Jim’s Tech Talk
By Jim Langley
Early this week I answered a question from a roadie wondering about the tire inflation capacity of his and his friend’s CO2 inflators. Since I only rarely use them, I’m hoping you CO2 aficionados will read the question and my answer and weigh in with your advice. Please share your favorite CO2 inflator, too.
If you don’t know what a CO2 inflator is and want to learn about them, here’s a video from Genuine Innovations, longtime makers of these tiny inflators so that you can watch one in action.
As you can see in the vid, these CO2s are mighty minis that air up tires extremely fast. That’s why CO2 pumps are so popular. They fit in a pocket or pack for quick access and the compressed gas blows tires up in seconds (no pumping required) – and may even be able to inflate to higher pressures than some mechanical pumps.
Here’s a link to the Genuine Innovations Microflate Nano to learn more about it ($22.29): https://www.genuineinnovations.com/collections/bicycle-co2-tire-inflators/products/microflate-nano-co2-bike-tire-inflator. Many other companies make these inflators, too.
The main knock against these inflators is that you need to buy the cartridges
“Mark’s” question
While on a group training ride today I ran into a friend. He was on a solo ride at our furthest point from home. He had just repaired a flat on his new Canyon Ultimate CFR with DT Swiss PRC 1100 Dicut Mon Chasseral rims and Schwalbe Pro One TT 28mm tires.
Our training ride started up again and my friend set course for home.
Later when I called him he said that on the way home his bike felt odd. He said he looked down and the rear wheel appeared to be out of true. Stopping to examine it he found the tire hadn’t seated fully after reinflating the tire with a 16g CO2 cartridge.
That reminded me that two weeks ago I flatted after hitting glass. I attached my CO2 cartridge (also 16g) cleanly, held it on until the pressure equalized, and removed it cleanly. After getting home I checked the pressure and found only 60 lb in my 700 x 28mm tires. I pumped them up and they’ve held for the past two weeks with an acceptable level of normal pressure drop, so the cartridge only had the capacity to inflate my tires to 60 lb.
My friend also used a 16g CO2 cartridge.
So my questions for you are:
- Is it possible that the volume of 28mm tires is too great to fill them to 85-plus pounds with a 16g cartridge reliably?
- If a 16g CO2 cartridge can’t adequately inflate a 28mm tire, is it possible it can’t generate the pressure to seat certain tire/wheel combinations?
- Should people running 28mm tires start carrying 20g Co2 cartridges?
Thanks Jim!”
My answer
I had to do a little digging trying to find a good answer to these questions. Unfortunately, I couldn’t find anything super specific or helpful. But as far as I can tell, 16g cartridges are supposed to be able to inflate tires to 88psi – see Genuine’s inflation chart:
So, if that’s true, I think your friend’s tire seating problem may have been an installation issue or a tight tire situation. So many tire companies now are undersizing tires making them way more seat-resistant, especially with tubeless-ready tires. So, my best guess is that it wasn’t so much not enough air pressure and probably just a part of the tire stuck and refusing to pop up and seat.
With your under-inflated tire and maybe with the tire that wouldn’t seat if it too was soft and not fully pumped up, the other wildcards are the CO2 cartridges and the use of them. I don’t know if all cartridges are made the same. Maybe some aren’t as full as others? Or maybe some don’t release the air as quickly and fully as others?
And, I think we’ve all had times when CO2 pumps didn’t seal that well and we lost some pressure or the valve might have had issues like unscrewing the valve core a little when we removed a screw-on CO2 inflator or lost air removing a press-fit one.
Those are my best guesses as to what might be going on. And, since it happened, I don’t see anything wrong with carrying the next larger CO2 cartridge just for a little insurance. But you’ll want to have an inflator with a shut off valve so you don’t over inflate by mistake.
Especially with wide rubber like anything over 32mm, over inflating can result in a scary explosion if you blow the tire off the rim. I speak from experience: https://www.roadbikerider.com/overinflation-explosion-a-cautionary-tale-about-very-wide-tires/.
