There are a million reasons you might need to take a wheel off your car - from fixing a flat tire to working on your suspension. I once had to take a tire off to replace the battery. (Curse you, Dodge Intrepid!) Doing any kind of work on a car can be dangerous, but doing anything under your car could be deadly. Don't sweat it - follow these simple steps, everything will go smoothly, and you'll look like boss.
Step 1: Block or Chock Your Wheels
The biggest danger you face is your car rolling. All cars have a small amount of play in the driveline that will allow a car to roll on you. A car that rolls a few inches forward or back - this is actually normal - could fall off its supports. Any tires that we aren't taking off, we will want to chock.
They sell purpose-built chocks at stores for this step, and they're not expensive. However, if you have some wood lying around, you can wedge that under the tire. All you need to do is keep the car from rolling. I'm on level ground, and my cars tires are 16", so this 2" x 3" piece of wood will do the trick. For bigger wheels, or if you're on an incline (or both), a 4" x 4" or a purpose-made chock behind the wheels is recommended.
Don't rely on your emergency brake for this job. For one thing, they can slip or fail. For another, if you're going to be working on your brakes, you won't be able to set the emergency brake anyway.
Fun Fact: The word "chock" comes from old french, and means a log or piece of wood.
Step 2: Break Your Lug Nuts
We're not literally going to break anything. "Breaking" refers to taking out the initial tension on the nuts that hold the wheel on. It can take twice as much force to initially loosen a lug nut as to tighten it, and when the force you apply to the lug nut finally overcomes friction, it happens all at once. So it feels like you broke something.
In this example, I'm using a 4-way lug wrench. This allows me to put a lot more force into the lug nut than the lug wrench that came with my car. They're not expensive, and they're pretty much universal for passenger cars. Trucks may require a different, larger 4-way wrench.
Important note: We do this step with the car on the ground. If you jack your car up, then start applying force to the lug nuts, the car's wheel will want to rotate. On some cars, the force you apply to the wheel will telegraph through the axle to the other wheel, and cause the car to move. Otherwise, your wheel might simply spin. Leaving the car on the ground for this step allows the tires friction to help you with this work. At this point, we only want to loosen the nut - no more than 1/2 turn.
Step 3: Jack It Up / Rest on a Stand
Now we can jack the car up. Trucks and older cars are build on a frame, so you can put the jack anywhere on the frame and jack the vehicle up. But modern cars (and a few trucks, like the Honda Ridgeline) are built using unibody construction. With unibody cars, there are specific points on the underside of the car where you can put a jack without damaging the vehicle. These are called hard points, and they're usually located behind the front wheels, and in front of the rear wheels. Check your owner's manual to be sure. If you put the jack anywhere else and start jacking it up, you can do serious damage to your car. (You can literally jack up your ride.)
Position your jack on the hard point, and raise the vehicle. In this example, I'm using a hydraulic floor jack. Hydraulic floor jacks are great because they can lift a lot of weight really quickly, but they have two shortcomings.The first is that because they lift on a lever, then tend to move around slightly as you raise the car, and change the angle of the arm relative to the jack. That's why they're all equipped with wheels. The key point here is, don't put your hand anywhere near the jack as you're jacking, lest it roll onto your fingers. Their second short coming is that they're hydraulic, and hydraulics tend to leak as they get older. A leaky jack will slowly lower the car after you have it jacked up. (The other kind of hydraulic jack - the "bottle jack" - is prone to the same issue.) You may not see the car slowly dropping, and really good jacks might take a day before the vehicle is all the way on the ground.
More than likely, your car came with a scissor jack. These have the opposite problem of floor jacks - they don't move. As you begin to raise the car and it tilts, the jack may tip with it. If your scissor jack or bottle jack leans more than a little bit, then let the car down, re position the jack, and try again.
The good news about scissor jacks is that they tend to not slowly lower the car. But, that doesn't really matter. Never, EVER work under or close to a car that is only supported by a jack. You need to instead support the car with a jack stand. Going back to the top of this setp, when you jack a car up, you want to make sure that you leave room on the hard point to position a jack stand nearby. As you jack the car into the air, you want to jack it up so that the wheel is about six inches off the ground. One of those inches are so that you can lower the car onto the jack stand. Three of those inches are because your suspension will drop the tire another few inches as it begins to relax, which could make putting the tire back on tricky. And whatever is left over is there if you're changing a flat tire - the tire you're putting back on - presumably - will not be flat.
