In the car designer when you go to add a transmission.
The last gear can’t go past say 75mph when my engine is set to red line at 4k rpm, but can go to 150 mph if i set the red line to 8k rpm.
Isn’t this a problem if you wanted to make an economical engine that would run at say 1800 rpm at 75 mph in 5th gear?
Well, of course for a given gear ratio, more RPM will mean a higher top speed, and we need to have a limit to how high you can set the gear ratios.
Perhaps the highest available gear ratios are currently too low though?
Or perhaps in addition to engine red lines, you add a fuel shut off rpm. For example.
1.8L Inline 4 engine
120hp @ 2200 rpm & 160hp @ 5500 rpm
Redline is set to 6000 rpm to allow for higher end ratio.
Fuel cutoff is set to 3000 rpm for Economy.
When choosing this engine, the performance of the car will be limited to the fuel shut off rpm, but the transmission would be geared for the red line.
That would be a bit strange as no car actually does that. Don’t forget though that in the simulated economy test it won’t be holding low gears. It’ll probably be doing 100kph in top gear, even though it could theoretically do 100kph at the red line in 2nd for example.