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Conventional wisdom lets me down...as usual.
October 5, 2010 5:04 PM   Subscribe

I thought a 5-speed manual always trumped an automatic for mpg, all else being equal?

I'm considering buying a Honda Element (I'm being specific in case it's something about this particular vehicle that determines the answer). I prefer to drive a stick, but one thing is kind of holding me back: the stated mpg for the automatic is 27/22, but for the manual it's 23/18. Huh? Why would the mpg for the manual be worse than for the automatic?

And, if you own an Element, manual or automatic, I would love to know what your real-world mpg is.
posted by bricoleur to Travel & Transportation (25 answers total)
 
Overall mass and engine size could account for differences between the two Element models. My friend and I have the same model year/trim Civic, but mine is a standard and his is automatic. I get 35mpg city and 40mpg highway, where he barely ever gets 30mpg mixed.
posted by vkxmai at 5:11 PM on October 5, 2010


What year are you looking at? Apparently the 2010 Element no longer comes with a manual available. Are you comparing the same years? The EPA changed the test in 2008, so the mileage isn't comparable between models before and after 08.

It usually has to do with gear ratios. Perhaps the gearing on the automatic is such that the engine turns at a lower RPM. You used to get much better economy on manuals when it was 5-speed man. vs. 3- or 4-speed autos, because 5th was more of an overdrive. But, with the new 5-, 6- and 7-speed autos, that gap is closing.
posted by hwyengr at 5:13 PM on October 5, 2010


Manual transmissions tend to be lighter than automatic ones, so that wouldn't explain it (for the Honda Element, the difference in overall weight is 60 lbs).
posted by halogen at 5:13 PM on October 5, 2010


Um... Are you sure you're not imagining a manual transmission Element? I can't find one on the Honda site, is all.
posted by Sys Rq at 5:18 PM on October 5, 2010


I tried to view the specs for manual vs. auto, but the Honda site sucks so I couldn't find it. However, I've seen in the past that some VWs in 5-speed manual get worse mileage than 6-speed automatic; perhaps that's the case here. I assume it's because of the closer gear ratios with the 6-speed, meaning you are operating closer to the motor's peak efficiency; this overcomes the losses inherent in an automatic transmission.
posted by Simon Barclay at 5:19 PM on October 5, 2010


Fwiw, the Mazda 5 van gets marginally better mileage in an automatic.
posted by plinth at 5:28 PM on October 5, 2010


Um... Are you sure you're not imagining a manual transmission Element? I can't find one on the Honda site, is all.

They definitely exist, according to wikipedia. Maybe they don't sell them anymore.

Also, I'm not seeing such a dramatic difference in the government numbers - more like 1 mpg. Where are you getting your numbers?

Generally, the mpg for the manual will be better - it's a bit strange it isn't. Maybe the gear ratios are different? Maybe they've optimized the automatic to upshift sooner than a driver normally would using a manual?
posted by Dasein at 5:29 PM on October 5, 2010


For what it's worth, my 6-speed manual Mazda 3 also gets lower mileage than its automatic twin.
posted by halogen at 5:36 PM on October 5, 2010


This used to be true, but recent innovations in automatic transmissions actually make them more fuel efficient than manuals.
posted by sanka at 5:40 PM on October 5, 2010 [4 favorites]


Old style auto's used to get worse mileage guaranteed because they had a lossy torque converter link between the engine and box. New automatics are essentially self-changing manual gearboxes for the most part and usually have a direct mechanical drive between the engine and gearbox which is as efficient as a manual box.

So the differences are much less. For a given car with identical differential (ie final drive ratio) and gear set-ups, there won't be too much difference between them, these days. Your data suggests there is more to the specs quoted than purely a comparison between identical cars with different styles of gearbox. Perhaps a different trim level (higher in the manual) produced a higher kerb weight for it? Was one car air con equipped and another not? All kinds of variables may be involved here.
posted by Brockles at 5:42 PM on October 5, 2010 [3 favorites]


^ What Brockles said.

I don't know about that specific Honda but some of the newer "automatic" transmissions are actually Dual Clutch Transmissions which is essentially a manual transmission with two clutches, one for even gears and one for odd gears, the shifting being computer controlled. The engine simply switches from powering one clutch to another in a fraction of a second when you need to shift gears - no need for "slack time" when you disengage the engine by holding down the clutch to change gears.

