How to change a flat
Removing Tire and Tube from Rim
Tires can be tightly fitted to the rim. Use tire levers to pry tire bead up and over rim sidewall. Do not use a screwdriver, knife, or other sharp object, which might damage tire or tube. Fully threaded valve shafts may have a locking nut next to rim. Loosen and remove locking nut before deflating.
1. Deflate tire completely. Even a small amount of air left in the tube can make it more difficult to get the tire off. For best results, press downward on wheel while depressing the valve.
2. Push one bead of tire toward rim center. The tire bead will be pressed tight against rim. Pushing it inwards loosens the bead from the rim. Repeat on other bead.
3.Engage one tire lever under bead of tire. Engage second lever 1-2\" (25-50mm) from first lever then pull both levers toward spokes to lift bead off rim. Disengage one lever. Move it two inches (5cm) along the rim and engage lever in the bead. Pull lever to lift next section of bead off rim.
4. Repeat engaging the lever until the bead loosens. Then slide the lever along the rim under the bead.
5. Starting opposite the valve, pull inner tube from tire. Lift valve from valve hole and remove tube from wheel.
6. Remove second bead from rim, which removes tire completely from rim. To fully inspect the tube and tire, it is best to remove both completely.
Inspecting the Inner Tube
When servicing a flat tire, always inspect tire and tube carefully to locate the cause of failure. This will help prevent future flats from the same cause.
1. Inflate inner tube if possible. Inflate until tube is twice its normal width.
2. Inspect for air leaks by holding tube close to the sensitive skin of lips or by holding tube near your ear to hear leaks. Move the tube around its circumference. If these steps do not work, submerge tube in water and watch for bubbles at the hole.
3. If you plan to repair the inner tube, use a marking pen to mark hole. Make four marks, one to each side of hole. Do not mark close to hole, as the mark may be sanded off.
The type of cut or hole in the tube will help determine the cause of the flat. Common causes of tire and tube failures are:
* Cut at valve core, commonly from misalignment of tube in rim or riding with low pressure. Be sure tube is mounted straight in rim and check pressure before rides.
* Leaky valve core, tighten with a valve core tool. More common with Schrader type valves, but also possible on some Presta valves.
* Blow causing a large shredded hole. These are usually not repairable. Check tire and rim as well for damage.
* Hole on inside edge of tube indicates a problem inside the rim, such as from rim strip failure, a protruding spoke or other sharp object inside the rim.
* A long cut or rip may indicate a tire blow out. Typically this is not repairable. Use care when seating tire during installation.
* A single puncture or small hole is commonly from a thorn, wire, or small nail. These may be repairable. Check tire as well for thorn, etc.
* Double slits are commonly from a rim pinch. The tube was pinched between rim and object in road/trail. Increase air pressure or use wider tires.
* V-shaped slits may be from nails or glass.
Inspecting the Tire
It is important to always inspect the tire as well as the inner tube. The cause of the flat, such as a nail or piece of glass may still be embedded in the tire or tread. Inspect both the outside of the rubber tread and the inside of the casing.
1. Inspect outside of tread for protruding nails, pieces of glass, thorns, or other objects. Squeeze any cut to look inside for objects such as slivers of glass.
2. Visually inspect inside of tire casing for nails, glass or debris. Wipe inside of casing with a rag, and then carefully feel inside with fingers.
3. Inspect sidewall for rips, holes, or damaged rubber and casing.
4. Inspect wire or fabric tire bead for damage.
Rim Strip and Rim Cavity
The wheel rim is made with holes between the rim sidewalls for spoke nipples. A rim strip covers the holes or nipples. The rim strip can be made out of different materials such as cloth, rubber, or polyurethane plastic. The strip protects the inner tube from sharp edges in the base of the rim and from spoke ends and nipples that might puncture the tube.
Inspect inside the rim cavity, looking at the rim strip and for any sharp corners or protruding spokes.
The rim strip should be wide enough to cover the bottom of the rim, but not so wide it interferes with the seating of the tire bead. Inspect the rim strip whenever changing a tire or inner tube. Look for tares and rips, and make sure rim strip is centered over the nipple holes. In the image below, the rim holes are exposed, which may cause a flat tire.
Installing Tire and Tube on Wheel
1. Note directional arrows of tire manufacturer, if any. Directional arrows printed on the sidewalls indicate rotation of wheel. Not all tires have direction orientation.
2. Inflate tube enough for tube to just hold its shape.
3. Install tube inside tire. Install with tube valve adjacent to air pressure recommendations written on tire sidewall.
4. Lower tire and valve into rim valve hole and align valve so it is pointing straight toward hub. A crooked valve can lead to a flat tire later.
5. Install one bead at a time. Work tire bead onto rim with hands. If tire bead will not seat using hand, use tire lever as a last resort. Use caution when using tire levers to avoid pinching inner tube. Engage tire lever using same orientation as removing bead.
6. Work tube over rim sidewall and into rim cavity.
7. Install second bead onto rim. Use care if using a tire lever.
8. Inspect both sides of tire for bead seating and for any sign of the inner tube sticking out. Re-install if necessary.
9. Inflate to low pressure and inspect bead again on both sides. Look for small molding line above bead. This line should run consistently above rim.
10. Inflate to full pressure and check with pressure gauge. It may be necessary to press downward above the valve in order to engage the pump head. For fully threaded valve shafts, re-install the locking nut, if any. Do not use wrench or pliers to tighten nut. Tighten finger tight.
* content from www.parktool.com