Thanks to everyone for the welcome, and to Butterburp for guessing the (very easy) reference ☺︎
@Evil Taco Since the mph roll back at 255 as shown by Marco in his glitch video, it’s very likely that the speed is stored in a single byte, which would make a version in km/h not possible. But I know very well that feeling of distinctly remembering something that actually was not! Probably your memories conflated GPC with a similar game, happens to me too.