Your turn
Okay readers, please leave a comment with your best answers and advice for CO2 inflators and their use. Especially useful would be your favorite inflators (brands and models) and replacement cartridges. Thank you!
Jim Langley is RBR’s Technical Editor. A pro mechanic & cycling writer for more than 40 years, he’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Tune in to Jim’s popular YouTube channel for wheel building & bike repair how-to’s. Jim’s also known for his cycling streak that ended in February 2022 with a total of 10,269 consecutive daily rides (28 years, 1 month and 11 days of never missing a ride). Click to read Jim’s full bio.
I have never had a problem using CO2 cartridges. If you allow just a little in and then check the tire to insure that it’s seated properly (tube not pinched, etc.) then finish filling there is no problem. Just remember that CO2 is less dense than O2 and will leak through the tube so you need to drain the tire when you get home and refill with your pump. I consider CO2 as a convenient finish the ride and get home safe choice.
As for the chart used in the answer, it’s largely useless for the upper listed categories. What is a road tire? Is it 23c, 25c, 28c, etc.? A 16g cartridge will fill each to different PSI’s. Why do most companies do this.
I totally agree with Michael. I, too, have long used CO2 cartridges (the Microflate Nano is easy to use and as small a Chuck as you’ll find). It’s to be expected, as he pointed out, that a CO2-inflated tire will not hold its pressure for more than a few hours. You’ll always have to reinflate at home.
I likewise agree with Jim that Mark’s friend likely did not adequately seat the tire. I doubt it was the CO2 at issue.
Finally, one last thing to keep in mind. I also aim for 80-85 psi inflation. But Jan Heine on his Rene Herse site (he’s been a leading advocate for lower pressures for years) has a nice feature that shows most of us still likely overinflate. https://www.renehersecycles.com/tire-pressure-calculator/ So that 65 psi Mark had when he got home after using his own CO2 was also probably just fine. He might even have had a more comfortable homeward ride!
I have two, though one, the Dynaplug “Air Tubeless Repair Kit” (for road), is not technically an inflator as much as it is designed to plug punctures. I use it exclusively on one of my road bikes that is running tubeless, and it works like a charm. I’ve never had a big enough puncture such that I drain the entire CO2 cartridge into the titre. That being said, it will inflate a 25mm tire (and bigger, so I’ve been told) to 80PSI, no problem. The other one, is a dedicated CO2 inflater. It’s made by Lezyne, the “Trigger Speed Drive” works the same as the one in your video, and works well. It’s small enough that it fits in the little pouch that the Dynaplug kits comes with.
Concerning Mark’s question: If he is using 28mm tires, it could very well be a 16g cartridge is not enough. I use 16g cartridges, but I have only used them on 23 and 25mm tires with no inflation issues. CO2 leaks through rubber faster than regular air. I remember reading somewhere that if you happen to flat early in your ride and you are on a long ride that will take hours to complete, you should let out the CO2 and refill with regular air if you happen to find a bike shop along the way. That way you don’t have to worry about air pressure dropping during your ride.
I use a Genuine Innovations Airchuck and never had an issue with it. Very small chuck that you just press on. I always wrap my glove around the cartridge so I don’t get frostbite. Cartridge brand I don’t pay attention to, main thing to look out for is if it is threaded/non-threaded and grams.
Sadly, the most common issue I have seen with CO2 inflators on the road or trail is not the size/number of CO2 cartridge(s) but simply improper device use. To many riders- properly seating & deploying the inflator’s head on the valve stem can be trickier than it looks….especially when stuck on the side of the road/trail some miles from home. If I had a dime for every rider I’ve seen freeze the fingers while hissing away half their only CO2 cartridge I’d have a new set of Zipp 404’s on my ride.
Always a good idea to try out a new CO2 inflator (or any ’emergency’ repair procedure) at home BEFORE you really need it.
