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Flat Tires

30 марта 2009

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:

  • The beads are two hoops of strong steel wire (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.

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.

Valves

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 removeable 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 hole which must be pushed in to put air in (or to let air out.) Before the introduction of the Zé 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 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 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, but a Schrader valve won't fit through the valve hole on a rim drilled for Prestas. Presta drilled rims may easily be drilled or reamed to accommodate Schrader valves.

Schrader valve

Presta valve closed

Presta valve open 

Presta valve with adaptor 

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

Rim Tapes

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.

Some rim tapes are simple strips of rubber, similar to the rubber used to make the inner tube. These are adequate for low-pressure use. Better rim tapes are adhesive cloth or plastic.

Types of Flats

When your tire goes flat, it means that 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

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, they 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

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

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.

Blow Outs

Blow Outs 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.

Wheel Removal

Although it is sometimes possible to repair a flat without removing the wheel from the bike, usually it is easier if you do take the wheel off.

Release the brake

Release the brake if your bike has hand brakes. 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.

Unfortunately, bikes 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.

Nutted or «bolt-on» axles

Nutted or «bolt-on» axles use nuts to hold the wheel to the frame. They are used on older or less-expensive bicycles. To remove the wheel, you will need to loosen the nuts on each end of the axle. It is usually not necessary to actually remove the nuts, just loosen them and leave them on the axle. (Less work and less risk of loosing 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.

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!

There should be a washer between each nut and the fork end, 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 fork end.

Quick-release axles

Quick-release axles are hollow, and a thin part 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 until it is loose enough to let you remove the wheel. 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

Front wheel removal is fairly straightforward: Lift the bike by the handlebars, and the wheel will just fall out.

Rear wheel removal

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

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 may 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.

Internal Gears

  • Indicator Chains. Sturmey-Archer 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.
  • Bell Cranks. Shimano 3−speed hubs (and some Sturmey-Archer 5−speeds) use a bell crank 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 bell crank.
    Sturmey-Archer
    S-5 bell cranks should be adjusted so that the cable is taut when the wide-range position is selected with the left shift lever.
  • Sachs Clickboxes. Sachs 5- and 7−speed hubs 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.
    Sachs 3−speed (including the 3 X 7) use an indicator spindle similar to that of the Sturmey-Archer hubs.
  • 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.

Tire Removal

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 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 fibreglas or other plastics.) Most tire levers have a rounded end and a hooked end.

Tire levers commonly come in sets of three, because three is the most you ever need. For a difficult tire, stick the rounded end of one tire lever under the bead (starting somewhere away from the valve--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.

Tube Inspection

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. 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.

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.

Tire Inspection

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.

Tire Repair

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.

Patching

Inner tube patching is a very old, well established technology, and is quite reliable if done properly:

  • 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. 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.
    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!
  • Peel the foil from the patch and press the patch onto the tube firmly.
  • Squeeze the patch tightly onto the tube. You're done!

If you follow this procedure, and use good materials, your patched tube should be basically as good as new.

Patch failure generally results from one of two errors:

  • Not buffing the tube sufficiently, or:
  • Applying the patch before the cement has dried fully.

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.

In the case of a brand new tube, it sometimes helps to stretch it out 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. 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.

You should start at the valve, so that the valve won't be a complicating factor when you are trying to lift the last bit of tire bead over the edge of the rim.

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 difficult, 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 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. If you have thick rim tape, consider replacing it.

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 my not be as round as it should be. If it isn't, it is usualy 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

Once the tire is inflated, you may see that it is not as round as the rim is. Usually this will take the form of having most of the circumference of the tire in the correct place, but there will likely be one place where the tire either bulges out too far, or dips inward toward the rim. It may do this on only one side.

Most tires have a «witness line» moulded 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. Note, it could be OK on one side of the tire but not the other.

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.

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, 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 temporariliy 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.

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!

Quick-release Wheels

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 wing nut, 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 it 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. Never, ever ride with the lever in the open position!

If the quick release is too loose, this flipping motion will be too easy, but it will not hold the wheel safely--flip it back, turn it clockwise some more, then try again.

If it is too hard to flip, and you cannot get it to flip far enough to lie flat, loosen the adjustment by turning the handle counterclockwise.

It should take a good firm push to get the handle to lie flat.

It is a good idea to set it so that the handle points toward the rear when it is closed. This reduces the chance of getting it snagged on something. Turn the handle and the cone-shaped nut together to align the handle once it has been adjusted.

It is customary to install the front wheel so that the quick release handle is on the bicycle's left side.

Nutted or «Bolt-on » Wheels

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.

Newer bicycles mostly have «vertical drop outs» 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 it or used a quick release to help remove the wheel.

Prevention

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 who get an unusual number of flats often do so 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.

Pressure

Tire pressure is the hardness to which a tire is inflated. This is commonly measured in PSI (pounds per square inch), BAR, or kPa (kiloPascals.)

Tires commonly have a recommended inflation pressure range, or at least a maximum value moulded 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 under-inflation. Under-inflated tires also have increased rolling resistance, making it harder to pedal.

