What Every Cyclist Should Know About Flat Tires
What's Inside Your Tire?
People usually think that tires are made of rubber. This is understandable, because rubber is all that you can see, but it's a serious oversimplification.
A tire is actually made up of three parts:
A bicycle tire is not airtight by itself, so it uses an inner tube , which is basically a doughnut-shaped rubber balloon. The inner tube has a valve to allow you to blow it up. (Tubeless tires are beginning to appear on bicycles, but are uncommon. They require the rim to be airtight, adding complications -- especially on a spoked wheel).
The beads are two hoops of strong steel cable (or, sometimes Kevlar ®.)
The cords, cloth forming the body of the tire, woven between the two beads. Most modern tires use nylon cords.
The rubber, which covers all the other parts. The rubber on the part that contacts the road is thicker, and is called the tread.
There are two types of valves in common use for bicycle tires:
Schrader valves are the same as the valves used on automobile tires. They are common on less-expensive bicycles, particularly those with wide rims and tires. Schrader valves are also sometimes called "American" or "automotive" valves.
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 or "French" valves. These are smaller in diameter than Schraders. This makes them a bit lighter, and allows a smaller hole to be drilled in the rim (desirable for very narrow rims). Presta valves are used on most high-performance bicycles, and all tubulars.
Presta-valve inner tubes come with valve stems of different lengths -- longer ones, for deep-section æro rims.
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.
Each type of valve requires a different type of pump fitting, but you can get an inexpensive adaptor to let you use a Schrader pump on a Presta valve.
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.
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
Types of Flats
A tire goes flat because there is a hole in the inner tube. There may or may not be anything wrong with the tire itself.
Flat tires can be divided into four groups:
Slow leaks take long enough to go flat that the bicycle may actually be ridden, but the tire will need to be pumped up more often than it should. It is normal for a tube to lose air over a period of weeks. If you put your bike away for the winter and come back in the spring, the tires will likely be soft or flat, but this doesn't necessarily mean that there is anything wrong with them: you may just need to pump them up.
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.
Punctures are caused by running over sharp things which poke a hole through the tire and into the tube. Punctures may be caused by glass slivers, thorns, nails, bits of wire or other small, sharp objects.
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 result from hitting stones, curbs, or sharp edges of holes in the road surface. When the tire hits a sharp edge hard enough, it compresses so that it bottoms out. The inner tube can get pinched between the rock and the rim. Pinch cuts usually put two small holes in the tube. This type of damage is sometimes called a "snake bite" because the two holes look like the wound made by the fangs of a snake.
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.
Blowouts are sudden losses of air, usually accompanied by a loud BANG! Since the inner tube is just a rubber balloon, if you pump it up outside of a tire, it will stretch bigger and bigger the more air you put into it, until it pops. The inner tube will not take much pressure by itself, it needs to be held inside of a tire to get up to full pressure. If the tire doesn't hold the tube in all around, the tube will pop.
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:
Optional step: Release the brake if your bike has handbrakes. If the tire is flat, it will slip out between the brake shoes, and if you replace it uninflated, it will slip back in. But then you will have to inflate it twice: once to test and once to ride.
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!
Nutted or "bolt-on" axles use nuts to hold the wheel to the frame. They are used on most bicycles with internal-gear hubs or a single speed, and on older or less-expensive derailer-geared bicycles. To remove the wheel, you will need to loosen the nuts on each end of the axle. It is usually not necessary actually to remove the nuts, just loosen them and leave them on the axle. (Less work and less risk of losing the nuts/washers.)
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.
There should be a washer between each nut and the forkend, but one of the places that newer bikes cut corners is by leaving these washers off. If your bike has axle washers, use them. If the washers are serrated (have teeth) the teeth should press against the forkends.
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!
Quick-release axles are hollow, and a thin rod called a "skewer" runs all the way through the axle. One end of the skewer is threaded, and has an acorn-shaped nut screwed on to it. The other end (usually placed on the bicycle's left side) uses a cam mechanism to secure the wheel. The cam is operated by a handle, which you can flip over to loosen the wheel. Pull the handle straight out away from the bike and flip it over. This will release the tension on the quick-release skewer, but you may need to loosen the mechanism a bit more before you can actually get the wheel out.
