Power consumption at motorway speed

[MG4ismycar]

More for info than anything.
I drove most of the M5 and M6 this week back and forth between Devon and Yorkshire.
On the way there, I rarely went above 60 mph. Consumption rate was 4.2 m/kWh.
On the return, I set the car to 70 mph and the consumption dropped to 3.1 m/kWh.
Range was severely impacted.
I used to have a diesel Land Rover and it acted similarly with consumption spiking when traveling above 65 mph.
It seems power consumption is not linear - there is some sort of exponential curve at speeds above 65 mph.
Used tja most of the way and it works really well. Effortless driving.

 

[Bluecar1]

the difference in the power consumption and the non linear nature is due to wind resistance and the power required to overcome this

which basically is the square of the change, eg double your speed = 4 times the power required
treble your speed = 9 times times the power required

also I find if I run on cruise control when I would lift right off foe slight downhills sections of road when driving myself, cruise still maintains a motor power, that's because we will accept a drop in speed of a few mph but cruise is trying to maintain an exact speed

 

[Rolfe]

I only managed 143 miles on a full battery (the 51 kwh one) yesterday, down to 4% when I got to the charger at the service station, thanks to tanking it up the M6 and the M74. It's how these cars behave. At least, if you're getting nervous about range, you can easily recover the situation just by dropping down to 60 mph or so.

 

[Macadoodle]

They're definitely very prone to efficiency drop as speed rises. Just basic physics of course but a slippery shape like a model 3 or first gen Ionic does much better.

Got 5.1 on a 20 mile journey yesterday, stuck behind a car and caravan mostly at 50 mph. Was utterly bored but quietly impressed by the frugality

 

[m4rmite]

Air resistance is proportional to the square of the speed.

And on a cold day, the air is thicker so the resistance is higher compared to a warm/ hot day.

 

[tsedge]

Indeed.... and the effect is typically stronger with EVs than ICE vehicles because EVs are inherently more efficient so the impact of higher speeds is proportionately greater.

 

[Buster72]

Yes. On the occasions I drive on the motorway, I tend to stay between 60-65mph.
That just feels the most comfortable.

 

[Ian Key]

It doesn't take that much longer travelling at 65 compared to 70.

100 miles at 70mph will take 85.2 minutes
100 miles at 65mph will take 91.8 minutes
100 miles at 60mph will take 99.6 minutes

 

[NLMGSAN]

Head wind or tail wind (biggest factor throughout the year), high or low temperature (even a couple of degrees), rain or dry, direct sunshine or none at all, it all has an influence.
I managed an average of 14,5 kwh/100 km when the temperature was a mild 22 degrees Celsius with a tail wind. In the opposite direction on the same day it wasn't better than 16.5. That is +14% and will cost me €4,21.

What we need to take into account is that we may be comparing with milage when using petrol cars. As an example, my hybrid toyota did an average of a little over 4ltrs per 100 km in favourable weather situations. It could increase to 4,8 ltrs when things got worse (equivalence of 43kwh/100km). That is a difference of about 20%. It would cost me €9,60 nowadays. But it did so, more or less, in winter or summer.

This extra 0,8 liter of petrol would cost me about €1,6. The two extra kwh's for my MG will cost me 60 cents...
Unless my kwh costs 60 cents, it isn't worse. And it isn't. So I'm fine with it.