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Discussion Starter · #1 ·
I see some refer to the Volts range display as a Guess-O-Meter (GOM). My range display is pretty darn accurate, so why do some refer to theirs as a "GOM"?

I suspect the issue is based on the driver not understanding (or forgetting) things that affect car range. The car's range display is based on the drivers last few trips, and it is basically saying, "Based on the last few days of driving, you should get this range, all things being equal."

That last part is important, if conditions change, the estimated range will be off. This is where people get tripped up.

Changes in condition include:
  • Tire Pressure. Low tire pressure will decrease range. It's very easy to loose 2-3 or more PSI when the outside air temps drop.
  • Weather. Cold, wet, snow will all decrease range.
  • Heater/A/C. Cranking these up will decrease range.
  • Aggressive Driving. The more aggressive the driver is in starts and stops, the more the range will be negatively affected.
  • Speed. Speed kills ...battery range. The faster you drive the more it will negatively affect the battery range.
The effective range of the car can drop (or increase) based on changes in the above compared to the previous days driving record. I think some people forget that, leading to calling the range display as GOM.
 
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In summer (for instance) my GOM shows 60 Km range. When I drive into town which is 9 to 10 Km. (on a 60 Km/hr. twisty up and down road of higher elevation, going from the coast to inland) the GOM will show 59 to 60 Km. I didn't pick up 8 or 9 Km. going up hill. Doing my errands and driving home (in the aggregate going down hill) I will have used up half my battery with associated Km accumulated. By then it all comes out in the wash (using full to half battery) but the GOM doesn't seem to be linear. It doesn't register the miles traveled at the beginning and seems to go a little faster at the end of range. The engine comes on when the battery reaches 0 but I haven't done that since the beginning of 2020 with the cancelled car club meetings because of COVID. This Thursday will be the first one since so it will get a test then to see if it still switches at 0 (plus what the Kwh. used is, it was 10.3).
 

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Discussion Starter · #3 ·
Yes, I forgot another variable, Terrain (how hilly or flat your daily drive is) will also affect the miles. Also the shorthand of saying it's based on your last few days driving may actually be referring to the last 5 charge cycles based on some older threads. If so, driving 4 days may not affect the range display unless each day resulted in a full recharge at the end of each day. I wish WOT were around to clarify.
 

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Mine is not particularly accurate. Part of it is the climate, here, especially this time of year. One drive you need heat, the next some air-con, the next no climate control. Also, my driving varies between short trips to those using the entire battery. Except for the rare bursts of acceleration, my driving style is probably the most consistent thing about how the car is used.
 

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Discussion Starter · #5 ·
Mine is not particularly accurate. Part of it is the climate, here, especially this time of year. One drive you need heat, the next some air-con, the next no climate control. Also, my driving varies between short trips to those using the entire battery. Except for the rare bursts of acceleration, my driving style is probably the most consistent thing about how the car is used.
Right. Hard for any thing or anyone to be accurate when the conditions keep changing. Most gas cars don't even try (maybe some new ones do?), they simply tell you how full the gas tank is. It's up to the driver to make the range estimate. You can do the same with the Volt of course. Just look at the battery bars and try to figure it out yourself. :)
 

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That's why it's called that. Because "all things being equal" doesn't. So while it's literal accuracy within that constraint may be good, the circumstances so seldom apply that it's just guessing at the next trip, which is the only one people care about while looking at the number.
 

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My only comment is that I would be surprised if it uses more than several minutes of driving history (rather than potentially 5 charge cycles) to update the display. My drive in to work is a net loss of ~800' over 10.5 miles. Many times I will start out with an estimated range of 40-43 miles. By time I get to work, the estimated range remaining is often in the upper 40s, or pegged at 50. On my way home the estimated range drops precipitously, especially in the last 3 miles where I go up the steepest part of the drive. In my ten mile trip home, the estimated range will often go down by nearly 30 miles, thus I conclude the update to the range is looking at the most recent very high kWh/mi needed to climb the hill home and updating accordingly.

In the end the overall range that was reported in the AM (about 40) is usually pretty close to what I observe (about 38-40 miles if I do not recharge). Of course this may be an early 2011MY programming that was smoothed out in later models? Mine has a low 004xx VIN #.
 

