Bicycles/Maintenance and Repair/Wheels and Tires/Fixing a flat

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Contents 1 Introduction 2 Terminology 3 How to fix a punctured bicycle tire 3.1 Evaluate the situation 3.2 What tools do you need? 3.3 How to do it 3.4 The slow Leak 4 If all else fails 5 Notes

Introduction A flat tire or puncture occurs when glass, thorns, flints or nails cut through the outer rubber tread of the tire and damage the inner tube. Although this is the most obvious way to get a flat tire there are other ways too. The way that the puncture presents itself often gives a clue as to the cause; for example: A single sudden and reasonably quick deflation, as mentioned above; is usually caused by a through and through puncture. A slow leak, on the other hand, where the tire slowly loses pressure over time, is often caused by valve stem abrasion or rubbing of the innertube on the inside rim. A series of "recurrent punctures", where altogether too much time is spent fixing punctures, might well signify that the tube has suffered too much and would best be replaced with a sturdier item.

Terminology

The basic parts of interest are these; tires (tyres), tubes, and valves.

• Wheels are the big round metal parts - with spokes - that the tires wrap around.
• Tires are the rubber outer parts that contact the road's surface. They have treads, smooth or patterned, depending on their use. Tubeless bicycle tires exist, but they are still quite rare on pushbikes; we will deal only with tires having inner-tubes.
• Inner-tubes are the inflatable parts between the tire and the metal parts of the wheel. They are invisible apart from their valves that protrude through the wheel-rims. There are three valve types in use; Schrader valves, Presta valves, and the lesser used Dunlop valves. Refer to the adjacent image.
• Rim-linings protect the bottom of the inner-tube. The ends of the spokes enter the rims, and this lining covers them so that the tube is not damaged.
• Anti-puncture linings protect the top of the inner-tube. Some high-end tires have these built-in, but most tires have none. As accessories, they can be easily added between the tire and the inner-tube. They prevent most punctures from thorns, glass, flints, and other sharp objects that contact the running surface of the tire, though they do not protect the outer tire itself.

[edit] How to fix a punctured bicycle tire

[edit] Evaluate the situation

First, ask yourself whether you really need to repair the puncture right now? Do you have means and knowledge to fix it? Would it be better take the bike (or the wheel) to a shop, or fix it somewhere else, perhaps where there are tools?

If the flat occurs on a regular short distance from a good place to perform the repairs, so it's probably better to walk the bike to this location. Some flats are a long way from such a location and it's usually easier to repair them on the spot. Some flats occur in remote locations, where thoughtful planning should mean that one has an abundant supply of patches, glue, tools, a spare tube or three and perhaps a spare tire or two.

Some punctures are easy to repair and some are terribly difficult to repair.

People who race or train over long distances without a support crew, can get a puncture, stop, repair it with a thin film of tube cement (blow on the glue), pump the tire back up and get going again - all in the space of a minute or two.

However, some people like to turn the flat tire repairs into an all day fiasco, much like a picnic, with food and drinks and a radio and some friends for moral support - in the great outdoors or the living room, as the case may be.

You can pick your style and work towards that.

The purpose of this page really is to assist people who have little or no idea on how to repair a puncture, and to perhaps assist the more seasoned puncture repairers amongst us.

When it comes down to it, repairing almost all punctures in bicycles is almost as easy as sticking a stamp onto an envelope.

If you only get the infrequent puncture and have plenty of time, it can take a little while, where as if you get LOTS of practice and you train at being very efficient, you can easily fix almost every flat in about 2 minutes or less.

[edit] What tools do you need?

• A pump that fits your valves.
• A replacement tube.

OR

• A puncture repair kit containing:
  • Rubber patches.
  • Rubber vulcanising solution (glue that sticks rubber together) if necessary (see below).
  • A small piece of sandpaper, a sharp pen knife, or other rough material.
  • A ball point pen, a felt pen, or some chalk.

Also helpful:

• Tire levers (at least two, preferably three) - sometimes included in a repair kit.
• If you have Schrader valves, a valve cap with a valve extraction key on it can make removing and re-installing the tube a lot easier.

• If the bike has nutted axles instead of quick-release skewers, you'll need some tools to remove the nuts so you can take the wheel off, e.g. "ring spanner" or some other type of wrench. Some bicycles require two wrenches. Try out your tools before riding to be sure that they are the right ones to carry.
• A talcum block (the small grey block included in some kits) or small bag of talcum powder.^[1]

Pre-glued patches are included in many kits. They are useful in case of rain or other wet conditions because you do not need to wait for glue to dry. However, they are less reliable than cemented patches.

To set a (non-pre glued) patch, the best glue is the "proper bicycle tube glue". In a pinch other glues (cements) can do the job, but all have their drawbacks, especially for on-the-road repairs.

