【How-to】What is a good highway rpm

4,000rpm at 110 km/h is about right for 4th gear, but too high for 5th (~3,300), and way too high for 6th (~2,700). If you’re talking about an automatic box, it’d depend on how many gears are in there. Modern autos would have anywhere between 5 and 8, so I’d say 4,000rpm would be too high.