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How to Fix a Flat Tire on a Bicycle

Preventing & Fixing Flats

Preventing Flat Tires

Before we tell you how to fix a flat, let's see how to prevent them. Better than knowing how to fix a flat tire is not getting one in the first place. Here are products which will help prevent flats, all available at your local friendly bike shop:

Slime. This is non-toxic goop that you put inside the tube. The slime automatically seals small punctures. Bike shops sell it, and they'll put it in for you if you don't know how to remove your valve stem. Only works with standard (Schraeder) tubes, because you can't remove the valve stems on Presta tubes. Note: Once a tube has been slimed, always make sure the valve is pointing down (12 o'clock position) before putting air in it, otherwise the slime will try to get out and clog the valve.

Tire Liners. A tire liner is a long strip of tough material that you put between the tube and the tire. The Mr. Tuffy brand has been popular for a long time (kind of like plastic/rubber), but a newer kind made out of Kevlar works even better -- albeit at a higher price ($15-20 per tire).

Thorn-Resistant Tubes. These thick tubes provide more protection against punctures.

Armadillo Tires. This brand of tires from Specialized is great at resisting punctures. The main disadvantage is a slightly harsher ride, and the fact that it's a bit hard to get the tires on and off the rims since they're so stiff. If you're going to use only one anti-flat product (instead of a combination of products), this is probably your best bet. (Read a review at Popular Mechanics or the opinions of several cyclists at Road Bike Review.)

Combinations of these. Any one of these products by itself may afford some protection, but using more than one can become a powerful combination. (A friend and I rode 550 miles from Austin to Baton Rouge using three slime/liners/tubes, and had zero flats.) Using all of them is probably overkill, though.

Air-free Tubes or Tires. These products are semi-solid rubber, with no air, so they can't go flat. You can get either an air-free tire, which replaces the whole tube & tire (e.g. Greentyre), or an air-free tube, which fits inside your existing tire (e.g., No-Mor Flats, Toobz). These are an as-yet unproven technology, and cycling equipment master Sheldon Brown thinks they damage wheels. (We don't know whether that's true, but we're loathe to disagree with the revered S. Brown.) Here are some reviews of these products.

Fixing Flat Tires

Understand the Terms. Just so we're on the same page: The Tire is the round rubber circle that actually makes contact with the road. The Wheel is the metal frame that the tire sits on. The Rim is the side of the wheel, where the tire lip rests. (The part that the brakes grab on to.) The Tube is the rubber thing that's filled with air. So you see, you don't really have a flat tire, you have a flat tube. Stop riding. Even if there's still "some" air in the tire, stop riding your bike, otherwise you'll damage the wheel rims. (Unless you don't mind buying another wheel.) Empty the tube. If there's any air left in the tube, release it by pressing on the valve. Remove the wheel. It's easier to take the wheel off if you turn your bike upside down first, so do so. If your wheel isn't quick release, then remove the nuts with a 15mm box wrench or a crescent wrench. You may have to release your brakes to get the wheel to move through the brake pads. (Squeeze the brakes together, then unhook the brake cable from the brake pad.) Note that it's possible to patch the tire without removing the wheel, but the hassle you save by leaving the wheel on might not match the added hassle of trying to fiddle with patching a tube that's still on the bike. Nevertheless, when you get advanced you might want to try this. This is a favorite trick of bike messengers.

Remove the tire. Use a plastic tire lever to move the lip of the tire over the rim, on one side of the wheel. (Plastic tire levers are cheap at ~$1.50, and bike shops sell a more elaborate model that hooks onto the axle for super-easy tire removal.) Slide the lever towards the left to pull the lip over the rim all the way around the tire. If tire keeps popping back into the groove, then use two levers, as shown in the last picture: Hook the tail of the first lever around a spoke, and then use the second lever to pull the tire lip over the rim. Once you've done the whole side, you can pull the tire & tube together off the rim. Thicker tires are easier to get off and on (e.g., mountain bike tires are much easier than racing tires).

Take the tube out of the tire. Okay, you got the wheel off the bike, and the tire off the rim.  You're about to take the tube out of the tire, but before you do, consider something:  Let's say in a minute you successfully find the hole in the tube.  You realize that the thorn or whatever that caused the puncture might still be in the tire.  How are you going to find that place in the tire when you've already removed the tube?  So when you remove the tube from the tire, make a note of how it was positioned.  The easiest way to do this is to make a mark on the tire where the air-inflation valve lines up. Super-inflate the tire. Now that the tube is out, pump it up like a balloon! The air will leak out of the hole faster and you'll be able to hear it. Don't worry, you won't pop the tube, unless you blow it up to 3x+ the size of the tire. It's easy to pop a tube when it's inside a tire, because the pressure builds up.  But outside the tire it's not a problem. I couldn't get a good picture of my super-inflated tire, because the leak was so big, the air kept escaping before I could take the picture.

