires up to 80 PSI (it's crazy, I know), just because the bike "rides much better on asphalt". So far, no explosion happened (except one with a very low quality tire targeted at 40 PSI max... The girl literally hugged the road, but she was ok...)

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This chart gives some reasonable details about inflation pressure vs tire size. For most adult bike tires the 16g cartridge will produce a pressure that's within the sidewall limit.

enter image description here

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  • Thank you. I've seen this chart. However, that wasn't really my question. I know how much air my tire takes, and I know how much air a 16g cartridge can put into a tire. My question was this. Since the cartridge can put in more air than my tire can hold, how do I avoid over-filling? – Randy Minder May 27 '12 at 20:47
  • If you have a good quality 27x7/8" tire (roughly the same as 700C-23) it should have a sidewall rating approaching 130PSI. What size tire do you have? – Daniel R Hicks May 27 '12 at 20:59
  • Max pressure for my tire, according to what's printed on my tire, is 115psi. – Randy Minder May 27 '12 at 21:04
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    BUT WHAT SIZE IS YOUR TIRE??? What numbers are printed on the sidewall? – Daniel R Hicks May 27 '12 at 21:32
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    Regardless of tire size, if the tire inflates beyond its max pressure, you need a more controllable way of filling it. Good Co2 inflators do not just inject the full contents of a cartridge, but rather have a valve release. The Lezyzne inflators are a good example of that. – zenbike May 29 '12 at 11:02
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Using a CO2 inflator is all about technique.

On the road, I have a 700x23 tire that wants ~100 - 115 psi; and a CO2 inflator with a 16g cartridge.

  1. Have a flat in the middle of nowhere.
  2. Patch the tube or replace with a spare and re-situate the tube and tire back onto the wheel.
  3. Attach CO2 inflator to the valve.

----Here's where the technique comes in----

  1. Don't just press the lever on the inflator and hold! You can easily explode the tube and have to start over (or find an alternative way home). Give the lever one short press, which should inflate the tube 2/3 - 3/4 full. Compare flat tire to un-flat tire by feel and make sure that it's seated properly. Give the inflator lever another quick press. Compare tires again. You may be good to go here, but sometimes it may take one more light shot of CO2. The actual pressure in the tire is good enough to get home or to a proper pump.

  2. Put the wheel back on and ride.

Note: I blew up one or two tubes back in the day before I figured out the technique.

Tip - To develop "feel" for tire pressure - Squeeze the tires before and after inflating to a known pressure. That way, you'll learn what the right pressure "feels" like.

Example of an old, well used, inflator that's been in a seat bag or jersey pocket for roughly 10 years (Notice the energy gel that is now permanently bonded to the inflator)... More modern ones can feature pressure indicators...

CO2 inflator

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I have used a CO2 inflator for almost 5 years. On average I use mine around 2 to 3 times a year not only to pump my tires when I have a flat while riding solo but also those of my friends when they suffer flats on group rides.

I have had no incident of the tire exploding and I don't even check what pressure the tire got to after inflating it with the CO2 inflator. What experience has shown me is you just pump your tire (700 x 23 or 25) and the pump will auto stop outputting CO2 when it reaches approximately 100 psi.

One cartridge if you are careful is good for inflating two 700 x 23c tires (or being used twice). I use a spring loaded Genuine Innovations Inflator which you just press a bit hard to engage.

Finally one should remember the CO2 seeps out of the inner tube faster than air so one should replace the CO2 with air after arriving home or at the shop.

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There's no fundamental difference between using a CO2 and using an old/portable hand pump - you guess. The major difference, obviously, is that the CO2 cartridge inflates the tyre much, much quicker, so you can get from 0 to 80/100 in a fraction of a second rather than after many, many hand pumps.

But the checking is the same - how hard is the tyre when pinched between your fingers and does it bounce 'properly' when dropped?

Unless you were really unlucky, you still have another tyre to use as a control and to compare the relative pressures (you'll be running the two tyres at roughly the same pressures, I assume, and the tyres themselves will be similar, probably the same model of similar age and wear).

The CO2 is only designed as a stopgap until you get to a proper shop with a track pump, so underinflate if you're concerned - enough to make sure that your rims will be protected!

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