Can Fast Acceleration Save Fuel?

something that noone mentions is that using the brakes cost fuel but instead it maintains the brake disc and clean them, which is in turn saving you money by not having to repair damages caused by rusted brakes and discs :) thats also important I think :)

Interesting video. The Kinetic Energy of a car of mass m at a given speed v is ½mv².
Conservation of energy and ignoring losses would suggest that it only needs that much energy to get to a given speed.

Maybe on hybrids (like Toyotas), if you want to get on the EV motor as much as possible.

Accelerating more quickly (but no crazy full throttle) gets you to cruising speed quicker, so you spend more time on EV.

And of course, for braking, it's the reverse, you decelerate and don't break. Let the EV do the regen breaking for as long as possible.

I'm not 100% on this, it's more a feeling that the car isn't struggling as much.

Plot twist: Somone was moving that frisbee between each run to mess with you.

Was reading the Finnish taxi driver's manual and it said accelerating faster to get to your speed was more economical, I knew it was wrong! Watch me fail the theoretical test now because of it 🤭

I kind i disagree on the results. I feel that if we leave a higher distance on cruise control on the lobg run the consumption will be better.

I drive an old MK4 Jetta 2L MSI (Multi-port Stratified Injection) aspired engine. With the assist from an OBD scanner i start noticing the car average consumption eas arround 12 and 14 l/100km so i start doing so many hypermiling techniques but without change on the instant, trip and average. Even going worse.

I start getting out late fron work so areas where the speed limit is 80 km/h since there wasnt car nearby and eas completly empty one nigth i decided to go full throttle and reach something crazy like 120-160 km/h and relasing the throttle when I start noticing the traffic lights, regardless of if it was green or red I would relase the throttle to start losing speed and something upshifting to the highest gear available but only if the traffic ligth was on green, if it was on red i would leave in 4th at high ROM to have an active engine braking.

My surprise was, that trip usually ends with 13l/100km and that day I was confused bc accelerated fast, went really fast and my trip consumption went down to 9.3l/100 km.

I thought the OBD got an error bc it was everything wrong so do speak. High speed increases wind resistance, so the engine has to work more to overcome the force that the wind is crating against the car, the tires are also making an opposite force (Rolling resistance?) And in order to keep a high RPM the engine requires more fuel. So my final conclusion was.thw OBD fuck up on something.

A few days later again I wnet out late from work, y restart the obd, double check all sensors and went for a run like the same time. I reached 140 i saw the red ligrh on the distance so i relase the throttle and let the engine slow me down, the green ligrh is up a few meters and my current speed was 60km/h so I downshift to second (i had to take a rigth turn and inmideantly go into a curved road so y prefer to keep the engine braking to had more control under that curve) when arrived home my new trip consumption was.9.1l /100km, i recorded an excel table and my average consumption went down from 14.3l/100km down to 13.7l/100km.

One nigth I run a test. I would run that road fast as I can and instead of going back to home I would drive back to my work and then drive at 80 km/h back to the same traffic ligth. I did 8 runs. One at fast speeds.and.other at 80km/h. I was at 5 am. Parked on a 24 hr store making calculations and figuring out the data. The 80km/h runs used 0.4 more litters than the high speed runs. I understand that an aspired engine is happy on cruise speeds at 2000 rpm so I would use higher gears as long as the rpm reached at least thay amount of rpms or slightly above that but the fact that the car was still injecting fuel even that they were at lower amounts those small amounts keep making more consumption at the long run.

The excel table also show up something. Once I reached the 80 km/h and keep that speed for 10 km my instant consumption was 3l/100 km which it seems very logical and the fuel flow rate is 1.3 L/h. And this number remains like this for 10 km more

On te fast runs I had higher consumption like 20l/100km but this only last for a few seconds then went down to 10l/100km and suddenly went down to 0 l/100km and due the RPM and location this areas where areas on the road where for safety I would engache 5th gear, let the car kind coast on gear bc it was areas I consider "risky" bc a car could incorporate on the road or infound out cars on the road and.kind expecting the worst I would let the car keep moving but try to no get close to them quickly in order to avoid an accident in case someone incorporate on the read and block my lane or suddenly change into ma lane and once that risk have been passed i would down shift.and go full throttle again up to the traffic ligth.

