auto vs manual trans MPG

[kr_bitog]

Originally Posted By: AZjeff
More and more new cars are listing higher MPG numbers for the auto version than the manual version. Is this a controlled environment/laboratory thing or is it possible in the real world of driving?

Does anyone know if an auto trans locked up in 5th is as efficient as a manual trans in 5th? (mechanically assuming same ratio)

thanks


In the past, old auto loses MPG due to less gear and no electric lock-up of clutch. Nowadays, auto comes with 5, 6, or more gear, this definitely will help to ensure the engine shift at the right rpm and the loss energy of torque converter is minimized with electronic controlled lock for the clutch. In the good design, this kind of auto will give better MPG than manual that is operated by human that prone to error.

 

[mechtech2]

May auto trans versions of the same car have higher final drive gearing. This can more than make up for pumping losses [even with a lock up conv]

 

[rjundi]

In a modern AT vs MT debate there is not significant MPG savings from one to the other. They are very close.

Modern EPA figures (repeatable results) show this.

Personal preference.

I enjoy driving manual transmission vehicles more.

However I am not convinced anyone is a better driver for the extra skill it takes drive one. The same folks who "mash the pedal" with an automatic would do the same with a manual shift.

Also the assumption of mash the pedal and go is a broad generalization of all automatic drivers.

 

[SteveSRT8]

Many modern autos are almost always locked up to some degree. My old Mercedes designed slushbox has infinitely variable lock up in all but first gear. It also has real roller bearings and such in places where many others use plain bearings. This pretty much means equivalent efficiency or even slightly better than a stick.

As a long term car enthusiast I have owned many of both types. Not all cars are automatically 'better' just because they have a clutch.

 

[sciphi]

Originally Posted By: SteveSRT8
Not all cars are automatically 'better' just because they have a clutch.


Quite true! I can think of some cars/trucks like the old Ford Explorer where a manual transmission was a deathwish for all but experienced manual transmission drivers.

 

[rjundi]

When I drive a minivan, truck, SUV I have no desire really to shift the car myself. Some cars yes very much but those vehicles put in D and forget about it.

 

[rpn453]

Despite the EPA ratings, manuals still seem to do better in real-world testing. Car and Driver recently did a comparison test involving the Hyundai Accent and the Kia Rio5, both with the same 1.6L engine but the Hyundai had a 6 speed manual (rated 30/40) while the Kia had a 6 speed automatic (30/39). On their 750 mile trip, the Accent returned 33 mpg while the Rio5 returned 28.

The EPA test procedure forces ridiculous shift points on manuals, while autos can use whatever shift points they want, so autos have a big advantage there. For my car, they slowly accelerate to 3300 rpm in first, then barely use second before holding both third and fourth gears about 10 mph higher than necessary.

 

[steveh]

I think its the gear ratio. Both of my manuals tach 3K at 80 MPH. My last automatic would tach about 2,200 at 80 MPH.

 

[AccordV6MN]

The nice thing about AT is that you can always add gears to 8 or even 10. it's hard for MT to go above 6. Where else you're going to push the shifter to? Dual shifter like semi?

Thus many auto makers going for DCT, somewhere b/w AT and MT. It can shift automatically and has as many gearbox like AT. And, it can also shifted manually (pedal shifter vs the good ol' stick), no slush box plus comes with more gearbox but lost the clutch.

I'm gonna miss the clutch and stick.

 

[d00df00d]

Originally Posted By: AccordV6MN
The nice thing about AT is that you can always add gears to 8 or even 10. it's hard for MT to go above 6. Where else you're going to push the shifter to? Dual shifter like semi?

Ask Porsche. They're about to release a 7-speed manual.

Originally Posted By: AccordV6MN
Thus many auto makers going for DCT, somewhere b/w AT and MT. It can shift automatically and has as many gearbox like AT. And, it can also shifted manually (pedal shifter vs the good ol' stick), no slush box plus comes with more gearbox but lost the clutch.

DCT is also really heavy, has more rotating mass, has hydraulics and electronics, and requires some fairly esoteric fluids.

 

[Cujet]

Fuel Economy dot gov

The above link is to a real world results page on www.fuelecomomy.gov. It's interesting to see the manual transmissions generally outperform the automatics. With a few exceptions.

