It will often say what handling capacity the speaker is on the back of the speaker: It'll say something like 20 watts printed on the back of the magnet in addition to the impedence of the speaker measured in ohms- 8ohms, 4ohms, and such are common for car speakers. If you were satisfied with the speakers that came with the car, original equipment replacements from the dealer might be ok, but there are always better speakers available from specialty suppliers- stereo shops and so on. Stock speakers can be high-priced and not all that high quality. There are exceptions, though. You be the judge based on your real experience.