yact: why is manual tranny's more fuel efficiant than automatics?

[JEDI]

lighter weight?

 

[Rallispec]

becuase it takes power to operate an automatic transmission


so part of the energy that could be going to the wheels to move the car is instead going to the automatic transmission to switch and hold gears.

 

[Mark R]

Part of the reason.

The major reason is that the torque converter (the device that connects the gearbox to the engine - used in place of a clutch on a manual transmission) is inefficient and wastes power. Other reasons include the use of inefficient planetary gear sets (instead of simple gears) and the need to power a hydraulic oil pump which works the gear selectors (whereas a manual just needs lubrication).

 

[Triumph]

yeah. a manual has a direct link surface to surface when your clutch is engaged. an automatic uses fluid to transfer energy. just go to howstuffworks.com and learn everything a layman needs to know about how stuff works.

 

[PingSpike]

The way I drive my car, I doubt I get better gas mileage than I would if it were automatic.

 

[Forsythe]

Originally posted by: PingSpike
The way I drive my car, I doubt I get better gas mileage than I would if it were automatic.

lol, same here. But that's also a part of why i prefer manual. You control the way you drive.

 

[MaxFusion16]

mechanical system versus hydraulic system

 

[BobDaMenkey]

Yep it's been pretty well stated already. And you can better pick your gears than an automatic would. There is no way to force it into high gear, you can only say "You can be in high gear".

I get 23mpg in a truck thanks to me and my 'frugal' foot

 

[Kenazo]

Also a 5 speed manual has one more gear than most automatics. Thus, better gear ratios. For example, I had a 1989 Daytona w/ a 5 speed that ran at 2100rpm @ 60mph, my friend had a similar car with an automatic and it ran at 3000rpm @ 60mph.

 

[PoopyPants]

the efficiency rating isnt ALLL that much better going from manual to auto. usually although i suppose there are cars out there that show a big leap in mileage when running a manual tranny
I gotta tell you though i've had a manual for many years now and im tired of it, im ready to go back to auto.
But i have repaired and swapped trannies before and let me tell you,, mechanically speaking a manual is a whole lot more efficient to change lol.

 

[vshah]

gear ratios also differ and could lead to differences in economy

 

[jfall]

It's not that significant. I had two identical cars, one was an auto, the other a 5-speed and the difference in gas mileage was hardly noticeable

 

[Mark R]

Thus, better gear ratios. For example, I had a 1989 Daytona w/ a 5 speed that ran at 2100rpm @ 60mph, my friend had a similar car with an automatic and it ran at 3000rpm @ 60mph.

That's unusual, at least amongst Japanese/European cars. The ratios on the manual are much closer, so that even in 5th (or 6th gear) the engine speed is considerably higher than it would be on an automatic (e.g. I've had both manual and auto models of the same car (Hyundai) - in the manual 5th gear would give 3500rpm @ 70mph vs. 2500rpm @ 70 for the auto).

People overestimate the impact of selecting gears on economy - an auto transmission which ditches the torque converter for an electro-hydraulic clutch approaches the economy of a manual transmission. You can make the transmissions even more similar by replacing the large planet sets with conventional gears and dogs as is done in 'sequential shift' transmissions. Even in full auto mode, such transmissions are almost as efficient as manual.

 

[Doggiedog]

In the past, manuals typically had one more gear than autos. It doesn't seem the case nowadays. I think MB has an auto with 7 gears excluding reverse.