Remember to look at the sample size and the year to year results. Some cars don't change year to year. The results should be quite similar.

 

[SwampDweller]

It is simple guys, dyno ANY cars, 2/Mustang GT's, 2/ Challenger R/T's, etc...one with an auto and one with a stick and see which has the most parasitic loss of HP. The auto is always lower on power to the wheels, sometimes by a lot. New auto's are not any different than autos of the 80's save for more gears. Lock up converters have been around production vehicles since IIRC-1978.

The only improvement I have seen lately is the DCT, which is an attempt at a melding of an auto and a stick.

 

[AccordV6MN]

Originally Posted By: d00df00d
Originally Posted By: AccordV6MN
The nice thing about AT is that you can always add gears to 8 or even 10. it's hard for MT to go above 6. Where else you're going to push the shifter to? Dual shifter like semi?

Ask Porsche. They're about to release a 7-speed manual.

Originally Posted By: AccordV6MN
Thus many auto makers going for DCT, somewhere b/w AT and MT. It can shift automatically and has as many gearbox like AT. And, it can also shifted manually (pedal shifter vs the good ol' stick), no slush box plus comes with more gearbox but lost the clutch.

DCT is also really heavy, has more rotating mass, has hydraulics and electronics, and requires some fairly esoteric fluids.


From what I can find, the 7speed is based on PDK. I still wonder where the shifter being pushed to. From the vid, it was only shown a split second at the part it was pushed upward.

Is DCT heavy by by nature or due to more gearbox? My understanding is that there are 2 different kind of DCT, wet (high torque engine) and dry (low torque). i.e. Fiesta has a DCT, but since it's a small engine with low torque, it'll use the dry DCT, I think.

 

[Mark_Walk]

Using the Mazda3 as an example...the 6spd MT is a close ratio manual.
The Automatic (what I have) is a 5spd but has a higher final drive ratio.

At 3,000 rpm in 5th I'm going 87mph.
A 6spd manual at 3,000rpm in 6th gear is only going 75mph.

It's all about the final drive gear ratio.

 

[d00df00d]

Originally Posted By: AccordV6MN
Is DCT heavy by by nature or due to more gearbox?

More gearbox.

At a bare minimum, it has two clutches, two input shafts, and some electrohydraulics to make it work.

 

[Patman]

For the 2006 to 2012 Civic, you'll get better MPG from the automatics simply because they have more favorable gearing on the highway. At 60mph, my automatic Civic revs at only 2000 rpm, while the manual trans versions will have the engine revving at about 2600.

 

[SwampDweller]

Agree with Patman, given the same car, same engine and same final drive ratio, the stick will always win in the real world.

It seems that in todays world of computer controlled engines, these engineers are also specifically writing fuel and timing programs( as well as valve timimg and auto shifting)just for the EPA ratings and its specific parameters. Seems we have seen more than a couple vehicles lately that do not get their rated mileage.

 

[yaris0128]

Im dreading the day when manual transmissions finally get phased out. Its already getting really close being in only cheaper cars but I flat out refuse buy an auto again. Have had nothing but problems with everyone Ive had. I dont care if they get a few mpg's better these days, not worth it!

 

[SteveSRT8]

Originally Posted By: demarpaint
I'd say it depends on the driver, a good driver with a stick can probably do better than an AT. OTOH an AT is a lot more forgiving of a less experienced driver.


This is it. Stick does not automatically 'create' a better driver out of a goofball!

Stick is driver dependent where many autos are not. And parasitic loss is obviously not as big an issue as everyone thinks. The epa numbers prove it. They are the only standardized results available.

And automated manuals come in MANY shapes and sizes. Single clutch, dual clutch, etc. Too many different designs, you can't lump them together any more than you can slushboxes.

 

[AccordV6MN]

Originally Posted By: yaris0128
Im dreading the day when manual transmissions finally get phased out. Its already getting really close being in only cheaper cars but I flat out refuse buy an auto again. Have had nothing but problems with everyone Ive had. I dont care if they get a few mpg's better these days, not worth it!


We can only hope that AT with slush box will be gone first before MT and in favor of AT based on DCT. DCT may cost more than AT slush box, much like any other MPG improvement tech yet survive. On top of that, on of Fiesta model comes with DCT, so no reason not to implement DCT in cars that already cost more than fiesta.