As I’m sure you’re already aware, gas in America is stupid expensive right now. Well, stupid expensive by American standards, which are, admittedly, not the same as the rest of the world, where I believe gasoline is sold by the hip flask in exchange for human kidneys. Currently in America the average price for a gallon of gas is $4.40, and that adds up fast here in the land of vast distances and thirsty cars. There are ways to cut down on the gas you use, but they’re generally no fun. So, to help, let’s sweeten that medicine with the sugar of science, straight from some experts.
There’s actually two types of experts we’ve reached out to in hopes of helping us understand how to save gas, an aerodynamicist and a powertrain engineer; both areas play into how many miles your car can go on each precious gallon. Let’s start with our engineer named Austin Wright, who majored in aerospace engineering and who works for a major automaker as a calibrator.
Then, we’ll go into the powertrain side of the equation, which will be laid out for us by ECR Engines Technical director Andy Rudolph, who helps develop NASCAR engines.
I’m sure you’ve heard that driving slower will use less gas. This feels intuitively correct, and plenty of studies have backed up claims like how driving at 60 mph uses 14% less fuel than driving at 70 mph. If you have a car that’s rated to get 25 mpg highway, that’s the difference between getting 22.5 mpg and 25 mpg, which, if you’re going on a, say, 500 mile road trip would be a bit over two gallons saved, which is between $8 and $10 depending on where you’re getting gas.
That’s something! But, nobody likes driving slower because, well, it’s slower. And when you’re on the highway, it hardly seems like you’re working your car that much harder at 70 mph compared to 60. But there’s a lot more going on, both regarding aero and your engine, which is why I’m going to pass this off to Austin now.
Aero Considerations
The primary reason efficiency tanks with speed is due to drag.Buckle up, lets go
Drag increases exponentially with velocity, as I’ll show below. Let’s look at the drag equation:
Drag coefficient is a fixed coefficient, determined through testing in a wind tunnel. Air density and frontal area won’t change either, so we can shove these terms into a black box I labeled ‘constants’.
Meanwhile, velocity can change, and it’s squared. In a nutshell – the force of drag depends on the constants we are boxing up, but it doesn’t change based on them.
Drag only changes based on velocity. And, by being squared, drag increases exponentially with velocity.
I’ll quantify how drag increases with velocity. We’ll look at the difference in drag between 65 and 80 mph:
I converted mph to feet per second, which is the units this equation likes (or m/s if you prefer). As I demonstrated above, a 15 mph difference causes drag to increase over 50%!
So, how does increased drag relate to fuel economy? Your engine burns fuel, and through that chemical process, a transmission, etc, accelerates the vehicle. Think of that acceleration as a forward acting force (Force is mass times acceleration – Newton’s 2nd law).
As a driver, when you press the pedal, you feel that force accelerating you forward! Once moving, drag creates an opposing force, ‘pulling back’ on your vehicle. To accelerate, the force from your engine must exceed the drag!
To travel at a constant speed, your engine has to match the drag produced. Knowing this, a car’s top speed is defined by its power output and its drag characteristics. At top speed, the car isn’t accelerating; max power in the highest gear is equal to the drag produced.
A great example you could use to demonstrate the exponential nature of drag is the Bugatti Veyron.
With 987hp (1001PS), the Veyron hit an average top speed (on ) of 254.04 mph. The Veyron Super Sport came out with another 197hp, for a grand total of 1184hp (1200PS). The Veyron Super Sport hit an average top speed of 267.86 mph.
Due to the exponential increase of drag with velocity, the Veyron Super Sport’s 20% increase in power output only increased its top speed by 5.16%.
(This is a great, but not perfect, comparison. Both top speeds were recorded at VW’s Ehra-Lessien test circuit, and the cars are relatively similar. But weather conditions could affect the results slightly. Additionally, the Veyron Super Sport had aero changes to reduce its drag coefficient, like sleek NACA duct intakes replacing the previous, upright intakes.)
Notice that weight is absent from the drag equation. This is why the Veyron and Chiron can be so heavy! Weight certainly affects acceleration (inertia), but it has little effect on top speed (beyond rolling resistance with the tires). Additional weight actually makes the car more stable at speed.
Affects of Speed On Powertrain Efficiency
First, I am assuming you are referring to a constant vehicle speed on a level road, in a spark-ignited engine running at stoichiometric air-fuel ratio. Obviously, fuel economy worsens whenever load transients are introduced, particularly if they involve braking or stopping.
