I often get collector's asking me "What scale are Micro Machines?"
A lot of times, it is a model railroad enthusiast asking that question.
N scale has been gaining in popularity over the last few years due to the amount of track you can have in a confined space. Some N-scale enthusiasts have been using Micro Machines on their train layouts instead of N-scale cars. Why? Micro Machines are fairly cheap, and they made a wide range of vehicles, better selection than any you will find for your model train set. 

Please note: The cars are pictured slightly larger than real life.

As you can see, the Racing Champions are about the same size as Micro Machines. The main difference between the two brands is the car height and width. "N" scale is quite a bit smaller than Micro Machines, but if you do the whole town with Micro Machines, you often won't notice the difference. Some model railroaders change the wheels on their micros and repaint them for added realism. I found another website that shows some such customs.