What does "Mag" mean in reference to BMX wheels?

Question

I know it's not 'Magnesium' cause these things are usually plastic. Anyone know what it means?

Answer 1

It is, indeed, magnesium.  The earliest modern lightweight automobile racing wheels were made of magnesium alloy and were called "mags."  Now, anything that remotely resembles them is called a mag, whether it is made of aluminum (usually), plastic, or whatever.  It's now just a slang for a wheel type -- one that is neither disk nor conventional spoke -- and not a reference to the material.

Real magnesium wheels were banned from auto racing years ago because they are flammable!  I know that sounds crazy, but it's true.

Answer 2

It is kind of a dated term. It means magnesium alloy in which the original mag wheels were constructed. Plastics started popping up around the mid 80's.