I’m fixing a hole where the rain gets in
And stops my mind from wandering
Where it will go
—Lennon/McCartney

Removing the tire from the rim.
How do you get a tire off? Try massaging it gently and sensually until…just kidding! Even if you haven’t found the puncture after inspecting the exterior of the tire, you can move to the next step: demounting the tire from the rim. To do this you’ll need to completely deflate the tire if it’s not already completely flat.

Tubes have either a Presta valve or a Schrader valve. (You’ll hear about Dunlop valves but I’ve never ever seen a bicycle tire with a Dunlop valve in all my years.) Schrader valves are also used on automobile tires, so if the valve looks like your car tire valve, you have Schrader. Deflate a Schrader valve by pressing in the little tip in the center of the valve; you may be able to do this with just a finger. But if not you’ll need to use something pointy like a pencil tip, small screwdriver, or the tip of a key. If you have Presta valves, just unscrew the captive nut on top and press down until it’s completely deflated. (If you have a tubeless tire with sealant, you may depress the Presta valve and little or no air comes out despite the tire feeling rather inflated. This is likely due to dried sealant clogging the Presta valve.) Your tube may be secured to the rim by a screw-on locknut. If your tube has a locknut over the valve to secure it to the rim, remove it first.

Tires are getting harder to remove and install. Tires are manufactured to more stringent standards now because of the introduction of so-called “hookless” rims. These rims have straight walls on the inside edge. A traditional rim has a “hook” i.e. a bulbous shape
that traps the tire bead and prevents it from moving upward and off the rim. Since there is nothing physical to block the tire bead from sliding up and off the rim, making the tire bead as tight as possible is essential for preventing a blow-off. (Also important is requiring users to inflate tires to lower pressure.) Hence tire manufacturers are now producing tires to be tighter fitting on all rims even if most of us aren’t using a hookless rim. So getting a tire bead on or off a rim, hookless or not, is generally more difficult now than it was in the past.

In order to remove a tire with less struggle you should push both tire beads into the center of the rim, ie. the well. This is because each tire bead sits on a ledge on the inside of the rim and that ledge is higher than the center. By having the tire beads in the center, the well, you’ll have more slack to pull the tire bead over the edge of the rim.

Using tire irons.
Tire “irons”, or levers, are the most common way to remove a tire and you will need at least two. They have a flat end that is intended to slip easily under a tire bead; the other end almost always has a hook to grab onto a spoke thus freeing your hand. There is another tool called a tire jack that you can use to remove a tire. By the way if you don’t have tire irons handy, you might be tempted to use something else to lift the tire bead off the rim such as flathead screwdrivers. My advice: don’t. Unlike tire levers screwdrivers (a) have sharp edges and (b) are invariably made of steel. Using a screwdriver is a great way to puncture your inner tube just by trying to remove (or install) a tire. Then you’ll have at least two punctures to fix! Tire levers have rounded edges and usually—but not always—are made of something softer such as plastic. Also, a metal screwdriver can damage the rim especially if it is carbon as well as the rim tape in the well of the rim.

The basic idea of a tire lever is to insert the flat end carefully under the bead and lever the bead up and over the rim edge at which point you can attach the hook end of the tire iron onto the spoke underneath to hold it in place and free up your hand. You must be careful not to pinch the inner tube with the tire lever. What do I mean by “pinch”? When you insert the tire iron under the bead, you can’t see for certain if you are also impinging part of the inner tube between the bead and the tool. The pressure of levering the bead over the rim edge is enough to break through the rubber of the tube. If you pinch it, you will very likely puncture it. I have done this with butyl, latex, and TPU inner tubes so no tube material is immune from this user error.

