[walrus01]

I can duplicate pretty much the same effect with cruise control in my gasoline powered car. If I go on a 5 hour freeway road trip with cruise at 65mph and spend 95% of my time in the right lane, there's definitely a 2-3 mpg improvement in fuel consumption, vs 75 mph. At that point it becomes a tradeoff in time vs money spent on extra fuel, and need to get somewhere in a hurry.

Over a 4.5 hour period if I can cruise at 75 mph, I will be 44.5 miles ahead of another car which departs at the same time, for the same destination, at 65 mph.

[sgc]

For ICE cars, it depends on what the mfg has optimized for. I had an Infinity years ago and I remember that it was optimized for 70mph precisely as per the owner's manual. Higher or lower speeds would be less efficient.

[alvah]

Interesting(ish) tangent - the UK fuel economy specs used to be published at a constant 56mph & 75mph. When the Mk3 Vauxhall Cavalier was launched in the late 1980s, it had great (theoretical) fuel economy, much better than its rivals, but a couple of noticeable flat spots under acceleration. Turned out Vauxhall had leaned the fuel maps at the exact engine revs that corresponded to 56mph and 75mph in top gear...

[mywittyname]

My old (14) Mustang had exactly the same thing: there was a very noticeable reduction in power at ~2000 RPMs. I always suspected that it was to improve highway fuel economy, as that's exactly where the engine was spinning at 74mph in sixth.

[londons_explore]

Defeat device...? Cheating...? Multi-billion pound fine?

[mft_]

Totally different, isn't it?

Presumably the Vauxhall mentioned would provide exactly the measured MPG when driven at the correct speed by any owner in the real world - hence the 'flat spot' noticed.

The defeat concept you're referring to (presumably VW's) was set to only function during a test, and not in the real world (AIUI).

[londons_explore]

VW's defeat concept was set to function only at the exact RPM's used during the test. If a real-world customer were to use those RPM's and conditions, it would activate too. In fact a CCC talk showed that 5% of regular driving activated it.

Perhaps about 5% of regular vauxhall driving was in those flat spots...

Seems the same to me.

[FullyFunctional]

Similarly; I used to drive a "somewhat" performance enhanced Subaru Impreza WRX. One month I tried an experiment of driving as fuel conscious as I could. It improved 1 mpg over the normal 21 mpg. However in my Model S, there is a very direct and obvious correlation between efficiency and acceleration/speed.

I don't really have a problem with my effective range being less do to my driving style as long as it's predictable (and it is).

[maccard]

I drive an unmodified Golf GTI. Sticking to speed limits, the difference between driving aggressively in Sport mode and driving normally in normal is about 20mpg. The difference between driving normally in Normal mode and more fuel consciously is probably another 10 mpg on top of that (on a 3 hr trip, no motorway i saw roughly 8-10 mpg driving aggressively and close to 38 when driving normally. Motorway driving is a little closer, but I live in Scotland so motorway isn't usually an option)

[Dylan16807]

I'd want to hear exactly how that was achieved.

It's one thing to have the engine+drivetrain efficiency peak at 70. But for total efficiency to be worse at 60, despite massively reduced wind resistance, is pretty suspicious.

[jcims]

Had same experience with a Honda Accord. ICE/drivetrain efficiency is extremely complex with very little linearity across a number of variables.

[londons_explore]

If you really really care about miles per gallon, nearly any ICE car the most efficient way to drive is at or near idle in top gear, going about 25 mph. The difference is remarkable - a car which usually gets 50 mpg can easily get 100mpg with that approach, although obviously you can't practically drive like that on the public highway.

[hvidgaard]

It's not that simple unfortunately. It's most efficient when it runs the most lean fuel mix and least engine vacuum (i.e. full throttle). That balanced with gearbox efficiency, other drive train loses, and wind resistance. As a real world example, Ford Fiesta 1.0 EcoBoost is most efficient running 28mph in 4. gear. closely followed by going 44mph in 5. gear.

[WalterBright]

I thought it was 35.

But the most efficient way to drive a gas car is to speed up, then turn the engine off and coast down to a slower speed, then engine on for quickly moving up to a fast speed again.

Of course, the only way you'd want to drive like that is if you are alone in the desert and need to get to a gas station.

[gambiting]

I noticed that my plug-in hybrid Volvo does pretty much exactly this - whenever you let go of the accelerator, not only the car goes into neutral, the petrol motor does actually switch off entirely. When you want to accelerate again the electric motor kicks in first and then the petrol motor follows, so in practice if it wasn't for the small indicator on the screen you wouldn't ever know that it's happening. Considering the size and weight of the vehicle I'm actually seeing some incredible MPG when driven carefully.