Overall powertrain fuel efficiency (BSFC: fuel burned normalized by power produced) is dictated by three mechanisms:
1) Volumetric efficiency: efficiency of inducting fresh charge and exhausting burned charge.
2) Thermal efficiency: efficiency of converting chemical energy of the charge inducted into thermal energy (combustion) phased optimally with respect to piston position.
3) Mechanical efficiency: losses due to rotating and reciprocating friction of the powertrain mechanical components plus power requirements of ancillaries (pumps, drives, electrical).
Let’s discuss each of these individually and relate how are impacted by vehicle speed.
Volumetric Efficiency
Volumetric efficiency is dictated by the flow efficiency of the intake and exhaust systems, and the amount of throttling employed. Modern dual-cam-phasing systems provide an excellent means of load control that reduces throttling losses. The two primary mechanisms are charge dilution via internal EGR (exhaust gas re-ingested into the intake tract) and late intake valve closing (reducing the effective compression ratio).
When loads are extremely low (low vehicle speeds), it becomes impossible to avoid throttling. Thus, efficiency is lost if vehicle speed, and hence required engine load, is too low. If the load is too high, efficiency is good but fuel consumption increases to provide the necessary motive power. The ‘sweet spot’ for fuel mileage is typically around 20 to 50 mph, depending on drag characteristics of the vehicle and engine displacement.
[Editor’s note: Imagine a throttle plate that’s barely cracked open, and think about the sound you tend to hear as the air gets sucked through that small opening — there are lots of pumping losses or throttling losses associated with the restriction. That’s what Andy is talking about in the second paragraph in this section. EGR is inert gas that goes into your engine, and takes place of air. One of its key benefits is that it lets you open your throttle fully (to get fewer pumping losses) while still keeping loads (and thus vehicle speed) down. -DT]
Thermal Efficiency
Thermal efficiency is also enhanced by independent cam phasing when implemented properly. For instance, a late-late valve timing strategy (delayed exhaust opening, delayed intake closing) provides pumping loss reduction by replacing throttling with late-intake-valve closing, while simultaneously increasing expansion ratio by delaying exhaust valve opening.
There is not an exhaust pumping penalty with this strategy at light engine loads because exhaust mass is low. In fact, delaying exhaust valve closing optimizes the exhaust event by balancing blowdown losses from opening the exhaust valve during the expansion stroke with pumping losses by not having the exhaust valve fully open early in the exhaust stroke. As with volumetric efficiency, this strategy for increased thermal efficiency is very effective at engine loads corresponding to vehicle cruise speeds between 20 and 50 mph.
[Editor’s note: If you didn’t 100% understand this, don’t worry, I’m not sure I do, either. But the point is that modern variable valve timing systems allow an engine to change when and how long valves open and close to maximize efficiency. Typical understandings of how vehicle speed/engine load affect efficiency (like the throttling losses we mentioned earlier) need to be reconsidered with this technology. Andy is saying that, even with this tech, thermal efficiency is maximized between 20 and 50 mph. -DT]
Mechanical Efficiency
Modern transmissions are amazing! Not many years ago, auto manufacturers had to select gearing that would provide reserve torque under vehicle cruise conditions to avoid frequent downshifts (gradeability). However, modern transmissions and the associated control systems provide near-seamless shifting, thus allowing aggressive calibrations that keep engine speed extremely low under cruise conditions.
Obviously, the faster the engine turns, the greater the parasitic losses, so adapting aggressive strategies to maintain low engine speed, and the associated minimal throttling, enables excellent mechanical efficiency. As vehicle speeds increase, and in turn the engine load required to move the vehicle increases, engine power at extremely low RPMs becomes insufficient. Thus, engine speed and the associated mechanical losses must increase.
[Editor’s note: Andy says high engine speed is associated with minimal throttling because, to drive at a given speed in certain conditions requires a given amount of power. So, let’s say you want to drive 55 mph on a certain road — that might require 25 HP. Power is a function of RPM and torque, the latter of which is referred to as “load” and corresponds to your throttle opening. So if you want to go a constant speed, you can do that at a low RPM and high load (like if you drove in a really high gear, which would minimize throttling) or a high RPM and low load (where you’d see more throttling losses, like if you were in a low gear). In either case, the product of the RPM and torque output will be the same. -DT]
The correlation between minimal achievable engine speed as a function of vehicle speed is again dictated by vehicle drag and the engine torque curve. As required load increases at a low engine speed, spark retard may become necessary to avoid abnormal combustion, which results in a thermal efficiency penalty.