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!
Front wheel removal is fairly straightforward: Lift the bike by the handlebars, and the wheel will just fall out.
Rear wheel removal is a bit more complicated, but not usually too difficult, if you go about it in the correct sequence:
Derailer Gears Derailer gears look as if they would be the hardest, but are actually the easiest type of rear wheel to remove and re-install! The trick is to shift to the smallest (outermost) rear sprocket before loosening anything. This gets the derailer as far out of the way as possible. (It doesn't matter where the front derailer is.)
After freeing the axle by loosening the quick release or axle nuts:
- Stand to the left of the rear wheel.
- Use your left hand to lift the bicycle by the seat tube.
- Use your right hand to pull the upper part of the rear derailer backward, so that the jockey (upper) pulley swings down and behind the cluster.
- If necessary, nudge the wheel forward with your right knee, and the wheel will fall out.
- Lay the bicycle down on its left side, so that there is no weight resting on the derailer...this is the most fragile part of the bike!
Hub Brakes, such as foot-operated "coaster" brakes, or hand-operated "drum" or "roller" brakes built into the rear hub will have a flat metal arm, called a "reaction arm" which will attach underneath the left chainstay. This must be disconnected from the chainstay before the wheel can be removed. In most cases, this means undoing the bolt which holds the end of the arm to the metal strap or braze-on on the chainstay.
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.
Indicator Chains Many Sturmey-Archer and older Sachs internally-geared hubs (most commonly 3-speed) use a small chain called an "indicator spindle" which fits into the end of the axle. The gear cable attaches to this chain. The threaded fitting at the end of the cable must be unscrewed from the end of this little chain. This will require re-adjusting the gears when the wheel is re-installed. This procedure is explained in my Sturmey-Archer article.
Bellcranks Shimano 3-speed hubs (and some Sturmey-Archer 5-speeds) use a bellcrank to translate a pull on the gear cable into a push on a loose fitting pushrod that fits into the axle.
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.
Sachs Clickboxes Sachs/SRAM 5- and 7-speed hubs, and newer SRAM 3-speeds, use a "Clickbox" which is held onto the axle by a thumbscrew. No adjustment is normally needed (or possible) to the Clickbox. Once the Clickbox is removed from the axle, take care that the pushrod(s) don't fall out and get lost.
Shimano Nexus Hubs require the cable to be unhooked from the control ring. This is explained on my Nexus Mechanics Page. With Nexus hubs, it is often easier to open up one side of the tire and patch the tube on the bike, because this type of hub is the most difficult to remove.
Before you remove the tire, take a quick look at it to see if the cause of the flat is obvious. There may be a nail sticking out, or a hole in the sidewall, or some other obvious problem. More often than not, the cause will not be obvious from the outside, but a quick look can sometimes save time.
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.
If the hole is on the outer side of the tube, check the inside of the tire especially carefully in the area where the tube was punctured. It is very frustrating to install a new or patched tube and forget to remove the pointy object that caused the original problem!
If the hole is on the inner side of the tube, check the inside of the rim. Although the rim tape is supposed to protect the tube from rim imperfections, sometimes it is not properly placed, and sometimes spoke ends can actually poke through the tape. Burrs and other sharp edges inside the rim can easily puncture tubes.
If you find two holes, one above another, you probably have what is commonly called a "snake bite," a pinch cut resulting from hitting a stone or pavement break and pinching the tube between the rim and the rock. This sort of failure is most often caused by insufficient tire pressure.
- If a Schrader valve is leaking, replacing the valve core will usually solve the problem.
While you have the tire off the rim, examine the inside of it carefully. Thorns and glass slivers can hide, and may be difficult to remove. I find that pushing them back out through the tread, using a sharp instrument, is often helpful.
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.
If you're on the road and have a tire with a bad cut that could allow the tube to bulge through, you can make a temporary repair by installing a "boot" on the inside of the tire. This can be made of any flexible but non-stretchy material. The ideal thing is a piece cut from an old tire, because this will have the correct curved shape to begin with. I usually like to carry a strip 2-3 inches (50-75 mm) long, cut from an old tubular tire or a high-pressure road clincher. Mountain bikers sometimes use dollar bills folded over, or Mylar food wrappers.