They have much faster gearshifting (hence acceleration) than is humanly possible and no energy losses via the torque converter. Also, because it's computer controlled, they can do other funky things with it by linking it to the the rest of the powertrain controls - like automatically shifting to neutral when you're coasting down so the engine isn't fighting the brakes. As to whether this translates into any meaningful fuel efficiency gains I have no idea but it could also be the effect of most R&D being put into this area so you're comparing a much newer tech automatic transmission against an older manual that hasn't been improved by much in the last few years.
posted by xdvesper at 6:36 PM on October 5, 2010


New automatics are essentially self-changing manual gearboxes for the most part and usually have a direct mechanical drive between the engine and gearbox which is as efficient as a manual box.

That's really only some new automatics. The majority still have a torque converter and planetary gearsets. (Although you're right insofar as there's basically no difference between a torque converter and a dry clutch when the converter is in lock-up.) The automated manual boxes are mostly higher performance vehicles and some VWs. Here and there, you'll find a Continuously Variable Automatic Transmission that uses a wet-clutch pack (like a motorcycle) instead of a torque converter to engage and separate the engine and trans.

The most likely causes of the automatic having a better MPG rating than the manual are the gear ratios of the respective transmissions and involvement of integrated computer controls. I imagine that the designers and engineers count on manual transmission drivers (in the US) to be more enthusiastic, sporty, and tuned-in drivers and the transmission is geared to make the care feel a little more responsive in the lower gears when compared to the automatic. Also, on a drive-by-wire electronic throttle vehicle, the onboard computer can fine-tune the efficiency when it has complete control over engine power output, torque converter lock up, and transmission gearing.
Additionally, some automatic transmissions have a variable final drive ratio. For instance, in a five-speed automatic, gears 1 2 and 3 will share a final drive ratio while 4 and 5 have a more economy tuned final drive. I don't know exactly how they achieve that mechanically, but I've seen it on spec sheets.
posted by Jon-o at 6:46 PM on October 5, 2010


It's true, they don't offer a manual transmission in the Element anymore. I'm looking at the 2008 model.

It's also true that the manual seemed much more responsive than the automatic, so maybe it can be explained by the combination of improved automatic powertrains on the one hand and some tilting of the manual gearbox in the direction of fun rather than economy.

Dang it.
posted by bricoleur at 7:06 PM on October 5, 2010


For instance, in a five-speed automatic, gears 1 2 and 3 will share a final drive ratio while 4 and 5 have a more economy tuned final drive. I don't know exactly how they achieve that mechanically, but I've seen it on spec sheets.

I don't know how they do that, nor can I imagine any possible situation where that would be necessary - if you want 1, 2, and 3 to have a different overall ratio (gear + diff ratio) then you just modify the gear ratio of 1, 2 and 3 to match that figure once you take the diff ratio into account. There is absolutely no rhyme or reason why (in the scenario you mention) you'd have a second final drive involved. Extra rotating mass, extra space required, extra cost, extra cost/space/rotating mass of the transfer method between the two and so on. It's bizarre, and there is either more to it than you describe, or that system was badly described in the specs.
posted by Brockles at 7:28 PM on October 5, 2010


Here's the breakdown: the electronic components of new auto boxes pretty much allow it to smartly allocate torque when shifts are made, thus making it more efficient than the average human drive.

Remember, the fuel mileage you quote is an estimate, based upon the average driver. It takes skill to be totally efficient with a manual box. You have to understand shift points for all gears at various torque levels in conjunction with the slope and trajectory which you're driving in.

The government's estimate of the average driver's capacity with the manual is thus scaled below. I would imagine you could theoretically match, if not marginally best any auto with a manual (the auto is still a torque converter in a sense, unless it is dual-shift and technically not an automatic), but it would take the precision of a machine; precision that probably cannot be replicated manually in a world of cars with electronic components governing engine utility.
posted by Hurst at 8:03 PM on October 5, 2010


I was on the verge of trying to say exactly what Hurst said.

The only thing I have to add is that in the vernacular, "theoretically" might be taken as: "barely possible." But even if the answer is "yes" that person isn't going to be doing it every hour of the day, every day of the year for the next decade.