Well the table on the fast run has a lot of 0 on the instant consumption and in total was arround like 5 km of 0l/100 km and my belive is that since 0 is lower than 3 those numbers helps a lot to "figth back" the high consumption from the times I go full throttle enjoying myself. After this yeah I start using more speed without worries but of course. On city i feel is kinds reckless bc something on the road migth force you to brake so I prefer keep my engine at 200-3000.rpm sometimes going up as much 4500 of the conditions allow it but not making early shifts so often. But you can also drive fast and keep very good consumption if you know and calculate when to relase the throttle (And as for me that's a fun way to drive bc you are fully focused.on the road trying to predict what the others are going to do).

I discover.this like 6 months ago and rn my current avg consumption it is on 10.3l/100 km and as fact I'm someone who always presumed that "it rarely uses his brakes" after using more speed I'm really amazed how much my consumption went down by driving more fast but also anticipating with 3 years of distance what could happened on the road or some unexpected hazard could occurred can be a game changer.

The time I went out on a trip I also find out that in some hills but taking them as "down hill" if you let the car earn a little bit of speed on gear can cause you can go on for various km without accelerating again. I took a downhill of 1.5km and since I was already in 5th, the max speed was 110km/h and I reached 130 without accelerating, I really wanted to brake but I decoded to let the car lose that speed over time, it ended up being the best option in terms of efficiency (On the safety point I belive the best at my point if view could be go down to 4th and maybe keep it on 120 km/h or even let him reach more but with an active engine braking on 4th on any case that something went wrong on the road) losing those extra 20km/h took the car arround 5-6 km during those km my consumption was 0. That trip was awesome bc I went to a forest with my friends was done with only 2.5 liters of fue and the trip consumption was 4l/100 km. (It went up to 6.5 on the way back) and I belive that was pretty good for not trying to hypermiling, we went in less than 2 hrs and went bsck home in an hour and for an engine that is not a turbo fuel injection engine I belive it was awesome).

I don't consider my driving style "economic" but also not consider my self a street racer. I would say it is efficient. If circunstances allow it, I will run and hammer it and if I can't then I'll just adapt to the traffic condition. I belive that the most economic way to drive this car is just always trying to keep it on 2000 RPM on the higher gears but I.never test it, maybe I'll try that next time my tank goes down to 1/8 of tank.

What about half-full throttle acceleration and skipping gears - one of the advantages of manual shifting? That avoids the acceleration interruption 2-3 times... provides possibility to accelerate harder and also use of higher gears which normally yield lowered fuel consumption. I recall Jason Cammisa mentioning it in one of his podcasts about hypermiling an M3 (?) that at full throttle - the throttle butterfly valve is asked to be fully open, reducing the airflow restriction... though I was also thought to avoid giving a full gas at low gears whilst learning how to ride a motorcycle - allegedly due to possible valve damage..? Not sure about the last part, but I'm pretty sure that modern cars with all the electronic magic happening - would find the most optimal and safest way to respond to my throttle pedal requests.

You literally have videos to all my questions

i think this results would have changed if the car was naturaaly aspirated cuz turbos use richer air fuel ratios at higher loads to avoid irregular combastion

I think it would have been more fair to test the economy up to 30miles/h instead of driving after reaching 30

Don't TSI engines have small superchargers too?
Could the sacrificial element effect the results?

Was this the same car as in the other video where you compared the fuel economy in different gears?

