# Fuel Economy Calculation Issues

The chosen gears and calculated fuel economy of this car I’m making are very weird. For starters, here’s an imgur album including the efficiency curve (screenshot 1), as well as fuel economy calculations of two versions of the same car, with the only difference being that the first one (screenshot 2) has its gear spacing at 50, while the second one (screenshot 3) has its gear spacing at 25:

A side note: I’m absolutely not an expert on this, but I don’t think engines with best fuel efficiency at 5000 rpm are actually a thing? This also doesn’t seem to be the case in beamng. Is this because the efficiency curve is solely about the engine on a test bench without stuff like air or rolling resistance as would be the case in a real car?

Regarding the actual issues:

1. The RPM target for the chosen gears is inconsistent. In case 1 (screenshot 2), for the 30 and 50 kph test, 5000rpm is targeted. At 70 and beyond, 2000 is targeted.

2. This seems odd enough by itself, but in case 2 (screenshot 3) with changed spacing, only the 30kph test targets 5000rpm while the 50kph one goes for the lowest it can achieve, with the latter probably being what would actually get better economy in real life.

3. Even though RPM is lower for the 30 and 50 kph tests in case 2 (screenshot 3), the fuel efficiency is actually worse, going from 6.7L to 7.0L. In the 50 kph test, the game could choose a lower gear to get closer to the 5000rpm mark which had yielded better results in case 1, but it sticks to sixth gear instead.

tldr: Sometimes it sticks to 5000rpm, which I don’t think would actually yield best fuel economy in real life. Sometimes it doesn’t do that and instead goes for the lowest rpm possible. When it does the latter, economy is worse.

Is this working as intended and if yes, could someone explain it to me?

Engines are most fuel efficient relative to power output up around peak torque so most efficient acceleration is relatively aggressive so that probably weights it (seeing as 30% is given to 2nd gear).

That certainly is odd, I would have expected slightly different behavior as well. We’ll take a look at that and add some more fuel economy calculation feedback on that page to better see what is going on.
Cheers