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A tire is actually made up of three parts:
Schrader valves have a removable valve core, which may be unscrewed with a special wrench that is often found on better valve caps. They have a spring-loaded valve mechanism. There is a small pin in the center of the valve opening which must be pushed in to put air in (or to let air out.) Before the introduction of the Zéfal HP pump in the 1970's, there was no portable pump that would do a decent job of inflating high-pressure tires with Schrader valves, which led to the popularity of:
Presta valves don't use a spring, but they have a captive knurled nut to hold the core tight. Before you can pump up a Presta tube, you must loosen this knurled nut. It is also a good idea to tap the end of the pin, to break the seal loose, because they are sometimes sticky. After inflating the tube, you should re-tighten the valve nut to keep air from escaping.
Presta tubes may be used in rims that are drilled for Schrader valves, though it is advisable to use a rubber grommet in the valve hole. A Schrader valve won't fit through the valve hole on a rim drilled for Prestas. Presta-drilled rims (except the narrowest ones) may be drilled or reamed to accommodate Schrader valves.
|Schrader valve||Presta valve
There is a third type of valve, very rarely seen, which has a bottom similar to a Schrader and necks down to about the size of a Presta. This is a Woods valve, formerly popular in the British Isles and Asia. This is also sometimes referred to as a "Dunlop" valve.
Older low-tech Woods valves work with rubber tubing and spit, but newer ones have spring-loaded mechanisms.
Woods or Dunlop valve
The interior surface of the rim sometimes has burrs which can damage inner tubes, and the ends of the spokes may also cause punctures. For this reason, a rim tape is needed to protect the inside of the inner tube. If a rim has recessed spoke holes, the rim tape must withstand the air pressure in the tire. If the edges of the spoke holes are sharp, the tape also must resist being cut by them.
Some rim tapes are simple strips of rubber, similar to the rubber used to make the inner tube. These are adequate for use in wider rims without recessed spoke holes. Better rim tapes are of adhesive cloth or plastic. The rim tape must be just wide enough to fit the bottom of the rim. Too narrow, and it doesn't cover what it needs to. Too wide, and it interferes with the tire.
Rim-tape failure at a recessed spoke hole, and resulting puncture
Flat tires can be divided into four groups:
If you use high-pressure tires, you should check the pressure at least once per week.
Slow leaks that take more than an hour or so to go down can often only be repaired by replacing the inner tube, since it may be impossible to find the hole.
The typical puncture puts a small hole in the tire, which doesn't matter. Patching or replacing the inner tube is the fix for punctures...but don't forget to remove the pointy thing from the tire before you put it back on!
Pinch cuts sometimes ruin tires as well as tubes, but usually the tire will not be damaged.
The impact that causes a pinch cut can also make a dent or "blip" in your rim.
Warning: dirty work. Tires pick up dust and dirt. Especially in winter, rim brakes scrape black particles off wet aluminum rims. For an on-road repair, it is not a bad idea to carry a pair of light garden gloves in your toolkit. Black tights, shorts or trousers also are advisable.
It is possible to repair a flat by patching the inner tube without removing the wheel from the bicycle, and that may be preferable if the hub has a brake arm or internal-hub gear. (The hardest part, if you leave the wheel on, is slipping the uninflated tube past the shoes of a rim brake, if you are unable to loosen the brake.) Usually it is easier if you do take the wheel off. If you are going to replace the inner tube, you must take the wheel off. Here's how:
Good-quality "road" bikes usually have caliper brakes with a special "quick-release" mechanism to let the brake shoes open up wide enough to fit the tire through. You don't actually need this feature to remove a flat tire, but it is helpful. There will be a button on the brake handle, or a lever on the caliper (or cable hanger) to release the brake a bit.
Bicycles with cantilever brakes, such as most mountain, hybrid, and touring bicycles, usually don't have quick releases on the brakes, so you may have to completely disable the brake by unhooking the transverse cable from one of the arms.
Many brake levers for flat handlebars have a slotted adjusting barrel. Unless it is set at its loosest position already, you may be able to pull on the cable housing to release pressure on the adjusting barrel, turn the adjusting barrel to loosen it all the way, align the slots, and rotate the cable out through them.
