Typical Energy Expenditure %
 

Just curious if there is any ballpark figure out there about what percent of motive energy is spent for the average vehicle to:

Accelerate
Overcome rolling resistance
Overcome aero resistance

By motive energy, I mean not factoring in engine (in)efficiency, drivetrain losses, accessories, etc.

My guess is that acceleration accounts for less than 5% of motive energy as an average, perhaps much less than that even. Obviously this figure would be higher for those that spend more time in stop and go traffic, and less for steady state highway cruising. As an average though, what do you think it would be?

There's highway, city and mixed tables for this.

I think there is a rolling resistance and drag calculator over on camaroz28 dot com.

You can roughly estimate this. For example with my FR-S, I was getting about 18-20mpg? while looking for parking in San Francisco. I recall estimating that rolling at 25mph with pulse and glide was getting me around 90mpg, and almost all of that consumption would be rolling resistance.

Engine on P&G that number drops to the 40s I think. But the average speed is really much closer to 10mph, so it's like 30mpg.

So I think it's fair to say acceleration is taking close to 40% of the energy in that stop and go scenario.

For long freeway drives, probably 80% air resistance?

Not quite that much for the typical car, I suspect, but some bro-trucks might be more. In a Prius L Eco, at 70 mph you're using ~64% of the energy to overcome aerodynamic drag and the rest for rolling resistance. A 2020 Ram in its lowest drag trim, Cd = 0.36, is around 74% to aero drag at the same speed. At Cd = 0.45, the same truck is 78% to aero drag.

But the total resistive force acting on the last truck example, and therefore the work required to move it a given distance at a constant velocity, is two and a half times as much as the Prius. That puts things in perspective.

https://i.kinja-img.com/gawker-media...2ozxh1uibt.jpg

Right, the answer for an individual use case and vehicle is, it depends on the individual use case and vehicle. Just curious if this has been estimated across the entire US fleet? I think even 5% for acceleration alone is high.

One way to roughly calculate this on an individual basis would be to keep track of how much electricity a hybrid or EV regens over time.

Ah you're right, I overestimated drag vs. rolling resistance.

FWIW, Enterprise had a discount a few months ago on Tesla rentals, and I drove a Model S 70D up a fairly steep hill. The battery drained very very fast going up, with the miles remaining estimate going down something like 20 miles for only 4 miles covered, and then on the way down it barely gained any miles back.

Since the speeds involved were low, that tells you rolling resistance is still quite significant. That said, a permanent magnet motor powered car would probably do a little better on the same run.

What does it mean to spend energy on acceleration? When you have accelerated you still have that energy in kinetic form. Only after losing the speed do you know where it went. (rolling, aero, braking etc)

Or two black stripes on the pavement :D

Exactly. The energy not accounted for by rolling or aero resistance; ie braking.

If you drag out your physics text book or other technical articles there are formulas to calculate energy required in each case. The mass of the vehicle is listed on the vehicle or there are weigh stations. Drag is most easily measured in a coast down test.

Right, but the curiosity is in fleet average, or typical figures.

The reason I'm curious is people have the idea that it's the weight of vehicles that causes poor fuel economy, and it doesn't seem like much of a factor to me. That got me wondering what percent of fuel is spent accelerating/braking compared to rolling and aero drag taking into consideration that some people drive very heavy vehicles almost exclusively in stop and go traffic, and others might drive small cars almost exclusively on the freeway, and everything in between.

Again, I think it's highly dependent on where you live and drive. If you live in a crowded city area, hell yes weight is a problem. My stock MR2 Spyder could get 25+ mpg with its ancient cheapo engine driving between stop signs or in traffic, while my FR-S with its extra 600lbs would do noticeably worse. That was like half my driving, so I would be pretty happy with 30mpg.

If you drive mostly on the freeway for long distances, then aero is very important for obvious reasons. Do the people who drive these long distances use a large portion of the whole fleet's fuel? I dunno...probably?

I don't think people are getting the question.

As an aside, I get better fuel economy in gridlock traffic than steady freeway cruising at 70 MPH in my Acura. The point isn't if I could get better economy not being a sheeple, but how the herd as a whole does.

