How to Repair a Bike Puncture - Patching an Inner Tube
How to Mend a Mountain Bike Puncture (Flat Tire)
I spend a lot of my spare time mountain biking around the back roads of Ireland and have got my fair share of punctures over the years. You will inevitably get a punctured tire (tyre) at some stage, but patching an inner tube is quite simple, requiring few tools. It should be possible to perform a repair in between 30 to 40 minutes and is an essential skill if you cycle a bike a reasonable distance and don't want to have to walk home!
What Causes Punctures?
Sharp objects such as glass, nails, tacks and thorns. I live in Ireland where the hedgerows in the countryside are a mix of elder, bramble, blackthorn, whitethorn and wild rose. When these are cut in the fall, thorns from whitethorn often litter the road surface and present a hazard to tires. Also when the tire of a bike hits a pothole, the tube can get pinched between the tire and wheel causing what is known as a pinch puncture. Ideally you should be vigilant and watch the road surface to avoid punctures and damage to the wheel and rim in the first place.
Only Basic Tools are Required to Fix a Flat
You only need a few tools costing a few dollars to repair a puncture.
- Wrench - A single tool is made so that it can cope with all the standard nut sizes on a bicycle
- Tire levers - These are used to lever off and separate the tire from the rim
- Puncture Repair Kit - Comprising patches, glue, sandpaper and chalk
- Pump - You're going to need this to pump the the tire back up- unless you have a strong pair of lungs!
- Head Torch - Useful if you unfortunately get a puncture at dusk and end up working in the dark (which happened to me recently). You can use the front light from your bike and try to clamp it somehow so that it directs light where needed, however a headlight is a much better choice.
Repairing The Puncture
Unless you are replacing the tube, you don't have to remove the rim from your bike to patch a hole. However it is much easier to manipulate the tube and locate the puncture if you do so.
Step 1 Detach the Brake Cable
First detach the end of the brake cable where it attaches onto the slot on the brake arms.
Step 2 Remove the Wheel
If the puncture is in the back tire, it's easier to remove the wheel by turning the bicycle upside down and resting it on its seat and handlebars. Using the wrench, loosen the nuts holding the wheel just enough that the wheel can be slipped out of the forks. If you are removing the back wheel, you will have to pull the chain and dérailleur out of the way so that the wheel can be removed. Some bicycles have quick release clamps which enable the wheel to be removed by pulling on a lever. Pull the lever out from the wheel and downwards. Forks have so called "lawyer lips" which act as a backup to prevent wheels dropping out if the lever inadvertently loosens, so you will likely need to hold the lever and loosen the round "nut" on the far side of the wheel to provide enough slack to remove the wheel.
Step 3 Release the Air From the Tube
Remove the cap from the tire valve. Use something to push in the central pin on the valve. A piece of stick or match or anything which comes to hand. This releases the air from the tube.
Step 4 Mark the Tire
It's quite likely that the object which caused the puncture is still stuck in the tire. If it's a thorn, the chances are that its pushed into the thread and you won't be easily able to find it, especially in low light conditions. However by aligning the puncture point in the tube with the tire, this narrows down the location where the tire was pierced.
Before you remove the tire, mark it with chalk in line with the tire valve. Once the tube is patched, then just lay the tube on the tire, lining up the valve with the chalk mark. The puncture point in the tire should then be close to this patch.
If you don't do this and replace the tube, you risk getting another puncture from whatever is stuck in the tire.
Step 5 Remove the Tire From the Rim
Push the blunt end of the tire lever in between the tire and the rim. Don't push it in too far as there is the danger of pinching the tube causing damage. Lever the tire out from the rim. Hook the other end of the tire lever under a spoke. Insert a second tire lever about 4 inches away and lever a further section of bead from the rim. It should now be easy to slide the tire lever sideways along the circumference of the rim to separate more tire from the rim. If the tire is a tight fit or rigid due to low temperatures, you may need lever out further sections before you can slide the lever sideways. You can also slide your fingers in between the tire and the rim and then slide your hand sideways to expose more tire. You should be able to remove the complete tire in this manner.
Step 6 Remove the Tube
First remove the valve from the rim and then it should be easy to remove the rest of the tube form the tire.
Step 7 Find the Hole in the Tube
If you are carrying a spare tube on your journey, you can skip this step. Alternatively you need to find the hole in the tube. Pump up the tire until it is semi-inflated. If you are at home, you can then find the hole by submerging the tube in a basin of water, rotating it bit by bit through the water, and watching for bubbles. If you're out in the countryside, you may be lucky and find a puddle or pool of water for doing the same thing. Once you find the hole, dry the area and mark it with chalk. If you don't have access to water, hold the tube up to your face and slowly rotate it until you feel air in your face. Sometimes bad quality tubes can develop pinholes on the inner side of the tube ( i.e. the side which makes contact with the rim), so check this also. Again mark the hole with chalk.
