Instead of halving the remainder, you can do 3/5 - since it’s always going to be a multiple of five - so 120kph is going to be more like 74mph because it’s 10kph less than 130, and 10kph=25kph≈23mph=6mph

Also, this doesn’t only work with Fibonacci numbers, it works with any Lucas sequence, since they all tend to phi, so as well as 2-3-5-8-13 you can also use the higher numbers from 1-3-4-7-11 to fill in some gaps and help estimate.

And as a bonus, it means if you know A kph is equal to B mph, you also know that A mph is ~equal to A+B kph.

So given your result above of 120kph=74.4mph, I would estimate 120mph≈194kph. And it turns out it’s actually 193.1koh, so… not far off.