Speed Kills Your Pocketbook

[Scott5114]

Every car has a "sweet spot" in terms of gas mileage where it runs at peak efficiency, and then it drops off again the further you go above that. On the PT Cruiser I used to drive, it was about 50 mph.

[GCrites]

Typically the less aerodynamic a vehicle is the lower the speed it reaches peak MPG. Note this isn't the Coefficient of Drag (cD) but Drag Area which is cD multiplied by the Frontal Area of the vehicle. Gearing and RPM also affect the peak MPG speed.

[Bickendan]

Every car has a "sweet spot" in terms of gas mileage where it runs at peak efficiency, and then it drops off again the further you go above that. On the PT Cruiser I used to drive, it was about 50 mph.

To be fair, it felt like PT Cruisers topped out at 70 and you had to floor it to maintain 50 going uphill.

[1995hoo]

I've found that most often, you'll get your best fuel economy if you can consistently hold the lowest speed that allows you to use your car's highest gear without lugging. Hype about particular speeds, such as 55 mph, is mostly oversimplification because so many automatic gearbox drivers have no concept of their car's gearing and also because Americans so often want bright-line rules for everything.

[JayhawkCO]

There's also the factor of once you reach a high enough speed, you can remain above a given speed by momentum alone, barely having to hit the gas at all to maintain it, or to maintain a slightly lower speed. If you hit 120 mph and then take your foot off the gas, and it takes you 30 seconds to slow down to 60, you just averaged 90 mph for 30 seconds without using any gas.

The gas to go from 90 to 120 is more than the gas saved from 120 to 60.

Chris

[Plutonic Panda]

Every car has a "sweet spot" in terms of gas mileage where it runs at peak efficiency, and then it drops off again the further you go above that. On the PT Cruiser I used to drive, it was about 50 mph.

To be fair, it felt like PT Cruisers topped out at 70 and you had to floor it to maintain 50 going uphill.

I always thought that PT Cruisers had a cool, retro look in a quirky way. The execution however was horrible and typical of many American cars during that time had awful reliability and was cheaply made. Chrysler's made some cool cars like the Prowler and the ME Four Twelve they should have built. If they just wouldn't have gone so damn cheap and maybe charged a few thousand more trading for a better made car I really believe they would have the reputation they do.

Now, aside from the charger, the 300 is the only car they make except for their minivans. I wonder if Fiat will give them the ax.

[renegade]

Every car has a "sweet spot" in terms of gas mileage where it runs at peak efficiency, and then it drops off again the further you go above that. On the PT Cruiser I used to drive, it was about 50 mph.

To be fair, it felt like PT Cruisers topped out at 70 and you had to floor it to maintain 50 going uphill.

I always thought that PT Cruisers had a cool, retro look in a quirky way. The execution however was horrible and typical of many American cars during that time had awful reliability and was cheaply made. Chrysler's made some cool cars like the Prowler and the ME Four Twelve they should have built. If they just wouldn't have gone so damn cheap and maybe charged a few thousand more trading for a better made car I really believe they would have the reputation they do.

Now, aside from the charger, the 300 is the only car they make except for their minivans. I wonder if Fiat will give them the ax.

Fiat probably might not give them the ax, but Stellantis might, although I hope they don't.  They also make the Challenger. 

[jakeroot]

Wait, are we talking about Dodge, or Chrysler, or Stellantis as a whole? The Durango sells very well.

[CoreySamson]

Chrysler needs to revive the Aspen as an electric SUV (otherwise, there is no reason for them to exist anymore) and Dodge should get in on the bandwagon of making SUV coupes, since they are now apparently a performance brand. Maybe they could resurrect the Magnum name for it and have it compete with the Mach-E?

[Plutonic Panda]

Wait, are we talking about Dodge, or Chrysler, or Stellantis as a whole? The Durango sells very well.

Chrysler specifically. Not the other brands under the corporation. I believe Fiat owns Chrysler and Ferrari but under the company I presumed they would use the Chrysler name as opposed to fiat. I really don't understand the full deal but as far as I know Fiat owns the Chrysler group which includes Dodge(RAM), Jeep, and I'm forgetting someone else other than Ferrari.

[jakeroot]

Wait, are we talking about Dodge, or Chrysler, or Stellantis as a whole? The Durango sells very well.