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.
Inner-tube patching is a very old, well established technology, and is quite reliable if done properly:
If you follow this procedure, and use good materials, your patched tube should be basically as good as new.
- Select a patch appropriate to the size of the hole(s).
Use the sandpaper provided in the patch kit to buff the surface of the tube for an area a bit larger than the patch. If you don't have sandpaper, you can sand the affected area of the inner tube on the pavement. You need to buff the tube so that it is no longer shiny. If there is a molding line running along the area where the patch is to be applied, you must sand it down completely, or it will provide an air channel. Jobst Brandt suggests carrying a Bic razor blade in your patch kit to slice off mold lines. [I tried this and cut a hole in the tube -- back to sandpaper. John Allen]
Avoid touching the buffed area with your fingers.
Apply a dab of rubber cement, then spread it into a thin coat, using your cleanest finger.
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.
- Allow the cement to dry completely.
- Make sure the cement has dried completely! You can check by tapping it with a knuckle.
- Peel the foil from the patch and press the patch onto the tube firmly.
- Squeeze the patch tightly onto the tube. You're done!
Patch failure generally results from one of two errors:
- Not buffing the tube sufficiently, or:
- Applying the patch before the cement has dried fully.
For more technical detail, see Jobst Brandt's comments.
Re-installing the Tire
Although you usually need tire levers or a similar tool to remove a tire from the rim, usually you should be able to re-install the tire with your bare hands.
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:
- Make sure the tire bead isn't sitting on top of the tube or rim strip anywhere.
- Make sure the tire bead you're working on is pushed as close to the middle of the rim channel as you can get it.
- The thinner the rim tape, the easier it is to mount the tire. Consider replacing the rim tape.
Some tire/rim combinations are just too tight a fit, and you may need to use a tool. The best tool for this is the "Kool Stop bead jack
" because this tool lifts the edge of the tire without going inside of it, so it is less likely to damage the inner tube than a conventional tire lever is.
Inflating the Tire
Once the tire is fully installed on the rim, you can inflate it, but it may not be as round as it should be. If it isn't, it is usually because the tire needs to be "seated" so that it sits at the same depth in the rim all the way around.
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.
Seating the Tire
If the tire is not seated properly, usually this will take the form of having most of the circumference of the tire in the correct place, but there will be one place where the tire either bulges out too far, or dips inward toward the rim. Note, it could be OK on one side of the tire but not the other.
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.
Seating A Bulging Tire
If one part of the tire bulges out farther than the rest, deflate it right away or it may explode with a loud BANG! Manually re-arrange the tire to get it centered on the rim before re-inflating it. Make sure the tire bead isn't sitting on top of part of the inner tube, or the rim strip. This can happen if the rim strip is too wide, or is installed off-center.
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.
Seating a Tire that Dips Inward
If your tire dips inward at one spot, without bulging out at another, it is usually a sign of an unusually tight fit. This may make it a bit of a struggle to install the tire, but it also means that you can get away with considerable overinflation with no risk of blowing the tire off the rim. Indeed, the best way to seat a "dipping" tire is by temporarily overinflating it until it "pops" into position.
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
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.
Twist or Flip?
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.
Check the Brakes!
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.
Many flat tires are avoidable, but some are not. Some people seem particularly prone to them. This is often caused by poor road position: people often get an unusual number of flats because they are riding in the gutter instead of the traffic lane.
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.
Tire pressure is the hardness to which a tire is inflated. This is commonly measured in PSI
(pounds per square inch), BAR
, or kPa
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.
Of all the inventions that came out of the bicycle industry, probably none is as important and useful as Dr. Dunlop
's pneumatic tire
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.
The fastest road tires have a thin tread and sidewalls, in the interest of low rolling resistance. Tires with deeper tread resist flats better. It's your choice to make!
Aftermarket tire liners, such as the well-known Mr. Tuffy, are not necessary for most cyclists. They make your wheels heavy and sluggish, and, if incorrectly installed, they can actually cause flats!
In some regions, notably the Southwestern U.S., "goat-head" (tribulus terrestris) thorns are so common that such liners, or thornproof tubes, are a desirable option.