Rotate the wheel about two to three inches and use the second tire lever to lift another portion of the bead out. This is going to be more difficult because most or all of the slack in the tire bead is now gone due to the first tire lever. You’re going to try to lift more of the bead that is (hopefully) already slightly lifted by the first tire lever, just enough to push the second tire lever under it. Be careful not to entrain the inner tube. Take your time and don’t rush. You should now have a larger section of bead over the rim. (You don’t always need to attach the second tire lever to a spoke but if you do, you will need that third lever.) You may have to remove the second lever and repeat this one or two more times a few inches further along the bead each time until you have enough tire bead over the rim and it becomes slack. Now the bead should be able to stay out on its own. At this point you can simply slide the second tire iron along the circumference while it’s still under the bead until the entire bead is off the rim on one side. Now you can remove the inner tube. Usually you do not need to remove both beads from the rim, i.e. completely separate the tire from the rim. One side is usually enough for inspection and roadside repair.

Ideally that’s how events should unfold. However I’ve had tire-rim combinations that have been so tight I could not insert a second tire iron under the tire bead without using a great deal of force. Even if I got the lever under the bead, I could tell that an undue amount of force would be required to lift the bead off the rim. Unfortunately that’s going to become the ’new normal’ as time goes on and older rims and tires go out of circulation (pun intended). I can attest that the use of force, the result of a lot of exasperation and disbelief, is not always productive; I have jammed the second tire iron in and ended up pinching and puncturing the inner tube. You might have more success than I especially if you are more patient. Another possible outcome is that your tire lever snaps—yes, this can happen occasionally (but rarely). There is a solution though: a tire jack, which I’ll discuss in the next post.

That said, tires and inner tubes eventually age after being installed and inflated and they will stretch and loosen slightly and this tends to make removing the tire easier in the future. When a tire is new is usually the hardest.

Note the orientation of the inner tube to the wheel. After you find the puncture in the tube you’ll want to inspect the tire at the same location to see if there is something still stuck in the tire. If you unknowingly flip either of them around, then you’ll end up inspecting the mirror image location of the tire, i.e. the wrong place. If you’ve lost track and don’t know if you’ve flipped the tube or tire around, don’t worry. You’ll just have to inspect two sites instead of one.

Looking for the leak on the inner tube.
With the inner tube out of the tire, pump it up enough to look for leaking air. You don’t have to pump it up a lot, just enough. If the tube doesn’t inflate at all, then you have a big puncture such as a gash or tear and you should be able to find it just by visually inspecting the tube. If the tube does inflate but deflates quickly, your puncture is likely bigger than a pinhole and you may be able to find it quickly. If you can’t see the puncture, hear it, or feel the air rushing out, you may have to be quicker or do double-duty: pump a bit and inspect sections of the tube while you pump. This is usually difficult or impossible with a mini pump if the tube deflates quickly. Another trick is to squeeze off half the tube while you pump; if the tube inflates normally, then the puncture is in the section you’ve squeezed off. Then squeeze off part of that section and try again until you narrow down the section that has a puncture.

Also pay attention to where on the inner tube the puncture is located. If you roll over something sharp like a thorn or a tack, the puncture site should be on the outer circumference of the inner tube. But punctures happen elsewhere as well. Sharp objects can also poke through from the side. So if you notice the puncture is on one of the side of the inner tube, you will want to check the sidewall area of the tire. Although something sharp can poke in your tire from the side, the most common cause is hitting a pothole or rock so hard that the tire compresses fully and pinches the inner tube against the rim; this causes a ‘snake bite’ puncture, which is two small gashes together where the rim has cut the inner tube and these are off-center. If you hit hard enough you can get a snake bike puncture on both sides of the tire too (but this is rare).

You can also get a puncture on the underside of the tube. Most rims have spoke holes that go completely through the rim. This is so a spoke nipple can be inserted to thread onto the spoke to tension it. Those holes are covered by rim tape so that when the inner tube is inflated, it doesn’t expand into the interior of the rim (if it has an interior chamber). It covers the spoke hole to prevent the edges of the hole from cutting the tube. Most spokes protrude above the nipple and are sharp. If the tube enters the spoke hole, the spoke itself can also puncture the tube.

