Just one question. Why are Manuals more fuel efficient than Automatics?
They’re not. They used to be, but modern computer processes in the automatic transmission are better at shifting than darn near any human.
I think I’ve heard the argument that the more direct transfer of energy in a manual clutch’s pressure plate gives better efficiency than the swirling transmission fluid in a ‘slushbox’.
Of course, I heard the argument that Fords better than Chevys cuz they just are.
But if the manual driver is making every shift timed perfectly, avoiding any jackrabbit starts, or other demonstrations of power, etc. I think he could have the mpg edge over the same make and model with a automatic.
My understanding is that the highest gear of an automatic tends to be slightly higher than the highest gear of a manual. Of course, with a 6 speed manual shifter the point would be moot, but for something like a Honda Civic, this difference in gear ratios can give the automatic an edge…
Ectually…
I suspect that the main reason these days is because people who drive manuals are gearheads who switch gears to get maximum torque. If you switch gears trying to keep your revs low, I suspect that you’ll have a higher MPG than an automatic.
I don’t believe so.
Compare this 2007 Civic with a 1.8 liter 4 cylinder engine:
The automatic has a city/highway EPA estimated mileage of 30/40 MPG.
The manual has a city/highway EPA estimated mileage of 30/38 MPG.
Nominally the same mileage in the city, but the manual loses out to the automatic on the highway. The EPA test is standardized by speed, acceleration, and course, so I don’t think you can chalk this difference up to differences in driving style.
Is that anything to do with the ratio of the final drive?
Also, I’ve seen some automatic gear boxes described as “automatic manuals” or “manual automatics” in car magazine, they’re not all slush boxes any more if that makes a difference. Some are manuals with a bit of machinery making the changes aren’t they?
The reason manuals used to be more efficient is a direct mechanical link between the engine and wheels, while automatics have a step that energy is converted to hydrolic pressure then back again. This is effectively moot now since most a/t’s have a locking torque converter, which gives that direct connection.
a/t’s has a lot more overhead then m/t’s, a lot of fluid and gearsets to move around, but m/t’s usually have heavier gear oil. a/t’s have computer controls, m/t’s have whatever happens to be sitting in the driver seat. In general a/t’s used to have less gears to chose from then m/t’s, for a a/t 3 gears use to be the norm, while m/ts were pushing 6.
I don’t know. I think that’s true to a certain extent, but I think it might come with certain caveats.
- It might only apply to the latest, state-of-the-art auto boxes at the high end of the market, but maybe not the majority of automatic cars out there on the road today - so we’d need to define “modern”. Five or ten years from now, it might be more universally true.
- It might apply now to a driver taking an automatic and then a manual version of Model X out for a spin on a test drive, but maybe not to a person’s own manual car (there is a learning curve for each different manual box and clutch that needs time).
I’d say this is it. In the old days, there was always slippage in the automatic’s torque converter - 100% slippage at a stop with foot on the brake, maybe 5% slippage at highway speed. Lockup torque converters engage in the higher gears when a certain speed is reached, and reduce that slippage to zero. Between that, the predominance of 4-speed overdrive automatics, and increased sophistication in their shifting strategy, the mileage difference has diminished or even disappeared.
Please note that it varies by manufacturer. Chrysler makes some pretty bad “slushboxes” that get significantly poorer fuel economy than their manual counterparts.
I think another reason that manuals often get better mileage than automatics is that you can see the road ahead and slow down, speed up, downshift, upshift, or whatever before you actually have to. Automatics are not able to anticipate road conditions.
Huh? Take your foot off the gas, it slows down. Put your foot on the gas, it speeds back up. Some cars have lighter or heavier flywheels, which might change the conditions from make to make. Maybe I’m misunderstanding? 
Many automatics don’t particularly slow down when you take your foot off the gas. Several typical automatics I’ve driven keep going basically the same speed.
Let’s say a curve is coming up, and an uphill part after that. With a 5-speed, I can take my foot off the gas to slow down a bit, downshift into 4th, and smoothly accelerate through the curve. With an automatic, you’d have to brake to scrub off enough speed and then to speed back up push the gas pedal enough to cause the car to shift down into a lower gear. I guess that’s my main quibble with automatics, to get the transmission to downshift, you have to push the gas pedal.
What you describe does not really save gas. Gas wise it doesn’t matter if you dissipate speed into heat via the brakes or via engine breaking. Actually if you are downshifting in this situation you may get worse mileage then a a/t (but getting the trade off of increased power), since the a/t may stay in the higher gear.
And though a/t’s can’t anticipate the road conditions, neither can a m/t, it is only the unit behind the wheel, and there are ways to signal a/t’s about time to up/down shift - yes it’s not as precise and your mind has to battle that of the a/t computer, but you can do it and most drivers of a/t’s do use these (and may not even realize it).
Again I think what you are stating is a performance benefit of a m/t, and I suspect it is at the expense of mileage.
Another factor is a a/t and it’s fluid weighs more then a m/t, which gives a slight advantage to the m/t in this category.
I remember early Chevrolet with automatic transmission. They were called “slushamatics.”
Oops, wrong thread.
Automatic transmissions generally have heavier and larger diameter rotating parts and more mass to move around. Most use some sort of planetary gearset to alter gear ratios, which have quite a bit if friction to them. They also have a pump inside to generate the hydraulic pressure they need, and this generates heat and drag. Automatic transmissions also have cooling lines that run through the radiator or an auxillary cooler to disapate the heat they generate that manual transmissions do not. This extra heat is due to the extra friction of the internals.
However, most modern automatic transmissions now used electronically computer controlled shifting and have direct-drive through the torque converter. These features, along with improved lubricants, mean the autos generate much less friction and heat than earlier models, and can be as efficient as a manual transmission, depending on the design and useage. The introduction of automatic transmissions with overdrive final gears also brought up efficiency and mileage.
Or, you can just not have transmissiion in teh conventional sense (as in the Prius)
Brian
I drive a manual & it is amazing just how much of the time i’m actually coasting. coming up to a junction, it’s clutch down & coast - also i’m generally in the right gear at the right time. When I drive autos, the car always wants to keep on going or be in the “wrong” gear, especially when driven hard.