# How does a modern automatic transmission know you're on a ramp? (making "1, 2" unnecessary on modern transmission)

I haven't rented a car in a while, and those are the only times when I drove cars with automatic transmission. In the past I always saw "1" and "2" on the shifter. If you're going uphill, especially if you're loaded, you needed to shift down yourself.

Nowadays all automatic shifters are a much cleaner "R, N, D, P".

Where did the "1, 2" go? Presumably modern cars are able to detect whether you're going up a ramp and whether you're loaded. Are cars now fitted with weight sensors and incline sensors to determine the appropriate gear?

For the sake of this discussion, let's assume we're on an n-speed (n=6, 7, 8) classical automatic transmission gearbox, not on an (e-)CVT gearbox.

#### Specifically

Another way to ask the question is this. Suppose you're riding at 40 kph / 25 mph, and the transmission has just switched from second to third. Now you hit a 10% ramp. If you were driving a manual transmission car, you would shift yourself back to second. If you're riding a car with automatic transmission twenty years ago, you'd shift to "2" yourself. Nowadays there is no longer a "2". A modern transmission will figure it out and (hopefully) go down to second gear until the top of the ramp. How does a modern automatic transmission know that you're on a ramp?

#### Aside

Is any permutation of "R, N, D, P" possible, or is there a standard, just as we can drive a manual transmission box while looking where we're going and without looking at the labels?

• Automatic means automatic - the transmission automatically switches gears based on gas pedal, rpms, and torque. Manually putting an automatic transmission into a low gear is for special situations where you know you really want to be in a specific gear. Nov 20, 2023 at 15:54
• @JonCuster Yes, understood. Now.. what is the technical advance that happened to make it possible for a car's design to forego the "1" and "2" on automatic transmissions. A modern car figures it out by itself, but not cars from the '90s. Why? Nov 20, 2023 at 15:58
• Many automatic transmissions offer the ability to select gears in a different way. My truck lets you pull the shifter to the left from drive to "manual" where you jog the shifter up/down to shift. My father's Subaru also moves the shifter to the left, but uses paddles on the steering wheel to shift up/down. Nov 20, 2023 at 16:04

Most automatic transmissions today are electronically controlled. If you look on the dash of any of these vehicles, you'll see where it "tells" you you are either in "D", "N", "R", or "P" describing what "gear" the transmission is in. Most of these vehicles also will allow you to put the shifting selector into a manual mode, and when doing so, will show you which gear the transmission is in while you are shifting it manually. So, bottom line is, "1" and "2" have not gone away. The systems are just showing it to you differently than it had been before.

As far as how does the vehicle know which gear it needs to be in, it takes into account throttle position (load), the speed of the vehicle, and other factors to know which gear the transmission needs to be in to propel the vehicle down the road as the driver demands.

As far as your Aside, without looking at the indicator? To my knowledge there really isn't any other way to know.

• The modern DSG autos I have driven are able to detect when a downshift is needed: going downhill, accelerating but no throttle or load on the engine. They are a world apart from the 1950s auto design still in use in some marques. Nov 19, 2023 at 23:20
• @WeatherVane - You are quite correct. Nov 19, 2023 at 23:38
• Perhaps I hadn't worded my question clearly enough. Could you read the "specifically" section? Nov 20, 2023 at 0:01
• @Sam7919 - I answered that ... Please re-read the 2nd paragraph. On top of that, it doesn't have to know. It only knows what you as the driver are requesting the vehicle to do. If you press the go pedal, the vehicle knows you want to go faster. If speed doesn't pick up, it knows it must do something else to assist. Then it downshifts. If that doesn't do it, it downshifts again. It is simply the programming. It doesn't have to know anything differently. Nov 20, 2023 at 0:10
• @Sam7919 in a sense, the slope is a red herring. It doesn't matter why the car isn't accelerating as expected - it could be due to the slope, it could be due to the load, it could be due to wind. There are many external causes, but from the point of view of the system, the effect is the same.
– muru
Nov 20, 2023 at 4:20