The combination of these three efficiencies determine overall powertrain efficiency and, hence, fuel consumption, as a function of vehicle speed. Drag increases as a function of velocity squared, so that alone suggests that lower vehicle speeds are best. However, if the vehicle speed is too low, engine efficiency is sacrificed by throttling requirements (assuming a spark-ignited engine with a 3-way catalyst). Thus, depending on the vehicle/powertrain combination, best fuel mpg will occur at a constant speed of around 20 to 50 mph.
So, there you go: both our aero expert and our powertrain expert have made pretty clear and compelling cases for lower-speed driving for optimal fuel economy, and, in the case of our powertrain engineer, we even have an optimal range of speed: 20 to 50 mph.
Which, of course, is miserably slow, especially on a highway. I don’t imagine anyone will actually drive 50 mph on a long trip, but maybe you could drive 65 instead of 80 and get some real improvement. Also, if your gas light just came on and you don’t see a gas station in sight, the smart thing to do would be to drop to 50 at that point, at least, since 50 mph is still way better than walking with a gas can to the next exit.
When I delivered my energy message last April, I hoped that the national 55-mile per-hour speed limit–already in force–would help reduce gasoline consumption, which is essential if we are to extend the world’s finite supply of oil. If we all drove within the speed limit, we could save more than 8 million gallons of gasoline a day. That’s nearly a third of the reduction in total gasoline consumption I asked for in my energy program.
We have saved gasoline by driving slower. Tests by the Federal Highway Administration indicate that, depending on the type of car, drivers can get from 17 to nearly 50 percent better gas mileage at 55 miles per hour than at 70.
One thing I’ve learned by driving a sadly underpowered car is smoothness and momentum conservation. Leave room in front of you to the next car, so you don’t need to tap the brakes. Change lanes when needed so you don’t need to accelerate or decelerate; looking ahead in traffic is very important. This keeps you from changing gears often, using non-optimal throttle openings, wasting energy with braking… Hypermilers might be saving gas via air resistance, but they constantly need to modulate the throttle and brakes, not to mention the idiotic amount of stress drafting big vehicles.
I also tend to always be behind schedule. Making turns to make up lost time is stressful and the gas gets burned, so I am nowhere near perfect.
So what i’m getting from the mechanical portion of it is… it’s more efficient to be in a low RPM high load state because it allows you to open up your throttle more to reduce pumping losses?
Those indented
block quote paragraphs
from the experts you
called in to help with
this article are hell to
read on a smartphone.
Imagine if this
comment scrolled on
for ten or fifteen screens
with every line only
having three or four
words, and the
whitespace on either
side taking up over
half of your screen. You
probably wouldn’t
bother reading it, just
like I didn’t bother
reading this article
even though the topic
is something I find
quite interesting.
It rendered fine on my phone. I’m using Firefox on a Pixel5a. What phone/browser are you using?
If it’s that bad on your phone, best bet is probably just turning it horizontal so you have room even with the indention.
That last sentence got me good.
Get a Citroen and you’ll know how important drag is. Wafting through air like a magic carpet is a sensation like nothing else!
Aerodynamics is definitely a consideration, our Saturn’s mileage took a hit when had bikes on the roof rack so removing your rack helps.
As for travel speeds, I will have real world report Monday after towing a camper on highway 97.
The last time gas prices rose sharply – was it 2008? – I noticed a change in freeway driving habits. Some bought smaller cars and most drivers slowed down closer to the speed limit. I haven’t noticed that happening this time – most folks are still freeway driving 10-15 mph above the limit, and every 10 mins or so, I get passed by someone who must be going at least 25 mph above the limit. I’m curious if anyone has studied this, and why people aren’t slowing down to gain fuel economy as they did in 2008.
Two things.
1. It’s still the early stages. In 2008, there were newspaper articles about people pawning family heirlooms to buy gas to go to work. Give it four months.
2. The conservatives who drive fast are thumbing their noses at the attempts to spoil their lives (see Tom Luongo, for example).
Bollocks to that. Drive fast and take chances!!