Step 4: Take the Lug Nuts Off, Then the Wheel
Now we can remove the lug nuts entirely. In this example, I'm using an electric impact driver. This just saves time. You can also use your 4-way lug wrench. You may be tempted to hold the end of the wrench, then spin it to get the lug nut off faster. Just make sure you keep clear; I've seen teeth knocked out by people doing that.
Once you take the lug nuts off, put them someplace where they won't roll away. When doing this job in an emergency situation (eg, on the side of the road), I always put them in the driver's side floor board. You don't want to accidentally kick them and have them scatter out into the road way.
With the lug nuts removed, you can now slide the tire off. You'll want to use both hand and lift the tire straight off the wheel hub. Don't let the tire roll off - there are brake lines and ABS sensor harnesses behind that wheel that could be damaged if hit with a carelessly removed wheel. (Not that easily, but I've seen it done. You think replacing a $140 tire is frustrating, try adding a $90 wheel speed sensor to the bill.)
If you're going to be working under the car, or if you're changing to the spare, I recommend shoving the wheel under the car at this point. If the jack stand fails, and your jack (which is still under the car) also fails, this gives you a little bit of safety margin against being crushed. Make sure it's in a spot that you can slide it back out of - eg, not behind the wheel.
Step 5: Snug the Lug Nuts
So let's skip to the part where we've put the spare or the wheel back on. Now we're going to thread the lug nuts back on, and snug them up.
We're not going to be able to apply final torque to the lug nuts while the car is off the ground for the same reason we couldn't brake the lug nuts with the car off the ground. But we can tighten them a little. Unlike before, where we just pulled the lug nuts off at random, you have to follow a certain pattern when tightening the nuts. On my wheel, where I have five lug nuts, I tighten them in an order similar to drawing a five pointed star. The same would be true whether it was four or six lug nuts - start with any one lug nut, and then go to the most opposite lug nut you can next. Keep this up until you've gone over each lug nut at least one, and then repeat until they're all snug.
The reason for this is that it will encourage the wheel to settle into the center of the hub. Also, if you're using a heavy duty impact driver, or you are particularly strong and over-torque the nuts, you can damage the wheel itself.
Step 6: Lower the Car, Torque the Lug Nuts
With our wheel on, we can down jack the vehicle up a bit, remove the jack stand (and anything else under the car), then gently lower the car down.
I emphasize gently - the wheel is not fully torqued down, and if you drop the car, it could push the wheel off center.
With the car on the ground, you now take your lug wrench and tighten the lug nuts, using the same star pattern as when you snugged them.
Your owner's manual will list the torque specifications for your lug nuts. In my case, it's from 65 foot-lbs to 80 foot-lbs. To be absolutely technical, you should use a specialized tool called a torque wrench. Over tightening a nut or bolt can damage the nut or bolt, or could damage the part being bolted. Under-tightening could allow the nut or bolt to work loose.
You'll notice I am not using a torque wrench, and here's why: 65 ft/lbs to 80 ft/lbs is a pretty wide range, so being perfectly exact on your torque is kind of pointless. Most people do not have the strength to over tighten lug nuts. I'm a big guy, and I could do it, but I'm also experienced enough to know the difference between a force of 65 lbs and a force of 80 lbs. (The 4-way bar is about 10 inches from center, so I'd have to work really hard to apply more than 80 ft-lbs.) Most people, using maximum effort and a little body weight, will have no problem getting to 65 ft/lbs.
Step 7: Check Your Air Pressure. Check Your Lug Nuts Again Later
Finally, with everything buttoned up, check your air pressure. If you replaced your tire, a decent tire shop will know your car's air pressure rating, and will have pre-filled it to that level. Otherwise, this is just good practice - modern tires can look fine with as little as half their rated pressure. I've had run-flat tires that held their shape down to 5 psi, when they're normally rated at 34 psi.
Your owner's manual will list your ideal tire pressure, and on many cars it's also on a sticker inside the door jam. Never under inflate your tires, and never over-inflate them. It will, in the very least, mess with your fuel economy. At worst, it can cause premature tire wear and catastrophic failure. (If you watch the video, you'll see an example of tread separation. I completely ignored this tire until it was a danger to myself an other drivers. Yeah, I feel total shame... )
Over the next fifty miles of driving, pay attention to how your car drives. If the lug nuts start to loosen up, it will show up first as a vibration in the steering wheel, then as a rattling noise coming from that wheel. You'll need to re tighten them better this time. Even if you don't see these signs, it's a good idea to re-torque them at 200 miles by giving them a quick twist with the lug wrench.
And remember... righty-tighty, lefty-loosey.