Any further or any farther?

Hello,

I've been trying to understand the difference between further and farther. I read that farther can be applied while talking about physical distance and further can be applied when talking about figurative distance. Can I use "farther" in this sentence that I've written or should it be "further" since this is figurative use?

The speed of the car didn't let his thoughts travel any further/farther than the next turn.