Rim tape itself can rub and abrade a tube on the underside especially if it isn’t laid down completely flat and even. Most rims have spoke holes and these must be covered with rim tape or sealant tape if you’re using sealant. Rim tape can slowly move and expose a spoke hole simply from the pressure of the inflated tube pushing on it. (This is why when the rim tape is replaced it is important to make sure it is centered over each spoke hole and the tape–if it has adhesive–most do but not all–that it is firmly pushed into the rim well to get it to stick and not move. Rim tape especially those made of plastic can also age and tear. Then the tube can be punctured by the edge of the spoke hole or if the tape moves sufficiently or tears, then the tube will be forced into the rim by air pressure and may fail.

Another thing that might confuse where the location of the puncture is on the tire: if your inner tube was twisted when it was inserted in your tire. Usually a tube will untwist as you inflate it. But sometimes it doesn’t completely untwist. If it is slightly twisted, then the location of the puncture on the tube will not match up exactly with the real location on the tire. For example a puncture that appears on the side of the tube might actually be on the tread side of the tire. Of course when you install an inner tube you should be careful to insert it so it’s not twisted in any way. (Easier said than done sometimes.) So when you are inspecting the tire for a sharp object, make sure to check the area around the suspected puncture site.

If you still haven’t been able to find a puncture, it might be due to an old puncture, i.e. it was patched before but now the patch is failing. So check any old patch sites on the inner tube to make sure they are not leaking air.

After you’ve found the puncture site, you don’t need to repair it until you get home. You’ve gone through this procedure in order to be able to find the puncture location on the tire so that you can make sure the culprit is completely removed. Note the puncture site and then hold the tube against your tire with the tube oriented the same way as when you removed it. Now you should be able to find the area on the tire that was punctured. Remember, if you’re not sure of the orientation, then you’ll need to flip the tube around and note the mirror image location on the tire. Inspect that spot as well.

Removing the sharp object from the tire.
Inspecting the tire involves looking and feeling for something remaining in the tire that pokes through the tire. The outside might look fine only because the thorn/wire/glass shard has been pressed completely into the tire rubber and is inconspicuous. But on the inside something sharp remains to puncture another tube. So look and palpate the inside near the suspected puncture site. Do your inspection carefully because overlooking something may cause you to puncture your spare tube. If you find an offending object, remove it.

But how do you remove it? If it’s large enough, you can use your fingers. If not, you might be able to use a pen knife or a flat screwdriver (on your multitool) to dig it out. If you’re fortunate to have tweezers (Swiss Army knife), try them.

One more thing: although unlikely there is a chance you have more than one sharp object embedded in your tire. This can happen when you roll through scattered broken glass or an area that has a lot of blackberry bushes adjacent to the road. Another cause is a patch of goathead thorns (puncture vine). So just because you’ve found one puncture in your tube doesn’t preclude that there might be another. So double-check.

After all that explanation, here’s online video that covers much the same ground adequately albeit briefly:

One thing of note: although the presenter completely removes the tire and tube from the wheel, this is not essential especially when you’re standing by the side of the road or trail rather than in a workshop.

I’m fixing a hole where the rain gets in
And stops my mind from wandering
Where it will go
—Lennon/McCartney

Removing the wheel. Your wheels are likely attached to the frame with either quick release levers or thru-axles. To remove your wheel you will have to know how to use either. If you have an inexpensive bike (or a fixed gear/singlespeed), your wheels might be retained by regular screw-on nuts; if so, you’ll need a wrench to remove the wheel. Do you carry one with you? If not you’ll have to get a lift home or to a bike shop.

