Assume I found a land route around the earth that followed a single line of latitude and was perfectly smooth.
I want to drive my car due west around the earth and return to the same point that I started at. Would I need to turn my steering wheel (assume the distance between my car's axles is negligible)?
Googling this has given me results about "Rhumb Lines", and I know that the Mercator projection has something to do with the answer, but I am battling to understand how these concepts fit together.
Yes, you'll need to turn a little if your line of latitude is not the equator. If you go always in front of your, you'll do a great circle :
http://en.wikipedia.org/wiki/Great_circle