The wheel must be removed to replace the tube and tire. If possible, begin by mounting bike in stand. If no stand is available, bike should be laid on its left (non-derailleur) hand side when the rear wheel is removed. Do not stand bike upright without the rear wheel in place, as this will damage the rear derailleur.
- Rear wheels: shift derailleur to outermost gear and innermost front chain ring.
- Release brake quick-release, if any. Typical MTB brakes and road brake quick release mechanisms are shown below.
- Release wheel quick-release by pulling quick release lever outward. Pull outward on end of quick release skewer lever. If necessary, loosen quick release adjusting nut to clear any tabs at end of fork. For wheels with axle nuts, loosen both nuts outside of dropouts.
- Front wheels guide wheel down and out of fork. For rear wheels, pull back on rear derailleur to allow cogs to clear chain. Lower wheel, guiding the wheel down through brake pads and forward to clear chain and derailleur. Guide the wheel through the brake pads and out the fork ends.
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.
- 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.
- 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.
- 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.
- Repeat engaging the lever until the bead loosens. Then slide the lever along the rim under the bead.
- Starting opposite the valve, pull inner tube from tire. Lift valve from valve hole and remove tube from wheel.
- 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.
- Inflate inner tube if possible. Inflate until tube is twice its normal width.
- 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.
- 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.
- Blowout 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.
- 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.
- 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.
- Inspect sidewall for rips, holes, or damaged rubber and casing.
- Inspect wire or fabric tire bead for damage.
INSPECTING THE 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.
There are two common types of valve stems on bicycles, Schrader (“American” type) and Presta (“French” type). The Schrader-type valve is common on cars and motorcycles. It is also found on many bicycles. The valve stem is approximately 8mm (5/16”) in diameter and has an internal spring plunger to assist in shutting the valve. To deflate the schrader valve tube, it is necessary to stick a small hex wrench or other object into the valve in order to press on the stem and release the air. Upon release of the stem, the stem spring shuts. Schrader-compatible pump fittings press on the internal stem with a plunger, allowing the tube to be filled.
The schrader valve core can be removed if necessary. This is rarely required, but a valve can become stuck and cause a slow leak. A loose core can also be the source of a slow leak. A special tool such as the Park Tool VC-1 will remove and or tighten the core.
The Presta valve is common on mid and higher priced road and mountain bikes. Presta stems are nominally 6mm (1/4”) diameter, thinner than Schrader valves. At the top of the stem is a small locknut, which must be unthreaded before air can enter the tube. To deflate the inner tube, unthread the locknut. Depress the valve stem to deflate. To inflate the tube, unthread the locknut and tap the valve to insure it is not stuck.
Presta valve tubes come with different length valves. The longer valve stems are needed for the deeper aerodynamic rims.
The rim valve hole should match the valve of the tube. It is possible to use the smaller Presta valve in a rim intended for the larger Schrader by using an adapter sleeve.
REPAIRING AN INNER TUBE
Simply replacing the punctured inner tube with a new tube is always the safest and most reliable procedure. However, it is possible in some cases to repair a small hole in an inner tube. If the hole is quite large, it may not be possible to repair. When in doubt replace the tube.
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INSTALLING TIRE AND TUBE ON WHEEL
- Note directional arrows of tire manufacturer, if any. Directional arrows printed on the sidewalls indicate rotation of wheel. Not all tires have direction orientation.
- Inflate tube enough for tube to just hold its shape.
- Install tube inside tire. Install with tube valve adjacent to air pressure recommendations written on tire sidewall.
- 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.
- 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.
- Work tube over rim sidewall and into rim cavity.
- Install second bead onto rim. Use care if using a tire lever.
- Inspect both sides of tire for bead seating and for any sign of the inner tube sticking out. Re-install if necessary.
- 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.
- 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.
INSTALLING WHEEL ON BIKE
The wheels must be properly mounted to the bicycle frame. Misalignment can result in problems with shifting and bike handling. If the wheel is not securely mounted in the dropouts, it may come out when the bike is ridden, possibly causing injury to the rider.