Quick Release Levers. Quick release levers are the more common wheel retention system but they are slowly being replaced by thru-axles. Quick releases do not require using any tools: you just flip the lever open to rotate a cam and then remove the wheel from the dropouts. Conversely you put the wheel back in the dropouts and flip the lever closed. It’s actually not quite that simple. Almost all bikes made in the last 40 years have so-called “lawyer tabs” on the front dropouts only. These little nubs prevent you from removing the wheel even after you open the quick release lever. After flipping the lever open, you have to unscrew the quick release nut on the end of the skewer until you can get both ends of the axle over the nubs at which point you can remove the wheel. Conversely after you insert the wheel back in the front dropouts, you have to screw in the quick release nut a bit before the quick release lever will tighten onto the dropouts. They’re called “lawyer tabs” because some people who didn’t know how to use quick release levers correctly had their front wheel come off and they crashed, of course resulting in a lawsuit. Rear dropouts do not have “lawyer tabs”. Before you try to replace your tube, be sure you know how to properly use quick release levers so you can loosen and tighten them correctly. You close a quick release lever by flipping it 180 degrees to tighten the cam onto the dropouts. The lever is not a wingnut, i.e. you do not tighten it on the dropouts by screwing it on. By the way, the quick release lever should be flipped fully so that it doesn’t stick out from the bike. If you can’t flip it about 180 degrees, then you need to loosen the end nut a bit until you can while still gripping the dropout tightly. And how tight should you tighten the lever? The traditional advice is that the pressure you use with the palm of your hand should leave an impression. It should be firm but not so firm that you cannot open the lever. Needless to say you do not want to have your quick release accidently open because it was not tightened sufficiently!

You do not need to fully unscrew the end nut to remove the wheel, just enough so the wheel drops out when the lever is fully open. By the way, if for some reason you’ve unscrewed the end cap completely and you have to reinsert the skewer through the axle, the lever should be on the left side of the wheel. (There is an exception: some front wheels with disc brakes and quick releases are designed so the quick release is supposed to be on the right side. But this is rare.) For the rear wheel this is important because putting the quick release lever on the right side potentially has it interfere with the rear derailleur; for the front wheel it usually doesn’t matter mechanically which side you put the lever is on. (But it looks strange to have the lever on the right side!) Quick release skewers also have two metal springs on them; make sure one is on each side on skewer (i.e. don’t put both springs on one side!)

Thru-axles. Thru-axles are a bit easier in concept but they usually require you have the proper tool—almost always an Allen wrench—to use them. (Some thru-axles as in the picture above have a proprietary lever for unscrewing them; others may require a Torx wrench.) A thru-axle is simply a big screw that holds your wheel in place. To remove the wheel you unscrew the axle and pull it out. The wheel just drops out. To replace the wheel you put the wheel in the dropouts and insert the axle, then screw it in tightly. This is where carrying a mini tool or the correct size Allen or Torx wrench is important. Without a tool you cannot remove the wheel. Currently thru-axles don’t have the equivalent of “lawyer tabs”. Even if the thru-axle isn’t screwed in tight, the wheel can’t come off without the axle completely unscrewing on its own and then falling out, a rather unlikely event. But you can see where this is going: someone is going to improperly screw in a front thru-axle and when it falls out and results in an injury or death, thru-axles in the future will end up having some kind of backup retention mechanism.

Front wheel or rear wheel? To remove a front wheel with rim brakes, first open the cable release on the rim brake. This lever opens the gap between the brake pads even more so that it is easier to remove a wheel. Some rim brakes do not have a little lever on the brake to open the brake. Instead there is a button on the brake lever you push to create more slack and widen the caliper arms. Most tires are wider than the rim and you’ll need to open that lever (or push the button) to get the wheel out. Of course if your tire is already completely deflated, it may not matter much. For some really tight tire-brake combinations in order to get the wheel inserted and positioned correctly you may have to deflate the tire and then inflate the tire. But that is an uncommon situation. If you’ve got center pull, cantilever, or V-brakes, the cable is released differently than for rim brakes and you’ll have to know how for your specific brakes. Of course this is irrelevant if your bike has disc brakes.

Removing the rear wheel is slightly more complicated than a front wheel. The chain wraps around the cassette and the rear derailleur pulleys; both will have to out of the way to get the wheel to drop out of the dropouts. Back in the day it didn’t matter what gear you were in because when it came time to reinsert the rear wheel it was obvious which cassette cog it needed to go around. But now that we have up to 13 cogs it’s harder to eyeball where it should go. You can make note of it when you remove the wheel or if you’ve got electronic shifting and it’s connected to your bike computer, you can look at the gear it is in as shown on your computer. I’ve found it easier just to shift the rear derailleur so it’s in the highest gear (= smallest cog); when you insert the wheel, it is easy to line it up over the smallest cog. So either shift into the smallest cog or make note of which cog you’re in.