• Some solvent-based contact adhesives such as "Quick Grip" (TM) will work initially, however they tend to chemically react with the rubber, and over time may cause a failure of the tube itself.
• Silicone Rubber (glass fish tank / window glue) works fine, but is more an over night glue (apply to both faces thinly, allow to partly dry and clamp together, and leave in a warm place over night).
• Pure latex liquid rubber works very well - if painted on both parts, allowed to mostly dry and then they are clamped together.
• Cyanocrylate (super glue) will glue the rubber tears and pin holes if the rubber is CLEAN.
• Two-part epoxies, model aeroplane glues, and PVA wood glues will work as as well but are not flexible when dried.
• Other cements such as construction adhesive will work, but only come in large bicycle-unfriendly packages.

Pay attention to the container that your patch cement is held in. You don't want to need it only to find that you can't open it, or that the cement is dried out.

The BEST patch kit is no patch kit. Simply carry a spare tube.

[edit] How to do it

Remove any tools you need from their hiding places, then stand the bicycle upside down on its handle bars and seat.

Examine both tires carefully. If you're lucky, you will find the item that has caused the puncture (glass, nail, thorn, etc.) but there may be more than one so don't stop when you find something. Mark the item with your pen so you can find the hole again, then remove it.

Also, look for any potential problems to your tires such as bulges (tearing carcass), exposed carcass cord, bits of glass that are working their way into the tire, and so on. If there is a failure in the tire itself - e.g. a rip or split - then repairing the tube is pointless. It will just poke out of the hole and quickly flat again.

If the hole in the tube is not fixable, or if the hole is so small that it requires re-inflating to search for the leak, then you will have to remove the wheel from the bike and the tube from the tire.

Step 1.

• Leaving the wheel in place.
  • If you know where the hole is and you using a patch instead of replacing the tube, you can do the repair with the wheel still on the bike. However, you may find it more comfortable to remove it anyway. Working around the wheel parts can be annoying, but you may find it easier than wrestling off a wheel and fussing with brakes and gears.
  • In Step 2, open the gap an pull out a section of tube right under the place you marked with the pen. You should be able to spot the hole in the tube easily.

• Removing the wheel.
  • Remove the wheel from the frame. On some bikes, you need to spread or detach the brakes to do this. It is best to position the bike upside down when removing a wheel, although it is possible to do it with the bike upright.
  • If your bike has Quick release wheels, remove the wheel by loosening and unscrewing the quick-release bolts (skewers).
  • If your wheel is attached to the frame by ordinary nuts, undo them with a ring spanner (wrench).
  • If you have to take off the back wheel, it is usually a bit more complicated, because you need to get the wheel past the chain. If your bike has multiple gears Dérailleur gears, change into the very top (smallest) rear gear to make it easier to get the wheel off past the chain.

Step 2.

• If the tire is not fully deflated, open the valve and let the rest of the air out, as any residual air will make it difficult to get the tire off and the tube out. If you have Schrader valves and the nifty cap, use the valve key ending to remove the valve and allow the excess air to escape from the tire. Don't lose the valve. Place the valve and the valve cap somewhere safe.

• Open a gap in the outer tire and remove the inner tube. With the wheel off, extend the gap around the whole rim. This can be easy or difficult: the large "balloon" tires on mountain bikes can be peeled off the rim with your fingers, while the tight-fitting high pressure road bike tires may need to be levered off the rim.
  • Be careful not to pinch the tube between the tire and rim, or under the levers, as it might cause you to inadvertently puncture the tube.
  • First, push the outer edge of the tire as far in towards the other side of the rim as possible. To do this, squeeze the edges of the tire inward and forward, and continue to do this right around the tire. This moved the bead of the tire, to the center of the rim which is smaller in diameter, than the part of the rim that the tire bead seats upon. The greater gap makes it easier to remove the tire.
  • Then, insert a tire lever between the wheel rim and the tire, and lever the edge of the tire up over the rim. The tire lever usually has a little hook at its non-levering end; use this to hook to a spoke and hold the lever in place.
  • Now get another tire lever, and a bit further up the tire, lever another bit of tire past the rim.
  • After you have a fairly large section of tire up over the rim, get a third tire lever and start to lever the rest of the tire over the rim. Work your way around until the whole side of the tire is over the rim.
• Now you will be able to remove the inner tube.
  • Carefully push the tire valve through the hole in the wheel where it sits and with your fingers (do not use anything sharp) gently ease the inner tube out from between the wheel and the outer tire,

Step 3.