Patch or Replace. You can usually either replace the whole tube or patch it. If the hole is really big (blowout) or the valve is torn away from the tube (as pictured) then you have to replace the tube. Both tubes and patch kits are cheap at your local bike shop, though patch kits are a little cheaper. If you go with patches, get the regular kind (black dot with a red border), not the glueless patches, since glueless patches often don't stick well. A properly-applied regular patch will last forever. There's no limit to the number of patches you can put on a tube, though once a tube has several patches you'll probably want to replace it because with several patches it's more likely that one of them will come off. Don't try to use a bit of old tube as a patch; it's too thick and will give you a bumpy ride, if it even bonds properly at all.

If Patching... Find the leak. Forget about putting the tube in the bathtub to find the leak. Simply pump the tube up to a slightly over-inflated size so it's bulging. You'll find the leak, and it won't permanently stretch your tube. Draw a circle and an X on the tube to mark the hole. (Submerging in water is useful only when the puncture is super-tiny, or when you suspect that you have a gazillion tiny punctures from riding through a sticker patch -- though if that's the case then you'll want to just replace the whole tube anyway instead of patching it.) Prep the tube for patching. Release all the air again. Use the sandpaper or metal file that came with the patch kit to scrape the hole area really well. This will allow the glue to bond better. Apply the glue. In a well-ventilated area, apply the glue to the leak area, to an area slightly larger than the patch. Wait for the glue to dry before applying the patch! (about five minutes) This may seem counter-intuitive, but you won't get a good bond if you put the patch on wet. Try not to breathe the glue vapors; it's not good for you. Apply the patch. Don't remove the clear plastic on the patch yet. Apply the patch to the tube, and mash down really hard. You may prefer to stand on it. Apply pressure for at least 60 seconds. THEN remove the clear plastic. If the patch comes off when you remove the plastic, you need to work on your technique (better sandpapering, more glue, wait longer for glue to dry, apply pressure for longer period of time).

If Replacing the tube...

Consider using a thick thorn-resistant tube. Also, note that you can cut your old tube to make an excellent bungie cord.

Find the cause of the flat. If whatever caused your flat is still in your tire, you'll get another flat right away.

Did the tire fail? (i.e., Is there a big hole on the tire where part of it flaked off?) If so, you'll need to replace your tire. In an emergency you can place a "boot" between the tube and the tire, using a dollar bill, cut pieces of an old tube, or a special boot patch that you can buy at a bike shop.

If the tire didn't fail, find the puncture. Match the location of the leak in the tube with its sister location on the tire. If you don't find it, run your finger slowly through the inside of the tire feeling for a tiny bit of glass or wire. If you don't find anything, check the wheel itself for sharp spots or rust.

Replace the tire with an Armadillo? Switching to an Armadillo tire will help prevent future flats. (See the previous section on Preventing Flats.)

Install a tire liner or Slime? If you didn't opt for an Armadillo tire, then you might consider at least installing a tire liner and/or Slime, to prevent future flats. (See the previous section on Preventing Flats.) Note: Once a tube has been slimed, always make sure the valve is pointing down (12 o'clock position) before putting air in it. This keeps the slime from trying to get out.

Reinstall the tube. Put a little air in the tube, just enough to give it a little form, and put it into the tire.

Reinstall the tire. Stick the valve through the valve hole. With your fingers, work the lip of the tire into the wheel rim, on only one side. You may need to use a tire lever for the last bit. Once you've done one side completely, do the other side. Be careful not to pinch the tube between the tire and the rim, especially when you're using the lever. If it's too hard to get the tire on the rim, try releasing more air.

Reinstall the wheel. Put the wheel back on your bike. If your wheel uses nuts, then alternate between each side a few times as you tighten -- don't tighten one side completely before starting the other. If you have quick release, make sure you put it on tight enough. It's tight enough when the quick release lever offers some resistance and leaves a mark on your hand. After you put the wheel on, tug on it pretty hard to double-check that it's not loose. Also make sure it's on straight -- if it's rubbing on the brakes when it spins, it'll be a lot harder to pedal.

Inflate and Release. Pump up the tire, then let most of the air out again. This will help work out any kinks where the tube might have been pinched. (A pinched tube will pop as soon as you air it up all the way and sit down on the bike.) There's some debate over whether this really helps, but it certainly can't hurt.

Reinflate the tire. Inflate the tire until it's very firm. You should be able to just barely make a small dent in the tire by pressing on it with your thumb while your fingers hold the wheel under it.

Put the valve cap back on. This will help keep the air in if the valve has a slow leak.

Reconnect the brake cable. Don't forget this part!

Celebrate. At this point, all the children of the world join hands and sing together in peace and harmony.

I blew a tire (a brand new Armadillo no less) last night on my commute . I hadn't changed a bike flat in years. I found your instructions on the web, followed them and had everything up and running in about 15 minutes. I was able to ride to work again today. :-) Thanks! -- Beej, Dec. 2005

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