4 ms·

Using Metromile data to determine a car's gear ratios

73 points by jeffonabike 10y ago

ilikeatari 10y ago
Great article! The gear ratio data would be useful to potentially derive more granular driver behavior model (acceleration) that is less mass dependent than accelerometer sensor. However, I do wonder if there is a way to determine the usage of the reverse gear itself. This data is currently not universally available via OBDII. The reverse gear data would be very useful since large amount of accidents are backing accidents.
- nickff 10y ago
  From the data provided, it seems likely that OBD is reporting any speed while reversing as 0, so you could probably guess that when the engine speed is changing slowly (while above idle), and OBD reports vehicle speed as 0, the car is reversing.
  - jeffonabike 10y ago
    This may be true - but even if the sensor is reading zero vehicle speed and greater than idling engine speed, it's difficult to assume these are in fact reverse and aren't just "engine revving" moments. Looking into a time-series breakdown of each moment - seeing if the engine speed is 'changing slowly' as you mention - would be key in properly identifying Reversing vs. Revving.
    - nickff 10y ago
      This is why I specified engine revving slowly; engines which are disconnected from the drivetrain tend to rev up very quickly. In addition, cars with automatic transmissions are a majority of the US fleet, and spend very little time in neutral.
      - hammock 10y ago
        > engines which are disconnected from the drivetrain tend to rev up very quickly So do engines which are in reverse and being controlled by drivers who are imminently about to have an accident :)
    - ilikeatari 10y ago
      This might also be specific to the Metromile hardware (OBDII interpreter). I just checked on my vehicle with STN OBDII interpreter reversing is showing non zero value (I increased the reporting frequency to 1Hz).
hammock 10y ago
What does this look like for a car with continuous variable transmission, like a late model Nissan Altima?
- hydrogen18 10y ago
  Most cars with a CVT are configured from the factory to have "gears". Even though the transmission is continuously variable, it is made to quickly move between distinct ratios. This is mostly because with a true CVT acceleration is very smooth and difficult for the customer to perceive. So the graph looks almost identical.
  - NikolaNovak 10y ago
    This is fascinating: This is mostly because with a true CVT acceleration is very smooth and difficult for the customer to perceive. Can you provide any more insight or further reading? I am considering a CVT (Subaru XT), and smooth acceleration without jumps is precisely what I would be looking for (which I believe was provided by my Scooter with a CVT as well). If companies are adding artificial jerks to a technology that is designer for smooth experience, I'm not sure whether i'd laugh or cry, but I feel I'd like to know more :-/ Thanks!
    - beamatronic 10y ago
      >> I'm not sure whether i'd laugh or cry Exactly... for me it's the same with electric cars that make fake engine noises. But that one I grudgingly accept, in parking lots, for safety reasons.
      - bunderbunder 10y ago
        I'm pretty OK with electric cars making fake engine noises. The Prius owner in my neighborhood would be semi regularly creaming people if they didn't have any auditory indication that he was about to come cruising out of the alley without slowing down to check for pedestrians. It doesn't have to be engine noises, it could be playing some sort of crazy "woop woop woop" sound for all I care, but I'm guessing the owner would prefer it be something a bit less embarrassing.
Sundog 10y ago
Neat
querious 10y ago
Actually a pretty good way to understand manual transmission. Very cool.
honkhonkpants 10y ago
130 km/h is a pretty good clip. Does Metromile charge clients more for high speeds?
- jeffonabike 10y ago
  Their fee structure is a base rate plus a fixed rate per mile. From what I remember, those rates are determined by the typical demographic info + driving record/past claims. There are other companies that I believe try to adjust their rate based on driver behavior data, but metromile doesn't (at this time).
- ajtaylor 10y ago
  75 mph is about the average highway speed in LA - assuming you're not in stop-and-go traffic of course. Speed limits seem to be more of a recommendation than an absolute.
- iav 10y ago
  California prohibits pricing based on driving habits like speed. Other states do permit it and Progressive offers snapshot device which does what you describe - offer discounts for safe driving behavior.
  - honkhonkpants 10y ago
    Wow really, that is amazing and unsurprising at once. I can only imagine the debate that led to this regulation.
frankus 10y ago
It would be neat if you could enter a tire size (e.g. 165-65R13) and estimate the overall diameter from that. Extra credit: figure out a plausible count of gear teeth for each ratio.