Agree with the comments above. I’ve used multiple CO2 inflators (different brands) over the years and never had a problem. For reference, I use 16g cartridges on my 25C road tires, which gets me around 90 PSI. On my old mountain bike, I used 20g cartridges on 26 x 2.2″ tires (new bike is tubeless). So Mark’s 28’s might need a 20g cartridge to reach a rideable pressure. Most of the issues I have seen people have with CO2 inflators is not knowing how to use them, not an issue with inflator itself. And the CO2 will definitely leak through the tube quicker than air; I’ve often woke up the next morning having another “flat” if I forgot to replace the CO2 with air. Never had the pressure go low during a ride after inflating with CO2, but I guess that’s a possibility on a longer ride.
Make sure you inflate the tube enough to hold it’s shape by blowing into it before stuffing in the tire, a little too much is better than not enough, and be careful to check the tube is seated in the tire properly without twisting or bulging it.
Try not to deform the tire/tube combo once you’re ready to inflate as it should fit naturally in the rim, and use a threaded stem with a nut (just lightly finger tight) to keep the stem from deforming the tube when you press and hold the inflator on.
I’m quite happy with Genuine Innovations chucks and the similar Silca, but I prefer the GI nano as it has no moving parts to go wrong and is smaller. I dislike anything fancier/more complex/bulky.
Remember that you still should carry a pump in case you run out of cartridges. Also, you cannot fly with cartridges, neither in your checked or carry-on bags, so if you are flying somewhere with your bike, you will need a plan to buy some cartridges at your destination or just you your pump.
The above comments are all spot-on. The tendency with CO2 cartridges is to inflate too fast. You need a CO2 device that allows for partial inflation to seat and then open it up to balance the pressure. If inflated too fast it is possible that the tire bead may not seat (in my head I see the tube a little wrinkled inside the tire and causing uneven inflation, which could cause a part of the bead to improperly seat – but what do I know?).
That said, there is another thing that is off here: A 28mm tire on 700 rims with a 21mm inside width should be inflated to about 65 psi. 80 is too much. Admittedly this is dependent upon the rider weight but even a 200-lbs rider still should only inflate to about 70psi. So if the CO2 is inflating to more than 60-psi then you should be good to go.
One other interesting thing about CO2: it is soluble in butyl. Therefor, you will find that a CO2 cartridge inflation will lose pressure noticeably faster than a standard air inflation. If I get a flat on a ride I will generally deflate the tire when home and re-inflate with the floor pump.
1. For 23mm tires, I use 12g unthreaded cartridges by the case of 25 from Walmart, the same cartidges they use in pellet guns. They are only about 50 cents each. I have an un-threaded inflator.
2. Always carry a spare cartridge.
I’ll have to give CO2 cartridges a try again. I gave up on them when trying them out because I kept breaking off the stems of my tubes in the inflator. And since it’s a good idea to keep a pump as a backup, I’ve always just carried the pump and skipped the CO2.
I run with a Topeak Road Mini Morph pump, in a mount that places it alongside a water bottle (said mount I’m having trouble finding again, sigh). The foldout foot pedal makes inflation really easy, and I like the in-line pressure gauge.
Practice at home. I have several different brands of inflators and they each work a little differently. Protect your hand from freezing as you use the cartridge. Finally, don’t use them in a hard rain – I did and instantly it sealed the valve and inflator in ice and froze them together. I had to carefully crack the inflator off the valve. I always carry a pump, and usually carry a CO2. A valve core tightening tool is handy too.
Ditto on above comments about misuse, reinflation at home with air, extra cartridge and/or pump, and protecting hands from cold cartridge.
Personally I prefer pressures at lower end of range. Some tires have questionably high recommended pressures.
I’m an old school inner tube kinda guy. I like to talc tubes for easier installation and smoother interface to tire. And as I initially inflate the tube, I deflate slightly to equalize tube distribution through the tires (no crinkles or wrinkles), then continue to full inflation.
