>The story is that 4ft 8 1/2 was the width of the Romans chariot wheels
Unfortunately, if you actually see original Roman road surfaces with original ruts, you realise "The story" is complete bolleaux ...
For obvious reasons, flanged wheels running on iron (later steel) rails have to be a pretty precise distance apart.
Otoh, the distance between chariot wheels never had to be that precise; given how big the Roman Empire was, how long it was around and how much detail about it survives, there isn't any mention of all these people all over it for hundreds of years ensuring the distance between chariot wheels was precisely 4' 8-1/2", which doesn't equate to any length unit used by the Romans?
Also if you see original Roman roads with original ruts, while wheels 4' 8-1/2" apart might fit into 'em, so would wheels considerably further apart and considerably closer together ...