If your bike has rim brakes, open the little brake release first just as you would for a front wheel. To remove the wheel after you’ve loosened the quick release or removed the thru-axle, lift the rear of the bike and gently pull back on the rear derailleur body so that the chain and the cassette are free of each other. The wheel should drop out easily.

Lay the bike down carefully. Be sure to position your bicycle now minus a wheel so that it is ‘safe’. By ‘safe’ I mean either upright—leaned against something or being held by somebody—or by laying it on the ground on its left side. Do not lay the bike on its right side. Why? Because that’s the side with the derailleurs. Laying it on its right side risks damaging the rear derailleur or bending the rear dropout or both. If you have removed the rear wheel, do not sit the bike upright and try to balance the rear of the bike on the rear derailleur! There’s no harm in balancing the bike by the fork dropouts if you’re working on a front wheel.

Looking for the leak on the tire. With the wheel off the bike it is now easier to inspect the entire tire. Inspect not just the center of the tread but also along the sides. It helps to palpate the tire as well as inspecting it visually. Run your hand to feel for something small stuck in the rubber. If you find something, note its position and attempt to remove it. If it’s really small or barely protruding, you may not be able to remove it with your finger. If the tire is already completely deflated, sometimes pinching the suspected puncture site will allow you to remove the object. Most sharp objects will come out—either now or later—in one piece. But you need to be careful if it’s a thorn especially a blackberry thorn because it’s soft enough that you think you’ve removed it but the tip may still be stuck through the tire and into the tube. Always palpate the inside of the tire casing at the puncture site to make sure there is nothing left sticking in that might flat your spare tube. The small blade of a Swiss Army knife may help you remove a recalcitrant sharp object; also some knives include a pair of tweezers. These are very helpful for removing the small metal wires from car radial tire carcasses that cause punctures.

If your tire still has some air, you may either hear it hissing or feel the air escaping by holding the wheel by your face and slowly rotating it.

If you’re still having difficulty spotting the cause of the puncture, there are a few things you can try. First, wipe down the tire carefully and slowly. If something is stuck in your tire, you may feel it as you run your hand around the circumference. Second, with grit and dirt rubbed off, you may be able to spot the puncture more easily. There is another option sometimes: use water if your tire still has some air (or you can pump it up a bit). If you’ve got a puddle nearby and your tire is still partially inflated, you can slowly dip the tire in the puddle to see any escaping bubbles. Rotate the wheel slowly in the water until you see bubbles.I’ve used my water bottle occasionally to confirm where I think the puncture is: pour water on the site and see if there are any bubbles. If you think you’ve found the puncture and want confirmation, you can rub some saliva over the site as well.

If you find something embedded make note of the location—count the number of spokes the site is away from the valve hole (and note the orientation of your wheel). This is so you will know where to look on the inside of the tire casing to ensure you’ve fully removed the cause of the puncture and to precisely locate the hole in the tube.

If you fail to find the cause of the flat from the outside, then you should proceed to demounting the tire and inspecting the inside of the tire casing and the tube.

A sidenote on tubeless tires. If you have tubeless tires, you’ll probably see sealant escaping. There should be an obvious wet spot on the tire with sealant oozing or spewing out. You should spin the wheel so that the puncture is at the bottom of the wheel. This lets the sealant pool above the puncture site and hopefully it will coagulate and seal. This may take several minutes. Then pump up the tire slowly and see if it can hold air. If the puncture is small enough, it will seal but it may not be able to seal at your typical tire pressure. If you have a seal and then pump up the tire but the seal fails again, you can try letting it sit longer to seal. If it won’t, then you can try tire plugs. Hopefully you’ve practiced at home and know how to insert a tire plug and remove the tool. If one plug doesn’t stop the leak, you can inserting a second plug. If that doesn’t do it, then you’ll have to decide whether to ride home on a low tire or…install your spare tube. (You do carry a spare tube and pump even though you are running tubeless tires, right?) And then we’re back to the same situation as if you were running tubes (except you have sealant in your tire and it will make a mess).

