Manual vs automatic What is desirable for MPG?

[mohammad]

Originally Posted by Caddylackn

I like manuals because you can quickly and safely put it in neutral in well under a second at any time by just pushing in the clutch or quickly back into gear by releasing it. If you want to maximize coasting with minimum amount of drivetrain drag, this is it.

Maybe a brand new vehicle can be this quick shifting into neutral with paddle shifters, or CVT, I don't know I have never driven one.

Shifting into neutral may not always be the best option. Most cars on the road have DFCO which means that costing in gear uses ZERO gas. Read more about it here.(the first 2 posts are most relevant) Apparently im not allowed to share links but google: "DFCO explained measured and how to utilize it" and click on first result.

[mohammad]

Originally Posted by freebeard

Automatics can't scan the road ahead and assess whether RPMs will be going up or down.

This is untrue. if you turn on the cars adaptive cruise control based on your set speed, your current speed and whether or not the person in front of you is slowing down the car will choose the appropriate gear.

if you are in a prius/toyota hybrid and have radar cruise on, if the car in front of you begins to slow down, the prius will shut down the ICE.

Another example of this is with the new electric bmw i4, according to wikipedia has the following feature "adaptive mode uses GPS data and driver-assistance systems to adjust the amount of regenerative braking."

bmw also has a prototype transmission that would use gps along with other factors to predict which gear is optimal

[Ecky]

Broadly speaking, automatics and CVTs are more lossy, if for no other reason than that they have hydraulic losses (torque converters, lubrication pumps, etc.). CVT belts have a certain amount of frictional loss as well.

Automatics typically have more economical gearing. My best guess is that people don't like to shift, so manuals typically have a much shorter top gear. Sometimes the difference can be dramatic.

In EPA testing, automatics almost always win. In the real world, manuals almost always beat older automatics (driver permitting). I'm not sure where things stand with autos made in the last 5 years.

I had a manual Fit for a while, and a friend had an automatic of the same year. His auto had a similar EPA rating (~30 combined). He regularly got low 30's, while my SO regularly clocked mid to high 40's tanks. The automatic had significantly taller gearing.

~

I'll use a 2020 Civic as an example. Lower ratios are taller, and will result in better economy, all else equal:

Manual:
6th gear = 0.686
Final drive = 4.105
RPM @ 80mph = 3000

CVT:
Top ratio = 0.405
Final drive = 3.238
RPM @ 80mph = 1400

This is the normal Civic, not the EX or Sport or Si trim, which have shorter manual gearing.

[freebeard]

mohammad -- I see what you're saying, but that's systems layered on top of the transmission.

I can see that a Tesla might read road signs and decide whether to shift down one or two gears for the optimal line through a corner.

[mohammad]

Originally Posted by freebeard

mohammad -- I see what you're saying, but that's systems layered on top of the transmission.

I can see that a Tesla might read road signs and decide whether to shift down one or two gears for the optimal line through a corner.

Teslas dont have gears. they are 1 speed direct drive.

[freebeard]

Are there any automatic transmissions with machine vision? I don't know of an example.

While you think in terms of an automatic pilot and following other cars, I would consider running switchbacks in the Coast Range.

[Joggernot]

I have a 2018 Honda CRV with CVT. I shift to neutral and coast whenever possible. My Scangage shows DFCO in effect only for about a half a second then the CVT seems to adjust and it's using gas again. This is why I use neutral when going downhill.

[cRiPpLe_rOoStEr]

Originally Posted by Ecky

Automatics typically have more economical gearing. My best guess is that people don't like to shift, so manuals typically have a much shorter top gear. Sometimes the difference can be dramatic.

Odd enough, the first cars that I remember having a better fuel economy rating for their automatic versions were sporty models, such as the Chrysler Crossfire. But anyway, Euro rides tended to rely on a wider ratio and also a greater gear spread than most American models, in part to get better use of a fewer power in a mainstream model, while some sporty trims often had a close-ratio manual supposed to be better suited for a more spirited driving with those very same low-output powerplants.

[MeteorGray]

My 2.0L Mazda3 has an automatic transmission and averages more than 45mpg on non-Interstate 55mph highways when driven with a steady throttle at posted speed limits. MPG on 70mph Interstates shaves the fuel economy to around 38mpg or so. My main hypermiling procedure is to obey posted speed limits.

I doubt having a standard transmission would yield much additional economy driving normally under similar circumstances.

However, should someone wish to exercise advanced hypermiling techniques such as the legendary engine-off engine-on coasting process, a standard tranny would be necessary and would likely yield significantly higher fuel economy. But IMHO, most folks who choose standard transmissions tend to be younger in age and do so for "sporty" reasons that do not include driving for maximum economy.

I will note that my last standard transmission car was a 1.8L MGB convertible that was fun to drive but was lucky to get 21mpg on the highway at 55mph. Needless to say, I was younger back then.

[cRiPpLe_rOoStEr]

Originally Posted by MeteorGray

should someone wish to exercise advanced hypermiling techniques such as the legendary engine-off engine-on coasting process, a standard tranny would be necessary and would likely yield significantly higher fuel economy

I once tried neutral-coasting with the engine off in 2007, in a short downhill stretch, with a 2004 Corolla, while I was still a minor and didn't have a driver license. I started to regret it when I felt like there were no brakes and tried to slow down with the parking brake...

IMHO, most folks who choose standard transmissions tend to be younger in age and do so for "sporty" reasons that do not include driving for maximum economy

My mother and maternal grandmother took quite a long time to get rid of the manual transmission, yet they still drive in a quite aggressive way.