Considering how much punishment that thin envelope of air in your dirt bike tire takes, it's amazing we're not repairing flats more often than we do. Fortunately, when it does happen, it's a repair you can do on your own.
Different bikes have different tires and sometimes different parts, but the following should give you the needed basics to get the job done.
1) Put the bike up on a stand. If you don’t have a stand, block it up somehow, under the frame. Those square plastic milk crates and a few 2x4’s work great.
2) Remove the wheel (rim and tire) from the bike.
3) Let the air out of the tube,
4) Remove the valve from the tube.
5) Remove the rim locknut.
6) Put the tire on a flat surface and, using your heel, break the tire loose from the rim. Do both sides.
7) Slip a tire iron between the tire and rim and start lifting the tire off and above the rim. Start far away from the rim lock.
8) About six inches from the first iron, slip in a second tire iron and do the same.
9) A third iron really helps here – you can repeat the above step and use the first two irons to keep the tire from popping back down – but you can usually do it with two.
10) Once one side of the tire is completely free, carefully remove the tube. Don’t just rip ‘er out... take your time and watch that valve stem.
11) Carefully remove the rim strip – the rubber strip that protects the inner tube from the spokes.
12) Remove the rim lock by lifting the tire out of the way.
13) Pop the tire completely off the rim. You may or may not need the tire irons to do so.
14) Clean everything. Get rid of all that stuff that’s built up inside the rim. If you’ve been thinking about replacing spokes, now’s a great time. We have instructions on this website.
15) Installation is basically the reverse of the above. Put the rim lock on first. Slip it through its hole and install the washers and lock nut – but don’t tighten things down yet. Note: some rim strips go on before the rim lock, some after -- if you have holes in the rim strip for the valve stem AND rim lock, then put the strip on first.
16) Put the rim strip back on and make sure you get it centered over the spokes and line up the hole for the valve stem. An optional step is to lay down a couple of layers of duct tape on the inside of the rim, over the spoke ends, and then put the rim strip on. The duct tape adds an extra layer of protection. On most rims, you can use half a width of the tape -- cut a long enough strip to go around the rim, hang one end up somewhere high, and split it down the middle with scissors or a knife. Wrap one layer around with just a very slight overlap, then lay the other layer down so its joint is opposite the first. Punch the holes for the valve stem and rim lock, then install the rim strip.
17) Slip one edge of the tire over the rim. Make sure you clear the rim lock.
18) Put a pound or two of air in the inner tube to make it easier to handle, then carefully guide it onto the rim, between the tire. Again, careful with the valve stem. Install the nut on the valve stem, but don’t tighten it up yet.
19) On the side opposite the valve stem, start popping the second edge of the tire onto the rim. Work in small sections at a time, and go from side to side instead of all the way around. Make sure the valve stem stays straight and centered. You can push on the sidewalls as you work to keep the inner tube away from the tire irons.
20) Push the rim lock in slightly, and guide the tire bead underneath it.
21) Double check to make sure everything is in place, and nothing is pinched or twisted.
22) Inflate the tire.
23) Tighten down the rim lock and valve stem.
24) Congratulate yourself on a job well done – unless you hear a hissing sound. Then go back to step one and make sure you don’t pinch the inner tube with a tire iron this time.
Soapy water can help ease the tire off the rim. It can also make things messy and slippery, so don’t overdo it.
Protect all those other parts on your wheel – brake discs for example. A 5-gallon pail or an old car tire rim can make a good stand.