The discussion in the article neglected to mention axle and transmission losses. Every time the power transmitted to the wheel needs to cross a gear mesh, you lose some of the energy. If the energy needs to go across an unlocked torque converter with speed difference across it, you lose more energy. Because of these factors, a traditional automatic transmission will be most efficient in direct-drive gear with the torque converter locked. For most cars, this will be well below your typical cruising speed, so the mechanical losses in the engine would be high due to high engine RPM. The overdrive gears help drop the engine RPM into the most efficient range at the cost of slightly increasing transmission losses.
So, you could figure out your absolute best cruising speed for mechanical efficiency by figuring out which gear in your transmission is direct drive, and then driving as slowly as possible while staying in that gear. For sure, it’ll be between 20 and 50 mph.
Man you people are over thinking this way too much. I moved back to my hometown and immediately bought a house across the street from the school my dad went to. It seemed to me if he had to walk to and from school 10 miles and it was uphill both ways, now anywhere I go within 10 miles it’s all done hill.
No problems.
I drove 55 all through college to save money. It helped that my main commute was over a mountain pass where that was a reasonable speed anyway, but it was a deliberate choice. Even now I mostly stick to the speed limits when not specifically in a hurry, there’s just honestly not much point to speeding.
Yes, I know I’m incredibly boring.
The car on the cover image for this article is a Tatra T77A. In 1935, it scored a drag coefficient of 0.21. For comparison, the average model 2022 year car is about 0.28, roughly the same as a 1921 Rumpler Tropfenwagen, and the 2022 Toyota Prius is a 0.24. It is possible to streamline a modern car to the mid 0.1X region regarding drag coefficient without sacrificing practicality. Just note the 2000 GM Precept with a 0.16, or the GAC Eno .146 which had a drag coefficient of 0.146.
If we did this, it would open the door to Dodge Charger Hellcats that get 40+ MPG highway, a Toyota Prius that approached 80 MPG highway, small Miata-sized diesel sports cars that approach 100 mpg, and electric cars that needed 1/3 less battery weight to go the same distance on the highway. In fact, we could have done close to this sort of drag reduction in the 1970s fuel crisis and gotten results almost as good.
But that would mean the auto industry has to give up planned obsolescence.
If you’re willing to squeeze into a one-seater vehicle, it’s possible to get into the thousands of miles per gallon range. In my profile is an electric microcar/tricycle thing that I built which consumes 0.008 kWh/mile, or the equivalent of about 4,000 MPG. That is at 30-35 mph cruising speeds, with light pedaling. It can’t reach 70 mph yet, but @ 45 mph, it uses about 0.015 kWh/mile.
My aerodynamics aren’t as good as they could be and there is potential to cut the drag to 1/5 of what it currently is, without giving anything up regarding usability or practicality. THAT would open the door to a non-bicycle single-seater commuter of roughly 200 lbs weight with a 49cc gasoline engine getting more than 1,000 MPG @ 70 mph, more than 1,500 MPG if it had a diesel, and the equivalent of more than 2,500 MPG @ 70 mph if it were electric. You could quadruple those figures respectively for 35 mph.
The auto industry doesn’t care and isn’t trying. They’ve known how to dramatically reduce aero drag for 100 years. The 1935 Tatra T77A is proof enough of that, with a drag coefficient that matches the slipperiest production car sold today, the Tesla Model S PLAID.
Ah, the Tatra T77. A car with an air-cooled V8 in the rear. A car that killed so many German officers during WW2 that the High Command forbid officers using it. (Not really the car’s fault, it was just that it had a lot of power, and a lot of weight in the rear, and if you went into a turn too fast, bad things happened.)
A couple of things. If you want to try this out for yourself, go to Yellowstone (in the off-season) and drive around the park. The distances are vast and the speeds are moderate with very little stop and go. It’s basically a low-speed freeway with few stops. You can get amazing economy there because of this. I got 36 mpg in a 1.8T Passat once (EPA highway mileage, 29), and even high teens in the Land Cruiser.
Secondly, this is exactly why class 8 (and lesser classes) heavy truck engines work the way they do. Many people don’t seem to get it that torque is meaningless on its own and that HP is what moves a load. These monster engines only really produce F150 levels of power but people focus on the huge torque numbers and assume that means something. What it means is that you can make sufficient power with very low engine speeds. Low mechanical losses, high VE, high TE. A Volvo D13 is a 12.8 liter I6 with between 1450 and 1850 lb-ft of torque, but only 375 to 500 hp.