If you divide by the engine efficiency you will get the numbers you want:

https://www.fueleconomy.gov/feg/atv.shtml

typical
 

oilpan 4 is correct,you've got to parse it out for urban,highway,mixed,level,mountainous and there's also a consideration for curve resistance.SAE had a lot of literature on this back in the late 70s,early 80s.Hucho's textbooks will show at least the European models used to break it out.
In town it's all about inertia and momentum.You get the best efficiency at city speeds,but the stop and go destroys all that,and it's the reason for hybrids.
Out of the city limits,and out of gridlock,it's all about aerodynamics.
In his second edition,Hucho commented,'With a medium-size European car,aerodynamic drag accounts for nearly 80% of the total road resistance at 100km/h (62-mph).' And considering that one can legally drive at 85-mph between Austin and San Antonio,Texas,it's even more of the total,as the power varies as the cube of the velocity.:p

...and then, after a sufficient sample size has been tested, the average % of energy expenditure on braking is what?

Perhaps it's not easy to obtain a reasonable estimate, and there isn't a defined purpose to know what that average is.

braking
 

General Motors Laboratory,in 1981,published that 50% of a cars energy was expended in acceleration,and 67% of that energy was lost to braking (33.5% of total energy).
Stop-and-go driving consumed up to 100% more fuel than in highway driving.
With 25-gallons of gas,you could get:
Ten 40-mile trips
Sixty 4-mile trips
Ninety 2-mile trips
or one hundred 1-mile trips
In: Transportation Research Board Special Report 286,Tires and Passenger Vehicle Fuel Economy,Informing Consumers,Improving Performance,National Research Council of the National Academies,copyright 2006,ISBN 0-309-09421-6,153-pages:
For EPA City cycle,23.07% energy= Aero,30.77% energy = rolling-resistance,52.84% energy = braking.
For EPA HWY cycle: Aero = 55%,Rolling-Resistance = 35%,Braking = 10%

There's a new Engineering Explained video out which bears some relation to this question:

https://www.youtube.com/watch?featur...Rw&app=desktop

video
 

Watched the video. Thanks! Jason needs to be commended for ferreting out the details.
SAE test protocols would have included continuous meteorological measurements and normalizing data to standard atmosphere. Temperature variability as related to rolling resistance would have to be accounted for. Topographic effects, A-B, back-to-back testing . Curves on the 'test track' would not be allowed. Climate control would not be allowed.(I have a note which suggests that a heat-pump-sourced AC unit absorbs 1.6 kW).The 18-inch wheels are an unknown quantity. Only a wind tunnel would tell, unless Tesla has made a claim as to their added efficiency.
What Jason and CAR and DRIVER has done, does reflect the 'real world', in terms of what the average motorist would probably be willing to put up with ,when compiling road trip data.
One telling road test, I believe,by MOTOR TREND, involved a Model S, with a BMW 5-series shadowing behind, at exactly the same conditions. On a Btu-basis, when the cars were 're-filled', the Tesla ended up with a brake-specific-fuel-consumption-equivalency equal to around 1/3rd that of the Bimmer., on the order of BSFC 0.138-pounds/bhp-hour. This is where the battery/inverter/motor/and planetary gearset really shine. I think Jason Fenske has used 'insane efficiency' to describe Tesla's performance. Quite fitting!:)

this

https://ecomodder.com/forum/attachme...1&d=1585708146

EPA cycles
 

There's a danger in this characterization of the energy breakdown,which needs to be emphasized.In the context of 'combined EPA cycles',and only within this context is this data correct.
In the real world, motorists might encounter what Wolf H. Hucho has attempted to emphasize since the mid-1970s;that out on the open road,of the power available to actually propel a vehicle,aerodynamic forces can absorb 80% or more of this power,depending on velocity.
The casual observer might be left with the impression that aerodynamics constituted only a minor fraction of the road load,which would be a gross under representation of reality.And an why an understanding of aerodynamics has failed to capture the minds of the motoring public.A recipe for disaster.

Yeah, I wasn't particularly happy with the breakdown here, but it is the first relevant reply to my question and seems useful.

1% on brake drag, huh?

Power steering is next to nothing now that hydraulic systems have been replaced by electric.

first relevant
 

I've given you #17 permalink as to braking.Some of that was done at the national level as far as statistical analysis goes.

I guess I forgot about that one, perhaps because it didn't seem realistic to me. 33.5% lost to braking?

I should watch an EPA cycle someday. 10% braking on the highway is absurd. Only time I touch the brakes on the highway is if someone cuts me off.

it's different on the hybrid model of the same SUV shown, as there is still some DIY improvements on the hybrid model that could take it down to 0.30 from 0.34 (the one shown is 0.367 or 0.38) considerable improvement over the previous model design which is 0.45 and the model design before that was 0.55 or higher (think square box shape)... the 2015 models are 0.34 as well as the 2021 model .


the 2015 only had a 2mpg gain going from the 2014 to the 2015 model.... and that gain is from the 8 or 10 speed transmission mostly..


heavy footed drivers