auto vs manual trans MPG

[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

 

[AandPDan]

Yes higher MPG is more than possible, it's very likely. The transmission can be programmed to shift at the optimal time for varying road conditions.

Many automatics are now 6 speed.

Yes, an auto locked up is just as efficient. It is locked, there is no slippage through the converter.

I still prefer (and drive) a stick though. I want to control the vehicle, not the other way around.

 

[JHZR2]

How can it be? There is far more parasitic load, e.g. The fluid pump(s), electronics, etc. For a true equal ratio, locked cruise, the AT has to be slightly less efficient due to parasitics. May be too small to make any practical difference though.

And you need to consider the lifecycle, for the cost of a clutch versus the cost of an AT rebuild or two clutches in a DCT. The MT has a far lower lifecycle cost.

MTs are often provided as a "performance" option, so are set up with stupid ratios compared to ATs.

ATs also don't let the driver fully understand the correlation between the physics of driving, acceleration and gearing. AT drivers mainly learn to mash the go pedal, which isn't a very good way to learn to appreciate the physics of driving.

 

[09_GXP]

The ATs can be programmed to better match the EPA drive cycles. An example I am familiar with is the CR-Z the CVT tests higher, by 2 mpg I think, but real world usage has shown the MTs to be putting up better numbers.

 

[ARCOgraphite]

The old 3 speed auto when planetaries are locked worked as a straight through the case shaft. On the MT you are going onto the mainshaft gear thru the lay shaft (which is under gear oil) then back to the tailshaft gear and out. Lots of loss there. mT are better around town when you would be on the converter in an auto. I was getting 30mpg avarage on my MT '11 ranger this summer not trying.

 

[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.

 

[yesthatsteve]

My xB with a 5-speed manual is rated 1 mpg less than the 4-speed automatic. It's largely because of the gear ratio. In 5th gear at 70 mph, my engine's cranking at 3500 RPMs. The auto in 4th gear at 70 mpg cranks at about 3300 RPMs, hence the 35 EPA rating (old) for the slushbox on the highway, compared to 34 for the manual.

I don't lead-foot it, and average about 36.5

 

[david_ES2]

to the OP its all about gear ratios. many automatic variants of the car have a lower gear ratio (numerically) than their manual counterparts.


many modern automatics have active torque converter lock up and assuming a MT and AT have the exact same gear ratios they would have the exact same Highway MPG because the converter would act like a clutch in a MT without any fluid coupling whatsoever.

Being a hypermiler. a MT would better suited for hypermiling style driving.

 

[AandPDan]

Originally Posted By: JHZR2
How can it be?


In a nutshell, people don't know how to drive anymore. They get in a car turn the key and hit the gas. Very few drive a stick, or even know how to drive a stick.

The average driver doesn't know when to downshift or upshift and does it by "sound" or some by RPM, but they don't consider what the engine is doing for load.

With the new Drive-By-Wire systems you can mash the pedal and the car will handle throttle opening to match wheel slip and also the shift points. All computer controlled to perfection.

It's so easy a (trunk) monkey could do it.

 

[NHGUY]

Stick shift drivers vary in technique wildly.Some short shift,skip gears,keep the revs low....others wind the engine to redline in 1st and 2nd,this cuts into MPGs seriously,and engine life.With an automatic,its a bit more consistent,unless you have the urge to use those "auto stick" or tiptronic type shift selectors,then the MPGs for the auto are out the window.In the old days (80s and before) manuals always trumped automatics,due to the converter slippage (no lockup clutch) and lack of overdrive (3spd automatics).However,the driver still was the final determining factor to final MPGs.

 

[fdcg27]

I suspect that in typical driving, for the reasonably attentive driver who doesn't linger in the lower gears, resists the temptation to redline the lower gears and takes advantage of the fuel shut-off on closed throttle in gear, a stick will yield better fuel economy.
Other than that, a stick is more enjoyable and more involving to drive than an automatic.
Anyone who never learned to drive a stick can't call themselves a competent driver.

 

[sciphi]

Having both a manual car (finally!) and an automatic car in the driveway right now, here are my thoughts.