73 points by jeffonabike 10y ago

Great article! The gear ratio data would be useful to potentially derive more granular driver behavior model (acceleration) that is less mass dependent than accelerometer sensor. However, I do wonder if there is a way to determine the usage of the reverse gear itself. This data is currently not universally available via OBDII. The reverse gear data would be very useful since large amount of accidents are backing accidents.

nickff 10y ago
From the data provided, it seems likely that OBD is reporting any speed while reversing as 0, so you could probably guess that when the engine speed is changing slowly (while above idle), and OBD reports vehicle speed as 0, the car is reversing.
- jeffonabike 10y ago
  This may be true - but even if the sensor is reading zero vehicle speed and greater than idling engine speed, it's difficult to assume these are in fact reverse and aren't just "engine revving" moments. Looking into a time-series breakdown of each moment - seeing if the engine speed is 'changing slowly' as you mention - would be key in properly identifying Reversing vs. Revving.
  - nickff 10y ago
    This is why I specified engine revving slowly; engines which are disconnected from the drivetrain tend to rev up very quickly. In addition, cars with automatic transmissions are a majority of the US fleet, and spend very little time in neutral.
    - hammock 10y ago
      > engines which are disconnected from the drivetrain tend to rev up very quickly So do engines which are in reverse and being controlled by drivers who are imminently about to have an accident :)
  - ilikeatari 10y ago
    This might also be specific to the Metromile hardware (OBDII interpreter). I just checked on my vehicle with STN OBDII interpreter reversing is showing non zero value (I increased the reporting frequency to 1Hz).

hammock 10y ago

What does this look like for a car with continuous variable transmission, like a late model Nissan Altima?

hydrogen18 10y ago
Most cars with a CVT are configured from the factory to have "gears". Even though the transmission is continuously variable, it is made to quickly move between distinct ratios. This is mostly because with a true CVT acceleration is very smooth and difficult for the customer to perceive. So the graph looks almost identical.
- NikolaNovak 10y ago
  This is fascinating: This is mostly because with a true CVT acceleration is very smooth and difficult for the customer to perceive. Can you provide any more insight or further reading? I am considering a CVT (Subaru XT), and smooth acceleration without jumps is precisely what I would be looking for (which I believe was provided by my Scooter with a CVT as well). If companies are adding artificial jerks to a technology that is designer for smooth experience, I'm not sure whether i'd laugh or cry, but I feel I'd like to know more :-/ Thanks!
  - beamatronic 10y ago
    >> I'm not sure whether i'd laugh or cry Exactly... for me it's the same with electric cars that make fake engine noises. But that one I grudgingly accept, in parking lots, for safety reasons.
    - bunderbunder 10y ago
      I'm pretty OK with electric cars making fake engine noises. The Prius owner in my neighborhood would be semi regularly creaming people if they didn't have any auditory indication that he was about to come cruising out of the alley without slowing down to check for pedestrians. It doesn't have to be engine noises, it could be playing some sort of crazy "woop woop woop" sound for all I care, but I'm guessing the owner would prefer it be something a bit less embarrassing.

Sundog 10y ago

Neat

querious 10y ago

Actually a pretty good way to understand manual transmission. Very cool.

honkhonkpants 10y ago

130 km/h is a pretty good clip. Does Metromile charge clients more for high speeds?

jeffonabike 10y ago
Their fee structure is a base rate plus a fixed rate per mile. From what I remember, those rates are determined by the typical demographic info + driving record/past claims. There are other companies that I believe try to adjust their rate based on driver behavior data, but metromile doesn't (at this time).
ajtaylor 10y ago
75 mph is about the average highway speed in LA - assuming you're not in stop-and-go traffic of course. Speed limits seem to be more of a recommendation than an absolute.
iav 10y ago
California prohibits pricing based on driving habits like speed. Other states do permit it and Progressive offers snapshot device which does what you describe - offer discounts for safe driving behavior.
- honkhonkpants 10y ago
  Wow really, that is amazing and unsurprising at once. I can only imagine the debate that led to this regulation.

frankus 10y ago

It would be neat if you could enter a tire size (e.g. 165-65R13) and estimate the overall diameter from that. Extra credit: figure out a plausible count of gear teeth for each ratio.