I drive a manual transmission car and I find my mileage to be comparable if not lower to an automatic transmission car. While activating cruise control, my mileage rises by a few kms because of this I have always wondered which transmission for my next car would be the best, considering mileage to be an important factor.
In: 35
The blunt truth: Driver skill/style is 10x more important than transmission.
If fuel consumption is a priority:
1) Drive at the speed limit. EVERY car (other than sports cars perhaps) will be a LOT more fuel efficient at 65mph or less. This can easily save 10-15% on fuel consumption on highways.
2) Accelerate gently and anticipate slowing down and coasting to more gentle stops. In stop and start traffic, this again easily saves 5-10% on fuel consumption.
3) Maintain tire pressures, tire alignment and maintenance of engine.
The differences in fuel consumption between a modern automatic transmission and a manual are small, if any, if a driver practices the above.
This is a very easy thing to test. Drive slower and less aggressively and monitor mileage. Do the comparison.
If the actual transmission technology and engine is the same, then automatic transmissions always win the efficiency game, unless the software used is ridiculously poor or you’re driving in extraordinary terrain.
The reason is simple: Automatic transmissions will keep your engine in the sweet spot of revolutions per minute, where power vs. consumption is optimal. If you’re getting slower than your current gear can support optimally, the transmission will automatically shift down, and vice-versa. In a manual transmission car, the driver is controlling all of these decisions. Even if the driver is considering these aspects (which they rarely are), they would still need to actually do the shifting of gears at the perfect times every time to beat the automatic transmission. And most drivers are too lazy for that, or they can’t shift gears at the perfect time because they are in the middle of a turn and need both hands at the wheels, or they have the radio so loud that they don’t realize the revolutions per minute are too high etc. Add to that, that the ordinary driver can’t shift gears nearly as fast and flawlessly as a modern automatic transmission can.
The only advantage a manual transmission car has in terms of mileage (apart from a little bit of weight reduction) is that the driver can anticipate the near future, while the automatic transmission can’t (yet). So if the driver knows that more power will be needed shortly, they can shift down before accelerating, which saves a little bit of fuel. And if the car is going downhills or will have to break soon, the driver can use the shift-down to add some breaking power without sacrificing fuel to idling.
So overall, unless you compare cars from the 1980’s or you’re regularily driving in extreme terrain, automatic transmissions are definitely more fuel efficient.
Edit: That being said, I’m a huge fan of manual transmissions and I have been driving manual shifts almost exclusively for 15 years. I have now switched to automatic transmissions and find it so relaxing, even if the loss of control can be felt at times, especially when maneuvering in narrow spaces or at steep hills.
Automatic transmissions use a torque converter, and there is a small loss in efficiency there, as compared to a manual gearbox which has a mechanical clutch. However, modern automatic transmissions use a lockup plus have had many technological advances and are very efficient compared to the old days.
For the typical driver, there’s very little difference in fuel consumption between the two. And for someone who loves revving the engine, an automatic might actually give slightly better fuel consumption because it will shift to a higher gear earlier.
With a good driver, manual transmission will give you slightly better fuel consumption because the driver is selecting the right gear for the speed/load/grade and also shifting efficiently.
I would personally recommend an automatic (assuming its a modern car brand/model), especially if you drive in a city with a lot of traffic because the overall difference is minimal, as compared to the hassle of shifting constantly imo.
Well, it ought to be obvious that a manual transmission is far more prone to the vagaries of how the driver drives the car than an automatic is. I’m sure that, driven properly, a manual car can easily do better than an automatic, if nothing else than because such a gearbox is usually lighter and thus saves a little bit of weight on the car, saving some fuel as well.
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