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Comment by WirelessGigabit | Hacker News Reader

That really depends on the brand of car / transmission.

Modern cars with the ZF-8 (which is like the number 1 automatic sold currently) are more efficient than their manual counterparts.

Extremely recent example in the USA: https://www.toyota.com/grsupra/2023/features/mpg/2385/2374

Toyota 3.0 Premium MT (6-speed Manual): 19/27/21 Toyota 3.0 Premium AT (8-speed Automatic): 23/31/26

And if you're like: Oh, the EPA's measurement sucks, here's the WLTP counterpart:

3.0 Petrol Twin-scroll turbocharger (335 BHP), 6-speed Manual: 32mpg / 198 g/km CO2 3.0 Petrol Twin-scroll turbocharger (335 BHP), 8-speed Automatic: 34.8mpg / 183 g/km CO2

Automatic has better mpg and less CO2 per distance travelled.

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Well, I should test drive each. EPA standard and reality don't match. For my stick shift cars, I always beat the EPA mileage.

Yes?

EPA is a standardised regime so cars can be compared. You can drive better than the EPA (or WLTP) test, especially if you're in better conditions.

I do wonder how much of this depends on the driving style, though.

In a manual I think you're much more likely to rev out the engine more, shift higher in the rev range, etc.

In an automatic unless you're in full "manual" mode and using the paddles/shifter to emulate that same style, then you're more likely to have the automatic's efficiency.

It's the difference in 8 speed and 5-6. Though the automatic still has some loss in a torque converter.

Historical higher mpg in a manual 5 and 6 speeds is due to driving style, 1st, the driver is more likely to drive based on what's ahead; 2nd (and related) the manual driver is likely more conservative in everyday driving.

The ZF-8 has a lock up clutch. That's why it's so efficient. It uses the torque converter as a pump to match the speeds but then engages that clutch to have a 1-1 connection. No losses.

some of that (the highway rating especially) is gearing, the final drive is shorter and the 6th gear in the ZF manual is not nearly as tall as the 8th in the 8HP. This is a common issue in auto vs manual MPG comparisons these days

From what I have seen, VAG DCT models tend to be invariably less efficient than their MT counterparts (and I don't know why ZF-8 would be more efficient than a DCT).

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