Efficiency at higher speed

[Pants]

I’ve always understood that the higher a cars speed the less efficient it is, and that dropping just a few miles an hour at motorway speeds can have a significant impact on range. Last week I drove from Lancashire to Stansted starting with 100% battery, and the sat nav indicated I would arrive at Newport Pagnell SuC with 22%. I presume navigation would plan for me driving at 70mph on the motorway. I travelled in the early hours, traffic was very light, I set autopilot to 80mph and maintained that speed for almost the entire journey. I was surprised that I arrived at the SuC with 21% battery remaining. Perhaps there were other variables involved but I really would have thought the extra 10mph would have had a greater impact on range.

I would have liked to have tried 90mph on the way back but didn’t want points on my license . . . .

 

[Adopado]

I’ve always understood that the higher a cars speed the less efficient it is, and that dropping just a few miles an hour at motorway speeds can have a significant impact on range. Last week I drove from Lancashire to Stansted starting with 100% battery, and the sat nav indicated I would arrive at Newport Pagnell SuC with 22%. I presume navigation would plan for me driving at 70mph on the motorway. I travelled in the early hours, traffic was very light, I set autopilot to 80mph and maintained that speed for almost the entire journey. I was surprised that I arrived at the SuC with 21% battery remaining. Perhaps there were other variables involved but I really would have thought the extra 10mph would have had a greater impact on range.

I would have liked to have tried 90mph on the way back but didn’t want points on my license . . . .

Windspeed and direction maybe? 10mph following wind and aero loss is roughly same as 70mph ... If that was the case (and wind/direction remained the same) then you maybe wouldn't have made it in the return direction at all!

 

[WannabeOwner]

Pre-condition for Supercharger destination less than expected - maybe?

Did you, by chance, use the Trip Graph? That might have adjusted the original prediction as you got closer - i.e. original estimate might have been "off" and revised during the journey (which might have taken into account the fact you were using less than expected because of e.g. a tailwind)

set autopilot to 80mph and maintained that speed for almost the entire journey

Notwithstanding that you arrived with more than you expected, if you drive at a higher speed the time to replenish battery (i.e. more kWh required because more used at higher speed) is less than the time saved by driving faster .... so overall a gain - provided that the charger you use is not throttled / running "slow".

Used to be that 90 MPH was the break-even, but faster chargers are available now so not sure where Aero is more than "refill" time

 

[Adopado]

Used to be that 90 MPH was the break-even, but faster chargers are available now so not sure where Aero is more than "refill" time

Yes, I seem to remember someone had worked out that the optimum/fastest time on a fast journey was to travel at 90 mph and despite increase in charging time you would get to your destination quicker than travelling slower (assuming a length of trip that was going to require a short charging stop anyway). Faster than that and the extra charging would start to eat into your advantage until at some higher speed you end up being slower than travelling at 70mph with shorter stops). None of this takes into account the time spent talking to police officers at the side of the road .

 

[AndrewGR]

The ability to maintain a constant speed on empty roads also helps with efficiency.

 

[thewishy]

Windspeed and direction maybe? 10mph following wind and aero loss is roughly same as 70mph ... If that was the case (and wind/direction remained the same) then you maybe wouldn't have made it in the return direction at all!

The battery-estimate-at-arrival system takes wind speed / direction, into account, among many many other factors

 

[Adopado]

The battery-estimate-at-arrival system takes wind speed / direction, into account, among many many other factors

Thanks for that reminder ... I forgot that an OTA update had introduced more sophisticated estimates.

 

[init6]

You can't break the laws of physics. Going faster will require more energy. There are lots of other variables that could account for your experience such as the weather forecast - goodness knows why they thought putting the UK's famously fickle weather into the calcs was a good idea

More importantly this thread details some concerns around the prediction at the start of the journey compared to once the journey started. Seems there is a discrepancy with the initial (or stationary) calculation. There are examples of it over and underestimating the predicted end charge.

 

[Jason71]

Yes, I seem to remember someone had worked out that the optimum/fastest time on a fast journey was to travel at 90 mph and despite increase in charging time you would get to your destination quicker than travelling slower (assuming a length of trip that was going to require a short charging stop anyway). Faster than that and the extra charging would start to eat into your advantage until at some higher speed you end up being slower than travelling at 70mph with shorter stops). None of this takes into account the time spent talking to police officers at the side of the road .

Over those extra stops your wallet gets lighter and lighter and that improves the efficiency as well.

 

[SageBrush]

Yes, I seem to remember someone had worked out that the optimum/fastest time on a fast journey was to travel at 90 mph and despite increase in charging time you would get to your destination quicker than travelling slower (assuming a length of trip that was going to require a short charging stop anyway). Faster than that and the extra charging would start to eat into your advantage until at some higher speed you end up being slower than travelling at 70mph with shorter stops). None of this takes into account the time spent talking to police officers at the side of the road .

This varies by charging speed.
If you can average 125+ kW then the police are the limiting factor in travel time.

 

[exlatccatsa]

Going down hill on the map (S) always uses less energy than going uphill (N) I've noticed that many a time.

 

[Tonybvi]

Going down hill on the map (S) always uses less energy than going uphill (N) I've noticed that many a time.

Ah but when I go home from the top of the Cairn although I’m going downhill I’m heading north!! What I love about that bit of the journey is I actually can arrive home with higher SoC than I have at the top which is some 10 miles away!

 

[exlatccatsa]

Ah but when I go home from the top of the Cairn although I’m going downhill I’m heading north!! What I love about that bit of the journey is I actually can arrive home with higher SoC than I have at the top which is some 10 miles away!

Yes there is that one exception Tony. Going past tomorrow.. Hopefully cleaning my rear brake discs before the MOT

 

[Medved_77]

Ah but when I go home from the top of the Cairn although I’m going downhill I’m heading north!! What I love about that bit of the journey is I actually can arrive home with higher SoC than I have at the top which is some 10 miles away!

From the top of the Cairn

Or bottom (can't remember)

 

[Tonybvi]

Yes there is that one exception Tony. Going past tomorrow.. Hopefully cleaning my rear brake discs before the MOT

Where are you going for the MoT? Dee Garage in Banchory wanted to do mine (he even bought the pucks) but their lift isn’t wide enough. Ended up going to Dinnet Garage who do the motorhome and they were very familiar with Teslas.

 

[exlatccatsa]

Premier coaches Kintore. I guess every garage will become familiar now, due to their popularity.

 

[roadcred]

I was travelling North on Sunday. Stopped at Ferrybridge with 6%. after 25 minutes it reached 80 %. Carried on up to 95% in a further 25 minutes. Travelling back in the evening reached Ferrybridge with 12%. Charged to 85% in 25 minutes to get me home! Best Supercharger experience to date after over 5 years EV driving! Wsasnt too warm either.

 

[Casss]

Probably a combination of things (weather changes + your driving style being different to how the car expects you to normally drive) and these offset the higher average speed over the distance.