My new car has three different displays of the current gas mileage or MPG. But I don’t know what they’re used for.
Obviously high gas mileage is good. Momentary MPG depends on lots of things, but whether you’re climbing or descending a hill is perhaps the biggest. Also, the size of the vehicle is important. Not driving too fast is helpful, so for example always targeting the speed limit, or 10% below the speed limit if you’re not blocking traffic. Wind speed and direction matters. Tire inflation and other vehicle maintenance matters too.
What of all these things are under the driver’s momentary control?
I try to maintain the speed limit. I influence the other things when possible, but they’re not possible on a momentary basis. I don’t know what to do with those three displays, colorful lit bar graphs dancing back and forth and distracting, which don’t seem to turn off. What am I missing here?
There are people who work at something called hypermiling, trying to get the best mileage they can. They avoid quick starts, heavy acceleration, and try to coast as much as they can.
I think the purpose of the instantaneous readout is to teach you to accelerate more gently, and maybe to remind you that the consumption difference between 60 miles per hour and 80 miles per hour is more than the ratio of the speeds.
Cycling power meters can display instantaneous power; which is absolute BS because no one can maintain the absolute same power thru a pedal stroke; that is why they all can be configured for various smoothings - 1, 3, 5, 10 seconds, etc.
My car displays a rather useless (other than to be amusing) instantaneous power display rather than any smoothing in it. I’ve watched it change 60-80 MPG in a single change, from 99 MPG ( the max it’ll display) down to somewhere around 20-40 while there was no conscious change to the amount of gas pedal pressure during those changes. Besides being useless for anything other than a laugh / questioning of whether it’s really displaying anything properly, I’m sure that some of that has to to with where the cylinder heads are at the time of measurement. It sounds like that is what your car is doing. Why the car companies do that rather than give you some smoothing (even over 1 sec would make those number jump around a heckuva lot less.
I’m curious if the OP’S car is a hybrid or electric — as opposed to a non-battery assisted IC vehicle. The hybrids and plug-ins I’ve owned have the MPG gauge. Has it appeared on standard engine cars?
As others have said, it’s to make drivers learn fuel efficient driving techniques. A common technique for improved hybrid mileage is “pulse and glide”, which is brief acceleration followed by an extremely light touch on the gas pedal. The MPG gauge lets you see just how much pressure you need to remain in high MPG mode while maintaining speed or losing speed very gradually. When you slow too much for safe traffic flow, you “pulse” again.
It’s possible to do pulse and glide without being extremely annoying to the cars behind you, but it’s best not to attempt it in bumper to bumper situations.
Yes. I have a 2015 Corvette, with a traditional internal combustion engine (a V8), and the dash gauges can show me:
Overall MPG since I last reset the counter (which I do each time I fill up)
MPG for the “current” trip (i.e., since the car was started)
“Instant” MPG
Average MPG for the last 50 miles
Of those, the only thing I actually care about is the first one. I occasionally look at the Instant MPG when I’m cycling through the display screens, for amusement, to see if I’m getting over 70 MPG in the moment that I’m going downhill at 70mph, with the cruise control on.
Are you asking about the use of all MPG displays, or only “momentary MPG”? Because I can think of several reasons one might want to know one’s overall estimated MPG (and the closely-related Miles Till Empty).
I presume you have an automatic transmission? For manual transmission (which is dominant in a lot of countries) it is helpful to see the effect of changing gear. I can imagine car companies do it primarily for that market and keep it for all cars (doesn’t make sense to remove it).
As well as the things mentioned already, if the general MPG has gone down it might prompt you to remove excess load, check tyre pressure, maybe the car needs maintenance etc.
My CMax has an instant readout for mpg and energy use, as well as a “brake coach” that gives you a score for braking events. The instant acceleration readout helps train you to accelerate smoothly, keeping the engine, or transmission (cvt), or both in an ideal state, which is better for gas mileage and battery power conservation. The brake coach trains you to keep the regenerative braking at the point of maximum efficiency.
Both are effective. Obviously non-hybrids don’t have much need for a brake coach, but I tend to ignore instant MPG readouts in other cars more readily than the one in the Ford, because the Ford display is more clear. I like it.
It can also alert the driver that something is wrong. If it always displays around 35 MPG at highway speed, for example, and it shifts to 30 MPG, then you should try to determine the cause. Perhaps the air filter needs replaced.
I’m asking about the bar graphs that seem to be momentary – they jump around constantly.
This car is less than a week old, and it has an automatic CVT transmission. And it includes a tachometer, which I’m interested to see hovers around 1000 rpm when driving at steady moderate speeds on flat ground. This is, to me, surprisingly low. It’s funny that right off the bat the tachometer is attracting my attention, because in the big picture I imagine tachometers are useless in automatic transmission cars.
The car I traded in had a manual transmission, but no MPG gages, momentary or otherwise. As you say, it would have been helpful to see the effect of changing gear. I typically kept the engine speed around 1700 or 2000 in the absence of some reason to keep it higher, but it would run pretty rough at 1500 and I’d be lugging it at 1000. I vaguely remember looking up fuel efficiency graphs 9 years ago when I got the car which informed this habit. Otherwise the thing I’d use the tachometer for is judging when to shift in very noisy traffic situations when I couldn’t hear the motor.
My current car doesn’t have an MPG readout, but I had it on a previous car and the trip MPG was useful, I think - there are a number of things people unconsciously do that are wasteful of fuel - for example continuing to accelerate toward a red light or some other situation where they have to stop, then braking hard, then accelerating hard, etc.
Driving the exact same route day after day on my work commute, with the trip MPG turned on, I was able to experiment with different general strategies for saving fuel.
The more modern versions of this, one of which I saw on a loan car that was a hybrid, give scores for braking, accelerating etc - I think I’d treat this as a challenge to try to improve my score over time and in general, that improved score probably means saved fuel, reduced wear on brakes and clutch, maybe some incidental safety benefits too.
Most of the same driving techniques that result in better MPG in a hybrid also apply in a pure-ICE engine. Not regenerative braking, of course, but even there, gentle braking is usually better than sudden braking.
As an aside, one other technique that helps that nobody has mentioned yet is learning the timing of the lights on your common routes. Sometimes, if you see where the light is in its cycle, you can just ease off the gas a block or three in advance and slow down enough that the light changes green just as you get to it, and you don’t need to brake at all. Or on a long stretch where the lights are all timed together, you know the speed you need to go to get them all (except for maybe the first one) green.
That, of course, depends on whether you have any maniacs on your ass at the time. I slowed down a mere half a block before I got to a red light this summer, only to have this lady gestuculate wildly in my rear view as she camped 3’ from my bumper, then zoomed around and cut in front of me. Did her no good as I subsequently was able to pace her for the next 6 blocks.
The wife and I play a game called ‘see you at the lights’ - whenever we’re aggressively overtaken like that, one of us (it’s sort of a race to see who says it first) will say ‘see you at the lights!’ - we take note of the colour/plate/model of the car (it’s usually a BMW), then look for it at the next lights or roundabout or other junction.
Almost invariably the car that overtook and zoomed off makes very little actual progress compared to us, even if the junction where we caught up was nowhere in sight at the time they overtook.
Above a certain density of traffic and frequency of junction stops, the advantage of trying to go very fast tails off really sharply.