In the worst case, you may have to remove, replace and reajust a brake shoe, and that is usually more trouble than inflating the tire a second time!
You will need a wrench for this. Most rear axles use the 15 mm size, fronts may use 1/2", 14 mm, or 15 mm. If you don't have the correct size wrench, you can use an adjustable wrench. Turn the nuts counter-clockwise to loosen them.
Do not try to do this job with pliers. Even if you do manage to loosen the nuts with pliers, you won't be able to get the nuts tight enough when you put the wheel back in. In addition, the pliers are likely to damage the nuts so that the correct wrench will no longer fit!
To loosen the quick release skewer, once you have flipped the handle, hold the acorn nut with one hand, and turn the handle counterclockwise with the other until it is loose enough to let you remove the wheel. For an on-road repair, you stand in front of the bicycle or behind it, holding the wheel between your knees, or hook the saddle over a tree branch, or have a friend hold the bicycle upright. Try not to completely unscrew the acorn nut, because there are a couple of little springs that could get lost if you take it off.
If you're not exactly clear how the quick release works, get somebody to explain it to you before you try removing your wheel. Misuse of the quick release can cause very serious injury!
After freeing the axle by loosening the quick release or axle nuts:
In the case of a hand-operated drum brake, you will also need to disconnect the brake cable, which can usually be done by unhooking it from the fittings it attaches to.
The Shimano 3-speed is adjusted in middle gear, so that the letter "N" is centered in the window of the bellcrank.
Sturmey-Archer S-5 bellcranks should be adjusted so that the cable is taut when the wide-range position is selected with the left shift lever.
To remove the tire, you need to pull the bead off the rim, one side at a time. The diameter of the bead is smaller than the outer diameter of the rim. As long as the tire is centered on the rim, it cannot come off. To remove one side of the tire, you need to put the bead off-center. One part of the bead needs to go down into the valley at the bottom of the rim, so that the opposite side of the bead can be pried over the edge of the rim. This can often be done by hand, but usually is much easier if you use tire levers (tire levers used to be called "tire irons", but nowadays, most of them are made of fiber-reinforced plastic.) Most tire levers have a rounded end and a hooked end.
Often, the bead will adhere to the rim. Push each bead toward the opposite side of the rim, all the way around, to make it easier to remove.
Tire levers commonly come in sets of three, because three is the most you ever need. If the rim is very narrow, the tire may not be able to sink down into the bottom of the rim at the valve, so, pull the tire out near the valve, and it will sink in opposite the valve. For a difficult tire, stick the rounded end of one tire lever under the bead, starting near the valve but not at it -- that only complicates matters.
Insert the lever right where one of the spokes lines up. Pry one side of the tire bead over the edge of the rim, then hook the end of the tire lever to the nearest spoke. Insert another tire lever two spokes away from the first, and repeat the process. The third lever goes two spokes away from either of the first two. When the third lever is in place, the middle one will fall out, and you can repeat the procedure. After some number of times, the tire will be loose enough that you can just run a tire lever around the rest of the rim to pull the whole side over.
This is the procedure for tight-fitting tires, particularly for narrow tires. Most tires will come off with less trouble.
After you have removed one side of the tire, reach in and pull out the inner tube. Remove the tube completely, while leaving the other side of the tire in place.
Keep track of which way the tube was facing in the tire, and pump it up. You will usually be able to find the hole by the hissing sound as the air escapes. If you have a slow leak, it may not make enough noise to hear, unless you pump the tube up enough to stretch it out. Tubes can commonly be inflated to twice their normal thickness or more without risk of popping them, and, as the tube stretches, the hole also gets bigger, making it easier to find. Your lips are very sensitive to touch, and if you hold the tube close to them, you can sometimes feel the air coming out. For very slow leaks, as a last resort, you can immerse the inflated tube in water and look for bubbles. Don't do this unless you need to, though, because you can't patch a wet tube.
Sometimes it is the valve that leaks, and with a Schrader valve, you can wipe spittle over the top of the valve and see whether it expands into a bubble.
When you find the hole, make note of where it is with respect to the valve hole, also whether it is on the inner or outer side of the tube.
