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What's Inside Your Tire?

 

 

 

 

 

    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.

    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.

        * 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.

    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.

Rim Tapes

Types of Flats

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

    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.

    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.  

      1. Select a patch appropriate to the size of the hole(s).

      2. 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.

      3. 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.

      6. Peel the foil from the patch and press the patch onto the tube firmly.

      7. 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.

        * Not buffing the tube sufficiently, or:

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.

    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.