The hardcore truck guys will tell you that the big torque number is what matters, not the little hp number. They are wrong. “Why don’t trucks just use hellcat motors then if hp is all that matters?!”, they shout through their beards – Because it’s hp AND economy that matters. A hellcat motor would move a fully loaded class 8 without issue and it would climb hills better and sound awesome…but it would be geared in such a way to get basically .5 mpg and wear out in a week. Nah, it’s big-ass motors with huge torque down low to develop the nessisary POWER required at the lowest possible engine speeds. These D13’s are hitting peak HP at like 1500 rpm. It all comes back to the 3 “E’s” ME, TE, VE. The goal is to get stuff moved as cheaply as possible and these truck engines are less about “stump pullin’ torque” and more about fuel sipping economy.
While that’s all true imo you’re completely ignoring the biggest waste of fuel, acceleration. Look how much the average person speeds up and slows down, that’s where you’re wasting tons of fuel, and getting nowhere for it. Except to the next red light, or left lane hog, quicker, if you consider that an achievement.
Want to save fuel and not drive like you’re on sedatives? Drive the average speed of traffic consistently, change lanes to avoid slowing down, coast to red lights and stop signs, think ahead, go around anyone that obstructs your view of what’s ahead so you don’t get caught off guard. Done right you not only save fuel but you get places quicker because you’re avoiding most reasons to slow down.
Truthfully it’s not accelerating that’s the problem, it’s braking. Accelerating hard gets you more kinetic energy per unit of fuel than does getting their slowly because your engine has higher BSFC under heavy load than light. The trick is to avoid transients, as the article says. The best way to get the most out of gas engine is to accelerate hard and then coast for a while. Brakes are pure waste. These are proven hypermiling techniques. It’s also why go up and down a mountain is more fuel-efficient that driving on a level road to go the same distance. Higher consumption on the way up the mountain, but a more efficient conversion of fuel to energy, then on the way down you cash in some of the energy you gained as gravitation potential energy and average out better than steady-state cruising.
If you can cruise long enough to average out the losses, accelerating hard is more efficiency that accelerating slowly.
For most BSFC curves, you will find peak efficiency of fuel to kinetic energy conversion somewhere between 1/2 and 2/3 max torque output somewhere near 1/4 of max RPM.
Efficiency climbing with load is also one of the reasons why smaller displacement engines tend to get better fuel efficiency, but the difference is marginal. The perception is thyat big V8 and larger engines guzzle greatly more fuel, but left unconsidered is that the bigger, heavier, less aerodynamic cars tend to get the biggest engines. When you compare EPA fuel economy for the same car but with different engine types, you’ll find a V8 is not much worse on overall economy than a 4-cylinder.
What would REALLY grab my attention is if some automaker built a tiny 2-seat streamliner like the little British Cars of yore except much more slippery, under 1,800 lbs curb weight, then gave it long-legged gearing, and then shoved a modern LS V8 engine in it. I think the potential for a 50+ MPG supercar that does 0-60 mph < 3 seconds and tops well over 250 mph exists(if and only if you can get basic stability, might have to restrict speed significantly lower, given drag reduction in the interest of fuel economy and acceleration, NOT downforce/looks is the goal).
Well said, all of it!
I mean, thats basically a C5, right? Slippery, light, long geared. They get exceptional highway mileage.
Yep, developing your vision of the road ahead will save you gas (and accidents). Also, don’t make other people nail their brakes – we all benefit if everyone uses less fuel.
There are some other pretty obvious tips.
Clean the junk out of your trunk. Carrying around your hoardings adds weight.
Drive on paved roads or at least roads. Fording riverbeds, chewing up forest floor and climbing rocks is pretty inefficient, not to mention the amount of fuel it takes to get your jacked up tractor there.
Drive with a destination. If you need to go somewhere, go there. Driving around in circles on a track gets you nowhere.
Don’t idle your vehicle – 0MPG
> There are some other pretty obvious tips.
I try to make it a game to avoid stepping on the brakes. Braking isn’t just inefficient, it’s throwing away energy. Most driving, if you’re watching far enough ahead, you can adjust speed so you don’t need to brake. Obviously city driving is where it’s the biggest winner.
I see absurdly good mileage in my Civic if I stick to ~45 mph.
Of course, it’s an Si, so that doesn’t really happen…
Sorry, you can’t drive at or under the speed limit on I-95. That is unless I want a semi truck rolling over me.
Can’t you just use them like a pusher locomotive and save even more gas?
“Yeah but…” says all those speed demons. “Time is money” so I must drive 80 mph not 65 mph. “In fact I’m actually saving money the faster I go.”