I have been using CO2 to inflate tires after a puncture for years. I use an inflator made by Zefal, called the EZ Control. It allows me to partially inflate the tube to verify that the tire i seated on the rim properly, and inflate my 700×25 tire to approximately 95 psi. I like this inflator because it allows me to regulate the flow of the CO2 into the tube, and it screws onto the Presta valve so there is no leakage. It’s important to put the valve at the 12 o’clock position so that only gaseous CO2 flows into the tube, not any liquid. Liquid C”O2 is so cold that it can cause the tube to be embrittled, and fail immediately. I’ve tried many different inflators and for me, this is the best.
Excellent reminder about cartridge position with CO2 inflators, Fritz!
Just a few months ago I was on a ride where a 1st time CO2 user froze & split his tube by ejecting liquid CO2 into it. Gave the experienced riders a good laugh. Fortunately, some one donated him another tube (& CO2) to continue the ride.
Beware that CO2 is soluble in rubber and therefore leaks through rubber much faster than air. When I get home after a ride where I used CO2 to fix a flat, I deflate the tire and pump it up with the floor pump or air compressor.
I haven’t carried a pump in over 10 years, & I don’t see one anywhere in my future either. I carry a Genuine Innovations Ultraflate. It has never failed me or given me any problems at all. I also carry3 16G cartridges in case of flats on both tires, (that’s happened to me) or if someone I’m riding with needs help. When thhey 1st came out I tried some of the very small ones with the head only. They didn’t work well for me, so I bit the bullet & got an Ultraflate. There’s no going back. I run 28mm tires & 1 16G is enough to fill a tire. When I get home I let the CO2 out & refill the tire with air via a floor pump because it’s been my experience when filled with CO2 the tires lose pressure overnight.
I have used co2 inflators for several years, mostly trouble free. On one roadside flat,the bead blew off while inflating. I probably didn’t have the bead set right,but with the inflator that I was using was difficult to control how much air was going,just a sudden rush of air. I now use a Pro bike tool inflator which has a valve on it’s side,making easy to control the flow of air. Now I start slowly inflating,while beading the tire by hand. Super easy!
I carried a CO2 cartridge (don’t remember the size or brand) for several seasons and when I needed it (several miles from anywhere and before mobil phones) it was dead.
Thanks for all the great tips everyone – very helpful!
Jim
I’ve already commented, and there’s something related that’s on my mind. When I see quotes like a 16G co2 cartridge fills my 28mm tires to 60 psi. My inflator with 20G fills my 28 mm tire to 110 psi. My question is: How do you know that? Do you carry a gauge with you? If you wait until you get home it’s likely that some of the CO2 will have leaked out. I was driving sag on a ride & stopped to help somebody fix a flat. I had my floor pump & the guy asked me if the gauge on my Zefal was accurate. My knee jerk reaction was to say yes, but how do I know how accurate it is? Same goes for any pump, floor pump, mini pump, full size frame pump…you name it. Just how do you know the pump is accurate? I use the gauge on my floor pump when I’m home, but when I’m on the road I use my digital gauge, which consists of my thumb & the first 2 fingers of my hand. So far, in 58 years of riding 170,000 miles, it’s worked pretty good.
I just went out and did a test to see what a few cartridges inflate to. My first point: inflation is imprecise (it is not unusual to lose a little CO2 around the valve & leave some in the cartridge) so as you point out – don’t expect this to be a science.
On my road 23s I used a 12g cartridge to inflate to about 100psi. On a 25 this inflates to 80psi. 28s get to 65psi (all slightly soft). My gravel 38s need the 16g to get to 60psi.
All this means is that for a road tire one should carry a 16g cartridge because the 12g seems to leave the tire a little on the soft side. There is no room for error or loss due to poor valve connection. On the gravel bike I would also up-size to the 25g
Been running 28c tire for the last 6 years on the road. Using 21, 23 and 25mm internal width rims.
Each time I repaired a puncture, I measured the pressure back home..always around 60psi. My thinking was this low pressure was caused by the solubility of CO2 in butyl, like some mentionned above. And that the pressure dropped during the completion of the ride.