• Now that you have the inner tube out, locate the puncture. If you've already found the nail (or whatever), you should know right where to look on the tube. If you haven't found the cause by inspecting the outside of the tire, feel (gently^[2]) around the inside of the tire. It's entirely possible that the flat wasn't caused be a foreign object, so don't stress if you don't find one.
  • The usual method is to pump up the inner tube and if it is a fast leak, you can put your ear to it and listen for the leak.
  • You can also dampen your hands, lightly wrap your hands about the tube, and slide them around it to feel for the air escaping.
  • If this doesn't work because the leak is very slow, pump up the inner tube and immerse the inner tube in a bowl of water. Watch for bubbles, which indicate a puncture.
• Use a ball point pen, felt marker, or the chalk supplied with your puncture repair kit to mark an X on the location of the puncture. Make the X somewhat wider than the patch diameter. This will enable you to centre the patch over the hole.

Step 4.

• After you have located the puncture, scratch the tube -lightly- with the sandpaper around the hole to give the glue a place to grip. You can also scrape a sharp blade across the tube surface, to remove the fine layer of rubber that has the talcum powder dust (French chalk) or mould release impregnated rubber off the surface of the tube.
• Then, apply a thin film (not too thick) of patch glue (usually) supplied with your puncture repair kit, making a wet spot slightly larger than your patch.
• While the glue dries to a tacky film, peel off the plastic coating on the back of the patch, and stick it squarely over the puncture. Press it down firmly for a minute or so until it is firmly stuck.
• It is usually a good idea to pump up the inner tube very gently after a minute or two to check that the patch has stuck properly to the tube and seals the puncture.
• Patches often have a clear fragile plastic layer on their top sides. You can peel this off or leave it there.
• If you have some talcum powder or some talcum block, make some powder by rubbing it on the sandpaper (preferably a separate piece kept for this purpose). Rub the powder over the patch and the glued area to prevent either sticking to the inside of the tyre when pumped up.

Step 5.

• Now replace the inner tube into the outer tire, and refit the outer tire. Before you do this, feel the inside edge of the outer tire with your fingers to make sure that no sharp objects are still pointing through.
• Insert the valve back into the tube and tighten to a firm touch with the valve cap key.
• Pump a very small amount of air back into the tube to give the tube a proper cylindrical shape. This is so that it goes back into the tire without flopping around (and liable to being pinched), and to position the tube properly inside the tire.
• Now with your fingers, carefully ease the inner tube back into the gap between the wheel rim and the outer tire, making sure that it is the right way around and isn't twisted.
• Replace the tire valve into the hole in the wheel where it sits. Make sure the valve is correctly located and fully seated, because if it is tilted or offset, the tube will bulge into the hole and spring another leak when inflated. If this happens, it will be unfixable because of its location.
• Now, lever the outer tire back over the wheel rim with the tire levers. This is usually easier than removing it-- you usually just need to gradually lever the tire edge over the rim until the whole tire is over it. Make sure you don't get the innertube caught between the outer tire and the rim.
• Finally, reattach the wheel to the frame, make sure it is firmly attached, and pump the tire up to operating pressure.

[edit] The slow Leak

Any tire or tube may be checked for a leak by inflating it, submerging it in water, and looking for telltale air bubbles.

A slow leak can sometimes be caused by a leaking tire valve. Absent a tub of water, remove the valve cap and with the tire inflated to a reasonable pressure, spit on your finger and wipe spit across top of valve. If it bubbles up there's a leak.

To try to fix a leaking Schrader valve, deflate the tire, unscrew the valve body with a keyed valve cap or valve tool, and examine the seat or rubber sealing ring for cuts or nicks, dust or lint, or fibers preventing the valve from closing fully. Likewise check the valve seat and the bore of the valve stem. Clean if necessary. The valve body may be replaced. If no spares exist the assembled valve can be "repaired" by inflating the tire and sealing the valve with silicon rubber or caulk. Obviously the tube will have to be thrown away after doing that.

A Presta valve cannot be disassembled. Replace the tube.

[edit] If all else fails

Resolve to bring your cell phone on the next ride.

Some people under the circumstances of remoteness and distance, after getting a flat, have had to pack their tires with grass and rags, and then have slowly ridden the bike to a place where repairs and supplies may be obtained.