My math says that if you drive 100 miles to your destination:
@
80 mph = 1 hour 15 mins
65 mph = 1 hour 32 mins
>> So 17 mins of your life is saved
Let’s say your car gets 25 mpg:
4 gallons of gas at $4.50 / gal. = $18
>> Save 15% fuel (Jason’s example above) by going slower so save $2.70 on this trip
Bottom line: Are willing to give up 17 minutes of your life to save $2.70?
(In other words, driving 80 instead of 65 is costing you $9.53 per hour of your life saved)
Lawyers and investment bankers say “I make that back easily”, some of us say “well maybe not”
– Lawyers and investment bankers say “I make that back easily”
Those guys can bill hours from anywhere so it makes no difference if they are driving, behind a desk, or snorting blow off a hookers chest.
I’m not a lawyer or investment banker but $9.53 per hour seems fairly inexpensive to enjoy driving than to slog along. I enjoy driving, I don’t enjoy commuting. If my commute is more like driving then the trade offs are worth it to me.
Is it really more fun to drive 80 than 65, though?
Doing 65 here involves being relentlessly tailgated and having to fight 64mph governed semis for the right lane, so definitely, yes.
I frequently drive between Oregon on Arizona, so through Utah, Idaho, Nevada, or California along the way. The speed limit often 80mph on freeways and 65mph on rural highways. As I drive a 5th gen 4Runner (brick on wheels)…. 72mph seems to be the sweet spot for has mileage, not straining the truck, in with the routes I take huge wind gusts to deal with. I’m usually in the middle of nowhere, don’t get tailgated much.
I think Mr Choppers that you have identified the elephant in the room, the simple fact that driving carefully and efficiently is boring! So how does that affect our behaviour? Well, to achieve our desired level of mental stimulation we increase speed (assuming no police speed enforcement) until limited by fear for our own safety. That’s the “fun”.
Experts call this “risk compensation”, just a fancy way of saying we constantly, subconsciously, adjust our behaviour to limit the risks we take to a manageable level.
As for me, I choose a third option: just hit the slow lane and travel so slowly that I can “zone out” and relax.
“I think Mr Choppers that you have identified the elephant in the room, the simple fact that driving carefully and efficiently is boring! ”
Oh dear, driving not exciting enough for you? Try it in a vintage British or Italian sports car with double digit horsepower. Imagine yourself with the top down, surrounded by towering, angry faced SUVs and pickups, pedal to the metal just to make the speed limit. Your senses on constant alert: What’s that smell?! burning electrical insulation? fried friction material? leaking hydraulic fluid? overheating coolant? grease fire? overly rich mixture? Oh crap, now there’s a vibration?! Ball joint? wheel bearing? drive shaft? broken fan blade? Better figure it out quick!
No screens or HiFi sound system to distract you from trying to figure out what the broken gauges can’t tell you. How much gas do you have left? How fast are you going? Do you have ANY oil pressure? No !@#$%$^ idea. Double your excitement with sketchy tires, triple it with an exhaust leak. Quadruple it with a constant smokescreen of burning oil. You’ll feel James Bond levels of excitement, third world style.
After a few days of THAT you’ll be happy to return to your boring old Prius driven in the most boring way possible.
Agree wholeheartedly – drive a vintage car if it is excitement you seek.
Been daily driving a 1971 Ford F100 since December, without even an AM radio.
> What is that noise when going around a corner? Are the ball joints about to go?
> Why is then engine making that clacking noise? Oil pump cease to work?
> Hmmm.. gas tank is right behind the seat, and there is a sudden smell of gasoline..
> Did the turn signals decide to stop working again?
And this is the short list!
It’s fun to goose the mpg average in the car. That game was made excellent with the 2nd gen prius and has grown to other cars from there with real time mpg tracking
Agree 100%.
I also got hooked on trying to get the “high score” when I had a 2nd-gen Prius, taking pride in regularly getting better-than-advertised efficiency (55-57 mpg) in Los Angeles’ less-than-ideal driving conditions.
That has carried over now that I’ve moved on to hauling two kids around in my big ole Honda Odyssey. The combined fuel efficiency is advertised as 22 mpg, but my lifetime average so far is around 28 mpg, even with the dreaded efficiency-sink of waiting in car-line every day to pick the kids up from school. It’s a far cry from Prius-level efficiency, but I am confident in my ability to wring better-than-average mileage out of anything I drive.
