1. Prevent flat tires before they happen by pumping up your tires at home before every ride with a floor pump.  This will prevent pinch flats, which are caused by an under-inflated tube getting pinched against the rim. 

2. If you ride through broken glass, take the time to stop and spin your wheels so that you can pick out any shards that got lodged in your tire. A lot of flats happen because small pieces of glass gradually work through the tire into the tube. Just because your tire didn't immediately go flat doesn't mean that you're in the clear.

What To Bring

These instructions won't be much help if you don't have the right tools for the job (fig 1). Always carry:

Fixing the Flat

1. First shift your bike into the smallest cog on your rear cluster (fig 2). Next, disconnect your brake. You may be able to get your wheel off when it is deflated, but you won't be able to get it back on with a full tire unless they are disconnected. Now you can open the quick release or unscrew the 15mm nuts to remove the wheel.

2. Time to remove the tire from the rim. For starters, try to simply roll the tire off with your thumbs (fig 3). If you have a tire that fits too tightly to roll off by hand, you will need to use tire levers. First, try to wedge a tire lever under one side of the tire and pry that side free of the rim by pulling the tire lever around the rim (fig 4). If that side of the tire keeps popping back onto the rim before you can pull the lever all the way around, wedge the lever under one side of the tire and hook the opposite end of the lever onto a spoke (fig 5). Grab a second tire lever, wedge it under the same side of the tire as the first one about 3 inches away, and pull it all the way around the rim until the tire is free. The second edge of the tire should roll off easily by hand.

3. Remove the tube and check the inside of the tire for foreign objects. Run the back of your thumbnail along the inside of the tire rather than the tip of your finger, as a shard of glass could slice it open. It is also helpful to inflate the tube a little bit when it is out of the tire to help locate the puncture point. Flats can be caused by many things, hitting a sharp edge in the road with not enough pressure can cause a pinch flat. This type of flat is often called a snake bite because the flat is caused by twin punctures where the rim pinched the tube. Other times broken glass, thorns or small pieces of metal can work their way into the tire and puncture the tube. With the tire off the rim, and some air in the tube, you can usually determine how the flat was caused.

4. Replace or patch the tube and re-install the tire on the rim. The easiest way to do this is to put one side of the tire back on the rim first, with the label right over the valve hole (fig 6). Then put just enough air in the tube so that it takes shape and insert that into the tire (fig 7). Next, starting near the valve, tuck the other bead of the tire back on the rim, being careful not to pinch the tube. Make sure the valve stays perpendicular to the rim.

5. The next step is inflating the tire. Do this slowly at first, making sure the bead is seated all the way around the wheel. If it is not seated and you inflate the tire quickly, the tire could blow off the rim and pop your tube again.  The label on your tire will tell you what your PSI should be, but if you don't have a gauge handy, try to get the tire up to a fairly high pressure so that you don't flat again.

6. Now put the wheel back into the dropouts and tighten down your quick release or axle nuts (fig 8). Then re-attach your brakes and spin the wheel to make sure the brakes aren't rubbing. If there are any bulges in the tire you will want to check and make sure that you aren't pinching the tube with the bead of tire at the point of the bulge.

7. Ride On!

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