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I need to flatten my bicycle tire. What is the safest and best way to do this?

What I mean by safest is: I want to reinflate it again afterward.

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    Using the valve would be the quickest and safest way.
    – KeithWM
    May 21, 2018 at 7:43
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    Just as long as its your bike, and not interfering with someone else's bike.
    – Criggie ♦
    May 21, 2018 at 8:25

3 Answers 3

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It's quite common to deflate a tube for some valid reason, like you want to change a worn out tyre or replace a spoke.

If your valve is a Schrader (a car style) then you remove the cap by twisting, then use a pokey object to depress the center pin in the valve to release the air slowly. A nail, or the end of a house key, or a Phillips-head screwdriver are all effective pokey things.

https://www.einradladen.com/media/image/product/449/lg/25-559-26-x-10-inch-inner-tube-with-schrader-valve.jpg

If you want to completely deflate the tyre fast, you can use metal cap with special screwdriver to remove the valve from its case. If the valve is not tight, you can tighten it or replace it using this tool.

enter image description here

If your valve is a Presta (a French valve, more common on high pressure road bikes) then it's easier. Remove the cap by twisting, then back off the knurled nut, by twisting two or three turns. No need to remove it completely. Finally press the end of the pin with your bare finger.

http://cdn.shopify.com/s/files/1/2113/8927/products/612292_754145299_product_1024x1024.jpg

If you have a Woods or Dunlop valve, then the valve core needs to be loosened, by twisting. (Seems like there's a common twisting element here!) The knurled nut holds the whole valve stem down, so back this one off til air comes out. If you undo it completely, the valve core can fly out and be lost. These are common on Japanese and German bikes, or old English bikes.

http://www.japancycling.org/v2/info/bikesj/img/woods.jpg

Regardless of the valve, escaping air makes a loud hissing noise. Don't be startled. The air coming out also smells rubbery and is prety cold - this is fine.

If you have airless tyres (foam filled ones), you cannot let the air out - they have to be cut off the rim generally. These don't have a valve stem at all and are quite unusual.

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    On the Dunlop valve type — I was seriously surprised to see just on how many seemingly not-so-old commuter bicycles it is used these days in some European countries! Apparently tubes with this valve type are still actively manufactured and sold. In some other countries, Dunlop valves are non-existent and can only be seen in a museum.
    – Grigory Rechistov
    May 21, 2018 at 8:58
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    At least in experience, which means being a "utility cyclist" (i.e. not an athlete or bike-head) in Germany, Dunlop is the default valve. If you want something else, you'll have to specifically ask for it.
    – Jörg W Mittag
    May 21, 2018 at 10:35
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    An alternative, on a Schrader valve, is to use a valve core tool (such as found on many Schrader valve caps) to partly unscrew the valve core.
    – Daniel R Hicks
    May 21, 2018 at 11:48
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    Renting bikes with the wife on small island in Japan, after getting a flat due to a broken Dunlop valve we discovered that all the local car garages carry spare Dunlop valve cores (for bicycles!). I suppose back in the days before the disposable-consumer-goods era, replacing the valve if it was broken was obviously better than tossing the whole tube.
    – Craig Hicks
    May 21, 2018 at 13:41
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    @GrigoryRechistov: Ball-type Dunlop valves (called Blitzventil in German) are easy to pump with a very simple hand pump that doesn't have very high requirements for the sealing rubber of the pump as the valve works while pumping: if the pump isn't that good, the valve simply never opens. And with a ball instead of hose, you loose hardly any pressure for opening the valve. For Schrader/car valves you loose lots of pressure to open the valve at each stroke, unless you press the needle - which needs well-working sealing.
    – cbeleites unhappy with SX
    May 21, 2018 at 17:59
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I've made a deflating tool for Schrader valves (car style). It's a plastic valve cap with two holes drilled across it to let the air out and a blunt-ended screw threaded in from the top. Simply screw it onto the valve and it lets all the air out. It works well with an adaptor for Presta.

Schrader deflating cap

This is really useful when you want to get all the air out, e.g. when rolling up a patched tube for storage.

This is a workshop tool; at the roadside (if on a bike with Schrader valves) I typically use the end of a plastic tyre lever. That's one reason for carrying that particular set of tyre levers (they hook onto the spokes and it's the hook that presses the valve). For Presta valves finger pressure does the trick.

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    The hooks on tyre levers are very useful. For deflating Schrader valves at the road side, a pea-sized piece of grit from the road can also be useful for depressing the valve pin.
    – David Richerby
    May 21, 2018 at 11:23
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    Workshop tools: Screw drivers for car valves (to take out/replace the inner part of the valve) are to be had for ≈ 1 €) this is how they look: duckduckgo.com/…. Also, there are valve caps that have this function built in.
    – cbeleites unhappy with SX
    May 21, 2018 at 18:06
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    @cbeleites, yes, and I've got one. I find the valve cap easier as you can fit it with a twist to a full-pressure tyre and walk away -- or fit it to a tyre and roll the tyre up tight, strap it up, and then remove the cap.
    – Chris H
    May 21, 2018 at 19:36
  • That's brilliant! I'm going to make one. Looks like what the 4 wheel drive deflator things below are for.
    – Criggie ♦
    May 23, 2018 at 5:43
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    Update - I did make this. I got some novelty tyre valve caps made from aluminium from china, shaped like bowling pins. Cut the top off, bored a small hole, threaddd for a M3 bolt to press down on the valve's pin, and a tiny jam nut. Then I crossdrilled just above where a schrader valve ended. Works well. I added a short string to help with not-loosing it. Sadly I gave it away, and haven't made another yet.
    – Criggie ♦
    Jul 10, 2020 at 5:34
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In my youth I did 4WDing, and it was a common accessory to have a set of four valve caps for schrader. They were pre-set to a specific pressure, so you could drive on road at road pressures of maybe 35 PSI, arrive at the meeting place and "air down" using these to drop your tire pressure to 25 PSI or 17 PSI or whatever your preset was.

They were a lot quicker than holding the pin and checking every 20 seconds. 4WD car tires hold a heap more air and can take minutes to come down to an off-road pressure.

https://i.ebayimg.com/images/g/s-gAAOSwZ1BXe14v/s-l1600.jpg ebay listing https://www.ebay.com/itm/X-BULL-Brass-Tire-Deflators-Kit-Automatic-Adjustable-6-30psi-Tyre-Deflator-/331964554493

The top part is adjusted to pressure and locked using the lock ring.

You wouldn't ride or drive with these in place.

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  • Interesting - though strictly speaking this does not answer the question. The question was how to "flatten" a tire, which these devices will not do, as they are specifically to make sure the tire retains some pressure.
    – sleske
    May 22, 2018 at 8:07
  • @sleske yes but you can back off the lock ring so they are a one way valve letting the air out only. Good for rolling tubes up too. Bad point - they are not cheap any more!!
    – Pete
    May 22, 2018 at 12:18

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