Kevlar ® is a very strong artificial fiber, used in bullet-proof vests and bicycle tires
. Kevlar is used in tires two different ways, for two different purposes:
Kevlar beads are used on some high performance tires. Replacing the normal wire bead with Kevlar ® saves about 50 grams per tire. Kevlar-bead tires have the additional advantage of being foldable, making them popular as emergency spare tires with touring cyclists. Kevlar-bead tires are somewhat harder to mount on a rim, and are more likely to blow off than wire-bead tires. They work best on "hook edge" rims.
- Kevlar-belted tires have a layer of kevlar under the tread surface, with the purpose of making the tire more resistant to punctures caused by small sharp objects, such as thorns and glass slivers. Kevlar-belted tires have slightly higher rolling resistance, price and weight than corresponding tires without the belt.
Special "thornproof" inner tubes protect against "goat-head" thorns and glass shards. These tubes are very thick on their outer circumference, so that a short thorn (or a small glass shard) may be embedded in the tube without being able to reach in far enough to let the air out.
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.
Some punctures are caused by glass slivers or thorns gradually working their way through the tire tread. What can happen is that a small sharp object may be picked up by the tire, then gradually work its way in over the course of several tire revolutions. The pointy thing is driven in like a nail into wood by repeated blows against the pavement. A formerly popular device called a "tire saver" or "flint snatcher" used a loosely-sprung piece of wire (generally made from a bicycle spoke) to brush the tire tread constantly in hope of dislodging glass slivers and the like before they could penetrate all the way to the inner tube.
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.
Pressure gauges come in three types:
"Pencil" gauges are the simplest and cheapest. They look like a pencil, with a fitting at one end that you can press against the valve. When you do so, a rod slides out of the other end. This rod is calibrated like a thermometer, and slides out farther the more pressure is in the tire. This type is most commonly used for Schrader valves (though Presta versions are also available.) Note that "pencil" gauges come in automotive and bicycle types. The difference is the pressure range they measure. Automotive pencil gauges commonly only read up to 50 PSI, while those intended for bicycle use run up to 120 PSI.
- "Dial" gauges are a bit more expensive, but are easier to read and may be a bit more accurate. Some dial gauges have double fittings, allowing the same gauge to work with both Schrader and Presta valves. Less expensive dial gauges must be read while they are on the valve, but better ones have a "memory" feature, and will hold their readings after being removed from the valve, until the "reset" button is pressed.
- "Digital" gauges have a liquid-crystal readout, and an electronic sensor. They are probably the most accurate, though real-world accuracy of any type of gauge is limited by the fact that a small amount of air is lost as the gauge is removed from the valve.
If you have Presta valves
, it is a good idea to carry a Schrader/Presta adaptor. It is a small thing and easily lost, unless you leave it screwed onto the valve of one of your tires. You can add a Schrader valve cap.
You have 7 possible choices of tools to inflate your tires:
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.
Floor ("Track") Pumps
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!
An less-common type of pump, similar to a floor pump
, also sits on the ground, but is operated by pressing with the foot. These are fast, but mechanically complex due to the extra linkages required. They also tend to be designed more for delivering volume than for pressure, so they don't generally pump up to high enough pressure for narrow road-type tires.
"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.
Frame Pump Technique
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.
One Is Not Enough
A frame pump is not a substitute for a good floor pump
; the well-equipped cyclist will own both. The floor pump is for routine pressure topping off at home, and the frame pump is for fixing flats that occur while you're out riding...it's too hard to use for non-emergencies.
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.
Patch kits are available in any bike shop. A patch kit is usually a small plastic box containing a few patches, a tube of rubber cement, and a bit of sandpaper or a metal scraper for preparing the tube surface. The metal scraper is not advisable for use on bicycle inner tubes -- it cuts too deep.
The best patch kit is the Rema "Tip Top" from Germany.
Make sure to follow the instructions.
Glueless (peel & stick) patches are available, and they are slightly more convenient than conventional patches. Unfortunately, they don't have a very good reliability record, and I can't recommend them--you're much better off with a standard patch kit.
Unless your wheels have quick release hubs, you'll need a wrench or two to remove the wheels. (The term "wrench" is not common in British usage, where the the term "spanner
" or "key
" is generally preferred.)
Wrenches are divided into two families:
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Last Updated: by Harriet Fell