I’m fixing a hole where the rain gets in
And stops my mind from wandering
Where it will go
—Lennon/McCartney

You’ve got a flat while riding and you’ve decided to replace the tube with your spare rather than fix the puncture immediately. Dealing with a flat is an inconvenience and you would like to have just one inconvenience on your ride, no more. Then it is worth being careful and not rushing the process in order to avoid flatting again due to a careless and hurried effort.

But why can’t I just ride home on a flat tire? You can try it if you’re absolutely desperate, e.g. you’re out of cell range and no one is likely to come by who might be able to help you. This is the one situation where riding a tubular tire has clinchers beat. Since tubular tires are glued onto the rims, they are much less likely to roll of the rim even when they’re flat. And since they stay in place the flat tubular provides some rudimentary protection for the rim being damaged when you roll on it. Clinchers are another story altogether: there is nothing holding the tire onto the rim despite there being a tight fit between the tire and the rim. So at the slightest turn they are likely to roll off the rim entirely. Once the tire rolls off it will jam between the fork and the wheel (front) or jam between the stays and the wheel (rear). You also won’t have any control riding just on the rim and it will feel terribly rough. Third, riding on a clincher rim hooked or otherwise—especially a carbon rim—is guaranteed to ruin it and you’ll have to replace it later.

But I have tire inserts! There is one possible exception for clincher tires: if you’ve got tire inserts in your tires, you might be able to ride it carefully since the insert provides some cushion and flotation and helps keep the tire beads from coming off the rim. Getting a tire off that has inserts inside can be difficult, so all the more reason to continue riding it if possible. Needless to say if you do try to ride a flat tire that doesn’t have inserts you can only go slowly in order to be safe. But this is an option I do not recommend unless the distance you need to ride is very, very short and for some reason you can’t just walk. Nota bene: I don’t recommend you do this!

Before changing the tube find the source of the flat. You might be tempted just to replace the tube as quickly as possible especially if you’re riding in a group and everyone is impatiently waiting for you to finish up. My advice: don’t! Take the time to ascertain the cause of the flat before you put in that spare tube. If you haven’t removed the cause of the flat, you may flat your spare shortly thereafter and be stuck. So take the time to ascertain the cause before you stuff in that spare!

There are myriad ways a tire can go flat: Something sharp poked through your tire and punctured the tube; you hit a sharp bump hard and flatted; an old patch failed; the tire valve failed; you rode on a worn tire and wore through the casing; you overheated the tire on a long descent by braking constantly (rim brake only) and it blew off; you didn’t have the tire bead properly seated and it blew off; you accidentally abraded the tire casing—I could go on. Most of these have an overt cause and you will usually be able to find the cause of the flat.

If your tire deflated very quickly perhaps accompanied by a loud bang, you’ll probably not have to look too hard to find the site of the flat. But not always. The cause of quick deflations include “snake bite” punctures, casing failure, an inner tube not properly seated inside the tire, or too high pressure perhaps caused by overheating due to prolonged braking. Quick deflations mean the hole is so large that all the gas escaped immediately. If it’s caused by a large gash—maybe you ran over a large glass shard that sliced open your tire—you’ll see it easily. But sometimes there is no sign of the cause when you inspect the tire surface. Often you should see a hole in the casing or tire tread. Casing failures may be obvious and be sure to check your tire sidewall, which is where they tend to occur. If your tire overheated and blew up, almost always the tire bead is blown off the rim and you’ll spot that location quickly. But sometimes it’s not so obvious as when you hit a pothole hard and you compress the tire and tube so much that the tube is gashed in two places by the rim—a “snake bite” puncture; the tire casing may be intact and only the tube is damaged and you might not see that until you pull the tube out to inspect.

