Griffiths is a good book, but from experience you can't just blow through it as if you're reading a Dr. Seuss book, especially if you find some of the notation unfamiliar. Math is a language and like any language you have to first learn its notations. For starters, you should immediately...
So I've been told that the speed of light remains constant despite length contraction and dime dilation because they each decrease proportionately. So a velocity of 4 meters/2 seconds in a relativistic scenario might see a halving of values of length and time so it may only traverse 2 meters but...