In addition to looking for sharp pointy things poking through, look also for broken cords or cuts in the fabric of the tire. If you find such cuts that run more than a millimeter or two, you should replace the tire when possible.
One thing that is often tried, but doesn't work too well, is the rubber patches made for inner tubes...they are too stretchy.
A boot doesn't need to be glued in place: it will stay put just from the pressure of the inner tube against the tire.
Even the best of boots should only be considered a temporary repair. The tire will be less reliable, and you will feel a bump every time the tire goes around.
Avoid touching the buffed area with your fingers.
Work quickly. You want a thin, smooth coat of cement; if you keep fiddling with it as it begins to dry, you'll risk making it lumpy. The thinner the cement, the faster it will dry.
Patch failure generally results from one of two errors:
For more technical detail, see Jobst Brandt's comments.
If you try to pry the tire on using tools, you are very likely to wind up pinching the inner tube between the tool and the rim, puncturing it.
It is usually helpful to have a little bit of air in the tube: just enough to make it sort of round rather than flat. With presta-valve tubes, I usually just blow air into the tube by mouth.
It sometimes helps to stretch a brand-new tube first. I do this by stepping into it and lifting away by hand.
Start by fitting the valve of the inner tube through the valve hole. You may need to lift a rubber rim strip up at the valve hole and slip it all the way onto the valve stem so the valve stem doesn't try to drag it into the valve hole. Loosely secure the valve using a valve cap or retaining ring so it won't fall back through the hole. If your valve is threaded for a retaining ring, don't tighten it down very far yet, just thread it on far enough that the valve can't fall out of the rim.
With the tube dangling down along one side of the wheel, install one edge of the tire onto the rim, so that the tube is hanging out of the open side. This is usually pretty easy.
Next, tuck the tube into the tire. It is best to start at the valve, work your way one third of the way around the tire, then go back to the valve and work around in the opposite direction.
Once the tube is in place, you're ready to install the second edge of the tire. This is the hardest part of the whole process, and the hardest part of this is the very last segment.
If you start at the valve, it won't be a complicating factor when you are trying to lift the last bit of tire bead over the edge of the rim. With a very narrow rim, you may have to start opposite the valve -- just don't finish right at the valve.
As you install the second edge of the tire, try to push it toward the middle of the rim channel, where the channel is deepest. This will give you more slack.
Make sure that the tire bead is not sitting on top of the base of the valve. If it is, push the valve almost back through the rim to raise the reinforced patch at the base of the valve, and push the tire down around it.
For the last few inches of tire bead, some considerable force may be needed to pop it over the edge of the rim. (Some rim/tire combinations are easier than others.) If it is giving you difficulty, resist the urge to press the middle part over. Instead, work alternately from each end of the section you're trying to lift over. Going back and forth from side to side will usually get it.
Most folks do this by holding the wheel horizontally, with the open side up. Wrap your fingers around over the tire to press on the bottom of the rim, while you push the tire either with your thumbs or with the heels of your hands.
If you just can't get it by hand, here are some things to check:
You are less likely to have a problem seating your tire if you have the wheel off of the ground before you start. If the tire is completely flat and is sitting on the ground with the weight of the bike on it, the part that is at the bottom is likely to seat incorrectly.
Generally, if your bike has quick-release brakes, it's best to inflate the tire before putting the wheel back on the bike. If you don't have quick-release brakes, though, it's easier to install the wheel before pumping up the tire.
It's best to start by inflating the tire just enough that it takes shape, maybe 20-30 PSI, and to check that it is seated properly before full inflation. Check the seating by spinning the wheel and watching the tire.
Once you're sure the tire is properly seated, inflate it to full pressure.
Most tires have a "witness line" molded into each sidewall. This is a narrow ridge of rubber running around the side of the tire, just outside of the rim. Spinning the wheel and observing the witness line will help you locate the place where the seating might be off.
If the bulge is right at the valve, this usually indicates that the tire is sitting on the reinforcing patch at the base of the valve. Completely deflate the tire, and push the valve up into the tire with your thumb, while pressing the tire down around it, then pull the valve back down before inflating.
