When making a purchase of a treadmill, there are a few things you need to know when you are evaluating your choices. Since not all treadmills are created equal, you have to be careful about your choices. I've purchased a few in my day, and let me show you the best things to look for when I compare treadmills.
The first and foremost thing to look for is the motor – It's the heart of your treadmill, and will generally cost the most to fix. Look for something with at least 2HP, and if you plan on running a lot, 2.5HP would be your best choice. Also look for warranty, the longer the warranty, probably the better the motor.
The next thing you should look at is the belt / deck. The average treadmill belt ranges from 17 to 22 inches in width. Never, I repeat never go any lower than 16 inches or you will be squeezed into a little space. The deck should be made of sturdy material, and the rollers should not be any less than 2 inches in diameter, or you risk replacing the belt early. Also look for cushioning under the belt to provide comfort during your workout.
Stability also plays an important role when you compare treadmills. You do not want something that is going to shake or wobble while you run. Also look for machines that are made from durable materials, and if possible, try and find one that is welded, as opposed to assembled with nuts and bolts.
Lastly, the warranty is always something you should look at when you compare treadmills. A decent machine will have a varying warranty for different parts. For example, Lifetime Motor, 5 year belt, etc.
Keep some of these things in mind as you compare treadmills. If you do, you will be on your way to pick the machine that will give you the best of what you are looking for.