Glad to have purchased one of the few remaining cars where the MT version eats the AT versions alive for fuel economy. The Eco MT is 28 city/42 highway, while the Eco AT is 28/39. All the other Cruzes are rated 26/38, except the LS which is 25/35. The Cruze Eco's MT is geared such that its final drive ratio is LOWER than the AT, and the final few gears are lower than the same gears in the AT. The real-world fuel economy figures represent that. Many MT Ecos are averaging right around 40 mpg, including mine. Most other Cruzes are averaging right around 29-30 mpg. Maybe that's a selection bias due to how most of the Ecos are driven by people who want a fuel-efficient highway cruiser, while the other Cruzes are driven wildly differently.

I'm spinning 1800 RPM at 60 mph in a 1.4 liter 4 cylinder. There's limited power to gain speed, and I'm okay with that. It's sipping fuel, as it's supposed to. If more power is needed, 3rd is quite usable at highway speeds.

Our Fit with its 5-speed AT spins 2000 RPM at 60 mph. The AT loves to shift at the slightest hill, though. So it unlocks the TCC and wildly revs when it could have gutted it out with the TCC locked. That's just how it's programmed, I guess so the car feels like it has tons of power instead of grumbling/groaning its way uphill. It can be over-ridden, but it takes careful throttle application to get it to stay locked up in 5th when going uphill.

As one can guess, the MT Cruze gets better fuel economy than the AT Fit, despite the Fit's 300 lb lighter weight, smaller wheels, less HP/TQ, and overall smaller exterior dimensions. The transmission certainly isn't the only factor in that discrepancy. The Cruze's driver drives for efficiency, while the Fit's driver is a typical "mash and go" AT driver.

Also, in winter an AT needs time to warm up before locking the TCC. No worries about warming up the ATF enough to not damage the TCC locking up with a manual transmission. The Fit will cover 1-2 miles wildly revving a cold engine to warm up the transmission. My old Buick did the same thing. A MT car won't do that, only idling the engine a little faster to warm up quickly.

My answer to the original question is: It depends on the season, on the car, and on the road conditions. In summer with both cars warmed up, the AT car might be slightly more efficient. In winter with cold transmissions needing to warm up, the MT car will be more efficient.

 

[rjundi]

I find my (first) automatic vehicle shifts to a high gear at a very low RPM. It runs the vehicle typically between 1200RPM and 1500 RPM in steady driving around town. I would never drive a manual transmission vehicle at 1200RPM in 4th gear, as I would know I need to downshift a gear or two to accelerate. I think this sips the fuel despite the loses associated with transmission. It likely all a wash.

I don't love automatics but at the same time it all comes down to personal driving preference and what is best suited to a driver. I had no choice in transmission as there are no 7 passenger vehicles currently I could find with manual transmissions.

 

[Spazdog]

Originally Posted By: NHGUY
Stick shift drivers vary in technique wildly.Some short shift,skip gears,keep the revs low....others wind the engine to redline in 1st and 2nd,this cuts into MPGs seriously,and engine life.With an automatic,its a bit more consistent,unless you have the urge to use those "auto stick" or tiptronic type shift selectors,then the MPGs for the auto are out the window.


I really only use the manual gate to select 6th gear early. It won't go to 6th until you are doing 42 mph. If I'm in a 40mph zone, I'll click it to 6th 2 mph early. It runs in 6th just fine down to about 35mph.

But long ago, when my wages necessitated having a roomate to live in a decent place, my roomate would not select the "circle-D" overdrive position on his '83 Camaro Sport Coupe 305 until he was on the freeway. Even where the speed limit was 40 or 45, he would shift past overdrive into just "D". He insisted that the engine had to "work too hard" in overdrive.

 

[sciphi]

Originally Posted By: rjundi
I find my (first) automatic vehicle shifts to a high gear at a very low RPM. It runs the vehicle typically between 1200RPM and 1500 RPM in steady driving around town. I would never drive a manual transmission vehicle at 1200RPM in 4th gear, as I would know I need to downshift a gear or two to accelerate. I think this sips the fuel despite the loses associated with transmission. It likely all a wash.