In some cases it may be beneficial to lubricate the side of the tire. This can be done with soapy water, but I usually use spray window cleaner for this, because it doesn't leave a soapy residue on the braking surface of the rim.
A tight fit will hold the tire in place if it blows out during a ride. A loose tire will flop around, making the bicycle impossible to balance.
Re-installing the wheel is a critical task, and if you don't do it right, the wheel can fall out, leading to a serious crash. This is particularly important on the front wheel. If it falls out you will probably land on your face!
Hundreds of people suffer gruesome injuries every year as a result of improper use of front-wheel quick releases, but if you understand their operation, they're quite safe and secure.
The quick release handle can move two ways: it can twist around like a wingnut, or it can flip 180 degrees outward and back, like a hinge.
The twisting motion adjusts the operating range of the quick release. You may have to hold onto the cone-shaped nut at the other end of the axle. You can't get the quick release tight enough by turning it.
The hinge-like flipping motion is the locking motion. In the "open" position, the quick release handle curves away from the bike. In the "locked" position, it curves toward the bike. (Very old levers are not curved, though -- but the tight position then is with the lever pointing clockwise at its base.) Never, ever ride with the lever in the open position, or partway closed!
If the quick release is too loose, the flipping motion will be easy, but it will not hold the wheel safely--flip it back, turn the adjusting nut clockwise some more, then try again.
If the handle is too hard to flip, and you cannot get it to flip far enough to lie flat, loosen the adjustment by turning the adjusting nut counterclockwise. There is a range of only a small fraction of a turn where the adjustment is correct, so you will probably have to repeat the adjustment.
It should take a good firm push to get the handle to lie flat. You will feel the resistance of the lever decrease for the last little bit before the lever lies flat; then it will come up hard against a stop. The decrease in resistance happens as the cam goes over center -- it actually loosens slightly as it reaches its closed position. Then vibration tends to tighten it rather than loosen it.
It is a good idea to set the quick release so that the handle points toward the rear when it is closed. This reduces the chance of getting it snagged on something. Flip the handle to the loose position, turn the handle and the cone-shaped nut together to align the handle once it has been adjusted -- then retighten.
It is customary for the quick release handle to be on the bicycle's left side, keeping the rear handle out of the way of the derailer.
Bicycles that don't use quick-release hubs normally have axles with nuts and washers that tighten against the fork ends of the bicycle. It is vitally important that these be securely tightened with a wrench.
Internal-gear hubs have tabbed or ridged anti-rotation washers which fit into the dropout slots, to keep the axle from turning. Generally, tabs should face the open ends of the slots. You will also have to reconnect and in some cases readjust the shifter cable.
When reinstalling the wheel, the chain on a non-derailer bicycle must be adjusted for minimum slack, so it won't fall off and doesn't bind. Instructions are here. If there is a brake reaction arm, attach it loosely, adjust the chain, then tighten the reaction arm. See advice here.
Newer derailer-equipped bicycles mostly have "vertical dropouts" for the rear wheel, so the wheel can only go in one spot. No adjustment is required with vertical dropouts.
Make sure to check the brakes after you have re-installed the wheel, especially if you disconnected the cable or used a brake quick release to make it easier to remove the wheel.
The main travel lanes of most roads are kept fairly clear of glass and other dangerous debris by passing motor traffic. Cyclists who travel in the normal traffic areas of the roadway benefit from this.
Many cyclists, however, hug the curb out of timidity and an irrational fear of being struck from behind by a motorized vehicle. The area close to the curb is where all of the glass shards, sharp rocks and other junk winds up. If you ride too close to the curb, you greatly increase the risk of tire punctures.
Riding too close to the curb also, paradoxically, increases your risk of being hit by a car! By cowering in the gutter, you reduce your visibility. You also encourage motorists to pass you even when there is insufficient room to do so safely. You also reduce your maneuvering room, and may have nowhere to go if evasive action is required.
Tires commonly have a recommended inflation pressure range, or at least a maximum value molded into the sidewall. These values are only very approximate, and experienced cyclists will rarely pay much attention to the rated pressure.
