Factorio Forums

I want to calculate maximum speeds of vehicles based on a car prototype (depending on vehicle, fuel, terrain, and stickers). Looking at the wiki I've found this about speed in reverse of the vanilla car:

The top speed of the car in reverse is ~70.7% of the forward top speed.

and tank:

The top speed of the car in reverse is ~70.6% of the forward top speed.

How did you calculate these factors? They differ so slightly (by just 1 per mille) that it's quite likely this is meant to be the same factor (i.e., a constant/fixed value) and the values on the wiki pages are different because of rounding errors. However, it's also possible that the factor depends on some properties set in the prototype. In this case, while the difference is insignificant for comparing car and tank, it could be considerable for modded vehicles.

So, is it safe to use the formula universally, or do I have to calculate the factor for each prototype -- and if so, how exactly?