I drive my MT Cruze around town in 4th or 5th all the time depending on speed. If I need to go faster I downshift.

Our Fit will try to keep the RPM's up even when slowing down. Driving my MT Cruze I'll let the RPM's drop in gear and throw it into N or downshift to keep it in deceleration fuel cut mode so it burns no gas while slowing down.

It does depend on the car, and on the driver's skill with a MT. A less skillful/attentive driver in a MT car will waste far more fuel than in an automatic car.

 

[JHZR2]

Originally Posted By: AandPDan
Originally Posted By: JHZR2
How can it be?

In a nutshell, people don't know how to drive anymore. They get in a car turn the key and hit the gas. Very few drive a stick, or even know how to drive a stick.

Exactly my point, ATs create poor drivers that dont understand the fundamentals.

But again, IMO apples to apples the AT will be less efficient than the MT, because there will always be the same gear inefficiencies, etc. so long as both arent direct-drive, but the AT has more pumping losses and other things to suck a little bit of power.

 

[ueberooo]

Originally Posted By: sciphi

I drive my MT Cruze around town in 4th or 5th all the time depending on speed. If I need to go faster I downshift.

Our Fit will try to keep the RPM's up even when slowing down. Driving my MT Cruze I'll let the RPM's drop in gear and throw it into N or downshift to keep it in deceleration fuel cut mode so it burns no gas while slowing down.


I also try to use DFCO mode when it doesn't involve extra shifts at least, and sometimes even when needing to do extra shifts. I never quite figured out what the better trade off was, saving grams of fuel or pennies worth of clutch.

I "lug" the engine at low rpm too all the time, when I don't need the acceleration. I'll often skip gears (1-3) (2-4) (2-5) or (3-5) too when I go from accelerating up to speed to only nearly maintaining speed.

 

[AZjeff]

Originally Posted By: JHZR2
Exactly my point, ATs create poor drivers that dont understand the fundamentals.

But again, IMO apples to apples the AT will be less efficient than the MT, because there will always be the same gear inefficiencies, etc. so long as both arent direct-drive, but the AT has more pumping losses and other things to suck a little bit of power.

Several years ago AutoWeek had an article about driver education in different countries, young drivers, etc. In it they referenced a study done in (maybe) Sweden that concluded that new drivers became proficient quicker when learning with an AT because the focus could be on driving, not shifting. This makes sense. After they got the driving part then they learned how to operate an MT. Food for thought.

Lots of opinions about AT vs MT mileage figures. Back to the original question, is it possible that the same model 2011 Honda Civic, Chevy Cruze Eco, etc. etc. is able to get higher MPG driven the same way by the same driver with an AT vs an MT? Gear ratios, pump losses, season, altitude, phase of moon, eye color, all irrelevant. Wonder if any mags have grabbed 2 cars off the lot and tried it?

 

[sciphi]

Originally Posted By: AZjeff
Lots of opinions about AT vs MT mileage figures. Back to the original question, is it possible that the same model 2011 Honda Civic, Chevy Cruze Eco, etc. etc. is able to get higher MPG driven the same way by the same driver with an AT vs an MT? Gear ratios, pump losses, season, altitude, phase of moon, eye color, all irrelevant. Wonder if any mags have grabbed 2 cars off the lot and tried it?

I'd do that test with a Civic since it's the most similar between MT and AT cars. Get about 3-4 experienced drivers and have a go over the same routes back to back. Do a city loop and a highway loop, making sure that traffic/weather is similar on each loop.

In a more rural environment, I'd bet the MT would do better. In a suburban environment, the AT would do better.

 

[AZjeff]

Originally Posted By: sciphi
I'd do that test with a Civic since it's the most similar between MT and AT cars. Get about 3-4 experienced drivers and have a go over the same routes back to back. Do a city loop and a highway loop, making sure that traffic/weather is similar on each loop.

In a more rural environment, I'd bet the MT would do better. In a suburban environment, the AT would do better.

Or you could trade that Fit on a Cruze Eco AT and report back..