A major cause of "snake bite" flats is underinflation. Underinflated tires also have increased rolling resistance, making it harder to pedal.
Less well known is the downside of overinflation; this causes a harsh ride and can also cause poor traction on bumpy surfaces (overinflated tires tend to bounce, and a tire that is airborne, even for a moment, has no traction!)
A correctly inflated tire will have a slight bulge where it is in contact with the road. The correct inflation pressure is determined by the weight load, the tire width, and, to some extent, the riding surface.
Airless tires have been obsolete for over a century, but crackpot "inventors" keep trying to bring them back. They are heavy, slow and give a harsh ride. They are also likely to cause wheel damage, due to their poor cushioning ability. A pneumatic tire uses all of the air in the whole tube as a shock absorber, while foam-type "airless" tires/tubes only use the air in the immediate area of impact.
Airless tire schemes have also been used by con artists to gull unsuspecting investors.
Thornproof tubes are heavy, and add to rolling resistance, so they are a poor choice for cyclists who don't ride in conditions that require them. See also tire liners.
These are of dubious value in practice, but may be of help in backward areas where throwaway beverage bottles are still legal, and glass slivers are a major problem.
CO2 cartridges are small cylinders of carbon dioxide, originally made for seltzer siphons. With a suitable adaptor, they can be used to inflate bicycle tires. When everything goes well, this is the fastest way to inflate a tire. They're also the lightest and most portable inflation device available, so they're fairly popular among competitive cyclists.
The downsides of CO2 cartridges are that they are expensive and wasteful, and that each cartridge is normally only good for inflating one tire one time. While a few of the cartridge systems do permit controlled release of CO2, most of them are "all or nothing" designs, so you can't use them for topping off a slightly soft tire. If you carry only one cartridge and get two flats on the same ride, you may be in for a long walk. I advise against relying on CO2 cartridges except in competition.
Compressors are a popular alternative, when available. Most gas stations will have a compressor available, either for free or coin operated. While these are convenient, they can also be dangerous. If you use a gas-station compressor, you risk blowing the tire off the rim, so you need to be extra-careful, and use a separate, hand-held pressure gauge, too. The problem with using gas-station compressors for bicycle tires is that the volume of a bicycle tire is so much smaller than that of a car tire, so the bicycle tire inflates too quickly.
Many gas stations have a hose connected directly to the compressor, which is typically set at 120 PSI. You can only avoid overinflating your bicycle tire with this kind of hose by holding the head against the valve for a tiny fraction of a second at a time, then checking with your pressure gauge.
The head on the gas station hose may have a gauge and a handle. These make it somewhat easier to use, because you can press the handle down momentarily to add air to the tire, then check the gauge.
A gas-station compressor may have a head with a crank on it. You turn the crank to set the display to the desired pressure value in PSI. As air flows into the tire a bell rings. Each time the bell rings, the gauge checks to see if the pressure in the tire is more or less than the desired pressure. If it is more, the flow is stopped.
With a small-volume bicycle tire, the difference from one "ding" to the next can be 20 PSI or so. If you set the dial to 100, the air will go "ding...ding...ding..." then there's, say, 99 PSI in the tire. This is under 100, so it'll give it another blast and check again, and your tire could well be close to 120 PSI This assumes that the gauge is accurately calibrated for pressures in this range, which is a big assumption. The bottom line is that you really can't trust these gauges for bicycle tires. Instead, you should use a separate, hand-held gauge.
The most effective human-powered inflation tool is the "floor" or "track" pump. This has a long vertical cylinder, with a "T"-shaped handle that you raise and lower with both hands. This type of pump has some sort of footrest to keep the bottom held in place, and a hose that connects to the valve. Floor pumps get most of their action from the user's back, and with an assist from gravity, as the actual pumping occurs on the downstroke.
A floor pump for bicycle use should have a barrel about an inch in diameter; a thicker barrel will make it too hard to pump up a high-pressure tire. The better floor pumps have built-in gauges and holding tanks, so you can see just how much pressure you've got, while you're pumping. This makes them very fast and convenient to use. They also provide a bit of upper-body exercise to balance out all the leg exercise which bicyclists get!