On preview: "Oh well, late again."
On review: Since you're wanting this info to help decide about buying a used car, and since you've expressed a preference for manual transmissions, I'll mention that an often unnoticed advantage of an automatic transmission when buying a used car is that you can be almost certain that the previous owner didn't over-rev or otherwise abuse the engine.
posted by Tuesday After Lunch at 8:41 PM on October 5, 2010


I don't know how they do that, nor can I imagine any possible situation where that would be necessary

Could it be something like the transmission locks the converter in 4th and 5th but doesn't in the lower gears, and that affects the numbers somehow? Honestly, I really have very little clue about this stuff so I don't even know if that makes sense.
posted by Opposite George at 8:43 PM on October 5, 2010


Manuals are lighter but that's not exactly why they get bette rmileage. They don't have a torque converter and have much less rotating mass. The only way an auto is going to get better mileage is if the gearing is differernt. It doesn't matter how much technology goes into the tranny, if it has more rotating mass and everything else on the car is identical, it's going to get lower mileage.
posted by WhiteWhale at 8:45 PM on October 5, 2010


Honda's website is showing 18/23/20 manual and 20/25/22 auto for a 2008.
http://automobiles.honda.com/certified-used/element-sc/2008/specifications.aspx
So that's only an *estimated* 2mpg difference when looking at the combined numbers. If you drive 50,000 miles, that's 2500 gallons of fuel for the manual, or 2272.7 gallons of fuel for the auto. That's a difference of ~227 gallons, which at $3 a gallon is less than a $700 difference. I suspect that Element with the automatic transmission will command a premium of around that much over one with the manual. My understanding is that manual transmissions are also cheaper to repair. Buy what you want to drive - the difference is trivial, and based on a bunch of crazy assumptions anyway.
posted by itheearl at 9:30 PM on October 5, 2010


And this is the technical reason - gear ratios here:
http://www.honda.com/newsandviews/article.aspx?id=4248
5-speed Manual Transmission
Gear Ratios: 1st: 3.533, 2nd: 2.042, 3rd: 1.355, 4th: 1.028, 5th: 0.825, Reverse: 3.583, Final Drive: 4.765
5-speed Automatic Transmission (Available)
Gear Ratios: 1st: 2.786, 2nd: 1.614, 3rd 1.082, 4th: 0.733, 5th: 0.566, Reverse: 2.000, Final Drive: 4.500
posted by itheearl at 9:36 PM on October 5, 2010


My Mazdaspeed3 (6sp manual) has two different final drive gears for 1/2/3/4 (4.19) and 5/6 (3.53). The claimed EPA average is 18/25 but I can get 29+ on highway w/ AC in 100+F and have done it this twice this summer between a 900 & 600 mi drive.

There's no automatic version to compare with but I definitely want to emphasize that hypermiling a manual transmission vehicle higher than EPA estimates does take skill, experience and familiarity with the vehicle. Also, you really should calculate how much variations in mpg will cost you over your estimated annual driving based on gas prices.

Lastly, feel free to peruse Fuelly, a MeFi project site to see what people are actually getting.
posted by liquoredonlife at 10:21 PM on October 5, 2010 [1 favorite]


My husband bought a 2008 Element when it first came out. We drove both the automatic and the manual, and I agree that the manual was much more responsive. He was convinced he was going to buy an automatic until he drove them, and then there was no question that he wanted the manual.

His average mpg is around 24, so I think Honda's estimates for the manual are a bit low. I have a friend with an automatic who also reports around 24 mpg average, so I think the difference is really minimal.
posted by thejanna at 6:28 AM on October 6, 2010


I have a 2004 Honda Element, manual transmission. Has about 76000 miles on it. Gets 23-25mpg for the most part, but 15mpg when towing a camper. May or may not apply to newer models of this vehicle; take that for what it's worth.
posted by cuddles.mcsnuggy at 7:08 AM on October 6, 2010


The only way an auto is going to get better mileage is if the gearing is differernt.

Nonsense. An automatic has the advantage of a computer deciding when to shift based on speed, gear, RPM, throttle position, engine temperature, etc. A computer can be carefully tuned in a R&D lab to optimize for efficiency. Most human drivers just play it by ear and shift when they feel like it.
posted by Rhomboid at 12:38 PM on October 6, 2010


Nonsense. An automatic has the advantage of a computer deciding when to shift based on speed, gear, RPM, throttle position, engine temperature, etc. A computer can be carefully tuned in a R&D lab to optimize for efficiency. Most human drivers just play it by ear and shift when they feel like it.

Yes. I agree with everything you are saying about the technology of an auto. Now show me on http://www.fueleconomy.gov/feg/findacar.htm where a vehicle with an automatic transmission and same gear ratios, gets better mpg than a manual. I'll save you the trouble and tell you it doesn't exist.
posted by WhiteWhale at 5:36 PM on October 6, 2010 [1 favorite]


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