How to Fix a Flat on a Mountain Bike

Mountain bikes are built for rugged terrain with heavy duty shocks and extra strength tires to handle all sorts of ground. But every once in a while, you’ll encounter terrain that is just too rugged for your bike and a flat will occur. When that happens, it’s useful to know how to patch up the tire yourself, and how to do it quickly so you can get back on the trail as soon as possible.

To fix a flat tire on a mountain bike, it is essential that you have something to patch it with, as well as glue, an air pump, and some basic household tools to help you get to the tire.

To start with, turn your mountain bike upside down and rest it on the seat and the handle bars. Now, when you turn the pedals, the tire is able to spin freely. If it’s the rear tire that went flat, you’ll have to disengage it from both the chain and the brakes but this is easily done. Put your bike into its top gear then lift the chain off the gears completely so it is not hooked around any part of the wheel. Try removing the wheel from your bike and wiggling the tire out from the grip of the brakes. If this doesn’t work, unhook the cable from a cantilever and squeeze the cantilevers together to create slack in the brake cables. With enough slack the wheel should come right off.

Next, make sure the tire is completely free of air and, using a screwdriver or tire lever if you have one, pry the tire carefully from off the rim. You may need two screwdrivers, one to dig a bit of the tire out of the rim and hold it in place while the other slides the rest of the tire off the rim in a circular pattern. Once the tire comes off the inner tube should slip right out of it, giving you complete access to find the hole.
To find the leak in your inner tube, if it’s not immediately visible, pump a small amount of air back into it and submerge the tube in water. A line of bubbles will form underwater marking the spot where the air escapes from the tube. Make sure you have found all the leaks if there are more than one, and mark the holes with some chalk or a pen.
Now, cut out a small square of rubber to patch the hole with. If you have ready-made patches, peel one off and keep it separate. If not, you may use a piece of a spare inner tube. Make sure the patch is large enough to completely cover the hole but not too large or unwieldy. Roughen one side of the patch with sandpaper to help it stick better. Also apply the sandpaper to the area around the hole in your inner tube.
Apply rubber cement to both the sandpapered side of the patch and the area on your inner tube around the leak. Make sure to apply the rubber cement to an area slightly greater than the size of your patch. Leave the glue to dry for a while, just long enough for it to lose its liquid form but still remain tacky. Stick the patch to the surface of your inner tube and continue to apply pressure for a couple of minutes. Once you are sure the patch is firmly stuck to the inner tube, try inflating the tube a bit to make sure it works. Submerge it in water again and make sure there are no more holes.
The inner tube will be easier to manage when putting the tire back on your bike if it is partially inflated. Make sure there is a small amount of air in it then tuck it back into your tire, and fit the tire back onto your wheel, making sure to insert the valve back through the hole made for it.
Once your wheel is back on your bike, pump up the tire as much as it will go and listen for any leakage of air. You may want to leave it for a while before going on any trips to make sure it is completely fixed.