Almost every bicyclist has experienced at least one puncture to their bicycle tire inner tube in their cycling career. And when it happens you want to make sure you can handle it.
You can help reduce their incidence simply by the way you ride, which is also consistent with safety, e.g. don’t ride in or near the gutter where there is more likely to be a buildup of debris, which can include tacks, glass splinters, thorns, or other sharp objects. That also puts you away from drain grates, which can, as with a rock or pothole, cause a pinch flat or “snake bite,” especially if your tube is under-inflated. In this case the tire is flattened against the rim by the impact, causing two parallel cuts in the tube, which instantly goes flat. (It happened to me once, both front and back tires, when going over a drain grate at speed after a truck passed me unexpectedly and I reflexively swerved sideways.)
Other causes include:
The tube is pinched when remounting the tire on the rim.
The tube deteriorates and starts to leak.
The tube can be stretched and scraped by the rim’s drop center.
The tire wears through.
The tire sidewall fails.
The rim tape moves, exposing sharp spoke heads or holes in the rim.
The tire blows off the rim, putting a long slit in the tube which cannot be repaired.
The maximum tire pressure is printed on the sidewall of the tire and you should normally inflate the inner tube to that pressure. The exceptions are when riding on rough terrain for a softer ride, and possibly during adverse weather conditions, e.g. rain, to increase road surface contact.
I recommend simply replacing the punctured inner tube and repairing the puncture only once you get home, rather than on the road. However, sometimes you may still need to do a puncture repair so carry the following:
Spare inner tube, preferably 2– In a Ziplock plastic bag in which you’ve sprinkled some talcum powder. The talcum doesn’t degrade the rubber but makes it slippery, aiding inner tube installation.
Patch kit – In case you have more punctures than spare inner tubes.
Pump – The full-size high pressure Zefal pump is my favorite.
Note: You should also have a good quality floor pump at home for more efficient tire inflation.
Tire levers – You need up to three of the regular variety, plastic being preferred to minimize inner tube puncturing when replacing it. However, I use and recommend the Crank Brothers Speed Lever, which clips on the wheel axle and can be rotated quickly around the rim to either remove or replace the tire without risk of puncturing the new inner tube.
The following is based on instructions in the original League of American Bicyclists Effective Cycling Road I manual, published in 1996. It suggests being patient and not skipping any steps:
1. Remove the wheel from the bike. If necessary, release the brake to allow the tire to clear the brake pads.
Note: If the flat is on the rear wheel, turn the crank by hand and shift to the smallest cog on the rear cluster, hold back the chain, and carefully remove the wheel.
2. Check the outside of the tire for visible signs of damage, such as a nail, and mark the location with a grease pencil or a marker.
3. Deflate the inner tube completely if it still contains air. If it’s a Schrader valve push in the valve pin, and if it’s a Presta valve unscrew the small locknut and then push in the valve pin.
4. To loosen the tire on the rim, push one side of the tire in towards the middle of the rim around the entire wheel. Following that, if it cannot be removed by hand, use tire levers to remove it.
(In the case of the Speed Lever, hook it under the bead of the tire, then clip the other end to the axle and rotate the hook around the rim. Then remove the Speed Lever.)
5. With the tube inside the tire, remove the tire complete from the wheel, starting at a point opposite the valve stem. Lay the tire and tube on top of the wheel exactly as they were originally oriented.
6. Remove the tube and lay it on top of the tire, still retaining orientation.
7. Inflate the tube sufficiently to find the puncture either by feeling or hearing the air escape. Usually the puncture will be on the outside of the tube so check the outside first.
If the problem is due to the tire, e.g. glass, the tube will be punctured on the outside.
If the problem is due to a snake bite there will be double punctures on the inside, and single punctures if due to spokes.
If you have no spare inner tube, mark the source of the puncture and repair it.
CAUTION: Running your finger around the inside of the tire to locate the cause of the puncture could lead to a cut due to a sharp glass shard or nail poking through, so is best avoided.
8. Once located, remove the object which caused the puncture from the tire, e.g. using a small screwdriver.
IMPORTANT! Make sure that whatever caused the puncture is removed before continuing.
9. To make tire remounting easier, coat the inside of the tire, the bead area of the casing, and the spare tube with talcum/baby powder.
It’s a good idea to carry spare tubes in a Ziplock bag containing a tablespoon of the powder.
Note: Talc is a slippery mineral which will not degrade the rubber.
10. Inflate the new tube with enough air to give it a soft shape.
11. Insert the tube into the tire so that the valve stem aligns with the label on the tire. This “indexing” allows you to easily match up the wheel, tire, and tube the next time you have a flat.
12. Treating the tire and tube as a unit, insert the valve stem into the hole in the wheel.
If a Presta valve, prevent it from coming out from the rim by screwing on the valve nut a turn.
Working from this point, install one side of the tire and the tube on the rim using only your hands. The talcum powder should facilitate this.
13. Adjust the tube if necessary.
14. Starting at a point opposite the valve stem. mount the other side of the tire on the wheel. It may help to let some air out of the inner tube but don’t deflate it completely.
You may be able to complete this operation with your hands only.
If not, this is where the Speed Lever proves itself. It cannot puncture the newly installed inner tube when being used to remount the tire since it remains on the outside of the tire, but regular tire levers, especially metal ones, can.
15. Check to make sure the tube is inside the tire. Then inflate it to about 30 psi.
Check to see that the tire is concentric on the wheel. Adjustments can be done with your hands.
Pump the tire up to the maximum recommended pressure shown on the tire sidewall. With the help of the talcum powder the tire should align correctly on the wheel.
16. Install the wheel on the bike. Connect any brake cables which you may have had to release.