Not So ‘Standard’ Anymore: The Manual Transmission is Almost Dead

[Daox]

I understand that many automatics and CVTs today get better mileage than their manual transmission alternatives. I also understand why this is.

If you look only at the transmission portion of the equation (exclude engine, etc), the efficiency of a manual transmission can not be beat. Energy loss is around 1% per gear set. I used to work at a gearbox manufacturer, and this is a common calculation for heat generation used by engineers. Automatics loose massive amounts of efficiency from their torque converters when they aren't locked up. Thankfully, auto makers have been more and more aggressive with locking up torque converters. CVTs also use torque converters, and their belts are not as efficient as a geared connection.

So, with the manual transmission actually being more efficient than other automatics, why do they get lower mileage? Mainly, because people are lazy. They don't like to downshift. They like power and they like it now, not after downshifting. Thus, auto makers design their top gear quite short in my opinion. So, while the manual transmission itself is very efficient, it cruises at a much higher rpm than its automatic counterparts. This runs the engine in an inefficient manner and you loose more fuel economy than the more efficient manual can provide.

However, if you were to gear the automatic, CVT, and manual transmission all the same, you would clearly see that the manual transmission would return the best fuel economy of the three. Its also extremely common for auto makers to gear transmissions taller to increase fuel economy ratings on cars. But, its always a balancing act between available power and efficiency in top gear.

I suppose one example of an automatic transmission that would be nearly as efficient as a manual would be a dual clutch transmission (DCT). There is no torque converter, so that helps a lot. However, it still has powered components that will eat up power in the form of hydraulics or electricity that the manual transmission doesn't have.

[MetroMPG]

Oh - I also read there's news from Nissan about this.

They have dropped the manual transmission Versa Note in the U.S. It's CVT only now.