Chrysler specifically. Not the other brands under the corporation. I believe Fiat owns Chrysler and Ferrari but under the company I presumed they would use the Chrysler name as opposed to fiat. I really don't understand the full deal but as far as I know Fiat owns the Chrysler group which includes Dodge(RAM), Jeep, and I'm forgetting someone else other than Ferrari.

I see. Looking at North America, Stellantis sells a fair number of cars: Chrysler 300, Alfa Romeo Giulia, Fiat 500X and 124 (sort of), and the Maserati Quattroporte and Ghibli.

If you look at the worldwide brands, they sell numerous five and three door hatchbacks, as well as sedans, especially lately through their purchase of PSA (which netted them Peugeot, Citroen, DS, and Opel).

[GCrites]

There's also the factor of once you reach a high enough speed, you can remain above a given speed by momentum alone, barely having to hit the gas at all to maintain it, or to maintain a slightly lower speed. If you hit 120 mph and then take your foot off the gas, and it takes you 30 seconds to slow down to 60, you just averaged 90 mph for 30 seconds without using any gas.

The gas to go from 90 to 120 is more than the gas saved from 120 to 60.

Chris

Aerodynamic drag increases by the square of speed.

[JayhawkCO]

There's also the factor of once you reach a high enough speed, you can remain above a given speed by momentum alone, barely having to hit the gas at all to maintain it, or to maintain a slightly lower speed. If you hit 120 mph and then take your foot off the gas, and it takes you 30 seconds to slow down to 60, you just averaged 90 mph for 30 seconds without using any gas.

The gas to go from 90 to 120 is more than the gas saved from 120 to 60.

Chris

Thanks for signing your name after every post easing confusion. How much gas is burnt while accelerating?

Just a habit -- similar to your needing to be kinda standoffish and/or rude in nearly every post you make.  I think mine is less offensive.

If you want me to give you exact answer, I'd have to have a little information like the gearing of the car, fuel efficiency, aerodynamic property of the vehicle, etc., but a quick Google search shows that your average car uses about 12x as much gas per second at full throttle vs. coasting at 30-60 mph. 24 g/s vs. 2 g/s respectively.

So, I'll pick a pretty fast car with good acceleration, a Dodge Charger.  It goes 0-60 in 5.2 seconds and 0-120 in 20.4 seconds.  So 60-120 takes 15.2 seconds.  So during that time, to accelerate, you're using 364.8 grams of gas, and then you use none for your deceleration back down to 60.

If you're coasting, for that same 15.2 seconds, you're only burning 30.4 grams of gas.  You'll need to continue using gas for the time it takes for the 120mph car to slow down from 120 to 60.  I don't have a great way of calculating that, but to spend as much gas as the accelerating car (364.8-30.4=334.4 grams), it would have to take 167 seconds (2 minutes, 47 seconds) to slow down that much.  Between air resistance, gravitational force, and force of friction on the tires, it would never take that long.  Maybe a minute tops.

Chris

[Occidental Tourist]

There's also the factor of once you reach a high enough speed, you can remain above a given speed by momentum alone, barely having to hit the gas at all to maintain it, or to maintain a slightly lower speed. If you hit 120 mph and then take your foot off the gas, and it takes you 30 seconds to slow down to 60, you just averaged 90 mph for 30 seconds without using any gas.

Okay, maybe I'm not that sorry about rolling the grenade into the thread.

I am enjoying visiting the thread every couple of days just for the schadenfreude.

[kphoger]

Speed kills your pocketbook.

NoDoz is cheaper.

[JayhawkCO]

There's also the factor of once you reach a high enough speed, you can remain above a given speed by momentum alone, barely having to hit the gas at all to maintain it, or to maintain a slightly lower speed. If you hit 120 mph and then take your foot off the gas, and it takes you 30 seconds to slow down to 60, you just averaged 90 mph for 30 seconds without using any gas.

Okay, maybe I'm not that sorry about rolling the grenade into the thread.

I am enjoying visiting the thread every couple of days just for the schadenfreude.

Chris

[kphoger]

The calculation for distance involved in acceleration is D=1/2AT ^2, which is why whatever your starting speed is, and whatever your ending speed is, whether accelerating or decelerating, regardless of how long is takes to change speeds, the distance will always be whatever is exactly halfway between the two speeds, times the time to change speeds. If you graph this speed vs time, the distance is the area underneath the line, which is the area of a triangle, which is 1/2 Base* Height, resulting in 1/2 A*T ^2. That's why I was claiming that you averaged 90 mph when decelerating from 120 to 60, simple physics, which is pure math. I didn't take into account idle gas usage, even if you are coasting, just from the engine being on, so the gas used accelerating may also always offset the coasting.