Step 8 Find What Caused the Puncture
This is essential. The puncture may have been caused by a piece of glass, barbed wire, sharp stick, nail or whatever which didn't actually remain stuck in the tire. My experience with trail riding however, is that all punctures were caused by small thorns which lodged in the tire wall. So you need to check if the offending item is still there, otherwise you'll get a puncture in the same place. Lay the tube on the tire, aligning the valve with the chalk mark on the tire. If there's anything still stuck in the tire, it will be in line with the hole in tube. I've had to do this in complete darkness with just the bike front light for illumination, so that's why its wise to carry a head torch with you. You can also do this by feel, and slide you fingers sideways along the inner surface of the tire. This is ok for thorns but probably not a good idea if a sliver of glass is stuck in the tire!
Step 9 Patch the Hole
Using the sandpaper, roughen an area of the tube slightly larger than the patch. Apply a blob of solvent/glue about the size of a small pea and spread it around with your finger to form a thin layer the size of the patch. Allow the glue to become tacky to the touch, this normally takes about 5 minutes depending on temperature. Remove the backing foil or plastic from the patch. Apply the patch and center it on the hole. Press down hard on the center and push outwards to remove any trapped air.
Step 10 Put Everything Back Together
- Inflate the tube just enough to remove the limpness. This helps to push the tube far enough back against the wall of the tire so that it doesn't get caught between the tire and rim.
- Place the rim flat on the ground and lay the tire down on top of it.
- Check the treads on the tire are facing the right way (You did check which way they go before you removed the tire?!) If you didn't, the treads which are often V-shaped, should face forwards in the direction of travel of the wheel. i.e. point backwards where the tire makes contact with the ground.
- The two sharp internal edges of the tires are called beads. Insert the bead closest to the ground into the bottom edge of the rim of the wheel. Fit the section of tube with the valve into the tire first and thread the valve through the hole in the rim. Continue to feed the tube into the tire. Now use your two thumbs or fingers to force the upper bead of the tire bit by bit into the rim. It might be easier to do this with the tire held vertically. This can be a little difficult as you get to the last section of the bead. You can use a tire lever to lever the bead into the rim as shown in the video below (similar to how you levered it out, but in reverse). Be careful you don't nip the tube with the lever.
- Inflate the tire while checking that the tire valve is at right angles to the rim. If it isn't, correct this by sliding the tire on the rim. Continue to inflate the tire to the rated pressure. Replace the wheel into the forks of the bike taking note of which way the thread points. Next tighten the nut which holds the wheel in place. If your wheel has a quick release lever, clamp the lever upwards, parallel to the forks so that it is out of the way. This takes a little bit of trial and error and the whole arrangement should be so tight that you need to wrap your fingers around the fork and use your thumb and palm to push the lever closed. Lastly don't forget to replace the brake cable on the brake arms.
Replacing the Tire
Using Levers to Feed Tire Bead Back into Rim
What to Do If You Get a Blowout
Check your tires regularly for any cracks or bulges, especially if they are old or have a lot of mileage. Rubber cracks naturally with age as a result of oxygen and UV exposure even if tires haven't been used. (Store tires in a cold dark place). Stones and potholes on roads and trails bruise tires leading to damage. Bulges indicate damage to the nylon reinforcement of the tire and are a sign of an impending blowout. A blowout is a failure of the tire as pressure of air in the tube forces it through the tire wall or tread. You may hear a sudden gush of air as the tire slowly deflates, or the event can be more catastrophic, with a bang and rapid deflation. This can rip a bigger hole in the tire and inevitably the tube may be damaged to the extent that is un-repairable. So always carry a spare tube with you.
Once the tire is damaged by a blowout, there's no point trying to inflate a new tube inside it until you block the hole. It's a good idea to bring a section of old tire with you and this can be used to cover the hole inside the tire at the site of the blowout (Assuming its not a huge tear or hole). This prevents the tube from pushing out through the hole when it's inflated. Inflate the tire to the minimum pressure and this should get you home! Don't use the tire again, replace it!
Max tire pressure for a mountain bike generally ranges from 50 to 65 pounds per square inch (PSI).
58 PSI approximately equals 4 bar = 400 kPa. Less pressure gives better traction, but it's more difficult to cycle when tires are softer.
Pressure Conversion: 1 bar = 14.5 psi = 100,000 pascals or 100 kPa
Schwalbe Landcruiser Puncture Resistant Tires
These are the tires I use on my mountain bike and I haven't had any thorn punctures this year (or any for that matter). The tires have an integral Kevlar layer which helps to prevent penetration. The middle section of the tire tread or rib is quite slick (smooth), so rolling resistance is reduced, making for easier riding on roads. The outer section has chunkier treads and this gives better grip on muddy roads / off road. These tires are available in 1.75 inch or 2 inch for standard 26 inch MTB wheels.
Remember always wear high-viz reflective clothing when cycling. If you have to repair a puncture, move to a location well in from the edge of the road, where you're safe from passing traffic. In the city repair the puncture on the pavement, but if you're out in the countryside, find the nearest gateway.
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© 2012 Eugene Brennan
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