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Discussion Starter · #1 ·
I have a loaner 2.0L with an automatic. My car is a 2.5L with a manual. At 70mph my car is running about 2500rpm. The 2.0L auto is running about 2000 rpm. That's a huge difference, and the engine is smaller/weaker. Very surprising that the 2.5L is geared so low in 6th.

Certainly explains part of the mpg superiority of the 2.0L auto. (I know that smaller engines are more thermally efficient.)
 
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It's because yours is a manual. My 2.5L automatic isn't even running 2000rpm at 70mph. Manuals are geared lower, and that's why they get such crappy fuel economy on the highway. Basically, the reasoning is that anyone who buys a stick-shift these days doesn't care about fuel economy, they're "enthusiast" drivers. Also, it'd be hard to use cruise control in a manual transmission with gear ratios like that; every time it needed to go uphill, it'd start lugging the engine. In an auto, that's not a problem, since it just downshifts.
 

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Discussion Starter · #4 ·
I don't consider 37+mpg crappy, which I get consistently when I'm not stuck in ATL traffic.

My 1989 MX-6 GT was running ~3100rpm at 70mph.
 

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I have a loaner 2.0L with an automatic. My car is a 2.5L with a manual. At 70mph my car is running about 2500rpm. The 2.0L auto is running about 2000 rpm. That's a huge difference, and the engine is smaller/weaker. Very surprising that the 2.5L is geared so low in 6th.

Certainly explains part of the mpg superiority of the 2.0L auto. (I know that smaller engines are more thermally efficient.)
Most OEM's have internal gradeability targets in top gear that are tougher with manuals compared to Automatics, based on some kind of attitude that drivers do not like to downshift on the highway. Mazda is pretty good about this compared to other OEMs, especially Honda, who throws all kinds of fuel mileage away for the manual tranny customers.

In the Mazda3, the Automatic and manual have the same highway gas mileage ratings because the lower highway engine rpm makes up for the added friction in the Automatic compared to the manual gearbox. If the manual had the same overall top gear ratio, it would surely get better highway mileage.

Dave
 

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It's because yours is a manual. My 2.5L automatic isn't even running 2000rpm at 70mph. Manuals are geared lower, and that's why they get such crappy fuel economy on the highway. Basically, the reasoning is that anyone who buys a stick-shift these days doesn't care about fuel economy, they're "enthusiast" drivers. Also, it'd be hard to use cruise control in a manual transmission with gear ratios like that; every time it needed to go uphill, it'd start lugging the engine. In an auto, that's not a problem, since it just downshifts.
Not quite true ^
 

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The real reason that automatics are geared taller isn't because manual drivers are enthusiasts. It's because automatics have torque converters that can trade RPM for torque when needed before having to downshift.
 
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