Definitely. Bigger returns with bigger vehicles, too. I’ve squeezed 27mpg round trip out of a Silverado 6.2L rated for 21 highway.
Around town was harder – I think the only time I got above the 15mpg rating was driving late at night on a road where the cross street lights had sensors.
Not on a freeway crawling with the fun police.
This is good thinking, but I assure you that the guy who hits 80 is not averaging 80. My FIL drives 80-85 on the highway, whereas my kei car is not happy above 60. When we drive somewhere together I almost always arrive first, just by being more willing to change lanes to avoid congestion.
Now I admit that this doesn’t prove that slower = faster, but it would be great to find out exactly how large the time savings would be. Especially if you occasionally have to slow down, because it is the accelerating that really uses gas.
Higher speeds may be worth it, but only if you drive a larger distance and can maintain a steady speed – Iowa yes, NYC no.
I think this is especially true if your trip involves traffic lights, and is under an hour in duration. Mis-timing a light, or getting caught at a long one can swing your travel time more than the speed differential on the high-speed portion of the trip.
Dude, this is so true. 4 years and 200k miles of driving (for work) around D.c. and I can tell you that 1 light is all it takes to add 10 times more time to a trip than anything you might save by trying to go faster. Any route that requires a left turn without an arrow during rush is never faster than the one that goes around and let’s you move with traffic.
This is the response to all the people who smuggly remind you that they went slow and still caught up to you at the next light.
How many more lights do you make going a little faster?
IIRC UPS spent a lot of time and money on a routing system for their trucks which avoids left turns across traffic as much as possible.
To a trucker friend of mine, those 17 minutes can be the difference between getting to his destination and having to sit around someplace because his electronic logging device says he’s driven his max number of hours for the day.
He also did mention that due to the gearing and other factors on his rig, he normally gets the best mileage at around 75mph.
And if you’re doing that 100 miles as a round trip commute (50 each way) every day, 5 days a week, 50 weeks a year, that’s 70 hours per year. Or 1296 more hours with your kid between when they’re born and when you ship them off to college.
The average human lifespan is 700,000 hours. So 10,000 people spending 17 minutes more a day in their car is roughly equivalent to a teenager dying in an accident in terms of lost lifetime.
If there’s only an hour between when you would have gotten home otherwise and kid bedtime that’s 30% more family time. Just for driving 15MPH faster.
It adds up!
Yup. Now do it for a longer trip.
I don’t care if it costs me $20-50 more to get somewhere, I want to get there 1 hour earlier.
What about higher-than-normal tire pressure?
That might work for Mustang owners.
Yeah, it helps a bit, but mind you aren’t sacrificing too much in abnormal tire wear, or worse traction.
I treat the car manufacturer’s doorjamb recommendations and the max on the tire sidewall as the minimum and maximum of an acceptable range, so 32-45 PSI for most cars.
Idk…I get the science… But if I chug my big V10 excursion along at 60 it will be getting single digit numbers per gallon. But hook a trailer up and rip down the interstate with 8k behind it at 75mph…and I get 16… Sooo…..?
What I was always told if you drive in the motors sweet spot ( high hp and tq) almost come together, it’s at its best efficiency. Is that not true? Because obviously works on my big ass truck.
It helps, but reducing rolling resistance helps more at lower speeds. Rolling resistance doesn’t increase quadratically, like aerodynamic drag does, so you’ll see big gains around town and small gains on the highway.
Depends on the car and tire. Some sets of tires on my car definitely did better inflated to sidewall max. The current set does best at just over door jamb pressure.
When I’m towing our camper with our CUV, all 4 get pumped to sidewall max. First it gets the sidewalls up away from the road since these 225/65-17 tires actually have sidewall. Second it returns the handling to normal. An extra ton of camper otherwise gets scary. Last it evens out the wear.
20-50? I can get into 6th gear at the upper end there, but without enough engine speed to spool the turbo if torque demands increase, making it less efficient for real world driving. I get that he specified spark ignition, but tall gearing exists in non-diesel applications too.
I would like to see drafting accounted for in the aero discussion. The only real difference in my driving with current prices is a much greater willingness to tuck in behind a similar sized or larger vehicle that’s going faster than I otherwise would. I can watch the returns on the real time consumption readout of 85 with a blocker vs 74 without.
In my last car, I drove 80MPH on 65MPH highways. When I got my Volt, I slowed that down to 72 – moreso than in gas engines, EVs take such a huge efficiency hit at high speeds. It’s the difference between making the round trip to the next city south on just electricity and dipping into my gas reserve.