[edit] Notes

Keep in mind the following:

• If you find two punctures close together, it may be a "snake bite", caused by an underinflated tire hitting a hard bump or crack, and pinching the tube.
• If the puncture is at the bottom of the valve stem, or if there is a large tear, it MAY be irreparable, depending upon how desperate you are, and what resources are available.
• Get your own pump, preferably one with a meter. Most bikes made in the last 15 years require pressures of 40-65 psi (Mountain bikes) or 100-120 psi (road/touring bikes). Pumps at fuel stations (at least in North America) normally are unable to fill higher than 35 psi. Pumps at fuel stations in Australia are frequently used for trucks. The Australian air pumps do on occasion go to 120 PSI. Beware: Pumping bike tires designed to be inflated to a maximum of 55 PSI up to 120 PSI will both make you deaf and could be quite hazardous, should the rapid deflation of the tire occur while riding.
• The recommended inflation should be written on the side of the tire.
• Note that there are two common types of valve: Presta and Schraeder. Schraeder is the type seen on most motor vehicle tyres, whereas Presta valves are smaller valves used on narrower tyres that can withstand higher pressures. Make sure that your pump will fit the type of valve you have (or both types). If it doesn't, you will need an adapter.
• Try to avoid the use of a screwdriver or the like as a tire iron to remove the tire from the rim, or worse yet, reinstall it with screwdrivers. They have sharp edges and when pressure is applied to them in the way of compressive force or they are "slid around" inside the tire, they can cut into the tube very easily.

Commercial car or motorcycle tire irons are TOO large and may damage the tire or rim by the greater leverage available and the very large size that the tyre is pulled over. The commercial bicycle tire irons or tyre levers, come in two styles, very thick and strong ones for road bike tires and very thin ones for mountain bike "ballon" tires. Most of the larger "ballon" tires are easy enough to install and remove the tire just by the strength of ones hands without them.

• Because tube prices have come down dramatically, it is sometimes suggested to replace the tube after one patch job, especially for high-pressure tires. However if you are smart, short on cash, and have a little free time, they can be patched almost indefinitely. You should still have a patch kit or spare tube with you on long rides. You can cut the old tube into strips of rubber and use it for a variety of things, including bungee-type straps.
  • However, such applications for used tubes can be quickly exhausted and the material to repair a tube is tiny compared to the entire tube itself (see Wikipedia:Environmentalism). Indeed, patched tubes on low pressure mountain bike tires are quite reliable even after being patched many times (unless a leak develops at the stem of the tube). Patching is more in line with the environmental ethos of many bicyclists.

The Ultimate After thought - Preventing Flats.

Some people live in nice clean and tidy locations, that have no thorns, broken glass or similar, and they ride on nice clean paved roads, and they rarely ride and so they may only ever get one puncture every 10 years.

However some people live in cities, that frequently have broken bottles, or glass from car crashes etc., spread along bike paths and roads, and they commute regularly and may get a puncture every week or so.

Some people live in rural areas (Australia) where thorns and such like grow in abundance (The Australia Bindi-Eye), where a less than diligent look out, can result in running across a Bindi patch, that will stick about 40 or 50 thorns into the said tyres in the space of 2 meters. (The thorns also get sprinkled along the sealed roads as well)

If you live in an area that is very clean and you ride rarely it's probaly not worth the effort to protect your tyres against punctures.

On the other hand if you commute in "glassed up" city areas and or live in Rural Australia, there are a number of options open to you to prevent punctures.

1. Keep on repairing the punctures.

2. Buy a thick walled tube (if possible)

3. Get a heavier treaded tyre.

4. Use a puncture re-sealing compound.

5. Use tyre liners.

Repairing punctures is fine, if you only have to do it rarely.

The steps 2 & 3, are sort of OK, if most of your punctures are caused by very fine bits of glass working their way in.

Puncture re-sealing compounds, as a composition of liquid and fibres that are injected into the tube through the valve stem.

From my own experience they are either randomly successful (unreliable) and have many drawbacks, such as leaving fibres under the valve seat, so as to cause slow leaks etc., and they do not seal especially well and they can leak their fluids out of the tire onto floor coverings. Some people think these products are brilliant, some people think they are a waste of good money.

Probably the best protection against punctures is from the use of TYRE LINERS. These are a kind of fibrous specially shaped strip of a pliable urethane. Using them, virtually guarantees that you will never have another puncture again, unless you ride over the pointy end of a 6" nail, poking 2" out of a wooden beam..

If they are carefully fitted, you are almost guaranteed that none of the glass chips or pieces, nor any of the usual thorns etc. will ever penetrate the liner.

There are a number of manufacturers of tire liners. Make sure that you buy the "size" of the liner, to suit your wheel size and tire size.

There ought to be directions on the pack, on how to fit them into your wheels. Or any competent and experienced cyclist or cyclist mechanic ought to be able to show you how to do it.

Reference:

1. ↑ REAL talcum powder can be bought at most supermarkets as Baby Powder - avoid the brands that are CORN STARCH, branded as baby powder, as it does not lubricate rubber very effectively and will rot and cause binding and chafing of the rubbers after wetting.
2. ↑ The puncture may have been caused by a hypodermic needle or something nearly as dangerous. Try probing first with something other than your fingers, like a cloth.