Even if your staying below 40 and not forcing rpms up automatics still just want to get to 5th and stay there as soon as it gets some distance.
Why shift to the highest gear when your barely making the first 4 do anything?
In: 0
If you let go of the gas, the default behaviour is to minimize how much speed you lose. At a mere 1000 RPM, even 5th gear (or any higher gear if you have it) isn’t very fast.
Engine RPM multiplied by gear ratio = wheel RPM. This is true even in an automatic, it’s just that the `=` symbol is a bit sloppy – so much so that you can have the engine running but wheels stopped. If you choose a lower gear, engine RPM goes up. If you’re not feeding the engine gas, it will want to come back down to 700-1000 rpm and it will drag the car’s speed down along with it. The transmission is trying to avoid that if it can. At highway speeds, 5th gear isn’t enough and you WILL lose speed this way. In fast-ish city speeds, it might be just the right engine speed, within tolerance.
(In a manual, the `=` is actually an equality as long as the driver is not pressing the clutch pedal.)
low rpm and high gear is most fuel efficient as long as the engine can pull it, i.e. you are not accelerating hard or going up hill
It’s more fuel efficient. You can accelerate faster by waiting longer to change gear, but it uses more fuel.
I bet if there is a race mode or sports mode on an automatic, then it would not change gear so quickly.
It’s part of how car makers they meet the government requirements for fuel economy.
Even certain years of manual transmission Corvettes actually had a shift skip built in that wouldn’t let you go from first to second gear in most circumstances, it would jump you straight to fourth gear.
The others already answered your question, but wanted to share that this isn’t special with automatic transmissions. The principle of “using the highest gear with the least amount of RPM without lagging the engine” is one end of spectrum to drive efficiently, on the other end it’s to get the most power from your transmission by “using the lowest gear at the highest rpm without going into redline” (generally the power band is near redline but there are exceptions)
In my manual, ~30 mph is where I go to 5th, and ~38 is when I go to 6th. Meanwhile if I’m driving aggressively, my first gear go to about 45 when it hits redline
Latest Answers