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My range display is pretty darn accurate, so why do some refer to theirs as a "GOM"?
The fundamental issue is there is no 100% accurate way to determine the amount of KWh left in a Lithium Ion battery. Yes, these estimates are accurate, but they're just that - estimates.
 

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Don't forget that the guess-o-meter can be fun ! One time after weeks of 70 mph highway commuting I took surface streets home and the guess-o-meter started ADDING ON
miles as I drove ! Gotta love those algorithms :)
 

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The thing corrects for the amount of juice left in the battery as you drive, but doesn't much alter its math for how far you can get for a given amount of juice during the drive. If it thinks you can get 4 miles per "voltage span as represented by a segment on the battery display" (hereafter "segment") and you go from 8 to 7 segments, it'll show remaining range correspondingly down as each quarter of that voltage span drops away. But it's not going to note that you only drove two miles since the last segment and halve the estimate remaining accordingly, because maybe that was a hill and now you're going to go down it. The car doesn't know, so it doesn't try, because trying would lead to VERY wild swings in the estimate, and make it even less useful for most drives and drivers. And it's up to you to figure out how that's going to be different if your drive isn't a closed loop on a single charge, and what conditions are going to be different from the last one you did.
 

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All this reminds me of the battery in my G1 Insight. The car knows how much 'lectricity goes in and how much 'lectricity goes out, and sort of keeps track of that, but it never has no real idea how much is there is in there.

In the Volt, for me, I look at it after charging to see if the number's reasonable, sort of glance at it to be sure it's behaving in its regular fashion, and that's about it. Unless I need to reserve some juice for slower-speeds after a highway drive, I sort of ignore it.
 

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And it doesn't even really know how much in or out, either. It knows voltage and how much is flowing at that instant. It can time-slice the flowing at that instant, rack up a couple ten thousand readings over an hour or so and have a PRETTY good idea how much came in or out, but that frequency of taking readings can always miss something. Voltage tells you where you are between full and empty and when you need to stop doing what you're doing and do something else, but again, that doesn't tell you WHEN you're going to have to change what you're doing, because the consumption and charging curves aren't perfectly flat either. There's a lot of math and estimation between the two things.
 

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You could say the range is accurate looking backwards, but going forward there are changes in driving technique, speed, weather, etc. that require the computer to make ongoing changes, or guesses, for your total mileage on a given charge.
 

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Discussion Starter · #17 ·
You could say the range is accurate looking backwards, but going forward there are changes in driving technique, speed, weather, etc. that require the computer to make ongoing changes, or guesses, for your total mileage on a given charge.
Yup, when the underlying conditions are changing compared to what was happening in previous drives, making an accurate long term estimate is not going to happen. I think the car does a reasonably good job of predicting the miles at the start of the day based on recent drives. If you drive like you have been, all is well. But all you need to do is, say turn heat and fan on full blast and drive at 80 MPH (assuming on previous drives you were not doing neither) to invalidate the estimate. I don't blame that range miss on the car. As the driver, you know you've changed the rules of the game and should expect less miles from the battery as a result.
 

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I'm not a Tesla fanboy but I think Tesla's range is a lot more accurate especially if you enter your destination. It's calculating more than historic trends to estimate range. However I don't own one so I would be parroting other Testa reviewers. I heard they're even taking temperature, elevation, traffic, speed limit, vehicle load and probably other variables I haven't even thought about into account.
 

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just like a normal gas gauge - top half goes forever, bottom half not so much :)
I once drove a panel-truck (9 mpg) with a 90-gallon cylindrical fuel tank, mounted horizontally.
  • 1st quarter = gone in a blink
  • 2nd quarter = took forever
  • 3rd quarter = took forever
  • 4th quarter = why ain't you filling the tank?
 
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The owner's manual clearly defines the electric range figure as an estimate, but the algorithm used must be fairly accurate as the actual mileage tends to be pretty close unless there are major variations - temp, speed, AC/heat, routes, tires, etc. Unless the estimate is unusually high or low I don't pay much attention. My Volt shows 42 mile electric range today - it may actually get 45 or 37, but either way it is not a big issue for me. I drive the car like I would any other car, the range is what it is, and the ICE extends it to whatever I need. The only numbers I really note are energy usage vs. miles, and total KW used at ICE start. They are a better reflection of vehicle operation and health.
 
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