Today, I tested in a more controled environment and measured right after inflating. Results: 60 psi on 28c and 25mm rim width. Measured with a digital gage and with my floor pump. Minimal leak during inflation.
Although 60psi can bring me home, the combo of tire / rim I am running fully seats at 70-85 psi (last “pop”). I can then defalte to desired pressure 72 psi (front) and 78 psi (rear).
So moving on, I will be carrying 20g CO2, knowing that I am not the only one not acheiving the 80+psi on 28c advestised on various manufacturer charts.
I use this Portland Design inflator because CO2 flow can be controlled. I’ve found it more foolproof to slowly increase the flow versus opening the flood gates with other inflators I’ve used.
https://www.amazon.com/s?k=portland+design+works+shiny+object+co2+inflator&crid=1IZAWV2QFVQ3D&sprefix=portland+co2+inflator%2Caps%2C159&ref=nb_sb_ss_pltr-ranker-24hours_1_21
I use a Silca EOLO III CO2 regulator. It is small enough to loosely screw onto a CO2 cartridge (I use whatever cartridges my LBS has in stock), and have the cartridge and CO2 regulator fit in the Specialized tool KEG that is use in lieu of a saddle bag or jersey pockets.
I particularly like the light spring action of the EOLO III to control the flow of CO2, from no flow at all to a full blast capable of seating tubeless-ready tires.
When I am ready to inflate a tire, I squirt water around the rim / tire bead junction where I unseated the tire. The lubrication provided by the water helps the tire bed seat properly when I fill the tube with the CO2.
Since 12g cartridges are a lot cheaper than 16g ones (can be purchased in bulk), why not carry 2 or use your pump to inflate part way?
I’ve had a lot of success with CO2. I carry a small pump and use it just enough to make sure the tire is seated correctly and then use my CO2 cartridge with an adapter that allows for controlling the air flow to slowly inflate the tire. If you are buying your cartridges from a bike shop, you are probably overpaying. You can buy them for about 1/3 the price from places like gas-depot.com. I usually buy a box of 30 and sell a few to my riding friends.
CO2 cartridge tip is to buy 12g air gun cartridges. They are much cheaper than 26g cartridges from the bike shop.
I just 12g cartridges for my road bike with 32mm tires. That’s plenty of “air” to finish a road ride. On the MTB I would use two 12g or one cartridge and top off with a pump.
Two comments:
1: I ride 28 mm tires and am well-experienced in the proper use of CO2 inflators. Yet, I had a tire that would not seat correctly after a flat even with a 20g cartridge. I had to ride a wobbly tire home. I used a floor pump to over-inflate the tire and still it would not seat. It was NOT a new tire; it was well broken in. I tried rotating the tire on the rim; didn’t help. I tried soaping the bead; didn’t work. I never did get it to seat correctly again and had to replace the tire.
2: A 20g cartridge will fill a 28 mm tire to a rideable pressure, but still not as much as I prefer. After fruitless attempts to top off the pressure with a mini-pump, I now use this process: I PRE-INFLATE the tire with my mini-pump, then use the CO2 inflator to top it off. Works great!
Another solution in search of a problem. Since a pump is needed anyway, just go with the pump
I’ve used GI ultraflate for years. Never had a pinch. And always seated because I can control air flow. As soon as you can though deflate tire and pump regular air. CO2 is much thinner and leaks through tire quicker
As an anesthesiologist, I understand that CO2 gas rapidly diffuses across mucous membranes in the body. This is why CO2 gas is used for laproscopic surgical procedures. Any CO2 gas that collects during surgery rapidly diffuses into the bloodstream and is expelled in each breath.
Similarly, CO2 gas rapidly diffuses across the walls of inner tubes an bicycle tires. Therefore, the pressure inside the tire rapidly decreases over 12 hours. Once I return home from a ride where I use CO2 to reinflate the tire, I drain the tire of CO2 and reinflate with air..