Quick release wheels use a hollow hub axle fitted with a shaft, a lever that operates a cam mechanism, and an adjusting nut. The cam puts tension on the shaft and pulls both the cam and the adjusting nut tight against the dropouts. This tension is what holds the wheel securely to the frame. The adjusting nut determines the amount of tension on the quick release lever and cam. Lubricate the cam mechanism if it appears sticky or dry.
The quick release is fitted with two conical shaped springs. The small end of the spring faces the axle, and the large end faces outward. These springs make the wheel easier to install. If one or both springs become twisted or damaged they may be removed. The springs serve no purpose once the wheel is tight on the bike.
DISC BRAKE NOTE
Bicycles using disc brakes at the hub need special attention to skewer use. Rim brake systems (Dual Pivot, Linear Pull, Cantilever, Sidepull, etc.) tend not to apply significant pressure on the axle. Disc brake systems are mounted on the fork and apply a load on the rotor, which is attached to the hub. There is an outward load on the hub axle that tends to push the axle out of the dropout.
It is especially critical the skewer be properly and fully secure on disc brake systems.
Non-quick release hubs use axle nuts outside the dropouts. The axle nut will have a washer built into the nut, or a separate washer. If the washer has teeth or knurling, these face the dropout to help secure the wheel. Lubricate the axle threads while the wheel is off the bike.
It is often easiest to install the front wheel when the bike is standing on the ground. The quick release skewer must be fully engaged on the dropout surfaces. By placing the bike on the ground, the axle will be fully up in the dropouts.
- Check that the quick release skewer lever is in open position. Check that brake quick release mechanism is open.
- Install front wheel between dropouts with skewer on left side (from rider’s point of view). Pull wheel fully up into dropouts. For non-quick release wheels with axle nuts, washers go to outside of dropouts.
- Rear wheels, pull back on rear derailleur to open chain. Place smallest cog between upper and lower sections of chain. Guide wheel between brake pads and engage smallest cog on chain.
- Determine final closing position of hub quick release lever. Rotate front lever and adjusting nut so the lever will end up just in front of fork. Position the rear lever so it falls between the chain stay and seat stays. Reposition the lever as necessary if it will not fully close.
- Adjust closing tension of quick release skewer. For most skewers, hold lever parallel to the hub axle, which is half way through its swing from fully open to fully closed. Tighten adjusting nut snug against dropout. Check results by moving lever back and forth through its swing. Lever should meet resistance to closing halfway through its swing. Close lever fully.
- For non-quick release wheels, tighten axle nuts fully.
- Close brake quick-release mechanism. View wheel centering in fork. Wheel should be centered between fork blades. To adjust wheel centering, open skewer, move wheel either left or right until wheel appears centered, then close skewer. For non-quick release wheels, loosen axle nuts and center wheel, then tighten nuts fully.
- Inspect brake pad alignment and centering by closing and opening pads with brake lever. If brake pads are not centered to wheel, see Chapter 6, Brake Systems. If wheel fails to adequately center in frame, either the frame or wheel may be miss aligned.
- Spin wheel and double check pad alignment to rim. Be sure pads do not strike tire.
- Orient skewer so lever will end up between the seat stay and chain stay, unless this prevents lever from fully closing.
- Close brake quick release or attach MTB brake release wire.
- View centering of wheel between chain stays and seat stays. Also sight rim centering to brake pads. Open skewer or loosen axle nuts and adjust as necessary to center wheel in frame. If brake pads are not adequately centered to wheel re-adjust brakes. If further attempts to align the wheel fail to adequately center it in frame, either the frame or wheel may be miss aligned. Seek a professional mechanic for help.
Note: So called “open cam” skewers may require more tension from the skewer. These skewer levers have the cam mechanism exposed, and should be lubricated often. Always check with skewer manufacturer for specific procedures.
Wheels may also be held on with a nut. The rear dropouts may also have a derailleur hanger that bolts to the dropout. There should be a bolt and nut that holds the hanger to the frame. The wheel installs over hanger bracket. The axle should extend to the back of this bracket. However, the left side axle will appear not to sit at the back of the dropout. This is because the right side is displaced forward by the hanger bracket. Center the wheel and fully secure nuts.