Mousetrap car

You have steps 3 and 4 mixed up, you need to set the trap before tying the string to it. Otherwise the string doesn't actually do much. I'd recommend doing something to stop the trap going off while you tie it (like tie it open with another piece of string, don't rely on the trap's latch while you're fiddling around)

Also if you can help it, don't wind it so close to the ends of the axle, that just makes it rub against the body.