"Frame" pumps are portable pumps designed to be carried on the bicycle's frame. They are typically about as long as one of the frame tubes, and have a spring-loaded handle that holds the pump in place along one of the frame tubes. Older bikes often had two brazed-on "pump pegs" to secure the ends of a frame pump. Many newer bikes have a single peg just below the top tube on the back of the head tube, for a pump running below the top tube.
Frame pumps are the best thing to carry on the bike for emergency, on-the-road use. They take a fair amount of work to get up to full pressure, but it beats walking! They pump fairly easily at first, but they can require a fair amount of strength as the pressure gets high.
Older frame pumps have a hose that screws onto the tire valve. This works poorly with a Schrader valve because air escapes when the hose is being unscrewed. Newer pumps have a clamp-on head that holds pressure better.
As you pump your tire up closer and closer to full inflation, the pump gets harder and harder to push. This is particularly an issue with narrow tires that need to be pumped up to high pressures.
Your arms may not be strong enough by themselves to get such a tire up to adequate pressure. Assuming you're right-handed, it can help to brace your left hand on the pump head. If there's a convenient tree, I'll often lean the pump head against the tree, so my left arm doesn't actually need to do any work. If there's no suitable tree or other solid object handy, or if I'm topping off a tire without removing the wheel from the bike, I'll kneel on my right knee and brace my left wrist against the inside of my left knee.
As I approach full inflation, and the pump gets harder to push full-stroke, I will start each stroke with my right arm free, then brace my right wrist against my chest for the final, hard part of the stroke, and use my back to complete the stroke.
It is very important that any type of pump be pushed all the way to the end of its travel on each stroke, otherwise you're wasting most of your effort. Air only goes into the tire once the pressure in the pump is higher than in the tire. You can feel the transition near the bottom of the pump stroke, when it stops getting harder to push.
Be careful that you do not bend or twist the valve stem when using a frame pump with an integral head. Bracing the pump against a tree, or a rock, can help to hold the valve stem straight, so you don't risk breaking it off or tearing the inner tube. A pump with a hose avoids this problem.
The most popular type of pump these days is the "mini" pump, a shorter version of a frame pump. A clip may attach a mini pump to water-bottle cage bosses or directly to a frame tube, or the pump may even be pocket-sized. Mini pumps are small and easy to carry, but they take much longer to use than full-sized frame pumps. I generally advise against buying mini pumps unless you have particular issues with theft. Their main advantage, though, is that they are small enough to be carried in a bike bag that you can remove when parking in high-risk locations. They also are lighter than than full-sized frame pumps. Some newer mini pumps engage the pressure chamber on both the push and pull stroke; these are faster than others. Topeak Morph ™ series pumps have some floor-pump features inlucding a footpad and hose.
Traditional tire levers, a.k.a. "tire irons" came in sets of 3, with a rounded business end, and a bent, hooked end for hooking onto a spoke. Newer ones are of fiber-reinforced plastic. I have an assortment of them for different tires. For very tight-fitting tires, you need tire levers with thin ends, able to get underneath tight beads. For less difficult tires, a single tire lever with a rounded, grooved end can be faster. I particularly like the "Quick Stick."
A similar unit, the Crank Brothers "Speed Lever" incorporates a telescoping extension that snaps onto the axle. This works very much like the power tools used in garages for mounting/dismounting automobile tires. This doesn't work too well on very tight tires, but on average tires, it is quite fast and easy to use.
The Kool Stop "bead jack" is an articulated tool for installing really tight tires. It has a comfortable handle and two ends, one of which is on a hinge. The rigid end uses the edge of the rim as a fulcrum, while the hinged end lifts the bead up and over the opposite edge of the rim. This is a very nice tool for dealing with really difficult tires.
Make sure to follow the instructions.
Wrenches are divided into two families:
Open-end wrenches don't get as good a grip as a box wrench, since they only engage two of the 6 corners of the nut. If you over-stress an open-end wrench, the jaws can spread, ruining the wrench.
Wrenches are sometimes confused with pliers, and naive users sometimes try to use pliers for jobs that really require a wrench. This usually results in damage to the nut or bolt so abused. It can also cause failure due to undertightening the part involved.
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