In the case of a failed tire valve it may not be obvious. The base of the valve is subject to stress and that’s why manufacturers strengthen that point on the tube. Even so they can fail through time either from stress on the base of the valve tube or by movement causing abrasion; also, tubes are rubber and rubber ages and can crack. If you look at your tire valve and it’s cockeyed, i.e. not straight up, The tube could have shifted on the rim and this puts extra stress at the base of the valve. If you have a retention nut holding the Presta valve onto the rim, it shouldn’t shift. But Schrader valves usually do not have retention nuts so they can shift. If you’ve put a tube with a Presta valve onto a rim intended for Schrader valve tubes, you can also abrade the base of the valve. This is because the hole in the rim for a Schrader valve is larger than for a Presta valve. That extra width can allow the valve to shift back and forth and cause abrasion. (To prevent this from happening in the future, you should install a Schrader-to-Presta adaptor.)

The base is underneath the rim and you can’t see it without removing the tire. A flat at the valve could also be due to the valve mechanism itself. Presta valve tubes almost always have a removable Presta valve core. The tiny valve mechanism is simply screwed into the inflation tube. Perhaps you or your mechanic removed it to inject sealant and failed to screw it back in all the way. Another cause could be that you failed to tighten the captive nut on the Presta valve after you inflated your tire. In the former case either a small wrench or a special Presta valve tool can be used to screw the valve mechanism down; for the latter, just screw down the captive nut tightly.

If you look at the top of your Presta valve, there should be a captive nut that you screw down to close the valve. The little stem that the captive nut screws onto is thin metal and it is very easy to bend by accident. It is also possible to break off accidentally. The most common way to bend the stem is when you attach a pump head to the valve to inflate the tube. Be careful! Rocking the pump head back and forth when pumping or when you release it or pulling it off at an angle is a good way to bend the stem. If you’ve bent the stem already, you may be tempted to straighten it. Again, be very careful because this is a great way to break off the stem altogether. I wouldn’t recommend trying to straighten it unless you absolutely have to, i.e. you cannot screw down the captive nut to close the valve. If you do break off the stem, your tube will probably be able to hold air but it will slowly (or quickly) leak. Presta valves are replaceable with a valve core tool and a spare Presta valve. Unless you’re carrying those along with you, you’ll definitely have to replace the tube and deal with the valve repair when you’re at home.

If your tire did not deflate quickly, then look for a puncture. If you are running tubeless tires with sealant, you should see sealant leaking if not squirting out of the puncture making the source obvious. The only reason you’re going to need to put in your spare tube is if (a) your sealant has either dried up or run out or (b) your puncture is so big that sealant is unable to seal it.

If your tire is wet you might be able to see air bubbling out of the tire; you may need to pump it a bit to check. Otherwise look around the tire including the sidewalls for a puncture or anything embedded in the tire. Sometimes whatever caused the puncture doesn’t remain embedded and it won’t be obvious. But often it is still in place and sometimes it’s very small and nearly invisible especially when it’s worn down and all you might see is a tiny dot. Needless to say that having a dirty tire may make it hard to spot the site. So wipe the tire down of as much dirt and debris as you can. (This may be difficult or pointless if you have knobby tires.) If you gently brush your hand over the tire, you may feel something stuck in the tire: lift the wheel, spin it slowly, and run your hand lightly over the surface of the tire. But be careful: if something very sharp is still in your tire, it may cut your hand or fingers; if you are wearing cycling gloves, it’s a bit safer to do this. This isn’t foolproof because the embedded object may have fallen out, not be above the surface of the tire, or sufficiently off to the side that you miss it completely.

Sidenote: If your vision is less than perfect—especially if you’re farsighted, you may end up struggling to see anything embedded in your tire. The offending object can be quite small—such as a thorn —and difficult so spot even with good vision. Make sure you have your reading glasses with you.

If you find the source of the flat, make note of its position on the tire by counting the number of spokes from it to the valve hole. You’re going to inspect the deflated tube after you remove it from the tire as well as the inside of the tire casing and this will help you find the corresponding location on both.

You may be able to find the puncture site without removing the wheel from your bike. It is also possible to patch your tube without removing the wheel. But most of the time it’s going to be much more convenient to remove the wheel in order to effect an orderly and quick repair. Note: you can’t replace an inner tube without removing the wheel. The one exception is if you have Cannondale Lefty front fork because the “fork” has only a left leg and you can remove the tube from the right side since no leg is blocking it.