Less well known is the downside of over-inflation; this causes a harsh ride and can also cause poor traction on bumpy surfaces (over-inflated 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.

For details on optimal tire pressure, see the «Pressure» section of my Tires Article.

Airless tires

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.

Tire Liners

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., cactus thorns are so common that such liners, or thornproof tubes, are a desirable option.

Kevlar ®

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.

Thornproof Tubes

In some regions, notably the Southwestern U.S., cactus thorns are so common that special «thornproof» inner tubes are needed. These tubes are very thick on their outer circumference, so that a short thorn (or a small glass sliver) 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.

Tire Savers

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 spring piece of wire (generally made from a bicycle spoke) to constantly brush the tire tread 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.

Tools

Pressure Gauges

Pressure gauges come in 3 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.

Valve Adaptors

If you have Presta valves, it is a good idea to carry a Schrader/Presta adpator

Pumps

You have 7 possible choices of tools to inflate your tires:

CO2 Cartridges

CO2 cartridges are small cylinders of carbon dioxide, originally made for seltzer siphons. With a suitable adaptor, they can be used for inflation of 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 down sides 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

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, be sure to use a separate, hand-held pressure gauge, because if you rely on the gauge built into the compressor outlet, you risk blowing the tire off the rim.

The typical gas-station compressor has 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.

The problem with using these gauges for bicycle tires is that the volume of a bicycle tire is so much smaller than that of a car tire that 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 actuall pumping occurs on the down stroke.

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.

Foot Pumps

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

«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 Techinque

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 or 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 indside 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.

With any type of pump, it is very important that the pump be pushed all the way to the end of its travel on each stroke, otherwise you're wasting most of your effort.

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…they're too hard to use for non-emergencies.

Mini Pumps

The most popular type of pump these days is the «mini» pump, a pocket-sized version of a frame pump. People like them because they're small and easy to carry, but they take much longer to use than full-sized frame pumps. I generally advise against buying a mini pump unless you have particular issues with theft, because they are so inefficient. Their main advantage is that they are small enough to be carried in a bike bag that you can remove when parking in high-risk locations.

Tire Levers

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 fibreglass or similar materials. 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

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 cememnt, and a bit of sandpaper or a metal scraper for preparing the tube surface. The best patch kit is the Rema «Tip Top» from Germany.

Make sure to follow the instructions.

Glueless Patches

Glueless (peel & stick) patches are avaialble, 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.

Wrenches

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 term «spanner» or «key» is generally preferred.)

Wrenches are divided into two families:

  • Fixed Wrenches are made of a single piece of metal, and only fit specific sizes of fasteners. Types of fixed wrenches include:
    • Box wrenches have a complete loop that surrounds the fastener. They are substantially stronger than open-end wrenches, and are the best use for high torque applications, both because the wrench is stronger, and because it can contact more than two corners of the fastener.
    • Open-end wrenches have ends shaped like a two-tined fork. They normally have two parallel surfaces which bear against two of the sides of a fastener. Open-end wrenches are faster to put on to fasteners, and are the only kind that can be used where there is not clearance to slip a box wrench over the end of the fastener.
      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.
    • Combination wrenches are double-ended wrenches with an open end and a box end, usually for the same size on each end. This is the most useful and most common general-purpose wrench style.
  • Adjustable Wrenches can be adjusted to fit different sized fasteners, usually by the use of a thumb screw. They don't fit as well as the correct size fixed wrench, so good, well equipped mechanics only use them as a last resort. See my Tool Tips article on Adjustable Wrenches.

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.

Событие

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joe
21 мая 2013

«Москва велосипедная» проводят конкурс сумасшедших велокостюмов :)

Авторы лучших работ примут участие в праздничном велозаезде, который телеканал «Дождь» устроит 30 июня, а самого сумасшедшего ждёт поездка в Европу на двоих.

Будь в курсе!

0
18 сентября 2011

18 сентября16:00, 17:30 — День открытых дверей в музее веломобилей19 сентября19:00 — Лекция «Smart City: теории и практики создания умного города»20:00 — Предпремьерный показ фильма о велосипедном путешествии из России в Португалию участников проекта Let’s Bike It!

0
27 мая 2011

Обсуждение проблем, связанных с велосипедным транспортом, с президентом «Велотранспортного союза» Игорем Налимовым, куратором проекта по развитию велодвижения в России Let's bike it Владимиром Кумовым, и координатором исследовательской темы «Общественное пространство» института медиа, архитектуры и дизайна «Стрелка» Федором Новиковым.

0
24 мая 2011

25−летняя англичанка Сара Оутен (Sarah Outen), совершающая одиночное кругосветное путешествие, вчера вечером добралась до Астрахани — последнего города в Европе на её маршруте.

0
19 мая 2011

Улучшенная трасса длинной 850 метров с перепадом высот до 100 метров уже была опробована сильнейшими мтб райдерами на первом этапе Кубка Сибири и Чемпионате который пошел в Новосибирске в прошлом году.