Going about 50 mph in 3rd gear, my old CJ5 could get about 12 mpg. With the hilariously small under-seat tank that meant I had to fill up every 100 miles. It could do 65 or 70 but the engine would be turning over 3000 rpm.
Cool article, and I love that it sits on the front page right next to: “The 2023 Cadillac Escalade-V Goes Ballistic With 682 Horsepower And A Claimed 12-Second Quarter Mile Time.”
You don’t need to convert that equation to fps, the math works the same in mph
Get all that crap off my website. Metric only.
SI or cgs?
Depends on the nerd. Physics nerds, SI. Engineer nerds, cgs. Definitely cgs in this case, since a physicist would reduce the car to a sphere with a point mass traveling in a frictionless environment.
As I learned from a chemist, cgs is the Convenient, God-given System and SI is Satan’s Invention.
Chemists are pretty much the best. We also get to use Angstroms!
Hear hear. Metric is the way forward.
Oh yay! I was always afraid you’d be one of those Imperial guys, please accept my apologies. I work in Architecture and every day I have to bang my head against the wall, dealing with what should be simple things (quick, what’s a third of 1-13/16?). Even Americans themselves don’t understand their system, our US-born staffers are constantly making an enormous mess while measuring things.
DOWN WITH COMMUNISM. Just multiply your divisor by 3, then add the equivalent 1/3 to it.
13/48 + 16/48 = 29/48
Plus now you’ve created an economy for measuring tapes using 48th chunked inches instead of the standard 32 or 64. That’s capitalism in all its glory, baby!
Base 12 is the magical OG system of the ancients!
I would be happier than a pig in shit if we had a base 12 system. You cant divide a meter into thirds (in a reasonable way) but dividing a foot by 3 is super easy.
In the UK (and most Commonwealth countries I think) measuring tapes and rulers come with inches down one side, and centimetres down the other.
Grew up working in a cabinet shop here. The answer is 9/16 strong. Carpentry doesn’t require decimal measurements to be adequate because no two pieces of wood are identical. Basically I use both depending on the situation because they both have their plusses and minuses.
The one I don’t get is cartridge reloaders. They use grains(imperial) but it’s still a decimal measurement, why not just go metric? You’re already 90% of the way there.
And whats wrong with 1/7000 of a pound? 😀
I will grant that it is odd that even Europe is firmly in the arms of “Big Grain” when it comes to bullets, cartridges, etc.
At least grains are still less confusing than shotgun bore sizes!
Metric Feet per second?
I measure exclusively in apple pies per bald eagle
I’m over here unreasonably piqued that mpg was used instead of the more useful/meaningful Gal/mile or L/km
miles/gal and gal/mile are inverses so they are equally useful if you understand the unit. For miles/gal higher is better; for gal/mile, lower is better. They measure the same thing.
They do, but comparing numbers does make more intuitive sense in fuel per distance. It’s the inverse, but it’s not linear.
This explains it a lot better than I can: https://www.greencarreports.com/news/1019426_miles-per-gallon-is-just-stupid-no-really-it-is
Ah yes, the difference between y=x and y=1/x.
The metric system is the work of the devil! My car gets 40 rods to the hogshead and that’s the way I likes it!
The metric is designed to cheat you out of beer. 330 ml rather than 12 oz. for the same price. They thought I would not notice.
Yeah, wasn’t sure what the point was. Velocity squared is the point.
I did some back of the napkin calculations, and it turns out my time and enjoyment make the speed worth it. (I may have fudged the numbers, since enjoyment is hard to quantify.) I also drive a ludicrously efficient PHEV, so those numbers may not hold for, say, a large SUV.
That said, this is a good article. I just had to be a little contrary.
My Ti-83 spit out the same answer.
“I did some back of the napkin calculations, and it turns out my time and enjoyment make the speed worth it. (I may have fudged the numbers, since enjoyment is hard to quantify.)”
Up to the speed limit. Beyond that the math gets real nasty with factors like “officer friendly”, “judge hard case”, and “insurance”.
I’ve noticed that I still get >40mg in my PHEV regardless of if I go 50 or 65, so I’ve stopped worrying about it.
Yep, this is all true. I see it in my fuel sipper compact car with better aero and a taller top gear than other models had. The sweet spot is about 57-60 mph where the turbo is right about to provide positive pressure.