I am brainstorming ideas for a school project and am considering building an app that can determine which gear the car is currently on and when to switch to which gear (on stick shift cars).

This app could potentially be helpful for people learning how to drive stick shift cars as well as completely new drivers who happen to learn on a stick shift car. The app will take in data from the phone's built-in accelerometer and gyrometer and I am planning to train my model on a 6 hour road trip where my friend (the owner and driver of a manual transmission car) will announce whenever she switches to which gear.

My TA posed this question to me which I am unclear about. He was wondering why I could not just solve this problem using the systems in an automatic transmission car to alert the driver of a manual car of when to switch gears. I have looked online and have been unable to find anything linking using parts from an automatic transmission system in a manual transmission car to tell the driver when and which gear to switch to. If anyone has any knowledge about whether or not something like that is possible that would be great!

  • Why not research the systems that exist in manual cars - Fiat has this change up/down indication on the dash for manuals...
    – Solar Mike
    Commented Mar 28, 2018 at 5:35
  • 1
    You need to do a lot more research, changing gears depends on several factors, like engine rpm, when you need torque etc. And these heavily varies from car to car, like a ferrari might be able to do 60mph or 100kmph on 1st gear, but your daily driver might not, also take hints from gear shift indicator in existing cars as said by Solar Mike
    – Nilabja
    Commented Mar 28, 2018 at 7:16
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    I'm voting to close this question as off-topic because it is hypothetical, broad, and has nothing to do with actual maintenance or repair of a vehicle.
    – CharlieRB
    Commented Mar 28, 2018 at 12:35
  • My truck has shift "suggestion" indicators and if you read the manual they are specifically to help optimize fuel economy. If the right person is instructing the new driver, and the new driver endeavors to listen and understand, he/she will know when to shift in short order. After all, the vehicle tells you when to shift, but not with electronic gizmos or lights. Commented Mar 28, 2018 at 16:21

4 Answers 4


This would not work. Apart from the technical challenges, an automatic transmission does not have the same gears. For example, due to the torque-converter an automatic does not need to such low a gear as the first gear in manual cars. The other gears are then often spaced a little different.

Also, there is often some "fuzzy logic" applied to when an automatic changes gear. Dependent on the load conditions different shifting-patterns will apply.

Your main indicators for when a gear-shift is appropriate are throttle-position and rpm. You´d also need the power-curve of the motor and some other characteristics of the specific car your app is running in. Still you will fail in some conditions where intent of the driver is not readable by technical values - typical example is when the driver wants to use engine-braking going downhill.

  • @Solar Mike: Read the whole post. it does work, but not like in automatic transmissions and it will not always produce optimal results. I have never seen a car with a gear-shift indicator that was smarter than an good driver!
    – Daniel
    Commented Mar 28, 2018 at 8:35
  • My first comment says it works and I definitely didn’t suggest it was smart or smarter than a good driver - but, looking at those on the roads they seem to be as rare as hen’s teeth...
    – Solar Mike
    Commented Mar 28, 2018 at 8:50
  • @Solar Mike: I don´t understand what you are getting at!?
    – Daniel
    Commented Mar 28, 2018 at 9:06

As Daniel explained using parts from an automatic transmission would not work.

Your best option would be to plug in a bluetooth OBD reader and use the data for a phone app, to determine if a gear shift would be needed. In that case you are using the same parameters (speed, rpm, load) as the gear shift indicators in most modern cars do. But even then your app would be limited to (or needs to adjust to) a certain engine type, because different engines have different characteristics and therefore different gear shifting points.


There is no reason to do this, other than as a fun hobby. There is no market for it. Two key points:

  • it is unlikely for an automatic transmission notifier to be useful on a manual transmission vehicle.
  • these already exist and are now relatively common on manual transmission vehicles, even small city cars.

But even barring those, they are of limited use. For most road cars, these indicators are simple indicators of being above a certain RPM level. They do not take into account driving styles, the road ahead, etc. Even in high performance cars, the indicator is often an indicator that you are approaching the red line.

Some more modern ones do use a combination of throttle position and rpm to provide an indicator at "best" change, but even these tend to err on the side of fuel economy rather than what the driver wants.


If you're talking a new computer-controlled automatic, then it'd be a matter of copying the software.

However it won't work with old school automatics. They do all that with hydraulic pressure differential.

In fact, automatic transmissions shift using a complex (for hydraulics) hydraulic computer called a "valve body". This is fed via pressurized hydraulic fluid coming from a pump (and you could use the power steering pump).

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The logic you are interested in has 3 inputs, all modulated-pressure hydraulic lines: a spinning-ball speed sensor on the engine side; a spinning-ball speed sensor on the driveshaft side, internal knowledge of what gear is currently selected, and a signal operated by engine vacuum which very coarsely indicates how hard the driver is pushing the accelerator pedal.

But consider what this would be. It would be a hydraulic computer for the sole purpose of controlling (advising) a machine that has no hydraulics at all - a machine that is quite simple.

While it would be an amazing technology demonstrator to make it actually work, it would be like building a Viking ship with Viking-era hand tools, or cracking the German Enigma code using only 1940 technology. You'd have to have a reason to even want to learn how to do that.

In this day and age, you would just use an Arduino for that. It would be a trivial exercise for such a machine.

In fact, most cars already have it: it's called an "upshift light" that warns you it's time to upshift.

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