People say that the pin must be pressed down in order for the air to get in. But when I try to remove the pump head by unlocking the lever, too much air leaks before I get to remove the pump.
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1Yes, the valve core's pin should be pressed in by the head during the inflation. And yes, some of the air can escape when detaching the pump head. Whether or not it is too much air depends on the pump head's design and your speed when operating it. If nothing else, you can overinflate a bit to account for the later air loss.– Grigory RechistovCommented Dec 17, 2020 at 7:47
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3I think most of the escaping air (assuming it’s just a short hiss) actually comes from the pump’s tube and head.– MichaelCommented Dec 17, 2020 at 7:57
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There is exactly one method that works: Be fast. Unlock the lever and remove it from the valve within a split second. If you can't do that, I think you need to reconsider using Schrader valves. Dunlop valves do not have this problem, they have a different problem of not allowing air to enter if it's not significantly higher pressure than the air inside, making it impossible to top of tires. Dunlop valves may need to be unscrewed, releasing all the air, before they can be blown free to pump up the tire.– cmaster - reinstate monicaCommented Dec 17, 2020 at 9:49
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2Answers in answers please.– Criggie ♦Commented Dec 17, 2020 at 9:51
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@alaskaboi32 Can you please confirm whether this happens the same on both wheels? If its just one wheel, then there may be a legitimate valve fault.– Criggie ♦Commented Dec 17, 2020 at 9:59
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2 Answers
I do two things - I overinflate the tyre by about one stroke of the track pump, and if the pump has a lever I flick it off pretty smartly. However my pump at home is a thread-on track pump and doesn't have any issues with pressure loss when slowly unscrewing the hose from the valve.
Also, try another pump. Borrow one from another cyclist, or check the LBS for an air line. Some bike fixup workstations have a pump built in too. Last resort is to try a car air pump at the local service station, though they can be quite brutal.
If you use a track pump, leave the handle in the up position while disconnecting the hose head from the valve, and you'll see the handle fall under its own weight. I bet the HISSSS of air moving stops at the same time the handle bottoms out, suggesting that the released air is coming from the pump not the tyre.
Lastly for self-reassurance, check your tyre pressure by hand before removing the pump hose, and again immediately after. You'll have a good-enough muscle memory for the pressure needed by your thumb to dent the tyre's tread. I expect it to have exactly the same perception of resistance to your thumb before and after hose disconnect.
Minor clarification - the pin does NOT need to be pressed down in a schrader valve to add air. If the air in the hose is high-enough pressure to overcome the internal tyre pressure plus the spring pressure, then air will go into the tube (barring no leaks or sticky valves)
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1“Lastly for self-reassurance, check your tyre pressure by hand before removing the pump hose, and again immediately after.” I’ve found that it’s easier to gauge and reproduce by pushing the whole wheel hard against a sharp edge (e.g. kerbstone). If you can push it until it bottoms out you probably need more air.– MichaelCommented Dec 17, 2020 at 15:25
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@Michael good point. I like the fingers around the rim and the thumb crooked to press the tip+nail on the tread.– Criggie ♦Commented Dec 17, 2020 at 19:20
There are different kinds of pumps. The usual pumps can indeed release too much air for certain purposes - mainly for high pressure low volume applications. That is the case for fork shocks and small wheels like my 8inch 7.5bar Skike wheels.
The solution is to use a . Those are designed for these applications, are detached quickly by unscrewing the inflator and release very little air in the process. It is also possible to put most off the air quickly by an ordinary high-volume pump and finish it off exactly with a shock pump. Some shock pumps also feature a high volume/high pressure switch.
shock pumps - https://www.bikeradar.com/advice/buyers-guides/best-shock-pumps/
However, I do also often just pump the Skike tyre with a cheep track pump. It can loose around 0.5 bar (remember - low volume!) but one can learn to disconnect the inflator quickly enough. Open the lever that holds it in place and then get the inflator from the valve as quickly and as directly as possible. You do lose some air, but it can be mitigated and you can also fill a bit more than you need if the amount becomes predictable.
answered Dec 17, 2020 at 11:27
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1I doubt anyone could fully inflate a tyre with a shock pump - it will take hours.– Criggie ♦Commented Dec 17, 2020 at 11:30
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@Criggie For two years I had nothing-but a shock pump when I lived in the UK. And my wheels need a frequent inflation due to frequent flats. It is much quicker than an emergency mini pump. And that one does not take hours either. Commented Dec 17, 2020 at 11:32
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@Criggie And my answer does mention that you can put most off the air i by a high-volume pump. Commented Dec 17, 2020 at 11:33
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That could be a good separate question - "can you inflate a tyre with a shock pump?"– Criggie ♦Commented Dec 17, 2020 at 11:43
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1@Criggie bicycles.stackexchange.com/a/59533/21133 My road bike tyres even where presta and I still inflated them with a shock pumps (two different models actually) just fine. Just use a presta to Schrader adaptor. Commented Dec 17, 2020 at 11:45