Did I miss something?  Who claimed that you don't average 90 mph when decelerating from 120 to 60 mph?

[JayhawkCO]

The calculation for distance involved in acceleration is D=1/2AT ^2, which is why whatever your starting speed is, and whatever your ending speed is, whether accelerating or decelerating, regardless of how long is takes to change speeds, the distance will always be whatever is exactly halfway between the two speeds, times the time to change speeds. If you graph this speed vs time, the distance is the area underneath the line, which is the area of a triangle, which is 1/2 Base* Height, resulting in 1/2 A*T ^2. That's why I was claiming that you averaged 90 mph when decelerating from 120 to 60, simple physics, which is pure math. I didn't take into account idle gas usage, even if you are coasting, just from the engine being on, so the gas used accelerating may also always offset the coasting.

Did I miss something?  Who claimed that you don't average 90 mph when decelerating from 120 to 60 mph?

Not I.  I didn't actually assume anything about the average speed during deceleration because it's immaterial.  I showed that to use the same amount of gas (or less as SafeSpeeder alleges), in a Dodge Charger, it would require that it takes upward of three minutes to decelerate from 120 to 60 without braking, which is not how it works in real life.  I would imagine you might be at a dead stop long before that time.

Chris

[kphoger]

From my experience slowing down from those speeds without hitting the brake, friction alone tends to slow you down at about 2 mph per second.

What do you do, put it in neutral and somehow remove wind resistance?

[JayhawkCO]

Still would most likely take around 30 seconds at least. From my experience slowing down from those speeds without hitting the brake, friction alone tends to slow you down at about 2 mph per second.

And hence why I said it took way more gas to go from 60->120->60 than to just coast at 60.

Chris

[renegade]

Still would most likely take around 30 seconds at least. From my experience slowing down from those speeds without hitting the brake, friction alone tends to slow you down at about 2 mph per second.

If your vehicle has that much drag, speed isn't the only thing killing your pocketbook.  Gasoline is.  My Charger only slows by 1 mph every second-and-a-half.  In gear. 

[JayhawkCO]

Still would most likely take around 30 seconds at least. From my experience slowing down from those speeds without hitting the brake, friction alone tends to slow you down at about 2 mph per second.

If your vehicle has that much drag, speed isn't the only thing killing your pocketbook.  Gasoline is.  My Charger only slows by 1 mph every second-and-a-half.  In gear.

So there you go.  Same car as my example.  1.5 seconds X 60 mph to slow down = 90 seconds, which is way less than the 167 seconds that it would require to make it "cost effective" to boost up to 120 and then drop back down.

Chris

[renegade]

Still would most likely take around 30 seconds at least. From my experience slowing down from those speeds without hitting the brake, friction alone tends to slow you down at about 2 mph per second.

If your vehicle has that much drag, speed isn't the only thing killing your pocketbook.  Gasoline is.  My Charger only slows by 1 mph every second-and-a-half.  In gear.

So there you go.  Same car as my example.  1.5 seconds X 60 mph to slow down = 90 seconds, which is way less than the 167 seconds that it would require to make it "cost effective" to boost up to 120 and then drop back down.

Chris

I thought the whole concept brought forth by the OP to be quite stupid, actually.  It takes way less fuel to cruise along at 60 than it does to jam it up to 120, then coast.  Besides, in my state, 120 mph would get him carted off to jail in a Michigan heartbeat. 

[JayhawkCO]

Still would most likely take around 30 seconds at least. From my experience slowing down from those speeds without hitting the brake, friction alone tends to slow you down at about 2 mph per second.

If your vehicle has that much drag, speed isn't the only thing killing your pocketbook.  Gasoline is.  My Charger only slows by 1 mph every second-and-a-half.  In gear.

So there you go.  Same car as my example.  1.5 seconds X 60 mph to slow down = 90 seconds, which is way less than the 167 seconds that it would require to make it "cost effective" to boost up to 120 and then drop back down.

Chris

I thought the whole concept brought forth by the OP to be quite stupid, actually.  It takes way less fuel to cruise along at 60 than it does to jam it up to 120, then coast.  Besides, in my state, 120 mph would get him carted off to jail in a Michigan heartbeat.

Well, I think most of us did.  I just figured I'd try to prove it with math because math don't lie.

Chris

[Rothman]

Math lies all the time.  Lies, damn lies and statistics...