Every engine got a clamshell diagramm you can often find online which tells you how efficient the engine is at which load in relation to the revs. Usually engines are most efficient at higher loads and lower revs. Often its rather close to max throttle in the 1000 to 2000 rev range. So pushing the accelerator quite hard and changing up at roughly 2000 rpm should theoretically give the best results. Thats because a modern warmed up engine with injection and electronic controls wont use a fat mixture so all the petrol/diesel is used up. Additionally on petrols the throttle valve will increase pumping loses at lower loads though Ive been told that there are valve options which reduce this effect or eliminate it mostly. Lower revs on the other hand mostly mean 3 things. Slower piston speeds decrease friction losses and you get less air into the cylinder so the ecu will inject less fuel. The slower piston speeds also means that especially in petrols the fuel/air mixture got longer to push the piston down so more of the energy is used for propulsion. Long story short in basically all circumstances high refs is what kills your fuel economy.

I'm used to drive gently, I like my my drive to be comfortable, Eco and safe. And the figures talk.
Obviously for security I sometimes have to push it hard, and I don't want to be too slow on speed and accélérations for other users.
And spending your time pushing your rpm high and low quickly don't seem to me very good for engine...
Trying to drive smoothly at approx 2500rpm is my way and my old cars seems to appreciate

Which app are you using for the test you are doing for your car?? Btw I’ve learnt a lot from your contents

You get better economy whilst you accelerate slowly. But you get the best when you stay still!

1. In all cases, you need to burn the chemical energy required to reach the kinetic energy level of your intended cruise speed. Right off the start, it doesn't matter much if you derate
2. If you derate from peak power to peak efficieny, you will save some gas as the friction losses inside the engine are lower for a few seconds. You will often be a nuissence to traffic though.
3. Your average speed may decrease, but then it's more efficient to reach the same avergage speed with a lower cruise setting and a quick acceleration.

That said, in order to drive fuel efficient:
- lower your cruise speed (especially on roads where it is easy to pass)
- don't use the friction brakes, retain as much kinetic energy as possible when maneuvering
(- don't open the windows as it will induce drag)
(- turn off unneccessary subsystems in your car)
(- don't load stuff in your car you don't need)
(- turn off the engine when you don't need it)

If you want to modify stuff:
- go for energy efficient tires (you have a conflict of goals as these offer less traction)
- inflate your tires to the high end
- use low viscosity motor oil, but it has to be approved by the car manufacturer for your climate

If you buy a car, go for a long one if you need space. The more surface area you put against the wind, the more your fuel burn will be.

Do you know that concorde used afterburners to accelerate to the cruse speed to save fuel?

This is like when I'm driving an automatic transmission.
Gentle throttle, then the transmission will shift around 1800 to 2200 RPM.
Full throttle, then the transmission will shit on the redline.

If you try this same experiment with a very efficient Electric Vehicle it might actually be more efficient the faster you accelerate as long as you take the same amount of time to cover the same distance. Work done accelerating varies with the square of change in speed. If you accelerate quickly you don’t have to reach the same top speed to have the same average speed.

You have to look at the torque curve of the vehicle. If you stay in the torque band, you'll have the best results. Not sure if staying at the lower end of the torque band or hovering in the middle might be better.

My diesel car makes 5.5 l/100 km.

I experimented a few full tankfuls with VERY economic driving, getting even down to 4.0 l/100km for a full tank, more than a 1000 km.

Surprise! When I filled up the car, the real consumption turned out to be more than 5 l/100 km. It shows that the computer calculates incorrectly when driving outside of normal parameters.

To make these tests relevant you need to keep to one style of driving for a full tankful and check the consumption at fill up.

Your car may be different.

Love the choice of music in the Kia onboard

i have experimented with this in my own car, a week commuting to work where i would floor it whenever i had the opportunity and then reset the trip computer, and driving in a very reserved style.
i noticed quite a significant difference, i had 35mpg with harsh driving and 42mpg with reserved driving.

Thanks captain obvious.

Accelerating slowly in a city makes you miss green lights more often, so it makes your journey a lot longer

Why u don’t go from 2 to 4 to 6 or 1 to 3rd to 5th

Great idea but the methodology is a bit questionable. The biggest issue is that you're using the vehicle's fuel economy calculator. You really need to do this with an independent flow meter.

gentle driving in modern diesels seems like a good way to block your DPF

My car has a realtime l/100km readout, so I see it all the time that moderate acceleration is most efficient. Acceleration quicker doesn't matter as much as driving in speed range that use more fuel for longer duration. It is 4 speed automatic, so the economy zone of 2000-3000RPM is only available at 50kmh, 80kmh and 100kmh. These 3 speeds use the same amount of fuel per km. They thought about this very well, it is Saab 9000, 2.3-16 with no turbo. It if it the turbo version, it will use less fuel at slightly higher speed and less efficient at 50kmh, which also is how many people say it use so much fuel. I average it at 9l/100km.

For an electric car, the less you press the go pedal, the further it will travel, your electrical losses are the square of the current times the electrical resistance, from which it follows higher load due to air resistance at high speed drawing more current, & high current from accelerating fast are both your enemy.

Such a good video showing the differences. Equally though, whats the point in getting up to "speed" if you're likely to have to stop shortly after reaching said speed for instance, in a town. This is all well and good in a situation where your in a highly controlled environment but that never the case. In my experience on busier roads, the faster you are going = the quicker you will have to slow down and the time you "made up" going fast is time you'll spend going slowly, that's how average speed works. so if you really want to be efficient i think we should consider the average speed of a jourey and stick to as near as we can to that whilst matching general slow.

The problem with this test is that it's not isolating for average speed. The gentle test has a significantly lower average speed, so this test really just confirms that lower driving speed is better for efficiency.

tl;dw
be a grandma and you will save fuel

Polacy tez to ogladaja😁. Pozdrowienia dla Zonki (Polka no nie?:). Great episode. More please!🙂

The increased wear on the transmission of accelerating quickly is also something to consider.

Honestly you don't get chance to go beyond 70mph due to speed limit or signal or road hump in urban area so consider braking at 3rd gear or 4th gear droping speed to 6mph then accelarate back.

See what figures you get

I'd like to see this test using an V8 Gasoline automatic pickup truck. I'm pretty sure that the result would be the same but to a higher degree. Loaded, 1/2 loaded, and unloaded would produce a very thorough resolve. Include Diesel pickup trucks would be even better. I'm very light footed and always wonder if the transmission shifts too soon for maximum economy.
Another question is: when I see a climb coming I speed up a-bit so as to carry momentum into the climb and then let my speed bleed off until my truck voluntarily downshifts out of overdrive and then I hold that reduced speed that maintains the one gear down throughout the climb. Softly speed up to enter the climb?????

Maybe you mentioned it and I missed it, but couldn't it be the turbo that's making such a big difference? I know on my car the turbo hardly does anything if I accelerate gently, but it ramps way up if I accelerate quickly. I'd be really curious to see a similar test with a car that doesn't have a turbo. Regardless, super interesting video!

At first I thought the speedometer was on the left, I was like Wow it’s changing a lot, Why is it down at 20??What’s goin on?!!??

I'm still gonna drive like a hooligan in my 75hp twingo

Interesting, but I could never drive like that! I'd die of boredom! Nearly every journey once the oils up to temp I'm hitting the limiter at 8800rpm!

What if you keep the max rpm constant but press the throttle different amounts. For example, in test one press the throttle all the way but change gears as soon as you reach x rpm. In test two press the throttle half way and again change gears as soon as you reach x rpm.

He's probablly a capricorn 😄

Before watching this i think optimal amount of acveleration is to put your gas pedal at same position where it would be at wanted cruising speed

Thanks for confirming what I always believed! I am curious if the results remain consistent on a slight incline?

Your AC is on... doesn't mean the compressor is constantly on. This could cause variance in the results.